Hormonal control of courtship and copulatory behavior in male Cnemidophorus inornatus, a direct sexual ancestor of a unisexual, parthenogenetic lizard

Neural control of reproduction in reptiles

Reptiles display considerable diversity in reproductive behavior, making them great models to study the neuroendocrine control of reproductive behavior. Many reptile species are seasonally breeding, such that they become reproductively active during their breeding season and regress to a nonreproductive state during their nonbreeding season, with this transition often prompted by environmental cues. In this review, we will focus on summarizing the neural and neuroendocrine mechanisms controlling reproductive behavior. Three major areas of the brain are involved in reproductive behavior: the preoptic area (POA), amygdala, and ventromedial hypothalamus (VMH). The POA and VMH are sexually dimorphic areas, regulating behaviors in males and females respectively, and all three areas display seasonal plasticity. Lesions to these areas disrupt the onset and maintenance of reproductive behaviors, but the exact roles of these regions vary between sexes and species. Different hormones influence these regions to elicit seasonal transitions. Circulating testosterone (T) and estradiol (E2) peak during the breeding season and their influence on reproduction is well-documented across vertebrates. The conversion of T into E2 and 5α-dihydrotestosterone can also affect behavior. Melatonin and corticosterone have generally inhibitory effects on reproductive behavior, while serotonin and other neurohormones seem to stimulate it. In general, there is relatively little information on the neuroendocrine control of reproduction in reptiles compared to other vertebrate groups. This review highlights areas that should be considered for future areas of research.

The Ancestral Modulation Hypothesis: Predicting Mechanistic Control of Sexually Heteromorphic Traits Using Evolutionary History

AbstractAcross the animal kingdom there are myriad forms within a sex across, and even within, species, rendering concepts of universal sex traits moot. The mechanisms that regulate the development of these trait differences are varied, although in vertebrates, common pathways involve gonadal steroid hormones. Gonadal steroids are often associated with heteromorphic trait development, where the steroid found at higher circulating levels is the one involved in trait development for that sex. Occasionally, there are situations in which a gonadal steroid associated with heteromorphic trait development in one sex is involved in heteromorphic or monomorphic trait development in another sex. We propose a verbal hypothesis, the ancestral modulation hypothesis (AMH), that uses the evolutionary history of the trait-particularly which sex ancestrally possessed higher trait values-to predict the regulatory pathway that governs trait expression. The AMH predicts that the genomic architecture appears first to resolve sexual conflict in an initially monomorphic trait. This architecture takes advantage of existing sex-biased signals, the gonadal steroid pathway, to generate trait heteromorphism. In cases where the other sex experiences evolutionary pressure for the new phenotype, that sex will co-opt the existing architecture by altering its signal to match that of the original high-trait-value sex. We describe the integrated levels needed to produce this pattern and what the expected outcomes will be given the evolutionary history of the trait. We present this framework as a testable hypothesis for the scientific community to investigate and to create further engagement and analysis of both ultimate and proximate approaches to sexual heteromorphism.

Male reproductive cycle in a population of the endemic butterfly lizard, Leiolepis ocellata Peters, 1971 (Squamata: Agamidae) from northern Thailand

Background

Fundamental knowledge on the seasonal reproductive microanatomy and endocrinology of reptiles has been collected from several studies of various species. The present study was to determine annual changes in hormonal profiles, and detailed histomorphometric and histochemical characteristics of the entire male reproductive system of the tropical agamid lizard, Leiolepis ocellata.

Results

Male L. ocellata individuals (n = 75) collected from the territory of two provinces (Lampang and Tak) in northern Thailand exhibited annual variation in sex hormonal, histomorphometric, and histochemical characteristics of the male reproductive system. The reproductive cycle was subdivided into eight reproductive periods (early first active, first active, resting, second recrudescent, second active, regressive, quiescent, and first recrudescent), thus displaying a bimodal pattern with two actively reproductive periods. Circulating sex hormones (testosterone, estradiol, and progesterone) peaked in the first active (February) and the second active (June–July) periods. Likewise, gonadosomatic index (GSI) and histomorphometric variables of the testes and of the genital ducts (rete testis, ductuli efferentes, ductus epididymis, and ductus deferens) revealed their highest values in the first active period. Marked increase in protein and carbohydrate production was detectable in the ductuli efferentes during the active periods.

Conclusions

The male reproductive cycle of L. ocellata showed a biannual pattern of the hormonal profile, and detailed histomorphometric and histochemical characteristics of the entire reproductive system. Hence, the present study provides improved basic knowledge on the reptilian reproductive biology with comparative viewpoints to other reptiles.

Evolutionary insights into sexual behavior from whiptail lizards

Is the brain bipotential or is sex-typical behavior determined during development? Thirty years of research in whiptail lizards transformed the field of behavioral neuroscience to show the brain is indeed bipotential, producing behaviors along a spectrum of male-typical and female-typical behavior via a parliamentary system of neural networks and not a predetermined program of constrained behavioral output. The unusual clade of whiptail lizards gave these insights as there are several parthenogenetic all-female species that display both male-typical and female-typical sexual behavior. These descendant species exist alongside their ancestors, allowing a unique perspective into how brain-behavior relationships evolve. In this review, we celebrate the over 40-year career of David Crews, beginning with the story of how he established whiptails as a model system through serendipitous behavioral observations and ending with advice to young scientists formulating their own questions. In between these personal notes, we discuss the discoveries that integrated hormones, neural activity, and gene expression to provide transformative insights into how brains function and reshaped our understanding of sexuality.

Conservation and dimorphism in androgen receptor distribution in Alston's singing mouse (Scotinomys teguina)

Because of their roles in courtship and intrasexual competition, sexual displays are often sexually dimorphic, but we know little about the mechanisms that produce such dimorphism. Among mammals, one example is the vocalization of Alston's singing mouse (Scotinomys teguina), which consists of a series of rapidly repeated, frequency-modulated notes. The rate and duration of songs is sexually dimorphic and androgen responsive. To understand the neuronal mechanisms underlying this sexual dimorphism, we map the sites of androgen sensitivity throughout the brain, focusing analysis along a pathway that spans from limbic structures to vocal motor regions. We find widespread expression of AR immunoreactivity (AR-ir) throughout limbic structures important for social behavior and vocalization, including the lateral septum, extended amygdala, preoptic area and hypothalamus. We also find extensive AR staining along previously documented vocal motor pathways, including the periaqueductal gray, parabrachial nucleus, and nucleus ambiguus, the last of which innervates intrinsic laryngeal muscles. Lastly, AR-ir is also evident in sensory areas such as the medial geniculate, inferior, and superior colliculi. A quantitative analysis revealed that males exhibited more AR-ir than females, a pattern that was most pronounced in the hypothalamus. Despite the elaboration of vocalization in singing mice, comparison with prior literature suggests that the broad pattern of AR-ir may be conserved across a wide range of rodents. Together these data identify brain nuclei well positioned to shape the sexually dimorphic vocalization of S. teguina and suggest that such androgen modulation of vocalization is evolutionary conserved among rodents.

