Snake gives 'virgin birth' to extraordinary babies

By Matt Walker
Editor, Earth News


Snakes without fathers: one of the unusual baby boas


A female boa constrictor snake has given birth to two litters of extraordinary offspring.

Evidence suggests the mother snake has had multiple virgin births, producing 22 baby snakes that have no father.

More than that, the genetic make-up of the baby snakes is unlike any previously recorded among vertebrates, the group which includes almost all animals with a backbone.

Details are published in the Royal Society journal Biology Letters.


Our finding up-ends decades of scientific theory on reptile reproduction

Biologist Dr Warren Booth
Virgin births do occur among animals.

Many invertebrates, such as insects, can produce offspring asexually, without ever having mated. They usually do this by cloning themselves, producing genetically identical offspring.

But among vertebrate animals, it remains a novelty, having been documented among less than 0.1% of vertebrate species.

In 2006, scientists discovered that two komodo dragons (Varanus komodoensis), the world's largest lizard species, had produced eggs that developed without being fertilised by sperm - a process called parthenogenesis.

Then in 2007, other scientists found that captive female hammerhead sharks (Sphyrna tiburo) could also reproduce without having sex.

But vertebrates generally reproduce sexually.

Not including genetic material from the father - essentially having just a single biological parent - reduces genetic diversity and makes it more difficult for organisms to adapt to, for example, changed environmental conditions or the emergence of a new disease.

Novel beginnings

Now, a team of scientists and snake experts based in the US has identified the first case of a boa snake having a virgin birth.

"Although parthenogenesis has been documented in a few snake species, our findings are truly novel for a number of reasons," says Dr Warren Booth of North Carolina State University in Raleigh, US.

He led the team that made the latest discovery, and also worked with the researchers who documented a virgin birth in a hammerhead shark.

VIRGIN BIRTHS



Many smaller invertebrate species embrace asexual reproduction, but almost all higher animals require sex to reproduce
On the rare occasions they do not, they usually give birth asexually via a process known as parthenogenesis
Read about how the world's largest lizard, the Komodo dragon, was discovered to be able to give birth to fatherless babies (pictured above)
Read about how a hammerhead shark also had an extremely rare 'virgin birth'
"The female [boa] has had not one virgin birth, but actually two, in spite of being housed with and observed to be courted by multiple males.

"All offspring are female. The offspring share only half the mother's genetic make-up," he told the BBC.

What is more, the female snake in question has produced offspring the like of which have never been seen before.

Special babies

In the two years following 2007, the captive-born female Boa constrictor produced two litters of live offspring, at the same time as being housed with four male snakes.

First impressions suggested there was something special about these babies: all were female and all had a particular, rare caramel colouration.

This colour is a rare recessive genetic trait, which is carried by the mother but not by any of the potential fathers.

So Dr Booth and colleagues conducted a series of genetic tests on the snakes to solve the enigma.

What they found was astonishing.

DNA fingerprinting revealed that the offspring had a number of genetic differences from any of their potential fathers, which ruled out all the males as sires of the litter.

That confirmed the first instance of a known virgin birth among boa snakes.

Half clones

All the offspring also had very unusual sex chromosomes.

Sex chromosomes are packages of DNA that drive the development of sexual characteristics; they essentially make animals genetically male or genetically female.

Humans for example have X or Y sex chromosomes; females have two X chromosomes and males have a combination of an X and a Y chromosome.

In place of X and Y, snakes and many other reptiles have Z and W chromosomes.

In all snakes, ZZ produces males and ZW produces females.

Bizarrely, all the snakes in these litters were WW.

This was further proof that the snakes inherited all their genetic material from their mother, as only females carry the W chromosome.

"Essentially they are half clones of their mother," says Dr Booth.

That is because the baby snakes have inherited two copies of one half of their mother's chromosomes, including one W chromosome.

SNAKES



Learn more about scaled reptiles: lizards, snakes and slowworms
More astonishing though, is that no vertebrate animal in which the females carry the odd sex chromosome (in this case the W chromosome) has ever been recorded naturally producing viable WW offspring via a virgin birth.

"For decades WW has been considered non-viable" says Dr Booth.

In such species, all known examples of babies that are the product of parthenogenesis are male, carrying a ZZ chromosomal arrangement.

The only previously known animals to carry this WW chromosome pairing were created by scientists in the laboratory, using intricate genetic techniques to artificially alter the way animal eggs develop.

"Essentially our finding up-ends decades of scientific theory on reptile reproduction," says Dr Booth.

One other mystery is what prompted the female snake to give birth this way.

"This female has given birth to sexually produced babies in the past, and only in years that she was housed with males has she produced offspring," Dr Booth explains.

"It appears that some interaction with a male is required.

"However, why she does not utilise his sperm is at present unknown."

Boas snakes are kept and bred all over the world as pets.

But, Dr Booth adds, "this study tells us we have much more to learn when it comes to reproduction in these primitive reptiles".