Covariation between Thermally Mediated Color and Performance Traits in a Lizard

Physiological changes in response to environmental cues are not uncommon. Temperature has strong, predictable effects on many traits, such that many traits in ectotherms follow stereotyped thermal performance curves in response to increasing temperature. The prairie lizard-an abundant lizard throughout the central United States-has thermally sensitive, blue abdominal and throat patches. Currently, the role of these patches is not well understood. In this study, we set out to investigate whether individual plasticity in patch color paralleled individual plasticity in sprint speed (do they covary), and if the plasticity in these two patches signal redundant or independent information, testing competing hypotheses suggested for the evolution of multiple signals. We found that both abdominal and throat patch hue follow classical thermal performance curves, suggesting that at the species level hue is a good predictor of sprinting ability. At the individual level, we found that color and performance were statistically repeatable, so individuals with relatively high phenotypic values maintain relatively high phenotypic values across all temperatures. Additionally, we found that abdominal and patch hue covary with sprinting speed at the individual level. Together, these results suggest that the bluest individuals are the fastest individuals across temperatures. However, we found that abdominal and throat patch hue do not covary with each other at the individual level, suggesting that these signals may have independent functions. The importance of examining the function of individual variation cannot be overstated, and overall, more work is needed to better understand both the proximate and ultimate mechanisms underlying signal plasticity in this species and others.

Not one hormone or another: Aggression differentially affects progesterone and testosterone in a South American ovenbird

Behaviors such as territorial interactions among individuals can modulate vertebrate physiology and vice versa. Testosterone has been pointed out as a key hormone that can be rapidly affected by aggressive interactions. However, experimental evidence for such a link is mixed. In addition, behaviors can elicit changes in multiple hormones, which in turn have the potential to synergistically feedback to behavior. For example testosterone and progesterone can act interdependently in modulating male behavior. However, if aggression can affect progesterone levels in males remain unknown and - to the best of our knowledge - no one has yet tackled if and how aggressive behavior simultaneously affects testosterone and progesterone in free-living animals. We addressed these questions by performing simulated territorial intrusion experiments measuring both hormones and their ratio in male rufous horneros (Aves, Furnarius rufus) during the mating and parental care periods. Aggression affected testosterone and progesterone differentially depending on the period of testing: challenged birds had higher levels of progesterone during the mating period and lower levels of testosterone during parental care compared to controls. Challenged individuals had similar progesterone to testosterone ratios during both periods and these ratios were higher than those of control birds. In summary, territorial aggression triggered hormonal pathways differentially depending on the stage of the breeding cycle, but equally altered their ratio independent of it. Our results indicate that multiple related hormones could be playing a role rather than each hormone alone in response to social interactions.

To fight or mate? Hormonal control of sex recognition, male sexual behavior and aggression in the gecko lizard

Squamate reptiles are a highly diversified vertebrate group with extensive variability in social behavior and sexual dimorphism. However, hormonal control of these traits has not previously been investigated in sufficient depth in many squamate lineages. Here, we studied the hormonal control of male sexual behavior, aggressiveness, copulatory organ (hemipenis) size and sex recognition in the gecko Paroedura picta, comparing ovariectomized females, ovariectomized females treated with exogenous dihydrotestosterone (DHT), ovariectomized females treated with exogenous testosterone (T), control females and males. The administration of both T and DHT led to the expression of male-typical sexual behavior in females. However, in contrast to T, increased circulating levels of DHT alone were not enough to initiate the full expression of male-typical offensive aggressive behavior and development of hemipenes in females. Ovariectomized females were as sexually attractive as control females, which does not support the need for the demasculinization of the cues used for sex recognition by ovarian hormones as suggested in other sauropsids. On the other hand, our results point to the masculinization of the sex recognition cues by male gonadal androgens. Previously, we also demonstrated that sexually dimorphic growth is controlled by ovarian hormones in P. picta. Overall, it appears that individual behavioral and morphological sexually-dimorphic traits are controlled by multiple endogenous pathways in this species. Variability in the endogenous control of particular traits could have permitted their disentangling during evolution and the occurrence of (semi)independent changes across squamate phylogeny.

Contributions of testosterone and territory ownership to sexually-motivated behaviors and mRNA expression in the medial preoptic area of male European starlings

Animals integrate social information with their internal endocrine state to control the timing of behavior, but how these signals are integrated in the brain is not understood. The medial preoptic area (mPOA) may play an integrative role in the control of courtship behavior, as it receives projections from multiple sensory systems, and is central to the hormonal control of courtship behavior across vertebrates. Additionally, data from many species implicate opioid and dopaminergic systems in the mPOA in the control of male courtship behavior. We used European starlings to test the hypothesis that testosterone (T) and social status (in the form of territory possession) interact to control the timing of courtship behavior by modulating steroid hormone-, opioid- and dopaminergic-related gene expression in the mPOA. We found that only males given both T and a nesting territory produced high rates of courtship behavior in response to a female. T treatment altered patterns of gene expression in the mPOA by increasing androgen receptor, aromatase, mu-opioid receptor and preproenkephalin mRNA and decreasing tyrosine hydroxylase mRNA expression. Territory possession did not alter mRNA expression in the mPOA, despite the finding that only birds with both T and a nesting territory produced courtship behavior. We propose that T prepares the mPOA to respond to the presence of a female with high rates of courtship song by altering gene expression, but that activity in the mPOA is under a continuous (i.e. tonic) inhibition until a male starling obtains a nesting territory.

Androgenic control of male-typical behavior, morphology and sex recognition is independent of the mode of sex determination: A case study on Lichtenfelder's gecko (Eublepharidae: Goniurosaurus lichtenfelderi)

Previous work on lizards has shown that many sexually dimorphic traits depend on testosterone (T), but the details of this control can vary among species. Here, we tested the role of T on the expression of morphological, physiological, and behavioral traits in Lichtenfelder's gecko (Goniurosaurus lichtenfelderi), from the lizard family Eublepharidae notable for interspecific variation in sexually dimorphic traits and the mode of sex determination. Experiments included three groups of males (intact control, surgically castrated, castrated with T replacement) and two groups of females (intact control, T supplemented). In males, castration caused reductions in 1) the size of hemipenes, 2) offensive aggression, 3) male sexual behavior in a neutral arena, 4) activity of precloacal glands, and 5) loss of male chemical cues for sex recognition. These reductions were not observed in castrated males with T replacement. Interestingly, castrated males performed sexual behavior in their home cages, which shows that the effect of T depends on the environmental context. Notably, tail vibration, previously reported as a courtship behavior in other eublepharids, is displayed by males of G. lichtenfelderi during interactions with conspecifics of both sexes, suggesting an evolutionary shift in the meaning of this signal. In females, T induced growth of hemipenes and male-typical courtship but did not induce precloacal pore activity, aggression, or mounting. In comparison to previous reports on Eublepharis macularius, our results indicate that effects of T do not depend on the mode of sex determination. Further, our results extend our understanding of the complexity of control of male traits and illustrate how lability in the effects of T can be a general mechanism causing evolutionary changes in the components of suites of functionally correlated traits.

Elevated testosterone is required for male copulatory behavior and aggression in Madagascar ground gecko (Paroedura picta)

Elevated levels of gonadal androgens are often required for the expression of male-specific behavioral and morphological traits in all classes of vertebrates, including reptiles. Here, we tested the role of male gonadal androgens in the control of male sexual behavior, aggressive behavior, and size of the hemipenes in the gecko Paroedura picta. We performed hormonal manipulations involving castration with and without testosterone (T) replacement in males and application of exogenous T and ovariectomy in females. Castration suppressed sexual behavior and hemipenes size in males, and these effects were fully rescued by exogenous T. Sexual behavior and growth of the hemipenes were masculinized by male-typical levels of T in females, while ovariectomized females retained female-typical expression of these traits. These results indicate that the development of male sexual behavior in adult females does not require early or pubertal organization. Elevated T increased the likelihood of aggressive behavior directed toward a male intruder, but aggression occurred only rarely. Elevated T is necessary and sufficient for enlargement of the hemipenes and the expression of male sexual behavior in both males and females of Paroedura picta. In contrast to sexual behavior, the expression of aggressive behavior is apparently more dependent on other factors in addition to T itself.

The reproductive hormone cycle of adult female American alligators from a barrier island population

Comparatively, little data are available detailing the geographic variation that exists in the reproductive endocrinology of adult alligators, especially those living in barrier islands. The Merritt Island National Wildlife Refuge (MI) is a unique barrier island environment and home to the Kennedy Space Center (FL, USA). Seasonal patterns of sex steroids were assessed in adult female American alligators from MI monthly from 2008 to 2009, with additional samples collected at more random intervals in 2006, 2007, and 2010. Plasma 17β-estradiol and vitellogenin concentrations peaked in April, coincident with courtship and mating, and showed patterns similar to those observed in adult female alligators in other regions. Plasma concentrations of progesterone, however, showed patterns distinctly different than those reported for alligator populations in other regions and remained relatively constant throughout the year. Plasma DHEA peaked in July around the time of oviposition, decreased in August, and then remained constant for the remaining months, except for a moderate increase in October. Circulating concentrations of DHEA have not been previously assessed in a female crocodilian, and plasma concentrations coincident with reproductive activity suggest a reproductive and/or behavioral role. Interestingly, plasma testosterone concentrations peaked in May of 2008, as has been shown in female alligator populations in other regions, but showed no peak in 2009, demonstrating dramatic variability from year to year. Surveys showed 2009 to be particularly depauperate of alligator nests in MI, and it is possible that testosterone could serve as a strong indicator of breeding success.

The reproductive cycle of the male house gecko, Hemidactylus flaviviridis, in relation to plasma steroid concentrations, progesterone receptors, and steroidogenic ultrastructural features, in Oman

The annual testicular cycle of the house gecko Hemidactylus flaviviridis in Oman was studied. Plasma testosterone (T), estradiol (E2) and progesterone (P) concentrations were measured using a sensitive HPLC-MS/MS detection technique. The ultrastructural steroidogenic features in Sertoli and Leydig cells, which were the major source of steriodogenesis, were examined, using transmission electron microscopy (TEM). In addition, progesterone receptors (PR) were examined throughout the testicular cycle, using an immunohistochemical technique. The steroidogenic ultrastructural features were characterized by the presence of smooth endoplasmic reticulum (SER) in the form of cisternal whorls and tubular cisternae, presence of swollen vesiculated mitochondria, and association between SER, mitochondria and lipid droplets. The rise in plasma steroid concentrations was closely associated with the development of the ultrastructural features and PR expression in Leydig and Sertoli cells. During the active phase (November-May), there was a significant rise in plasma steroid concentrations (P<0.05) related to well developed steroidogenic features and strongly expressed PR. During the quiescent phase (June-August) there was a significant decline in plasma steroid concentrations, undeveloped steroiodogenic features and weakly expressed PR. The Renal Sexual Segment (RSS) was fully developed during the active phase. The data provides strong evidence that these ultrastructural steroidogenic features were related to the plasma sex steroid concentrations during the testicular cycle.

Androgens coordinate neurotransmitter-related gene expression in male whiptail lizards

Sex steroid hormones coordinate neurotransmitter systems in the male brain to facilitate sexual behavior. Although neurotransmitter release in the male brain has been well documented, little is known about how androgens orchestrate changes in gene expression of neurotransmitter receptors. We used male whiptail lizards (Cnemidophorus inornatus) to investigate how androgens alter neurotransmitter-related gene expression in brain regions involved in social decision making. We focused on three neurotransmitter systems involved in male-typical sexual behavior, including the N-methyl-d-aspartate (NMDA) glutamate receptor, nitric oxide and dopamine receptors. Here, we show that in androgen-treated males, there are coordinated changes in neurotransmitter-related gene expression. In androgen-implanted castrates compared with blank-implanted castrates (control group), we found associated increases in neuronal nitric oxide synthase gene expression in the nucleus accumbens (NAcc), preoptic area and ventromedial hypothalamus, a decrease of NR1 gene expression (obligate subunit of NMDA receptors) in the medial amygdaloid area and NAcc and a decrease in D1 and D2 dopamine receptor gene expression in the NAcc. Our results support and expand the current model of androgen-mediated gene expression changes of neurotransmitter-related systems that facilitate sexual behavior in males. This also suggests that the proposed evolutionarily ancient reward system that reinforces sexual behavior in amniote vertebrates extends to reptiles.

Seasonal androgen cycles in adult male American alligators (Alligator mississippiensis) from a barrier island population

The seasonal patterns of two primary plasma androgens, testosterone (T) and dehydroepiandrosterone (DHEA), were assessed in adult male alligators from the Merritt Island National Wildlife Refuge, a unique barrier island environment and home to the Kennedy Space Center in Florida. Samples were collected monthly from 2008 to 2009, with additional samples collected at more random intervals in 2007 and 2010. Plasma T concentrations peaked in April, coincident with breeding and courtship, and declined rapidly throughout the summer. Seasonal plasma T patterns in smaller though reproductively active adult males differed from those in their larger counterparts during the breeding season. Both size classes showed significant increases in plasma T concentration from February to March, at the beginning of the breeding season. However, smaller adults did not experience the peak in plasma T concentrations in April that were observed in larger adults, and their concentrations were significantly lower than those of larger males for the remainder of the breeding season. Plasma DHEA concentrations peaked in May and were significantly reduced by June. This is the first study to demonstrate the presence of DHEA in a crocodilian, and the high plasma DHEA concentrations that paralleled the animals' reproductive activity suggest a reproductive and/or behavioral role in adult male alligators. Similar to androgen variations in some birds, plasma DHEA concentrations in the alligators were considerably higher than T concentrations during the nonbreeding season, suggesting a potential role in maintaining nonbreeding seasonal aggression.

Relationships among hormones, brain and motivated behaviors in lizards

Lizards provide a rich opportunity for investigating the mechanisms associated with arousal and the display of motivated behaviors. They exhibit diverse mating strategies and modes of conspecific communication. This review focuses on anole lizards, of which green anoles (Anolis carolinensis) have been most extensively studied. Research from other species is discussed in that context. By considering mechanisms collectively, we can begin to piece together neural and endocrine factors mediating the stimulation of sexual and aggressive behaviors in this group of vertebrates.