Male whiptale lizards

Intrahypothalamic Implantation of Progesterone in Castrated Male
Whiptail Lizards (Cnemidophorus inornatus) Elicits Courtship and
Copulatory Behavior and Affects Androgen Receptor- and
Progesterone Receptor-mRNA Expression in the Brain
David Crews, John Godwin, Vesta Hartman, Michael Grammer, Ellen A. Prediger, and Rebecca Sheppherd
Department of Zoology and Institute for Reproductive Biology, University of Texas, Austin, Texas 78712
A primary tenet of behavioral neuroendocrinology is that gonadal
steroid hormones act on limbic nuclei to activate mating behavior
in vertebrates. Traditionally, research has focused on the regulation
of male-typical sexual behavior by testicular androgens and
female-typical sexual behavior by ovarian estrogen and progesterone.
Indeed, progesterone generally is regarded as an antiandrogen,
acting centrally to inhibit sexual behavior in males.
However, experiments with lizards, and more recently with rats,
have challenged this paradigm. For example, exogenous progesterone
induces mating behavior in some, but not all, castrated
male whiptail lizards. The present study determined that implantation
of progesterone into the anterior hypothalamus preoptic
area of castrated, progesterone-sensitive males completely
restored sexual behavior but failed to elicit sexual activity in
castrated, progesterone-insensitive males. Further, androgen
receptor- and progesterone receptor-mRNA expression in specific
brain regions was significantly different in progesteronesensitive
versus progesterone-insensitive animals. Progesteronesensitive
males showed significantly higher relative abundance of
androgen receptor-mRNA in the preoptic area, amygdala, and
lateral septum, as compared with progesterone-insensitive animals
receiving the same treatment. In contrast, progesterone
receptor-mRNA abundance was lower in preoptic area of
progesterone-sensitive males than in progesterone-insensitive
males. No differences were found in the baseline abundance of
androgen receptor- or progesterone receptor-mRNA in these nuclei
between control groups of progesterone-sensitive and
progesterone-insensitive males who were castrated but not implanted.
This suggests that progesterone differentially regulates its
own receptor as well as androgen receptor in areas of the brain
involved in the control of sexual behavior of males and that the
nature of this regulation shows individual variability.
Key words: steroid hormone receptor; gene expression; intrahypothalamic
implantation; septum; amygdala; preoptic
area; sexual behavior; autoregulation; androgen; progesterone;
reptile; lizard; male
In the little striped whiptail lizard (Cnemidophorus inornatus),
as in many other vertebrates, males rely on elevated circulating
levels of androgens for the seasonal activation of sexual behaviors
(Lindzey and Crews, 1986). However, in a subset of these
lizards, exogenous progesterone can also reinstate sexual behavior
in castrated males (equals progesterone-sensitive or
P-sensitive males) (Lindzey and Crews, 1986, 1988a,b). Restoration
of sexual behavior in P-sensitive males by synthetic
progestin agonists indicates that it is progesterone, and not a
metabolite of progesterone, that produces this behavioral effect
(Lindzey, 1988a); binding studies suggest that progesterone
receptor (PR) mediates this response (Lindzey and Crews,
1993). Initially, this progesterone activation of sexual behavior
in castrated male whiptail lizards was puzzling, given the well
known observation that androgen-dependent sexual behaviors
in male mammals and birds are inhibited by progestins (Diamond,
1963; Ericksson et al., 1967; Erpino, 1973; Griffo and
Lee, 1973; Bardin et al., 1984; Bottoni et al., 1985). However,
inspection of the original reports will show that the milligram
amounts administered were likely to result in circulating concentrations
of hormone in excess of the normal physiological
range and, hence, were pharmacological. Further, physiological
studies indicate that male rats have a pronounced circadian
rhythm in progesterone secretion, with fivefold higher peak
levels occurring at the onset of dark phase of the photoperiod
when most sexual activity occurs (Kalra and Kalra, 1977).
Experiments with another lizard (Young et al., 1991) and, more
recently, rats (Witt et al., 1994, 1995) indicate that, whereas
pharmacological dosages of progesterone inhibit sexual behavior
in intact and in castrated, androgen-treated males, lower dosages
that result in circulating levels within the physiological range
stimulate sexual behavior in castrated males. Such progesteronetreated
castrates court and copulate with females with an intensity
equal to that shown by castrates receiving androgen replacement
therapy. Further, subthreshold dosages of progesterone and androgen
synergize to elicit mounting behavior in castrated males,
much as estrogen and progesterone do in eliciting sexual receptivity
in female lizards and mammals (Lindzey and Crews, 1988a;
Young et al., 1991; Witt et al., 1995). It seems, therefore, that
Received July 9, 1996; revised Aug. 29, 1996; accepted Aug. 30, 1996.
This research was supported by National Institute of Mental Health MERIT
Award 41770, Research Scientist Award 00135, and Training Grant 18837 (all to
D.C.), National Institutes of Health National Research Service Award NS09219 (to
J.G.), University of Texas Undergraduate Biomedical Training Program (to V.H.
and M.G.), and National Institutes of Health National Research Service Award
MH10372 (to E.A.P.). We thank Ron and Sherry Hall and Ross and Frank Stavely
for their hospitality and assistance with lizard collections in Sanderson, Texas, and
the Southwestern Research Station of the American Museum of Natural History for
the use of its facilities. We also thank Donald K. Clifton for providing the Grains
image analysis program.
Correspondence should be addressed to Dr. David Crews, Institute of Reproductive
Biology and the Department of Zoology, University of Texas at Austin, Austin,
TX 78712.
Dr. Prediger’s present address: Ambion Incorporated, Austin, TX 78744.
Copyright q 1996 Society for Neuroscience 0270-6474/96/167347-06$05.00/0
The Journal of Neuroscience, November 15, 1996, 16(22):7347–7352
progesterone and androgen both are necessary for the display of
sexual behavior in intact males, but neither is sufficient for complete
restoration of sexual behavior after castration. Thus, in
terms of its role in the neuroendocrine control of sexual behavior,
progesterone may be as much a hormone that affects mounting
and copulatory behavior in males as it affects receptive behavior in
females.
Exploring the neuroendocrine mechanism underlying
progesterone-activated courtship and copulatory behavior in male
whiptail lizards may provide insights into the regulation of sexual
behavior in male vertebrates generally. We find that males who
are behaviorally sensitive to systemic progesterone are also responsive
to intrahypothalamic implants of progesterone, whereas
P-insensitive males do not respond to such implants. Further,
P-sensitive males exhibit significantly higher AR-mRNA expression
than P-insensitive males in the medial preoptic area (POA),
lateral septum, and amygdala, brain regions known to be involved
in the regulation of sexual behavior in males. These same
P-sensitive males had significantly lower expression of PR-mRNA
in the medial and periventricular POA. P-sensitive and
P-insensitive males that did not receive an intrahypothalamic
implant did not have differential baseline abundance of AR- or
PR-mRNA in these nuclei.
MATERIALS AND METHODS
Animals. Cnemidophorus inornatus were captured near Sanderson, Texas,
and in and around Portal, Arizona. The lizards were transported to the
University of Texas at Austin, where they were maintained as described
in Lindzey and Crews (1986). Male study animals were housed individually,
and females were housed in groups of four with one male.
Surgical procedures. All surgery was performed by using hypothermia as
anesthetic. Castrations were performed by the technique described in Crews
et al. (1978). Briefly, an incision was made on each side of the animal lateral
to the abdominal midline. Silk ligatures were used to cut off blood flow to the
testes, which subsequently were removed. Gonadal arteries and veins were
cauterized to prevent further bleeding, and the incision was closed with silk
sutures passing through both the skin and peritoneum. All of the animals
included in the study displayed male typical courtship and copulatory behaviors
in the laboratory before castration. Males were castrated at least 2 weeks
before receiving intraperitoneal implants and were behavior-tested to insure
that the castration was effective.
Intraperitoneal implants of progesterone were made with similar surgical
technique. Intraperitoneal hormone implants were made of 10 mm
of SILASTIC surgical tubing (inner diameter, 1.47 mm; outer diameter,
1.96 mm; Dow Corning, Midland, MI) filled with progesterone (Sigma,
St. Louis, MO), as described previously in Lindzey and Crews (1986). The
ends of the tubing were sealed with SILASTIC adhesive, and a 1 cmpiece
of silk surgical thread was embedded in one of the ends to serve as an
anchor after surgical implantation.
With the use of a Kopf stereotaxis modified for small reptiles, each
experimental animal received an intrahypothalamic progesterone implant
using methods detailed in Rozendaal and Crews (1989). The point of
intersection of the two frontal parietal scales and the interparietal scale was
used as a reference point to determine stereotaxic coordinates. A 1-mmround
dental burr was used to drill a hole in the skull overlying the target
area. A cannula of 30 gauge hypodermic tubing (Hamilton, Reno, NV)
containing progesterone was lowered to the desired site, and the hormone
pellet was ejected by pushing a cleaning wire through the cannula. The
cannula was withdrawn, and the hole in the skull was filled with Gelfoam.
Animals were allowed 24 hr to recover in their home cages before behavioral
testing began.
Intrahypothalamic hormone implants consisted of progesterone, red
Crayola wax, and bone wax in a 3:1:9 ratio by weight. Implant pellets were
formed by tapping the end of the cannula into the mixture. The cylindrical
implants averaged a 140 mm inner diameter 3 0.5 mm in length,
indicating an implant volume of 0.008 mm3. This represents ,10% of the
volume of the anterior hypothalamus (AH)-POA of a male C. inornatus,
which averages 0.096 mm3 (Crews et al., 1990; Wade et al., 1993). Pellets
were found to have an average mass of 22.4 mg (mean of five pellets
weighed on a Cahn microbalance) and, thus, to contain an average dosage
of ;5.20 mg of progesterone per implant. Each experimental animal
received one intrahypothalamic implant targeted for the AH-POA (coordinates
11.85 mm ventral and 20.35 mm posterior to the reference
point). Control animals did not receive an intrahypothalamic implant.
Behavioral testing procedure. All behavioral tests were conducted by introducing
a stimulus-receptive female into the home cage of the experimental
male. Tests were conducted during the high activity period between 10:00
A.M. and 2:00 P.M. A 3 min test was administered daily to all subjects during
periods of behavior testing, and tests were scored in accordance with the
hierarchy of sexual behavior described by Lindzey and Crews (1986). Animals
showing no interest at all in the stimulus female were scored 0, those
that approached and made contact scored 1, swiggle walking received a 2,
mounting a 3, riding a 4, assuming a copulatory posture a 5, and copulating
a 6. Increasing scores represent increasing intensity of male sexual behavior.
All but the last behavior testing period consisted of five sequential days of
testing. An animal scoring a 3 or greater in three of the five tests was
considered as giving a positive response and classified as a “courter.” For the
tests conducted after intrahypothalamic implantation, animals were tested
for seven consecutive days.
Experimental design. The present report combines traditional behavioral
endocrine methods, including castration, hormone replacement therapy, and
intrahypothalamic hormone implantation, with a modern molecular method,
quantitative in situ hybridization to identify AR- and PR-mRNAs in brain
nuclei. The experimental design is summarized in Figure 1. Intact males were
tested for courtship and copulatory behavior. Those displaying sexual responses
as described above (“courters”) were used for the study. After
behavior testing in the intact condition, males were castrated, allowed 10 d to
recover, and then tested to insure the extinction of sexual behavior. Then
animals were given intraperitoneal pellets of progesterone, allowed a 10 d
Figure 1. Schematic illustrating steps in experiment. Control males experienced
the same procedures, with the exception of intrahypothalamic
implantation. For details, see Experimental Design.
7348 J. Neurosci., November 15, 1996, 16(22):7347–7352 Crews et al. · Progesterone Activation of AR and PR Expression in Males
recovery, and behavior-tested again to determine whether sexual behavior
was reinstated by systemic progesterone treatment. Males for whom the
sexual behavior was reinstated with systemic progesterone were classified as
P-sensitive; those in which sexual behavior was not reinstated were classified
as P-insensitive. The intraperitoneal progesterone pellets were then removed,
and the animals again were tested for extinction of behavior. Finally,
each experimental animal was implanted (or not) with an intrahypothalamic
progesterone pellet targeted to the AH-POA and tested double blindly for
stimulation of sexual behavior (experimental: 11 P-sensitive, 7 P-insensitive).
A single score of 3 or greater was designated a positive response, and
these animals were killed immediately. If an animal had not given a
positive response by the seventh day of testing, the animal was considered
to have shown no response and was killed at that time. A second group
of males was given five behavior tests and designated as courters or
noncourters on the basis of behavioral scores as described above. After
castration and extinction of sexual behavior, these males were tested for
P sensitivity in the reinstatement of courtship behavior by intraperitoneal
implants of progesterone as described above. After their classification as
either P-sensitive (n 5 6) or P-insensitive (n 5 6), the implants were
removed, and the males were allowed 1 week to clear the exogenous
progesterone before they were killed for brain removal. This second
group of males was intended as a control group comparing P-sensitive
and P-insensitive males in the unimplanted condition and under similar
baseline hormonal conditions.
Tissue samples. Animals were killed by rapid decapitation and the
intact brains immediately removed, frozen on dry ice, and stored at
2808C until sectioning. Coronal cryosections (20 m thick) were melted
onto RNase-free poly-L-lysine-coated microscope slides, dried at room
temperature, and stored in slide boxes with desiccant at 2808C. Sections
were collected across a series of seven slides so that adjacent sections
could be hybridized to different probes.
In situ hybridization and silver grain quantification. The protocols and
validation of the in situ hybridization, autoradiography, and grain quantification
procedures used in this study have been described (Young et al.,
1994, 1995; Godwin and Crews, 1995). Briefly, all slides in all treatment
groups were processed in the in situ hybridization procedure at the same
time. After hybridization, slides were dipped in Kodak NTB-2 emulsion
and allowed to expose at 48C for 11 d for quantification of PR-mRNA and
3 weeks for AR-mRNA, developed in Kodak D-19 developer, and fixed.
Silver grain density was defined as number of grains per cluster, in which
clusters were groups of silver grains lying over cell somata in discrete,
cresyl violet-defined brain nuclei on sections that were matched anatomically
between individual lizards [Young et al. (1994), their Figs. 2–4] (see
Fig. 2 for anatomical maps of the whiptail brain). Silver grain density was
quantified in the medial and periventricular POA for PR-mRNA and in