Neuronal nitric oxide synthase as a substrate for the evolution of pseudosexual behaviour in a parthenogenetic whiptail lizard

The evolution of neuroendocrine mechanisms governing sex-typical behaviour is poorly understood. An outstanding animal model is the whiptail lizard (Cnemidophorus) because both the ancestral and descendent species still exist. The ancestral little striped whiptail, Cnemidophorus inornatus, consists of males and females, which exhibit sex-specific mating behaviours. The descendent desert grassland whiptail, Cnemidophorus uniparens, consists only of females that alternately exhibit both female-like and male-like pseudosexual behaviour. Castrated male C. inornatus will mount a conspecific in response to exogenous androgen, although some are also sensitive to progesterone. This polymorphism in progesterone sensitivity in the ancestral species may have been involved in evolution of progesterone-mediated male-typical behaviour in the descendant unisexual lizards. We tested whether progesterone activates a typically androgenic signalling pathway by investigating hormonal regulation of neuronal nitric oxide synthase (nNOS) using in situ hybridisation and NADPH diaphorase histochemistry, a stain for nNOS protein. NADPH diaphorase is widely distributed throughout the brain of both species, although only in the periventricular nucleus of the preoptic area (pvPOA) are there differences between mounting and non-mounting individuals. The number of cells expressing nNOS mRNA and NADPH diaphorase is higher in the pvPOA of individuals that mount in response to progesterone or androgen. Furthermore, the nNOS promoter has both androgen and progesterone response elements, and NADPH diaphorase colocalises with the progesterone receptor in the pvPOA. These data suggest that a polymorphism in progesterone sensitivity in the sexual ancestor reflects a differential regulation of nNOS and may account for the male-typical behaviour in unisexual whiptail lizards.

Molecular characterization and brain distribution of the progesterone receptor in whiptail lizards

Progesterone and its nuclear receptor are critical in modulating reproductive physiology and behavior in female and male vertebrates. Whiptail lizards (genus Cnemidophorus) are an excellent model system in which to study the evolution of sexual behavior, as both the ancestral and descendent species exist. Male-typical sexual behavior is mediated by progesterone in both the ancestral species and the descendant all-female species, although the molecular characterization and distribution of the progesterone receptor protein throughout the reptilian brain is not well understood. To better understand the gene targets and ligand binding properties of the progesterone receptor in whiptails, we cloned the promoter and coding sequence of the progesterone receptor and analyzed the predicted protein structure. We next determined the distribution of the progesterone receptor protein and mRNA throughout the brain of Cnemidophorus inornatus and Cnemidophorus uniparens by immunohistochemistry and in situ hybridization. We found the progesterone receptor to be present in many brain regions known to regulate social behavior and processing of stimulus salience across many vertebrates, including the ventral tegmental area, amygdala, nucleus accumbens and several hypothalamic nuclei. Additionally, we quantified immunoreactive cells in the preoptic area and ventromedial hypothalamus in females of both species and males of the ancestral species. We found differences between both species and across ovarian states. Our results significantly extend our understanding of progesterone modulation in the reptilian brain and support the important role of the nuclear progesterone receptor in modulating sexual behavior in reptiles and across vertebrates.

Male sexual behavior does not require elevated testosterone in a lizard (Coleonyx elegans, Eublepharidae)

Male sexual behavior depends on gonadal androgens in species of all major vertebrate lineages, including reptiles. However, male sexual behavior includes distinct appetitive and consummatory phases, typically denoted as courtship and mounting, with potentially different hormonal control. Different proximate controls of courtship versus mounting could enable disconnected evolutionary losses and gains of various aspects of male sexual behavior. Male courtship display, which is activated by testosterone (T) in many species, is an ancestral trait in the lizard family Eublepharidae. However, Coleonyx elegans (Yucatan Banded Gecko) lost the courtship display, while retaining a highly simplified male sexual behavior that involves only mounting for copulation. We performed surgical manipulations (castration with and without T replacement in adult males; implantation of adult females with exogenous T) to investigate hormonal mechanisms involved in this evolutionary novelty. Our results indicate that the expression of simplified sexual behavior in C. elegans does not require elevated circulating levels of T, a finding that is previously unreported in lizards. In females, however, exogenous T induced male-like mounting. Thus, the mounting phase of sexual behavior is not activated by T in the traditional sense of this term but probably requires post-natal, maturational organization (if not periodic reorganization) by androgens. We conclude that the simplification of male sexual behavior and its independence from elevated levels of circulating androgens in C. elegans evolved via 1) evolutionary loss of the androgen-activated courtship display and 2) retention of the mounting phase, which has a longer "functional memory" for the effects of androgenic steroids.

Testosterone response to courtship predicts future paternal behavior in the California mouse, Peromyscus californicus

In the monogamous and biparental California mouse (Peromyscus californicus), paternal care is critical for maximal offspring survival. Animals form pair bonds and do not engage in extrapair matings, and thus female evaluation of paternal quality during courtship is likely to be advantageous. We hypothesized that male endocrine or behavioral response to courtship interactions would be predictive of future paternal behavior. To test this hypothesis, we formed 20 pairs of California mice, and evaluated their behavior during the first hour of courtship interactions and again following the birth of young. We also collected blood from males at baseline, 1 hr after pairing, 3 weeks paired, and when young were 4 days old to measure testosterone (T). We found that male T-response to courtship interactions predicted future paternal behavior, specifically the amount of time he huddled over young when challenged by the temporary removal of his mate. Males that mounted T increases at courtship also approached pups more quickly during this challenge than males who had a significant decrease in T at courtship. Proximity of the male and female during courtship predicted paternal huddling during a 1-hr observation, and a multiple regression analysis revealed that courtship behavior was also predictive of birth latency. We speculate that male T-response to a female in P. californicus is an honest indicator of paternal quality, and if detectable by females could provide a basis for evaluation during mate choice.

Testosterone stimulates mounting behavior and arginine vasotocin expression in the brain of both sexual and unisexual whiptail lizards

In nonmammalian vertebrates the abundance of arginine vasotocin (AVT) neurons in the brain is sexually dimorphic, a pattern that is modulated by testicular androgen. This peptide is thought to be involved in the control of male-typical mounting behaviors. The all-female desert-grasslands whiptail (Cnemidophorus uniparens) reproduces by obligate parthenogenesis and in nature no males exist, but eggs treated with aromatase inhibitor hatch into individuals (called virago C. uniparens) having testes, accessory sex structures, high circulating concentrations of androgens, and exhibiting only male-like copulatory behavior. To examine the 'sexual' dimorphism of AVT-containing neurons in these animals, we compared AVT immunoreactivity in gonadectomized control and virago C. uniparens, with that of gonadectomized male and female Cnemidophorus inornatus, a sexual species that is the maternal ancestor to the parthenogenetic species. Mounting behavior is elicited in both species and both sexes by testosterone, and it was predicted that the distribution and abundance of AVT cell bodies and fibers would reflect the propensity of males and females of the two species to display male-typical copulatory behavior. Since both this propensity and AVT abundance are controlled by androgens, we compared testosterone-implanted and control animals within each group. Testosterone treatment generally increased AVT abundance, except in lab-reared parthenoforms, in which testosterone treatment was the least effective in inducing male-like copulatory behavior.