the medial and periventricular POA, amygdala, and lateral septum for
AR-mRNA with the “Grains” program (Donald K. Clifton, University of
Washington, personal communication) on a Macintosh IIci computer
equipped with an image capture system exactly as described previously
(Young et al., 1995). Because of the small size of whiptail lizard brains,
well-labeled cells are clustered typically on only one section of experimental
slides. For both mRNA species, we counted the 10 most densely
labeled cells in the medial POA, periventricular POA, and lateral septum
and the 20 most densely labeled cells in the amygdala, as in previous work
(Young et al., 1995). The control slides hybridized to sense strand control
probes exhibited uniform background densities of silver grains and no
specific labeling of cells. Sample sizes differed for different nuclei because
sections were sometimes lost in cryosectioning.
Statistical analysis. The proportions of males in the P-sensitive and
P-insensitive groups in which behavior was reinstated by intrahypothalamic
progesterone implants were compared with Fisher’s Exact test (Zar, 1984).
Mean silver grain densities (grains/cluster) measured in given nuclei were
compared between P-sensitive and P-insensitive males with two-sample t
tests. Data were log10-transformed to reduce heterogeneity of variance
between comparison groups, as necessary (Zar, 1984). All analyses were
performed by Systat 5.1.2 on an Apple Macintosh computer.
RESULTS
Intrahypothalamic progesterone implantation and
behavior reinstatement
Intrahypothalamic progesterone implants reinstated sexual behavior
in a significantly higher proportion of males identified as
P-sensitive on the basis of systemic progesterone administration
(8/11) than in males identified as P-insensitive (1/7; Fisher Exact
test, p , 0.05).
PR- and AR-mRNA expression in P-sensitive and
P-insensitive males
P-sensitive implanted males showed significantly lower abundance of
PR-mRNA than P-insensitive implanted males in both the medial
and periventricular POA ( p , 0.05 in each case) (Table 1, Fig. 2).
The pattern was opposite for AR-mRNA in the medial POA, in
which P-sensitive implanted males had significantly higher ARmRNA
abundance ( p , 0.01). AR-mRNA abundance did not differ
between the groups for the periventricular POA ( p . 0.5).
P-sensitive implanted males also showed significantly higher ARmRNA
abundance than P-insensitive implanted males in the amygdala
externae ( p,0.05) and lateral septum ( p,0.01) (Table 1, Fig.
2). There were no statistical differences in PR- or AR-mRNA abundance
in these nuclei among nonimplanted P-sensitive and
P-insensitive control males (Table 1). Because the individuals receiving
intrahypothalamic implants were processed in separate in situ
hybridization procedures from the nonimplanted control males,
these groups cannot be compared directly.
The cryosectioning and preparation for in situ hybridization interfered
with locating the implant in some of the individuals, but
implant position was identified in over one-half of the brains and did
not differ between P-sensitive and P-insensitive animals. There were
also no significant differences found in steroid receptor expression
patterns in the medial or periventricular POA between the side of
Table 1. Comparison of relative PR- and AR-mRNA abundance in hypothalamic nuclei of strong-courting and weak-courting males in
intrahypothalamic P-implanted and castrated nonimplanted control conditions
Nucleus
Intrahypothalamic P-implanted
t test
Nonimplanted control
P-sensitive P-insensitive P-sensitive P-insensitive
PR-mRNA
MPOA 12.63 6 0.70 (11) 15.90 6 1.40 (5) p , 0.05 8.43 6 1.64 (6) 9.10 6 0.54 (6) N.S.
PvPOA 25.19 6 3.30 (11) 32.38 6 2.20 (5) p , 0.05 22.35 6 1.63 (6) 20.67 6 1.56 (6) N.S.
AR-mRNA
MPOA 11.11 6 1.00 (11) 8.21 6 0.58 (5) p , 0.01 23.79 6 3.04 (6) 23.47 6 4.04 (6) N.S.
PvPOA 4.49 6 0.42 (11) 4.12 6 0.94 (5) N.S. 8.92 6 0.67 (6) 11.62 6 3.26 (6) N.S.
Amygdala 21.24 6 1.63 (11) 16.23 6 1.89 (5) p , 0.05 41.66 6 3.70 (6) 42.92 6 7.48 (6) N.S.
Lateral septum 18.43 6 1.45 (11) 13.52 6 0.55 (5) p , 0.01 27.24 6 2.73 (6) 28.74 6 3.37 (6) N.S.
Implanted and nonimplanted control male brains were processed in separate in situ hybridization procedures and cannot be compared directly. Relative mRNA abundance
is assessed by silver grain density over labeled cells (mean 6 1 SEM). Numbers in parentheses equal n values.
N.S., Not significant.
Crews et al. · Progesterone Activation of AR and PR Expression in Males J. Neurosci., November 15, 1996, 16(22):7347–7352 7349
the brain receiving the implant and the side left intact (either with the
P-sensitive and P-insensitive groups considered separately or when
lumped together) ( p . 0.5 paired-sample t tests).
DISCUSSION
Intrahypothalamic progesterone administration was effective in reinstating
sexual behavior in castrated males determined previously to
be P-sensitive by systemic administration of progesterone, indicating
that the behavioral effects of exogenous progesterone are mediated
centrally, rather than peripherally. The site of action is likely one or
more nuclei of the anterior hypothalamus and preoptic area (AHPOA),
such as the medial and periventricular POA. In vertebrates,
the neural circuit mediating mounting and intromission behavior
involves the AH-POA as the final common pathway. Not only is it a
target area of sex steroid hormones, but administration of androgen
directly into this area of castrated, sexually inactive males stimulates
mounting and intromission behavior, whereas bilateral lesions of this
area in sexually active males abolish such behavior (Crews and Silver,
1985; Sachs and Meisel, 1994).
P-sensitive males with intrahypothalamic implants had significantly
higher AR-mRNA abundance, as compared with P-insensitive males
in the medial POA, amygdala externae, and lateral septum, areas
Figure 2. Relative abundances of AR- and PR-mRNA in various nuclei in strong- and weak-courting males from individuals with intrahypothalamic
progesterone implants and control individuals lacking implants. Strong courters are shown in clear bars and weak courters in filled bars. Values for mRNA
relative abundances in weak courters are expressed relative to those in strong courters (defined as 100%) for each treatment group.
7350 J. Neurosci., November 15, 1996, 16(22):7347–7352 Crews et al. · Progesterone Activation of AR and PR Expression in Males
that exhibit the strongest labeling for AR-mRNA in the whiptail
lizard brain (Young et al., 1994). The medial POA is critical to the
control of male-typical sexual behavior in whiptail lizards (Kingston
and Crews, 1994), and the amygdala has been implicated in the
mediation of sexual behavior in various species (Kling and Brothers,
1992; Sachs and Meisel, 1994). In the green anole lizard (Anolis
carolinensis), bilateral lesions of the amygdala externae abolish male
courtship behavior (Greenberg et al., 1984). This area receives olfactory
information in other vertebrates, has afferents to the AHPOA,
and has been suggested to affect perception of social stimuli
(reviewed in Kling and Brothers, 1992; Perkins et al., 1995). Little is
known of possible behavioral functions of the septal area in reptiles,
but this area does have afferent connections with the hypothalamus
and in the green anole lizard is important in sociosexual behavior
(Crews, 1979).
The differences in AR- and PR-mRNA expression between castrated
P-sensitive and P-insensitive males could represent either (1)
differential responses to intrahypothalamic progesterone administration
or (2) intrinsic baseline differences in expression of these mRNA
species. The lack of differences between control P-sensitive and
P-insensitive animals argues against the second possibility. [Unimplanted
intact males differing in courtship intensity representing
these two populations also do not have differential baseline abundances
of androgen receptor- or progesterone receptor-mRNA in
these nuclei (D. Crews, J. Godwin, and M. Grammer, unpublished
data)]. Progesterone is known to downregulate nuclear AR protein,
but not cytosolic AR, in the AH-POA and pituitary of male guinea
pigs administered either progesterone or the synthetic progestin
agonist R5020 (Connolly and Resko, 1989). A progesteronemediated
regulation of AR-mRNA could be important in the medial
POA, because AR- and PR-mRNA are codistributed in this area.
However, this seems unlikely in the lateral septum or amygdala
externae, because no significant labeling of PR-mRNA is found in
these areas (Young et al., 1994).
The finding that implanted P-insensitive males had significantly
higher PR-mRNA abundance in both the medial and periventricular
POA than P-sensitive males was not expected. As argued
above, the lack of PR-mRNA differences in control P-sensitive
and P-insensitive males suggests this difference between
P-sensitive and P-insensitive males reflects differential downregulation
of PR-mRNA in response to intrahypothalamic progesterone
administration. Because the nonimplanted control group
males were processed in a separate in situ hybridization procedure
and are not an appropriate group for baseline comparisons to the
implanted groups, we cannot say whether the greater PR-mRNA
abundance in the implanted P-sensitive males reflects downregulation
in P-sensitive males or upregulation in P-insensitive males.
Likewise, the difference in AR-mRNA abundance could reflect
either upregulation in P-sensitive males or downregulation in
P-insensitive males. However, it is known that progesterone
downregulates its own receptor in both peripheral tissues and the
ventromedial nucleus of the hypothalamus in female mammals
(Selcer and Leavitt, 1988; Blaustein and Turcotte, 1990). This
effect of progesterone is also seen with PR-mRNA in the ventromedial
hypothalamus of female whiptail lizards (Godwin et al.,
1996). These patterns suggest intrahypothalamic progesterone
primarily is affecting the P-sensitive males, but this has not been
conclusively shown.
It is curious that there was no difference in the abundance of AR
or PR message relative to the side of the implant. One possible
explanation is that hormone leaked from the implant site in the
AH-POA into the systemic circulation, and hence both sides of the
brain were exposed to hormone, leading to the bilateral regulation of
AR- and PR-mRNA expression. However, extensive studies using
the same technique in our and other laboratories indicate this unlikely,
because implants nearby, but not in hormone target nuclei, fail
to elicit mating behavior. Further, in the present study, three
P-sensitive individuals failed to respond to the intrahypothalamic
implantation, and a single P-insensitive individual copulated after
intrahypothalamic implantation. A second possibility is that the hormone
implant stimulated steroid hormone-concentrating neurons in
the ipsilateral AH-POA via activated hormone receptor–genome
mechanisms as well as induced neurophysiological changes that were
communicated via commissural connections to the contralateral nuclei,
thereby regulating their hormone receptor expression. In this
regard it is perhaps significant that, in general, unilateral intrahypothalamic
implants into AH-POA are effective in restoring sexual
behavior in castrated males, yet unilateral lesions of the AH-POA
fail to abolish mating behavior in sexually intact males. It is possible
that in both instances compensatory stimulation of the nuclei contralateral
to the treated nuclei is responsible for the behavior.
There are several possible mechanisms by which progesterone
could activate sexual behavior in castrated male whiptail lizards.
First, progesterone may bind and activate AR. As in mammals,
progesterone will bind the AR in lizards, albeit with less affinity
than androgens, and high dosages lead to an inhibition of
androgen-dependent responses (Bullock et al., 1978; Connolly
and Resko, 1989; Lindzey and Crews, 1993). Also, there is a
significant positive correlation between circulating levels of progesterone
and the intensity of sexual behavior in intact male
whiptail lizards (Lindzey and Crews, 1993). Second, the AR of
whiptail lizards may be unusual in its affinity and specificity.
However, the affinity and kinetics of the AR found in male
whiptail lizards is comparable to that of mammalian AR (Lindzey
and Crews, 1993). Third, progesterone may be converted to androgens
or estrogens within the CNS. Neural conversion of steroid
hormones is well documented in other vertebrate species,
including mammals (Schlinger and Arnold, 1990). However,
administration of R5020, a synthetic progestin that cannot be
converted to other steroids, is as effective as progesterone in
stimulating sexual behavior, and the antiprogestin RU486 inhibits
the progesterone-induced reinstatement of sexual behavior in
castrated whiptail lizards (Lindzey and Crews, 1988). A fourth
possibility that has not been excluded by experiments is that
progesterone may bind to and activate PR in neurons that are
components of, or functionally linked to, neural circuits controlling
male sexual behavior. As in the rat (Brown et al., 1987;
Lauber et al., 1991), both AR and PR are codistributed and
concentrated in the AH-POA of the sexual whiptail lizard (Young
et al., 1994). Administration of androgen (testosterone or dihydrotestosterone)
to gonadectomized whiptail lizards upregulates
PR in the medial and periventricular POA (J. Godwin, V. Hartman,
P. Nag, and D. Crews, unpublished data). The present report
demonstrates that intrahypothalamic implantation of progesterone
activates sexual behavior in castrated, P-sensitive males and,
further, differentially regulates AR and PR in the medial and
periventricular POA in P-sensitive, as compared with
P-insensitive, males. The question to be answered now is whether
AR and PR are colocalized in the same neurons or whether they
reside in separate neurons that are in functional communication.
Progesterone activation of sexual behavior in male lizards has
parallels in the laboratory rat. Androgen replacement therapy in
castrated male rats does not reinstate sexual behavior in all
individuals, and in those that do show sexual behavior to an
Crews et al. · Progesterone Activation of AR and PR Expression in Males J. Neurosci., November 15, 1996, 16(22):7347–7352 7351
estrous female, the behavior often is deficient. Further, administration
of the antiprogestin RU486 to intact males inhibits the
expression of aspects of sexual behavior (Witt et al., 1995). We
have shown that, if physiological levels of progesterone are maintained
in conjunction with androgen replacement therapy, complete
sexual responses will be restored in castrated male rats (Witt
et al., 1995). Indeed, the sexual behavior of these progesterone
plus androgen-treated castrated males is equivalent to that of
intact males. This is significant because castrated males given
androgen replacement therapy alone usually never regain the full
expression of sexual behavior. Also similar to the whiptail lizard,
the medial POA and other nuclei in the AH-POA of rats express
PR in both males and females, and no sex differences have been
reported in the distribution or concentration of PR in the medial
POA, although sex differences do occur in the ventromedial
nucleus of the hypothalamus and the arcuate nucleus (Brown et
al., 1987; Lauber et al., 1991).
The following has been established empirically: (1) the AHPOA
is involved in the regulation of sexual behavior of males (2)
and contains both AR and PR; (3) there exists a pronounced
circadian pattern of progesterone secretion in males, and (4)
progesterone synergizes with androgen to reinstate sexual behavior
in castrated males, whereas (5) antiprogestin treatment leads
to deficits in sexual behavior. Together, these indicate that progesterone
and its interaction with its receptor play an important
role in mediating androgen-dependent sexual behavior in males.
The similarity of action of progesterone in both lizards and rats
suggests that this hormone behavior interaction may be conserved
evolutionarily and of fundamental importance to the control of
sexual behavior in male amniote vertebrates.
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Intrahypothalamic Implantation of Progesterone in Castrated Male
Whiptail Lizards (Cnemidophorus inornatus) Elicits Courtship and
Copulatory Behavior and Affects Androgen Receptor- and
Progesterone Receptor-mRNA Expression in the Brain
David Crews, John Godwin, Vesta Hartman, Michael Grammer, Ellen A. Prediger, and Rebecca Sheppherd
Department of Zoology and Institute for Reproductive Biology, University of Texas, Austin, Texas 78712
A primary tenet of behavioral neuroendocrinology is that gonadal
steroid hormones act on limbic nuclei to activate mating behavior
in vertebrates. Traditionally, research has focused on the regulation
of male-typical sexual behavior by testicular androgens and
female-typical sexual behavior by ovarian estrogen and progesterone.
Indeed, progesterone generally is regarded as an antiandrogen,
acting centrally to inhibit sexual behavior in males.
However, experiments with lizards, and more recently with rats,
have challenged this paradigm. For example, exogenous progesterone
induces mating behavior in some, but not all, castrated
male whiptail lizards. The present study determined that implantation
of progesterone into the anterior hypothalamus preoptic
area of castrated, progesterone-sensitive males completely
restored sexual behavior but failed to elicit sexual activity in
castrated, progesterone-insensitive males. Further, androgen
receptor- and progesterone receptor-mRNA expression in specific
brain regions was significantly different in progesteronesensitive
versus progesterone-insensitive animals. Progesteronesensitive
males showed significantly higher relative abundance of
androgen receptor-mRNA in the preoptic area, amygdala, and
lateral septum, as compared with progesterone-insensitive animals
receiving the same treatment. In contrast, progesterone
receptor-mRNA abundance was lower in preoptic area of
progesterone-sensitive males than in progesterone-insensitive
males. No differences were found in the baseline abundance of
androgen receptor- or progesterone receptor-mRNA in these nuclei
between control groups of progesterone-sensitive and
progesterone-insensitive males who were castrated but not implanted.
This suggests that progesterone differentially regulates its
own receptor as well as androgen receptor in areas of the brain
involved in the control of sexual behavior of males and that the
nature of this regulation shows individual variability.
Key words: steroid hormone receptor; gene expression; intrahypothalamic
implantation; septum; amygdala; preoptic
area; sexual behavior; autoregulation; androgen; progesterone;
reptile; lizard; male
In the little striped whiptail lizard (Cnemidophorus inornatus),
as in many other vertebrates, males rely on elevated circulating
levels of androgens for the seasonal activation of sexual behaviors
(Lindzey and Crews, 1986). However, in a subset of these
lizards, exogenous progesterone can also reinstate sexual behavior
in castrated males (equals progesterone-sensitive or
P-sensitive males) (Lindzey and Crews, 1986, 1988a,b). Restoration
of sexual behavior in P-sensitive males by synthetic
progestin agonists indicates that it is progesterone, and not a
metabolite of progesterone, that produces this behavioral effect
(Lindzey, 1988a); binding studies suggest that progesterone
receptor (PR) mediates this response (Lindzey and Crews,
1993). Initially, this progesterone activation of sexual behavior
in castrated male whiptail lizards was puzzling, given the well
known observation that androgen-dependent sexual behaviors
in male mammals and birds are inhibited by progestins (Diamond,
1963; Ericksson et al., 1967; Erpino, 1973; Griffo and
Lee, 1973; Bardin et al., 1984; Bottoni et al., 1985). However,
inspection of the original reports will show that the milligram
amounts administered were likely to result in circulating concentrations
of hormone in excess of the normal physiological
range and, hence, were pharmacological. Further, physiological
studies indicate that male rats have a pronounced circadian
rhythm in progesterone secretion, with fivefold higher peak
levels occurring at the onset of dark phase of the photoperiod
when most sexual activity occurs (Kalra and Kalra, 1977).
Experiments with another lizard (Young et al., 1991) and, more
recently, rats (Witt et al., 1994, 1995) indicate that, whereas
pharmacological dosages of progesterone inhibit sexual behavior
in intact and in castrated, androgen-treated males, lower dosages
that result in circulating levels within the physiological range
stimulate sexual behavior in castrated males. Such progesteronetreated
castrates court and copulate with females with an intensity
equal to that shown by castrates receiving androgen replacement
therapy. Further, subthreshold dosages of progesterone and androgen
synergize to elicit mounting behavior in castrated males,
much as estrogen and progesterone do in eliciting sexual receptivity
in female lizards and mammals (Lindzey and Crews, 1988a;
Young et al., 1991; Witt et al., 1995). It seems, therefore, that
Received July 9, 1996; revised Aug. 29, 1996; accepted Aug. 30, 1996.
This research was supported by National Institute of Mental Health MERIT
Award 41770, Research Scientist Award 00135, and Training Grant 18837 (all to
D.C.), National Institutes of Health National Research Service Award NS09219 (to
J.G.), University of Texas Undergraduate Biomedical Training Program (to V.H.
and M.G.), and National Institutes of Health National Research Service Award
MH10372 (to E.A.P.). We thank Ron and Sherry Hall and Ross and Frank Stavely
for their hospitality and assistance with lizard collections in Sanderson, Texas, and
the Southwestern Research Station of the American Museum of Natural History for
the use of its facilities. We also thank Donald K. Clifton for providing the Grains
image analysis program.
Correspondence should be addressed to Dr. David Crews, Institute of Reproductive
Biology and the Department of Zoology, University of Texas at Austin, Austin,
TX 78712.
Dr. Prediger’s present address: Ambion Incorporated, Austin, TX 78744.
Copyright q 1996 Society for Neuroscience 0270-6474/96/167347-06$05.00/0
The Journal of Neuroscience, November 15, 1996, 16(22):7347–7352
progesterone and androgen both are necessary for the display of
sexual behavior in intact males, but neither is sufficient for complete
restoration of sexual behavior after castration. Thus, in
terms of its role in the neuroendocrine control of sexual behavior,
progesterone may be as much a hormone that affects mounting
and copulatory behavior in males as it affects receptive behavior in
females.
Exploring the neuroendocrine mechanism underlying
progesterone-activated courtship and copulatory behavior in male
whiptail lizards may provide insights into the regulation of sexual
behavior in male vertebrates generally. We find that males who
are behaviorally sensitive to systemic progesterone are also responsive
to intrahypothalamic implants of progesterone, whereas
P-insensitive males do not respond to such implants. Further,
P-sensitive males exhibit significantly higher AR-mRNA expression
than P-insensitive males in the medial preoptic area (POA),
lateral septum, and amygdala, brain regions known to be involved
in the regulation of sexual behavior in males. These same
P-sensitive males had significantly lower expression of PR-mRNA
in the medial and periventricular POA. P-sensitive and
P-insensitive males that did not receive an intrahypothalamic
implant did not have differential baseline abundance of AR- or
PR-mRNA in these nuclei.
MATERIALS AND METHODS
Animals. Cnemidophorus inornatus were captured near Sanderson, Texas,
and in and around Portal, Arizona. The lizards were transported to the
University of Texas at Austin, where they were maintained as described
in Lindzey and Crews (1986). Male study animals were housed individually,
and females were housed in groups of four with one male.
Surgical procedures. All surgery was performed by using hypothermia as
anesthetic. Castrations were performed by the technique described in Crews
et al. (1978). Briefly, an incision was made on each side of the animal lateral
to the abdominal midline. Silk ligatures were used to cut off blood flow to the
testes, which subsequently were removed. Gonadal arteries and veins were
cauterized to prevent further bleeding, and the incision was closed with silk
sutures passing through both the skin and peritoneum. All of the animals
included in the study displayed male typical courtship and copulatory behaviors
in the laboratory before castration. Males were castrated at least 2 weeks
before receiving intraperitoneal implants and were behavior-tested to insure
that the castration was effective.
Intraperitoneal implants of progesterone were made with similar surgical
technique. Intraperitoneal hormone implants were made of 10 mm
of SILASTIC surgical tubing (inner diameter, 1.47 mm; outer diameter,
1.96 mm; Dow Corning, Midland, MI) filled with progesterone (Sigma,
St. Louis, MO), as described previously in Lindzey and Crews (1986). The
ends of the tubing were sealed with SILASTIC adhesive, and a 1 cmpiece
of silk surgical thread was embedded in one of the ends to serve as an
anchor after surgical implantation.
With the use of a Kopf stereotaxis modified for small reptiles, each
experimental animal received an intrahypothalamic progesterone implant
using methods detailed in Rozendaal and Crews (1989). The point of
intersection of the two frontal parietal scales and the interparietal scale was
used as a reference point to determine stereotaxic coordinates. A 1-mmround
dental burr was used to drill a hole in the skull overlying the target
area. A cannula of 30 gauge hypodermic tubing (Hamilton, Reno, NV)
containing progesterone was lowered to the desired site, and the hormone
pellet was ejected by pushing a cleaning wire through the cannula. The
cannula was withdrawn, and the hole in the skull was filled with Gelfoam.
Animals were allowed 24 hr to recover in their home cages before behavioral
testing began.
Intrahypothalamic hormone implants consisted of progesterone, red
Crayola wax, and bone wax in a 3:1:9 ratio by weight. Implant pellets were
formed by tapping the end of the cannula into the mixture. The cylindrical
implants averaged a 140 mm inner diameter 3 0.5 mm in length,
indicating an implant volume of 0.008 mm3. This represents ,10% of the
volume of the anterior hypothalamus (AH)-POA of a male C. inornatus,
which averages 0.096 mm3 (Crews et al., 1990; Wade et al., 1993). Pellets
were found to have an average mass of 22.4 mg (mean of five pellets
weighed on a Cahn microbalance) and, thus, to contain an average dosage
of ;5.20 mg of progesterone per implant. Each experimental animal
received one intrahypothalamic implant targeted for the AH-POA (coordinates
11.85 mm ventral and 20.35 mm posterior to the reference
point). Control animals did not receive an intrahypothalamic implant.
Behavioral testing procedure. All behavioral tests were conducted by introducing
a stimulus-receptive female into the home cage of the experimental
male. Tests were conducted during the high activity period between 10:00
A.M. and 2:00 P.M. A 3 min test was administered daily to all subjects during
periods of behavior testing, and tests were scored in accordance with the
hierarchy of sexual behavior described by Lindzey and Crews (1986). Animals
showing no interest at all in the stimulus female were scored 0, those
that approached and made contact scored 1, swiggle walking received a 2,
mounting a 3, riding a 4, assuming a copulatory posture a 5, and copulating
a 6. Increasing scores represent increasing intensity of male sexual behavior.
All but the last behavior testing period consisted of five sequential days of
testing. An animal scoring a 3 or greater in three of the five tests was
considered as giving a positive response and classified as a “courter.” For the
tests conducted after intrahypothalamic implantation, animals were tested
for seven consecutive days.
Experimental design. The present report combines traditional behavioral
endocrine methods, including castration, hormone replacement therapy, and
intrahypothalamic hormone implantation, with a modern molecular method,
quantitative in situ hybridization to identify AR- and PR-mRNAs in brain
nuclei. The experimental design is summarized in Figure 1. Intact males were
tested for courtship and copulatory behavior. Those displaying sexual responses
as described above (“courters”) were used for the study. After
behavior testing in the intact condition, males were castrated, allowed 10 d to
recover, and then tested to insure the extinction of sexual behavior. Then
animals were given intraperitoneal pellets of progesterone, allowed a 10 d
Figure 1. Schematic illustrating steps in experiment. Control males experienced
the same procedures, with the exception of intrahypothalamic
implantation. For details, see Experimental Design.
7348 J. Neurosci., November 15, 1996, 16(22):7347–7352 Crews et al. · Progesterone Activation of AR and PR Expression in Males
recovery, and behavior-tested again to determine whether sexual behavior
was reinstated by systemic progesterone treatment. Males for whom the
sexual behavior was reinstated with systemic progesterone were classified as
P-sensitive; those in which sexual behavior was not reinstated were classified
as P-insensitive. The intraperitoneal progesterone pellets were then removed,
and the animals again were tested for extinction of behavior. Finally,
each experimental animal was implanted (or not) with an intrahypothalamic
progesterone pellet targeted to the AH-POA and tested double blindly for
stimulation of sexual behavior (experimental: 11 P-sensitive, 7 P-insensitive).
A single score of 3 or greater was designated a positive response, and
these animals were killed immediately. If an animal had not given a
positive response by the seventh day of testing, the animal was considered
to have shown no response and was killed at that time. A second group
of males was given five behavior tests and designated as courters or
noncourters on the basis of behavioral scores as described above. After
castration and extinction of sexual behavior, these males were tested for
P sensitivity in the reinstatement of courtship behavior by intraperitoneal
implants of progesterone as described above. After their classification as
either P-sensitive (n 5 6) or P-insensitive (n 5 6), the implants were
removed, and the males were allowed 1 week to clear the exogenous
progesterone before they were killed for brain removal. This second
group of males was intended as a control group comparing P-sensitive
and P-insensitive males in the unimplanted condition and under similar
baseline hormonal conditions.
Tissue samples. Animals were killed by rapid decapitation and the
intact brains immediately removed, frozen on dry ice, and stored at
2808C until sectioning. Coronal cryosections (20 m thick) were melted
onto RNase-free poly-L-lysine-coated microscope slides, dried at room
temperature, and stored in slide boxes with desiccant at 2808C. Sections
were collected across a series of seven slides so that adjacent sections
could be hybridized to different probes.
In situ hybridization and silver grain quantification. The protocols and
validation of the in situ hybridization, autoradiography, and grain quantification
procedures used in this study have been described (Young et al.,
1994, 1995; Godwin and Crews, 1995). Briefly, all slides in all treatment
groups were processed in the in situ hybridization procedure at the same
time. After hybridization, slides were dipped in Kodak NTB-2 emulsion
and allowed to expose at 48C for 11 d for quantification of PR-mRNA and
3 weeks for AR-mRNA, developed in Kodak D-19 developer, and fixed.
Silver grain density was defined as number of grains per cluster, in which
clusters were groups of silver grains lying over cell somata in discrete,
cresyl violet-defined brain nuclei on sections that were matched anatomically
between individual lizards [Young et al. (1994), their Figs. 2–4] (see
Fig. 2 for anatomical maps of the whiptail brain). Silver grain density was
quantified in the medial and periventricular POA for PR-mRNA and in