Androgen receptor expression and morphology of forebrain and neuromuscular systems in male green anoles displaying individual differences in sexual behavior

Investigating individual differences in sexual performance in unmanipulated males is important for understanding natural relationships between behavior and morphology, and the mechanisms regulating them. Among male green anole lizards, some court and copulate frequently (studs) and others do not (duds). To evaluate potential factors underlying differences in the level of these behaviors, morphology and androgen receptor expression in neuromuscular courtship and copulatory structures, as well as in the preoptic area and amygdala, were compared in males displaying varying degrees of sexual function. This study revealed that individual differences in behavior among unmanipulated males, in particular the extension of a throat fan (dewlap) used during courtship, were positively correlated with the size of fibers in the associated muscle and with soma size in the amygdala. The physiological response to testosterone, as indicated by the height of cells in an androgen-sensitive portion of the kidney, was also correlated with male sexual behavior, and predicted it better than plasma androgen levels. Androgen receptor expression was not related to the display of courtship or copulation in any of the tissues examined. The present data indicate that higher levels of male courtship behavior result in (or are the result of) enhanced courtship muscle and amygdala morphology, and that androgen-sensitive tissue in studs may be more responsive to testosterone than duds. However, some mechanism(s) other than androgen receptor expression likely confer this difference in responsiveness.

Testosterone induction of male-typical sexual behavior is associated with increased preoptic NADPH diaphorase and citrulline production in female whiptail lizards

In rodents, male-typical copulatory behavior is generally dependent on gonadal sex steroids such as testosterone, and it is thought that the mechanism by which the hormone gates the behavior involves the gaseous neurotransmitter nitric oxide. According to one model, testosterone induces an up-regulation of nitric oxide synthase (NOS) in the preoptic area, increasing nitric oxide synthesis following exposure to a sexual stimulus. Nitric oxide in turn, possibly through its effect on catecholamine turnover, influences the way the stimulus is processed and enables the appropriate copulatory behavioral response. In whiptail lizards (genus Cnemidophorus), administration of male-typical levels of testosterone to females induces the display of male-like copulatory responses to receptive females, and we hypothesized that this radical change in behavioral phenotype would be accompanied by a large change in the expression of NOS in the preoptic area. As well as comparing NOS expression using NADPH diaphorase histochemistry between testosterone-treated females and controls, we examined citrulline immunoreactivity (a marker of recent nitric oxide production) in the two groups, following a sexual stimulus and following a nonsexual stimulus. Substantially more NADPH diaphorase-stained cells were observed in the testosterone-treated animals. Citrulline immunoreactivity was greater in testosterone-implanted animals than in blank-implanted animals, but only following exposure to a sexual stimulus. This is the first demonstration that not only is NOS up-regulated by testosterone, but NOS thus up-regulated is activated during male-typical copulatory behavior.

Serotonergic modulation of male-like pseudocopulatory behavior in the parthenogenetic whiptail lizard, Cnemidophorus uniparens

Hormone-neurotransmitter interactions form an important link through which hormones influence a variety of behavioral processes. Typically, sexual behavior is dimorphic with males mounting receptive females. In the all-female lizard species Cnemidophorus uniparens, individuals display both male-like pseudocopulation and female-like receptivity. These respective behavioral states are correlated with high circulating concentrations of progesterone following ovulation and of estrogen preceding it. In sexual species, serotonin is involved in male-typical mounting, and, as reported here, in male-like pseudosexual behavior in this unisexual species. In the first study, C. uniparens were ovariectomized and treated systemically with exogenous androgen, a hormonal regimen that results in individuals displaying only male-like pseudosexual behavior. An increase in serotonin levels in the preoptic area coupled with the suppression of male-like pseudocopulation was observed in androgen-treated lizards injected with 5-hydroxytryptophan (the precursor of serotonin) and clorgyline (a monoamine oxidase inhibitor) compared to vehicle-treated controls. Our second experiment involved ovariectomizing lizards and either injecting them with estradiol or implanting them with either an empty (Blank) or a progesterone- or testosterone-containing Silastic capsule. Treatment with para-chlorophenylalanine (an inhibitor of tryptophan hydroxylase) facilitated male-like pseudosexual behavior depending on the circulating hormonal milieu and decreased serotonin levels in the preoptic area. Our data suggest that serotonin is inhibitory to male-like pseudosexual behavior in C. uniparens but more importantly that the hormonal environment modulates the serotonin system at the level of the preoptic area, with the serotonergic system then establishing behavioral thresholds that allow for this behavior to be "gated".

The many faces of progesterone: a role in adult and developing male brain

In addition to its well documented action in female-typical behaviors, progesterone exerts an influence on the brain and behavior of males. This review will discuss the role of progesterone and its receptor in male-typical reproductive behaviors in adulthood and the role of progesterone and its receptor in neural development, in both sexual differentiation of the brain as well as in the development of "non-reproductive" functions. The seemingly inconsistent and contradictory results on progesterone in males that exist in the literature illustrate the complexity of progesterone's actions and illuminate the need for further research in this area. As progestin-containing contraceptives in men are currently being tested and progesterone administration to pregnant women and premature newborns increases, a better understanding of the role of this hormone in behavior and brain development becomes essential.

Does male sexual behavior require progesterone?

In this article, we provide a concise review of the past and current literature on the neglected influence of progesterone on male sexual behavior. Although there has been increased interest in all aspects of male sexual function, and the importance of androgens in the regulation of male copulatory behavior has long been well documented, knowledge of the role of progesterone on male sexual behavior is still patchy. Very little human data exist on this theme, and most of the literature concerns animal research, in particular reptiles and rodents. This review attempts to outline specific progesterone mechanisms involved in male sexual behavior, showing that this hormone plays a more relevant role in the control of male sexual behavior than commonly assumed. Exploring the neuroendocrine mechanisms of progesterone in the sexual behavior of males may provide insights into the regulation of sexuality in this gender.

Steroid hormones and aggression in female Galápagos marine iguanas

We studied steroid hormone patterns and aggression during breeding in female Galápagos marine iguanas (Amblyrhynchus cristatus). Females display vigorously towards courting males after copulating (female-male aggression), as well as fight for and defend nest sites against other females (female-female aggression). To understand the neuroendocrine basis of this aggressive behavior, we examined changes in testosterone (T), estradiol (E2), corticosterone (CORT), and progesterone (P4) during the mating and nesting periods, and then measured levels in nesting females captured during aggressive interactions. Testosterone reached maximal levels during the mating stage when female-male aggression was most common, and increased slightly, but significantly, during the nesting stage when female-female aggression was most common. However, fighting females had significantly lower T, but higher E2 and P4, than non-fighting females. It remains unclear whether these changes in hormone levels during aggressive interactions are a cause or a consequence of a change in behavior. Our results support the "challenge hypothesis", but suggest that E2 and/or P4 may increase in response to aggressive challenges in females just as T does in males. Females may be rapidly aromatizing T to elevate circulating levels of E2 during aggressive interactions. This hypothesis could explain why non-fighting females had slightly elevated baseline T, but extremely low E2, during stages when aggressive interactions were most common. Although P4 increased rapidly during aggressive encounters, it is unclear whether it acts directly to affect behavior, or indirectly via conversion to E2. The rapid production and conversion of E2 and P4 may be an important mechanism underlying female aggression in vertebrates.

The nitric oxide synthase inhibitor l-NAME suppresses androgen-induced male-like pseudocopulatory behavior in whiptail lizards

The synthesis of nitric oxide by the enzyme nitric oxide synthase (NOS) is involved in the androgen-dependent gating of male-typical copulatory behavior, both centrally, particularly in the preoptic area, and peripherally, notably through its role in penile erection. In the all-female whiptail lizard species Cnemidophorus uniparens, individuals display copulatory behaviors indistinguishable from males of similar species if gonadectomized and treated with testosterone. In this experiment, androgenized individuals were treated with a NOS inhibitor, which eliminated male-like behavior in half the individuals, suggesting that the central role of nitric oxide synthesis is conserved in this species. The deficit was principally in mounting, suggesting that sexual motivational systems were affected, rather than consummatory mechanisms.

Neural substrates for sexual and thermoregulatory behavior in the male leopard gecko, Eublepharis macularius

The preoptic area-anterior hypothalamus (POAH) continuum is critical for the integration of environmental, physiological, and behavioral cues associated with reproduction in vertebrates. In the present study, radiofrequency lesions in the POAH abolished sexual behavior in the leopard gecko (Eublepharis macularius). Furthermore, results suggest a differential effect of POAH lesions on those behaviors regarded as appetitive (tail vibration and grip) and those regarded as consummatory (mounting and copulation), with consummatory behaviors being affected to a greater extent. E. macularius is an ectothermic vertebrate that modulates body temperature behaviorally relative to ambient temperature. In vertebrates, the POAH is also an important integrator of thermoregulation. Thus, the present study investigated whether lesions that disrupt reproductive behavior also disrupt body temperature regulation. While virtually all males displayed diurnal rhythms in thermoregulatory behavior prior to surgery, this pattern was abolished in a small proportion of animals bearing POAH lesions. Lesions that abolished thermoregulatory rhythms involved the suprachiasmatic nucleus (SCN), whereas lesions confined to the POAH, while dramatically influencing sexual behavior, did not affect thermoregulatory rhythms or temperature set point. Together, these findings identify the POAH as an important neural locus regulating sexual behavior but not thermoregulation and suggest that the SCN acts as a pacemaker controlling daily behavioral temperature regulation in this species.

Evolutionary insights into the regulation of courtship behavior in male amphibians and reptiles

Comparative studies of species differences and similarities in the regulation of courtship behavior afford an understanding of evolutionary pressures and constraints shaping reproductive processes and the relative contributions of hormonal, genetic, and ecological factors. Here, we review species differences and similarities in the control of courtship and copulatory behaviors in male amphibians and reptiles, focusing on the role of sex steroid hormones, the neurohormone arginine vasotocin (AVT), and catecholamines. We discuss species differences in the sensory modalities used during courtship and in the neural correlates of these differences, as well as the value of particular model systems for neural evolution studies with regard to reproductive processes. For example, in some genera of amphibians (e.g., Ambystoma) and reptiles (e.g., Cnemidophorus), interspecific hybridizations occur, making it possible to compare the ancestral with the descendant species, and these systems provide a window into the process of behavioral and neural evolution as well as the effect of genome size. Though our understanding of the hormonal and neural correlates of mating behavior in a variety of amphibian and reptilian species has advanced substantially, more studies that manipulate hormone or neurotransmitter systems are required to assess the functions of these systems.

Tyrosine hydroxylase expression is affected by sexual vigor and social environment in male Cnemidophorus inornatus

Although the distribution of catecholamine-synthesizing cells has been described for a variety of taxa, less is known about the functional significance of particular populations in nonmammalian species, especially reptiles. To understand the role of these populations in the display of social behaviors in lizards, we studied the interactive effects of sexual vigor (sexually vigorous vs. sluggish) and social condition (housing in isolation vs. with females) on the number and somal areas of cells expressing tyrosine hydroxylase (TH), a rate-limiting enzyme in catecholamine synthesis, in male whiptail lizards, Cnemidophorus inornatus. We found that, regardless of social condition, sexually vigorous males had more TH-immunoreactive (TH-ir) cells in the dorsal hypothalamus (DH) relative to sluggish males. Sexually vigorous males also had more TH-ir cells in the substantia nigra pars compacta (SNpc), but this difference was significant only among males housed with females. Sexually vigorous males that had been housed with females had smaller TH-ir cells in the preoptic area (POA) than vigorous males housed in isolation. On the other hand, no significant differences were found in the anterior hypothalamus. These results highlight the regional heterogeneity in the plasticity of TH expression and suggest that, just as in other species, the DH, SNpc, and POA might be involved in the expression of social behaviors and in behavioral plasticity following social experiences in lizards.

Seasonal steroid hormone levels and their relation to reproduction in the Western Diamond-backed Rattlesnake, Crotalus atrox (Serpentes: Viperidae)

We report seasonal variation in steroid hormone levels in blood samples from free-ranging Western Diamond-backed Rattlesnakes (Crotalus atrox), and the relationship between these hormones and events in the reproductive cycle. At a field site in the Sonoran Desert of south-central Arizona, we collected monthly blood samples over the course of two active seasons from 17 radiotelemetered females, and over three active seasons from 103 randomly encountered males. We used radioimmunoassay to measure plasma levels of 17beta-estradiol, progesterone, corticosterone, and testosterone in samples from females, and corticosterone and testosterone in samples from males. Non-reproductive females have consistently low levels of circulating 17beta-estradiol, progesterone, and testosterone throughout the year. In reproductive females, 17beta-estradiol levels increase dramatically and testosterone levels increase modestly during vitellogenesis in April and May, while progesterone levels increase dramatically at ovulation in June and then steadily decline until parturition in August. Corticosterone levels appear relatively constant in non-reproductive females, whereas reproductive females show increased levels at the end of gestation. Plasma testosterone levels in males are low in early summer and are elevated during spring and late summer, corresponding to the two mating periods of C. atrox. Plasma corticosterone levels in males did not vary seasonally and were not related to testosterone levels.

Sexually dimorphic regulation of estrogen receptor α mRNA in the ventromedial hypothalamus of adult whiptail lizards is testosterone dependent

Female, but not male, whiptail lizards will respond to exogenous estrogen with an increase in estrogen receptor alpha (ER alpha) mRNA in the ventromedial hypothalamus (VMH). The current study tested whether differences in long-term testosterone exposure may be responsible for this sex difference. In the first experiment, female whiptails were gonadectomized and implanted for 6 weeks with either a Silastic capsule containing testosterone or an empty capsule after which the implant was removed. In a second experiment, male whiptail lizards were castrated for 1 week or for 6 weeks. In both experiments animals were then injected with either estradiol benzoate or steroid suspension vehicle and the brains collected 24 h later. Brain mRNA expression was assayed using in situ hybridization. Chronic testosterone treatment reduced estrogen-induced ER alpha mRNA levels (number of grains per cell) in the VMH in females. In contrast, there were no significant effects of time after castration or estrogen treatment on induction of ER alpha mRNA in the VMH in males. The abundance of estrogen-induced ER alpha mRNA in the VMH, therefore, appears to be responsive to testosterone environment in the female but not in the male, suggesting a difference in this species between the sexes in the mechanism of steroid receptor regulation.