the medial and periventricular POA, amygdala, and lateral septum for
AR-mRNA with the “Grains” program (Donald K. Clifton, University of
Washington, personal communication) on a Macintosh IIci computer
equipped with an image capture system exactly as described previously
(Young et al., 1995). Because of the small size of whiptail lizard brains,
well-labeled cells are clustered typically on only one section of experimental
slides. For both mRNA species, we counted the 10 most densely
labeled cells in the medial POA, periventricular POA, and lateral septum
and the 20 most densely labeled cells in the amygdala, as in previous work
(Young et al., 1995). The control slides hybridized to sense strand control
probes exhibited uniform background densities of silver grains and no
specific labeling of cells. Sample sizes differed for different nuclei because
sections were sometimes lost in cryosectioning.
Statistical analysis. The proportions of males in the P-sensitive and
P-insensitive groups in which behavior was reinstated by intrahypothalamic
progesterone implants were compared with Fisher’s Exact test (Zar, 1984).
Mean silver grain densities (grains/cluster) measured in given nuclei were
compared between P-sensitive and P-insensitive males with two-sample t
tests. Data were log10-transformed to reduce heterogeneity of variance
between comparison groups, as necessary (Zar, 1984). All analyses were
performed by Systat 5.1.2 on an Apple Macintosh computer.
RESULTS
Intrahypothalamic progesterone implantation and
behavior reinstatement
Intrahypothalamic progesterone implants reinstated sexual behavior
in a significantly higher proportion of males identified as
P-sensitive on the basis of systemic progesterone administration
(8/11) than in males identified as P-insensitive (1/7; Fisher Exact
test, p , 0.05).
PR- and AR-mRNA expression in P-sensitive and
P-insensitive males
P-sensitive implanted males showed significantly lower abundance of
PR-mRNA than P-insensitive implanted males in both the medial
and periventricular POA ( p , 0.05 in each case) (Table 1, Fig. 2).
The pattern was opposite for AR-mRNA in the medial POA, in
which P-sensitive implanted males had significantly higher ARmRNA
abundance ( p , 0.01). AR-mRNA abundance did not differ
between the groups for the periventricular POA ( p . 0.5).
P-sensitive implanted males also showed significantly higher ARmRNA
abundance than P-insensitive implanted males in the amygdala
externae ( p,0.05) and lateral septum ( p,0.01) (Table 1, Fig.
2). There were no statistical differences in PR- or AR-mRNA abundance
in these nuclei among nonimplanted P-sensitive and
P-insensitive control males (Table 1). Because the individuals receiving
intrahypothalamic implants were processed in separate in situ
hybridization procedures from the nonimplanted control males,
these groups cannot be compared directly.
The cryosectioning and preparation for in situ hybridization interfered
with locating the implant in some of the individuals, but
implant position was identified in over one-half of the brains and did
not differ between P-sensitive and P-insensitive animals. There were
also no significant differences found in steroid receptor expression
patterns in the medial or periventricular POA between the side of
Table 1. Comparison of relative PR- and AR-mRNA abundance in hypothalamic nuclei of strong-courting and weak-courting males in
intrahypothalamic P-implanted and castrated nonimplanted control conditions
Nucleus
Intrahypothalamic P-implanted
t test
Nonimplanted control
P-sensitive P-insensitive P-sensitive P-insensitive
PR-mRNA
MPOA 12.63 6 0.70 (11) 15.90 6 1.40 (5) p , 0.05 8.43 6 1.64 (6) 9.10 6 0.54 (6) N.S.
PvPOA 25.19 6 3.30 (11) 32.38 6 2.20 (5) p , 0.05 22.35 6 1.63 (6) 20.67 6 1.56 (6) N.S.
AR-mRNA
MPOA 11.11 6 1.00 (11) 8.21 6 0.58 (5) p , 0.01 23.79 6 3.04 (6) 23.47 6 4.04 (6) N.S.
PvPOA 4.49 6 0.42 (11) 4.12 6 0.94 (5) N.S. 8.92 6 0.67 (6) 11.62 6 3.26 (6) N.S.
Amygdala 21.24 6 1.63 (11) 16.23 6 1.89 (5) p , 0.05 41.66 6 3.70 (6) 42.92 6 7.48 (6) N.S.
Lateral septum 18.43 6 1.45 (11) 13.52 6 0.55 (5) p , 0.01 27.24 6 2.73 (6) 28.74 6 3.37 (6) N.S.
Implanted and nonimplanted control male brains were processed in separate in situ hybridization procedures and cannot be compared directly. Relative mRNA abundance
is assessed by silver grain density over labeled cells (mean 6 1 SEM). Numbers in parentheses equal n values.
N.S., Not significant.
Crews et al. · Progesterone Activation of AR and PR Expression in Males J. Neurosci., November 15, 1996, 16(22):7347–7352 7349
the brain receiving the implant and the side left intact (either with the
P-sensitive and P-insensitive groups considered separately or when
lumped together) ( p . 0.5 paired-sample t tests).
DISCUSSION
Intrahypothalamic progesterone administration was effective in reinstating
sexual behavior in castrated males determined previously to
be P-sensitive by systemic administration of progesterone, indicating
that the behavioral effects of exogenous progesterone are mediated
centrally, rather than peripherally. The site of action is likely one or
more nuclei of the anterior hypothalamus and preoptic area (AHPOA),
such as the medial and periventricular POA. In vertebrates,
the neural circuit mediating mounting and intromission behavior
involves the AH-POA as the final common pathway. Not only is it a
target area of sex steroid hormones, but administration of androgen
directly into this area of castrated, sexually inactive males stimulates
mounting and intromission behavior, whereas bilateral lesions of this
area in sexually active males abolish such behavior (Crews and Silver,
1985; Sachs and Meisel, 1994).
P-sensitive males with intrahypothalamic implants had significantly
higher AR-mRNA abundance, as compared with P-insensitive males
in the medial POA, amygdala externae, and lateral septum, areas
Figure 2. Relative abundances of AR- and PR-mRNA in various nuclei in strong- and weak-courting males from individuals with intrahypothalamic
progesterone implants and control individuals lacking implants. Strong courters are shown in clear bars and weak courters in filled bars. Values for mRNA
relative abundances in weak courters are expressed relative to those in strong courters (defined as 100%) for each treatment group.
7350 J. Neurosci., November 15, 1996, 16(22):7347–7352 Crews et al. · Progesterone Activation of AR and PR Expression in Males
that exhibit the strongest labeling for AR-mRNA in the whiptail
lizard brain (Young et al., 1994). The medial POA is critical to the
control of male-typical sexual behavior in whiptail lizards (Kingston
and Crews, 1994), and the amygdala has been implicated in the
mediation of sexual behavior in various species (Kling and Brothers,
1992; Sachs and Meisel, 1994). In the green anole lizard (Anolis
carolinensis), bilateral lesions of the amygdala externae abolish male
courtship behavior (Greenberg et al., 1984). This area receives olfactory
information in other vertebrates, has afferents to the AHPOA,
and has been suggested to affect perception of social stimuli
(reviewed in Kling and Brothers, 1992; Perkins et al., 1995). Little is
known of possible behavioral functions of the septal area in reptiles,
but this area does have afferent connections with the hypothalamus
and in the green anole lizard is important in sociosexual behavior
(Crews, 1979).
The differences in AR- and PR-mRNA expression between castrated
P-sensitive and P-insensitive males could represent either (1)
differential responses to intrahypothalamic progesterone administration
or (2) intrinsic baseline differences in expression of these mRNA
species. The lack of differences between control P-sensitive and
P-insensitive animals argues against the second possibility. [Unimplanted
intact males differing in courtship intensity representing
these two populations also do not have differential baseline abundances
of androgen receptor- or progesterone receptor-mRNA in
these nuclei (D. Crews, J. Godwin, and M. Grammer, unpublished
data)]. Progesterone is known to downregulate nuclear AR protein,
but not cytosolic AR, in the AH-POA and pituitary of male guinea
pigs administered either progesterone or the synthetic progestin
agonist R5020 (Connolly and Resko, 1989). A progesteronemediated
regulation of AR-mRNA could be important in the medial
POA, because AR- and PR-mRNA are codistributed in this area.
However, this seems unlikely in the lateral septum or amygdala
externae, because no significant labeling of PR-mRNA is found in
these areas (Young et al., 1994).
The finding that implanted P-insensitive males had significantly
higher PR-mRNA abundance in both the medial and periventricular
POA than P-sensitive males was not expected. As argued
above, the lack of PR-mRNA differences in control P-sensitive
and P-insensitive males suggests this difference between
P-sensitive and P-insensitive males reflects differential downregulation
of PR-mRNA in response to intrahypothalamic progesterone
administration. Because the nonimplanted control group
males were processed in a separate in situ hybridization procedure
and are not an appropriate group for baseline comparisons to the
implanted groups, we cannot say whether the greater PR-mRNA
abundance in the implanted P-sensitive males reflects downregulation
in P-sensitive males or upregulation in P-insensitive males.
Likewise, the difference in AR-mRNA abundance could reflect
either upregulation in P-sensitive males or downregulation in
P-insensitive males. However, it is known that progesterone
downregulates its own receptor in both peripheral tissues and the
ventromedial nucleus of the hypothalamus in female mammals
(Selcer and Leavitt, 1988; Blaustein and Turcotte, 1990). This
effect of progesterone is also seen with PR-mRNA in the ventromedial
hypothalamus of female whiptail lizards (Godwin et al.,
1996). These patterns suggest intrahypothalamic progesterone
primarily is affecting the P-sensitive males, but this has not been
conclusively shown.
It is curious that there was no difference in the abundance of AR
or PR message relative to the side of the implant. One possible
explanation is that hormone leaked from the implant site in the
AH-POA into the systemic circulation, and hence both sides of the
brain were exposed to hormone, leading to the bilateral regulation of
AR- and PR-mRNA expression. However, extensive studies using
the same technique in our and other laboratories indicate this unlikely,
because implants nearby, but not in hormone target nuclei, fail
to elicit mating behavior. Further, in the present study, three
P-sensitive individuals failed to respond to the intrahypothalamic
implantation, and a single P-insensitive individual copulated after
intrahypothalamic implantation. A second possibility is that the hormone
implant stimulated steroid hormone-concentrating neurons in
the ipsilateral AH-POA via activated hormone receptor–genome
mechanisms as well as induced neurophysiological changes that were
communicated via commissural connections to the contralateral nuclei,
thereby regulating their hormone receptor expression. In this
regard it is perhaps significant that, in general, unilateral intrahypothalamic
implants into AH-POA are effective in restoring sexual
behavior in castrated males, yet unilateral lesions of the AH-POA
fail to abolish mating behavior in sexually intact males. It is possible
that in both instances compensatory stimulation of the nuclei contralateral
to the treated nuclei is responsible for the behavior.
There are several possible mechanisms by which progesterone
could activate sexual behavior in castrated male whiptail lizards.
First, progesterone may bind and activate AR. As in mammals,
progesterone will bind the AR in lizards, albeit with less affinity
than androgens, and high dosages lead to an inhibition of
androgen-dependent responses (Bullock et al., 1978; Connolly
and Resko, 1989; Lindzey and Crews, 1993). Also, there is a
significant positive correlation between circulating levels of progesterone
and the intensity of sexual behavior in intact male
whiptail lizards (Lindzey and Crews, 1993). Second, the AR of
whiptail lizards may be unusual in its affinity and specificity.
However, the affinity and kinetics of the AR found in male
whiptail lizards is comparable to that of mammalian AR (Lindzey
and Crews, 1993). Third, progesterone may be converted to androgens
or estrogens within the CNS. Neural conversion of steroid
hormones is well documented in other vertebrate species,
including mammals (Schlinger and Arnold, 1990). However,
administration of R5020, a synthetic progestin that cannot be
converted to other steroids, is as effective as progesterone in
stimulating sexual behavior, and the antiprogestin RU486 inhibits
the progesterone-induced reinstatement of sexual behavior in
castrated whiptail lizards (Lindzey and Crews, 1988). A fourth
possibility that has not been excluded by experiments is that
progesterone may bind to and activate PR in neurons that are
components of, or functionally linked to, neural circuits controlling
male sexual behavior. As in the rat (Brown et al., 1987;
Lauber et al., 1991), both AR and PR are codistributed and
concentrated in the AH-POA of the sexual whiptail lizard (Young
et al., 1994). Administration of androgen (testosterone or dihydrotestosterone)
to gonadectomized whiptail lizards upregulates
PR in the medial and periventricular POA (J. Godwin, V. Hartman,
P. Nag, and D. Crews, unpublished data). The present report
demonstrates that intrahypothalamic implantation of progesterone
activates sexual behavior in castrated, P-sensitive males and,
further, differentially regulates AR and PR in the medial and
periventricular POA in P-sensitive, as compared with
P-insensitive, males. The question to be answered now is whether
AR and PR are colocalized in the same neurons or whether they
reside in separate neurons that are in functional communication.
Progesterone activation of sexual behavior in male lizards has
parallels in the laboratory rat. Androgen replacement therapy in
castrated male rats does not reinstate sexual behavior in all
individuals, and in those that do show sexual behavior to an
Crews et al. · Progesterone Activation of AR and PR Expression in Males J. Neurosci., November 15, 1996, 16(22):7347–7352 7351
estrous female, the behavior often is deficient. Further, administration
of the antiprogestin RU486 to intact males inhibits the
expression of aspects of sexual behavior (Witt et al., 1995). We
have shown that, if physiological levels of progesterone are maintained
in conjunction with androgen replacement therapy, complete
sexual responses will be restored in castrated male rats (Witt
et al., 1995). Indeed, the sexual behavior of these progesterone
plus androgen-treated castrated males is equivalent to that of
intact males. This is significant because castrated males given
androgen replacement therapy alone usually never regain the full
expression of sexual behavior. Also similar to the whiptail lizard,
the medial POA and other nuclei in the AH-POA of rats express
PR in both males and females, and no sex differences have been
reported in the distribution or concentration of PR in the medial
POA, although sex differences do occur in the ventromedial
nucleus of the hypothalamus and the arcuate nucleus (Brown et
al., 1987; Lauber et al., 1991).
The following has been established empirically: (1) the AHPOA
is involved in the regulation of sexual behavior of males (2)
and contains both AR and PR; (3) there exists a pronounced
circadian pattern of progesterone secretion in males, and (4)
progesterone synergizes with androgen to reinstate sexual behavior
in castrated males, whereas (5) antiprogestin treatment leads
to deficits in sexual behavior. Together, these indicate that progesterone
and its interaction with its receptor play an important
role in mediating androgen-dependent sexual behavior in males.
The similarity of action of progesterone in both lizards and rats
suggests that this hormone behavior interaction may be conserved
evolutionarily and of fundamental importance to the control of
sexual behavior in male amniote vertebrates.
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Ants give up sexuality to maintain social harmony

Thu, Nov 20 02:02 PM

Toronto, Nov 20 (IANS) Highly specialised worker ants represent the pinnacle of social organisation in the insect world.

As in any society, however, ant colonies are filled with internal strife and conflict. So what binds them together? More than 150 years ago, Charles Darwin had an idea and now he's been proven right.

Evolutionary biologists at McGill University have discovered molecular signals that can maintain social harmony in ants by desexualising them.

Ehab Abouheif, of McGill's department of biology and post-doctoral researcher Abderrahman Khila, have discovered how evolution has tinkered with the genes of colonising insects like ants to decide who gets to reproduce.

'We've discovered a really elegant developmental mechanism, which we call 'reproductive constraint', that challenges the classic paradigm that behaviour, such as policing, is the only way to enforce harmony and squash selfish behaviour in ant societies,' said Abouheif.

Reproductive constraint comes into play in these ant societies when evolutionary forces begin to work in a group context rather than on individuals, the researchers said, according to a McGill release.

The process can be seen in the differences between advanced ant species and their more primitive cousins.

Ants - organised in colonies around one or many queens surrounded by their specialised female workers - are classic examples of what are called eusocial organisms.

'More primitive, or ancestral, ants tend to have smaller colony sizes and have much higher levels of conflict over reproduction than the more advanced species,' Abouheif explained. 'That's because the workers have a much higher reproductive capacity and there is conflict with the queen to produce offspring.'