Tracing the Evolution of Brain and Behavior Using Two Related Species of Whiptail Lizards: Cnemidophorus uniparens and Cnemidophorus inornatus

Cnemidophorus whiptail lizards offer a unique opportunity to study behavioral and neural evolution because unlike most genera, ancestral and descendant species are still extant, and comparisons between species provide a window into correlated changes in biological organization through speciation. This review focuses on the all-female or parthenogenetic species Cnemidophorus uniparens (descendant species), which evolved through several hybridization events involving the sexually reproducing species Cnemidophorus inornatus (ancestral species). Data compiled over more than 2 decades include behavioral, endocrine, and neural differences between these two related species of whiptail lizards. For example, unlike females of the ancestral species, individuals of the descendant species display male-like mounting behavior (pseudocopulatory behavior) after ovulation. Pseudocopulatory behavior in the parthenogen is triggered by the progesterone surge after ovulation, and the behavioral capacity to respond to progesterone appears to be an ancestral trait that was inherited from C. inornatus males through the hybridization events. Interestingly, the regulation of sex steroid hormone receptor mRNA in brain areas critical for the expression of sociosexual behaviors differs between females of the two species and suggests that evolutionary changes in the regulation of gene expression could be a proximate mechanism that underlies the evolution of a novel social behavior in the parthenogen. Finally, because the sexual species is diploid, whereas the parthenogen is triploid, differences between the species could directly assess the effect of ploidy. The behavioral and neuroendocrinological data are pertinent for considering this possibility.

Differential effects of testosterone and progesterone on the activation and retention of courtship behavior in sexual and parthenogenetic whiptail lizards

Both testosterone (T) and progesterone (P) facilitate the expression of male-typical sexual behavior in a variety of animals, including rodents and lizards. In two species of whiptail lizards, Cnemidophorus inornatus and C. uniparens, both hormones elicit the full repertoire of courtship behavior. However, the relative efficacy of the two hormones is unknown. In Experiments 1 and 2 we assessed differences in capacity of exogenous T and P to induce male-typical courtship behavior in gonadectomized whiptail lizards. In both species, individuals implanted with T showed more frequent courtship behavior relative to those implanted with P or cholesterol. In Experiments 3 and 4 we examined whether T and P differentially affected the retention of courtship behavior following implant removal. In both species, individuals implanted with T showed more courtship behavior following implant removal than those previously given P. In these experiments, implants were removed at a time when individuals in both groups were behaviorally similar; therefore, the differences in behavior following implant removal were not due to differences in the amount of courtship experience. Taken together, the hormone that was more effective at activating courtship behavior was also more effective at maintaining courtship behavior following implant removal. In summary, though both T and P can elicit identical sexual behaviors in both whiptail species, T has a greater and more lasting effect on courtship behavior and possibly on the neural circuits underlying courtship behavior.

Heterosexual housing increases the retention of courtship behavior following castration and elevates metabolic capacity in limbic brain nuclei in male whiptail lizards, Cnemidophorus inornatus

In male vertebrates the display of courtship behavior depends on the presence of testicular androgens. However, social experiences in adulthood can alter the hormonal dependence of courtship behavior in a variety of species, and we have previously proposed that these behavioral changes are linked to changes in neural metabolic capacity (cytochrome oxidase activity). Here we investigated the effects of prior social experience (housing with females vs housing in isolation) on the retention of courtship behavior following gonadectomy and on cytochrome oxidase (CO) activity in male little striped whiptail lizards, Cnemidophorus inornatus. In Experiment 1, we found that males that were previously housed with females (HWF males) continued to display courtship behavior longer after castration than males previously housed in isolation (ISOLATE males). This is similar to the behavioral plasticity found in rodents and cats. On the other hand, courtship behavior while gonadally intact was indistinguishable between HWF and ISOLATE males. Because all males were housed individually following castration, the difference is due to different social experiences prior to castration. In Experiment 2, we found that gonadally intact HWF males had significantly elevated CO activity in the preoptic area, amygdala, and anterior and ventromedial hypothalamic areas relative to intact ISOLATE males. No significant differences in metabolism were found in the lateral septum, lateral hypothalamus, and habenula or in hindlimb muscle, suggesting that the increase in metabolism is specific to brain nuclei involved in courtship behavior. Altogether, this demonstrates that elevations in metabolic capacity correlate with experience-dependent increases in robustness to castration.

Lizard reproductive medicine and surgery

Lizards are a diverse group of some 4470 species, a wide variety of which are now kept in captivity. Interest in captive lizards continues to increase, wild populations seem to be declining in some areas, and herpetoculturists continue to succeed in breeding more species; consequently, veterinarians must understand basic lizard reproductive biology to successfully treat lizard patients with reproductive problems. Just obtaining First Filial Generation (F1) offspring is an accomplishment. But we must look down the road to maintain a species in captivity for succeeding generations, and a lineage may not continue if attention is not given to details of appropriate husbandry and proper reproductive pursuits. One study documents the senescence of lineages in parthenogenetic lizards in captivity apparently associated with husbandry problems [99].

Does paradoxical sleep deprivation and cocaine induce penile erection and ejaculation in old rats?

A recent study has established that paradoxical sleep deprivation (PSD) and cocaine administration elicit genital reflexes (penile erection and ejaculation) in young rats. To discover whether the same effects occurred in old animals submitted to PSD, we administered cocaine (15 mg/kg) to young (3-month) and old (22-month) male rats after a 4-day period of PSD or at the equivalent time-point in control animals. We then evaluated erections and ejaculations. Sixty per cent of the old-PSD group displayed erection, although ejaculation was not observed. Genital reflexes were absent in young and old control groups. We found that PSD reduced testosterone and increased progesterone levels in both young and old PSD groups. In conclusion, our results suggest that although genital reflexes usually decrease with age, testosterone levels alone cannot account for these changes. The interaction of PSD and cocaine probably enhances dopamine transmission in the brain and may elicit penile erection in old rats.

Evolutionary changes in dopaminergic modulation of courtship behavior in Cnemidophorus whiptail lizards

Preoptic dopamine release is integral to the display of copulatory behaviors in male mammals and birds. However, while the anatomical distributions of the dopamine synthesizing enzyme tyrosine hydroxylase are similar among vertebrates, evolutionary changes in the functional role of dopamine are poorly understood. In this study, we tested whether a dopamine D1 receptor agonist would facilitate the display of courtship and copulatory behaviors in two related Cnemidophorine lizards (Cnemidophorus inornatus and Cnemidophorus uniparens). Cnemidophorus lizards offer a unique system to study evolutionary changes in functionality because ancestral (e.g., C. inornatus) and descendant (e.g., C. uniparens) species can be studied in parallel. Cnemidophorus uniparens is an all-female, parthenogenetic species and is the triploid descendant of the sexual and diploid species C. inornatus. Here we report that in castrated male C. inornatus and ovariectomized C. uniparens a dopamine D1 agonist increased the proportion of individuals mounting and decreased the latency to mount. Moreover, there was a species difference in sensitivity to the agonist: Mounting was elicited at a lower dose in C. uniparens than in C. inornatus. One possible explanation for this heightened sensitivity in the triploid parthenogen is that, by virtue of the increased ploidy, the parthenogen has elevated levels of D1 receptor in limbic brain areas modulating courtship behavior.