To their surprise, Khila and Abouheif discovered that 'evolution has tinkered with the molecular signals that are used by the egg to determine what's going to be the head and what's going to be the tail, to stop the worker ants from producing viable offspring,' Abouheif explained.

The existence of sterile castes of ants tormented Charles Darwin as he was formulating his Theory of Natural Selection, and he described them as the 'one special difficulty, which at first appeared to me insuperable, and actually fatal to my theory.'

The study appeared in Tuesday issue of the Proceedings of the National Academy of Sciences.

200 million years of non-reproductive sex

Female monkeys challenge Darwin theory -- Part II

(Our site strongly disagrees with the misleading term Lesbian to define females when they have sex with other females amongst animals)

Lesbian monkeys challenge Darwin theory
Wed Feb 26, 7:35 PM ET

A psychologist claims that a group of lesbian monkeys in Japan shows that Darwin's theories of evolution are incorrect.

Paul Vasey, of the University of Lethbridge in Alberta, Canada, has been studying the sex lives of Japanese macaques.

According to Darwin's theory of sexual selection, said Vasey, the male monkeys should compete amongst themselves for access to potential mates -- but the macaques don't follow that pattern.

A colony of 120 wild macaques in the mountains in Kyoto shows enormous sexual diversity, including female-female relationships. Females will reject the advances of a pursuing male in favor of their existing female partner 92.5 percent of the time.

"If females are choosing female sexual partners over male reproductive partners," Vasey told the American Association for the Advancement of Science (news - web sites), "that suggests a pretty fundamental revision of sexual selection theory.

"We've got females that are competing for males with other females, we've got males that are being choosy, males that are sexually coercing females ... we've got females sexually harassing males that don't want to copulate with them, we've got females that have sex with each other, we've got females that are competing with males for other females, we have females that are mounting males."

Vasey said it is clear the females are deriving sexual pleasure when they mount other females. In some positions, he said, a female will rub her clitoris against her partner's back, while in others, "it's common for females to masturbate with their tails" where there is no direct genital contact.

"The traditional evolutionary theory says you do things in order to reproduce," he said, "so why would you do all this non-reproductive sex? To me, that's a really compelling evolutionary puzzle."

Female monkeys challenge Darwin assumptions - Part I

Same-sex bonds in marine animals

Diversity, Gender, and Sexuality in Nature and People

Editorial Reviews from Amazon.com

Amazon.com

Bruce Bagemihl writes that Biological Exuberance: Animal Homosexuality and Natural Diversity was a "labor of love." And indeed it must have been, since most scientists have thus far studiously avoided the topic of widespread homosexual behavior in the animal kingdom--sometimes in the face of undeniable evidence. Bagemihl begins with an overview of same-sex activity in animals, carefully defining courtship patterns, affectionate behaviors, sexual techniques, mating and pair-bonding, and same-sex parenting. He firmly dispels the prevailing notion that homosexuality is uniquely human and only occurs in "unnatural" circumstances. As far as the nature-versus-nurture argument--it's obviously both, he concludes. An overview of biologists' discomfort with their own observations of animal homosexuality over 200 years would be truly hilarious if it didn't reflect a tendency of humans (and only humans) to respond with aggression and hostility to same-sex behavior in our own species. In fact, Bagemihl reports, scientists have sometimes been afraid to report their observations for fear of recrimination from a hidebound (and homophobic) academia. Scientists' use of anthropomorphizing vocabulary such as insulting, unfortunate, and inappropriate to describe same-sex matings shows a decided lack of objectivity on the part of naturalists.

Astounding as it sounds, a number of scientists have actually argued that when a female Bonobo wraps her legs around another female ... while emitting screams of enjoyment, this is actually "greeting" behavior, or "appeasement" behavior ... almost anything, it seems, besides pleasurable sexual behavior.

Throw this book into the middle of a crowd of wildlife biologists and watch them scatter. But Bagemihl doesn't let the scientific community's discomfort deny him the opportunity to show "the love that dare not bark its name" in all its feathery, furry, toothy diversity. The second half of this hefty tome is filled with an exhaustive array of species that exhibit homosexuality, complete with photos and detailed scientific illustrations of the behaviors described. Biological Exuberance is a well-researched, thoroughly scientific, and erudite look at a purposefully neglected frontier of zoology. --Therese Littleton --This text refers to an out of print or unavailable edition of this title.

From Publishers Weekly

A brilliant and important exercise in exposing the limitations of received opinion, this book presents to the lay reader and specialist alike an exhaustively argued case that animals have multiple shades of sexual orientation. The book is broken into two sections, the second containing species "portraits" detailing recorded homosexual/transgendered behaviors. The main portion of the book sets out to reveal and, indeed, revel in the documented evidence to date that some 450 species engage in both sustained and occasional "gay," "lesbian" and transgendered pairing, parenting and play. Animals (both heterosexual and homosexual) also rape and divorce, commit "child" abuse and infidelity and can be lifelong celibates. Human claims to uniqueness in this arena are shown to be increasingly difficult to maintain. The overall effect is to detonate the myth that animals are solely driven by heterosexual reproductive urges, as Bagemihl, a biologist, amasses evidence with case study after case study of species ranging from whiptail lizards to bottlenose dolphins, flamingoes, vampire bats and giraffes. But his book offers more than a zoological laundry list. Biologists who have long classified these behaviors as taking place only in "abnormal" conditions or as "pseudo-copulation," "mistakes," "practicing" and domineering sexual bullying are frequently shown to be willfully ignoring behavior that does not reflect their own worldview or accepted scientific thought. What might so easily have turned into a tub-thumping activist tract hitched to the need for acceptance of homosexuality among humans is instead elevated to a hugely inclusive, celebratory biological interpretation of the world. Bagemihl convincingly overturns previous inviolable "truths" that scarcity and functionality are the prime agents of biological change, and advances instead the idea that abundance and extravagance?"biological exuberance"?are just as crucial to the mosaic of life. Numerous illustrations by John Megahan.
Copyright 1998 Reed Business Information, Inc. --This text refers to an out of print or unavailable edition of this title.

From Kirkus Reviews

A scholarly, exhaustive, and utterly convincing refutation of the notion that human homosexuality is an aberration in nature. Biologist Bagemihl, who formerly taught cognitive science at the University of British Columbia, argues persuasively that our current understanding of biology and evolution is tainted by a heterosexually biased interpretation of animal behavior. He intends as his audience both a scientific and a general readership; he reaches both with his clear and straightforward presentation. Focusing primarily on mammals and birds, and citing only strictly documented case studies, he firmly establishes in part one of this work that homosexual and transgendered behaviors occur widely in the animal world. Bagemihl's definition of homosexuality includes a diverse range of activities organized under five headings: courtship, affection, sex, pair-bonding, and parenting. He views the challenge before us now as the need to abandon a traditional point of view, whereby ``same-sex activity is routinely described as being `forced' on other animals'' or is viewed as a substitute for heterosexual coupling that occurs only when no other (i.e., no heterosexual) mate can be found as the first choice of those concerned. A new understanding of animal relationships should therefore also recognize that not all animal sexual activity is aimed at reproductionwe must reconsider traditional explanations of the links between reproduction, evolution, and natural selection. Part two is organized as a thorough reference guide to homosexual behaviors in individual animals and birds, complete with extensive examples and rigorous footnotes. Bagemihl does realize that some among us will never be convinced that homosexuality occurs freely and frequently in nature. But his meticulously gathered, cogently delivered evidence will quash any arguments to the contrary. -- Copyright ©1998, Kirkus Associates, LP. All rights reserved. --This text refers to an out of print or unavailable edition of this title.

Review

"A scholarly, exhaustive, and utterly convincing refutation of the notion that human homosexuality is an aberration in nature . . . Bagemihl does realize that some among us will never be convinced that homosexuality occurs freely and frequently in nature. But his meticulously gathered, cogently delivered evidence will quash any arguments to the contrary."—Kirkus Reviews

"A brilliant and important exercise in exposing the limitations of received opinion . . . an exhaustively argued case that animals have multiple shades of sexual orientation."—Publishers Weekly

"Bagemihl has done an extraordinary job in compiling a vast bestiary . . . This book should surely become the standard reference work for research on the topics covered."—Nature

"A landmark in the literature of science."—Chicago Tribune

"By producing a work that is accessible to the general reader while engaging for the specialist, Bagemihl has accomplished a most extraordinary feat. In the tradition of the finest nonfiction, this is a book that will force us to reexamine who we are and what we believe."—The Philadelphia Inquirer

"For anyone who has ever doubted the 'naturalness' of homosexual, bisexual, and transgendered behaviors, this remarkable book, which demonstrates and celebrates the sexual diversity of life on earth, will surely lay those doubts to rest. The massive evidence of the wondrous complexity of sexuality in the natural world that Bagemihl has marshaled will inform, entertain, and persuade academic and lay readers alike. Biological Exuberance is a revolutionary work."—Lillian Faderman, author of Odd Girls and Twilight Lovers: A History of Lesbian Life in Twentieth-Century America

Review

"A scholarly, exhaustive, and utterly convincing refutation of the notion that human homosexuality is an aberration in nature . . . Bagemihl does realize that some among us will never be convinced that homosexuality occurs freely and frequently in nature. But his meticulously gathered, cogently delivered evidence will quash any arguments to the contrary."—Kirkus Reviews

"A brilliant and important exercise in exposing the limitations of received opinion . . . an exhaustively argued case that animals have multiple shades of sexual orientation."—Publishers Weekly

"Bagemihl has done an extraordinary job in compiling a vast bestiary . . . This book should surely become the standard reference work for research on the topics covered."—Nature

"A landmark in the literature of science."—Chicago Tribune

"By producing a work that is accessible to the general reader while engaging for the specialist, Bagemihl has accomplished a most extraordinary feat. In the tradition of the finest nonfiction, this is a book that will force us to reexamine who we are and what we believe."—The Philadelphia Inquirer

"For anyone who has ever doubted the 'naturalness' of homosexual, bisexual, and transgendered behaviors, this remarkable book, which demonstrates and celebrates the sexual diversity of life on earth, will surely lay those doubts to rest. The massive evidence of the wondrous complexity of sexuality in the natural world that Bagemihl has marshaled will inform, entertain, and persuade academic and lay readers alike. Biological Exuberance is a revolutionary work."—Lillian Faderman, author of Odd Girls and Twilight Lovers: A History of Lesbian Life in Twentieth-Century America

Book Description

A Publishers Weekly Best BookOne of the New York Public Library's "25 Books to Remember" for 1999Homosexuality in its myriad forms has been scientifically documented in more than 450 species of mammals, birds, reptiles, insects, and other animals worldwide. Biological Exuberance is the first comprehensive account of the subject, bringing together accurate, accessible, and nonsensationalized information. Drawing upon a rich body of zoological research spanning more than two centuries, Bruce Bagemihl shows that animals engage in all types of nonreproductive sexual behavior. Sexual and gender expression in the animal world displays exuberant variety, including same-sex courtship, pair-bonding, sex, and co-parenting-even instances of lifelong homosexual bonding in species that do not have lifelong heterosexual bonding.Part 1, "A Polysexual, Polygendered World," begins with a survey of homosexuality, transgender, and nonreproductive heterosexuality in animals and then delves into the broader implications of these findings, including a valuable perspective on human diversity. Bagemihl also examines the hidden assumptions behind the way biologists look at natural systems and suggests a fresh perspective based on the synthesis of contemporary scientific insights with traditional knowledge from indigenous cultures.Part 2, "A Wondrous Bestiary," profiles more than 190 species in which scientific observers have noted homosexual or transgender behavior. Each profile is a verbal and visual "snapshot" of one or more closely related bird or mammal species, containing all the documentation required to support the author's often controversial conclusions.Lavishly illustrated and meticulously researched, filled with fascinating facts and astonishing descriptions of animal behavior, Biological Exuberance is a landmark book that will change forever how we look at nature.