Androgen receptor immunolocalization in brains of courting and brooding male and female ring doves (Streptopelia risoria)

Nuclear androgen receptors (ARs) were localized immunocytochemically in the brains of courting and brooding male and female ring doves (Streptopelia risoria). AR immunoreactivity (AR-ir) in courting birds was localized in cell nuclei in the telencephalon, diencephalon, and mesencephalon. In the anterior hypothalamus, high density of AR-ir was concentrated in several nuclei including the nucleus lateralis hypothalami, nucleus periventricularis magnocellularis, nucleus preopticus anterior, nucleus preopticus medialis, and nucleus preopticus paraventricularis magnocellularis. In the posterior hypothalamus, areas showing high density of AR-ir included the nucleus lateralis hypothalami posterioris, nucleus medialis hypothalami posterior, nucleus ectomamillaris, nucleus mamillaris lateralis, and nucleus tuberis. No sex differences in the density or localization of AR-ir were observed. Compared to brains from courting birds, AR-ir density was either extremely low or absent in most brain regions of brooding birds. It is concluded that in the dove, central ARs are closely associated with the sexual stages of the reproductive cycle.

Androgen metabolism in the brain of the green anole lizard (Anolis carolinensis): effects of sex and season

Courtship behavior in male green anoles is partly mediated by the 5alpha-reductase enzyme, which converts testosterone (T) to 5alpha-dihydrotestosterone. This study aimed to determine whether the activity of 5alpha-reductase is enhanced in breeding males compared to females and nonbreeding males who do not normally display masculine behaviors. In some cases, aromatase, which converts T to 17beta-estradiol, also was assessed to determine whether the pattern of its activity in anoles is similar to that in other vertebrates. 5alpha-Reductase is greatest in the brainstem, so its activity was determined separately in homogenates of whole brain and brainstems. The following comparisons were done in different assays: (1) breeding males with breeding females, (2) nonbreeding males with nonbreeding females, and (3) breeding males with nonbreeding males. Aromatase activity was greater in breeding males (mean +/- SE, 0.61 +/- 0.06 fmol/min/mg protein) than in breeding females (0.41 +/- 0.08 fmol/min/mg protein). It was also greater in breeding males (0.84 +/- 0.16 fmol/min/mg protein) than in nonbreeding males (0.33 +/- 0.07 fmol/min/mg protein). In contrast, sex or seasonal differences did not exist in 5alpha-reductase activity. The results are consistent with those of other vertebrate species in which male-biased sex dimorphisms and seasonal differences occur in aromatase, but not in 5alpha-reductase activity. The greater levels of aromatase activity in breeding male anoles suggest that this enzyme might mediate male-specific functions. The equivalently high levels of 5alpha-reductase activity in both sexes suggests that, in addition to facilitating male courtship behavior, the enzyme has a basic function common to both sexes.

Androgenic regulation of steroid hormone receptor mRNAs in the brain of whiptail lizards

Sex and species differences in androgenic regulation of steroid hormone receptor mRNAs were examined in the diencephalon of two species of whiptail lizards: Cnemidophorus inornatus is a sexual species and the direct evolutionary ancestor to Cnemidophorus uniparens, an all-female parthenogenetic species. Lizards were gonadectomized and treated with different doses of either aromatizable testosterone or nonaromatizable dihydrotestosterone. The relative abundances of androgen-, oestrogen-, and progesterone-receptor mRNAs were compared in various nuclei following in situ hybridization with homologous riboprobes. A diversity of patterns in androgenic regulation was observed, with effects differing according to brain region, the steroid-receptor mRNA being considered and, in some cases, between androgens. In the ancestral sexual species, intact males had lower androgen-receptor mRNA abundances than castrated, blank-implanted males in the medial preoptic area. Testosterone significantly decreased androgen-receptor mRNA abundance in the medial preoptic area of castrated males. Males had higher androgen-receptor mRNA levels in the preoptic area than females generally and neither the sexual or parthenogenetic females showed a decrease in androgen-receptor mRNA with androgen treatment. Both testosterone and dihydrotestosterone increased oestrogen-receptor mRNA abundance in the ventromedial hypothalamus of C. inornatus, but no sex differences in this effect were observed. Gonadectomy decreased, whereas androgen treatment increased, progesterone-receptor mRNA abundance in the ventromedial hypothalamus. There was a sex difference in this response to androgen in the sexual species, with males having greater amounts than females in this brain area. The parthenogenetic species exhibited a similar pattern to females of the sexual species, but the levels were higher overall, possibly because Cnemidophorus uniparens is triploid. The periventricular preoptic area showed a different pattern, with testosterone treatment increasing progesterone-receptor mRNA abundance in both sexes of the sexual species and in the parthenogenetic species, while dihydrotestosterone did not. The diversity of patterns in androgen effects indicates that gonadal sex, aromatization of androgen, and perhaps gene dosage all influence the expression of steroid-receptor mRNAs in the lizard brain.

The role of 5alpha-reductase activity in sexual behaviors of the green anole lizard

Both testosterone (T) and its metabolite, 5alpha-dihydrotestosterone (DHT), can facilitate male sexual behavior in the lizard Anolis carolinensis. The present study addresses the role of DHT synthesis in regulating male sexual behavior by inhibiting 5alpha-reductase, the enzyme that converts T into DHT. In two separate experiments (one replacement and one maintenance paradigm), breeding adult males were castrated and implanted with capsules of T, DHT, or a control capsule (blank, BL). The animals were then injected with the 5alpha-reductase inhibitor, FCE, or with steroid suspending vehicle (SSV) as a control. Both experiments produced similar results. Overall, T was most effective in eliciting courtship and copulatory behaviors above control levels. In both experiments, treatment with FCE attenuated the T-induced effects on courtship behavior, whereas the inhibition of 5alpha-reductase activity resulted in modest and inconsistent effects on the latency to intromission and the proportion of copulating males. DHT treatment did not significantly increase courtship or copulatory behaviors above control levels. These results suggest that (a) 5alpha-reductase activity is necessary but that DHT alone is not sufficient for stimulating courtship in male A. carolinensis; and (b) courtship behavior is more sensitive than copulatory behavior to the activity of the androgen metabolizing enzyme.

Regulation of male sexual behavior by progesterone receptor, sexual experience, and androgen

Recent studies have demonstrated that physiological doses of progesterone may facilitate the androgen-dependent display of male sexual behavior in laboratory rats and three species of lizard. We used mice with a targeted disruption of the progesterone receptor to investigate whether such interactions exist in male mice and whether they may be modified by sexual experience. We found that naive intact male progesterone receptor knockout (PRKO) mice exhibit reduced mount frequencies compared to wild-type (WT) mice. Also unlike WT mice, sexually experienced PRKO males show profound losses in many measures of sexual behavior following castration. In a second experiment, we tested whether male mice heterozygous for a null mutation at the progesterone receptor locus were responsive to testosterone and progesterone treatment. We found that heterozygous males showed a reduced response to testosterone. The data are consistent with experiments indicating that the progesterone receptor is able to facilitate male-typical sex behaviors in other species and suggest novel mechanisms underlying the interaction of androgens and experience.