From the Publisher

"Bagemihl has done an extraordinary job in compiling a vast bestiary....This book should surely become the standard reference work for research on the topics covered." -Nature

"By producing a work that is accessible to the general reader while engaging for the specialist, Bagemihl has accomplished a most extraordinary feat. In the tradition of the finest nonfiction, this is a book that will force us to reexamine who we are and what we believe." -The Philadelphia Inquirer

"A monumental and captivating work...Biological Exuberance affirms life in all its richness, abundance, and complexity." -DEB PRICE, Detroit News syndicated columnist

"Thrillingly dense with new ideas and with scandalous animal anecdotes. In other words, an ideal bedside read." -Salon

"A landmark in the literature of science." -Chicago Tribune

About the Author

Bruce Bagemihl, Ph.D., is a biologist and researcher who has served on the faculty of the University of British Columbia, where he taught linguistics and cognitive science. He has published diverse essays and scientific articles on issues pertaining to language, biology, gender, and sexuality. He lives in Seattle, Washington.

Selected Readers' Reviews

70 of 77 people found the following review helpful:

Fascinating account of animal homosexuality, February 20, 1999

Reviewer:

Duane T. Williams (Pittsburgh, PA USA) - See all my reviews

The first part of the book is an independent 262 page exposition of homosexual, bisexual and transgendered animal sexuality. If you want to know what the birds and the bees are doing when Jerry Falwell isn't looking, this is the place to find out. Don't expect to find traditional family values in these pages. What you will discover instead is that animals aren't doing it for Darwin, they are doing it for fun. There are amazingly detailed descriptions, pictures and illustrations here of animals having all kinds of sex (that will amaze you), and most of it isn't for procreation.

More interesting to me, though, is the speculation on the sexual origins of language and culture in chapter 2 and the devastating examination in chapter 3 of bigotry in the biological sciences in over two hundred years of observations of animal homosexuality. Bagemihl shows, for example, that in science as in society, there's a presumption of heterosexuality. Field researchers have commonly assumed, with no independent verification, that whenever they see a pair of animals engaging in what appears to be sexual behavior they are observing a male-female pair. Conversely, whenever they observe a known same-sex pair engaging in behavior that would be classified as sexual between a male and female, they classify it in some other way. This protocol largely precludes the gathering of data about animal homosexuality even when it's being observed. In some cases, though, it resulted in published studies being repudiated as much as 20 years later when it was discovered that what was presumed to be heterosexual behavior in a population was really entirely homosexual. (It's an interesting fact that in some species heterosexuality has never been observed by scientists even when they go to great lengths to observe it over periods of many years.) Also, a lot of animal homosexuality that has been recognized as such has simply been excluded from the published reports. As a result, there is still widespread belief among scientists and the public that animal homosexuality is rare or nonexistent. People will believe otherwise after reading this book.

Chapter 4 looks at the attempts to explain away animal homosexuality and chapter 5 considers arguments on the other side that try to attach evolutionary value to homosexuality. Bagemihl rejects all the proposals on both sides, demonstrating the weakness of all the explanations and typically showing that they are plainly inconsistent with the evidence of animal behavior. Finally, he arrives at the question that the reader has been waiting for for almost 200 pages: "Why does same-sex activity persist--reappearing in species after species, generation after generation, individual after individual--when it is not 'useful'?" His answer is not to show that it is useful, but rather to treat the plain existence of homosexuality as a reductio ad absurdum argument against the biologists' assumption that only traits that contribute to reproduction will survive (i.e. are useful). In pursuing this line of thought Begemihl offers interesting descriptions of animals that are nonbreeders, animals that suppress reproduction, animals that segregate the sexes so that reproduction can't happen, animals that engage in birth control, and animals that engage in other nonreproductive behaviors. He also shows that a lot of the sex that actually occurs is not for reproduction, but apparently for pleasure. All of this he believes calls for a new conception of the natural biological world.

The last chapter describes some ideas for a new paradigm, which he calls Biological Exuberance and I must say that it is much less convincing than the rest of the book. It is interesting nonetheless. Much of the last chapter is a description of the myths about animals of native North Americans, the tribes of New Guinea, and indigenous Siberian people. When I started reading this chapter I began to wonder if I had accidentally picked up a different book, but in the end he makes a connection between the myths and biological reality. In fact, he shows that some of these myths contain more facts about animals than you can find in any scientific text. Some of the most bizarre of the myths turn out to be true.

So where does it end? In mystery. "Our final resting spot--the concept of Biological Exuberance--lies somewhere along the trajectory defined by these three points (chaos, biodiversity, evolution), although its exact location remains strangely imprecise." "Nothing, in the end, has really been 'explained'--and rightly so, for it was 'sensible explanations' that ran aground in the first place."

That's not a very satisfactory answer to my mind, but the book is nonetheless a source of many interesting phenomena and ideas. I enjoyed it greatly. I expect most people who read this long book will do as I have done--read part one completely and then selectively read about some particular animals in part two. The second part is an encyclopedia of the queer sexuality of approximately 300 species of mammals and birds. An appendix contains a long list of reptiles, amphibians, fishes, insects, spiders and domesticated animals in

21 of 28 people found the following review helpful:

At 800 pages, it exceeds my interest, but good, August 17, 2002

Reviewer:

Paul Doland (Houston, TX USA) - See all my reviews

As a straight person, I guess I only have so much interest in the animal homosexual behavior - and this book exceeds it. It is 800 pages and I really didn't finish all of it. But, I have some amount of interest as I at least used to hear Christians claim that homosexuality is "unnatural" which this books seems to show fairly convincingly otherwise.

I enjoyed the chapters discussing possible reasons for the existence of homosexuality. The author agrees that it doesn't serve any obvious purpose. However, he discusses a few possible theories. One theory about at least one species of bird is that male pairs do better at gathering food and protecting territory. So, a male pair, so long as at least one of the males engages in some heterosexual activity to produce an offspring, could have some evolutionary advantage. But the author admits the evidence for this or other theories is scant at best. The conclusion seems to be that much sexual behavior, in animals and people, serves no obvious purpose - it just is.

So, if you have some interest in the subject, I'm sure you'll like it. But if your interest is only moderate, it may be too much.

Biological Exuberance, September 14, 2006

Reviewer:

K. Freeman (Apple Valley, CA USA) - See all my reviews

A well-supported and engagingly written study of homosexual behavior in animals, particularly mammals and birds. The book discusses the behavior of individual species, ways in which behavior can be studied, the implications for evolutionary theory and for the study of corresponding behaviors in humans, the place of reproduction in the natural world, and more.

I read natural history and nature writing voraciously and had no idea that these behaviors were so prevalent, which seems like an argument in itself for Bagemihl's criticism of zoologists' ignoring them. As he points out, all mating behaviors are hard to observe (it was amazing to learn that at the time the book was written Black-Headed Grosbeaks had only once been observed mating; they are a common bird that breeds in North America). At times, it seems to me that Bagemihl's analysis overinterprets, assuming that all incidences of mounting, for example, are sexual. Still, enough of his evidence appears irreproachable to make the book a real eye-opener.

8 of 12 people found the following review helpful:

Animals have gay marriage!, August 3, 2005

Reviewer:

Todd Brennan (Cincinnati, Ohio) - See all my reviews

Wow. I knew that homosexuality was biologically natural - i.e. it occurs naturally to various degrees and in various forms in numerous species including humans - but I had no idea of the extent, or of the similarity of many species to human sexuality.

If one thinks of heterosexual animals that pair bond, in some cases for life, as the animal equivalent of human heterosexual marriage, then logically, homosexual animals that pair bond, in some cases for life, are the animal equivalent of human gay marriages. Guess what? From such a perspective, animals have gay marriage!

The species' that are most similar to humans (based on the categories of courtship, affection, sexual behavior, pair-bonding, and parenting) are the Bonobo (or pygmy chimpanzee - which is the species most directly related to humans), the Orang-utan, and the Bottle Nose Dolphin.

Homosexual sexual activities among animals include mounting, anal intercourse, clitoral penetration, oral intercourse (for both males and females), mutual masturbation (including face to face GG-rubbing - genito-genital [i.e. mutual clitoral] rubbing by females), solitary masturbation, the use of tools for masturbation (equivalents of a dildo and a vibrator), penile fencing, rump-rubbing (mutual rubbing of genital and anal areas), digital genital and anal stimulation, the use of natural herbal abortion medicines, and in one species, the delay - in some cases permanent - of conception by manually stimulating the nipples (some species don't go into heat while suckling occurs, and the animals have learned to prevent themselves from going into heat by manually stimulating their nipples.) Dolphins have some tricks I'd never heard of. They have "nasal sex" - the insertion and stimulation of the penis by the blow hole; and "sonic sex" - the stimulation of the genitals using sonic pulses; as well as "beak-genital propulsion" - when the nose is inserted into the male of female genital slit, manually stimulating the genitals while propelling them along. I couldn't possibly describe all of it here.

The book also describes non-reproductive heterosexual activities, which are also quite common, if not ubiquitous. It also covers intersexuality and transvestism among animals.

Gay animals court each other (sometimes with specifically homosexual courtship rites), express affection, have all kinds of gay sex, pair-bond, and parent. Many animal species are functionally bisexual, but the same range of sexuality that occurs in humans also occurs in animals, such that even among a species that is primarily bisexual, there will be individuals who are exclusively heterosexual or homosexual.

The last half of the book ends with a breakdown of currently known species in which homosexuality occurs, and the form it takes (pair-bonding, courtship, etc.), as well as other broader info on the species.)

It's a great read, and a great resource for those who are ignorant of the existence and extent of animal homosexuality.

(Source: Amazon.com)