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

Effects of testosterone on urogenital tract morphology and androgen receptor expression in immature Eastern Fence lizards (Sceloporus undulatus)

In non-avian reptiles, the onset of sexual dimorphism of the major structures of the urogenital tract varies temporally relative to gonadal differentiation, more so than in other amniote lineages. In the current study, we used tonic-release implants to investigate the effects of exogenous testosterone (T) on postnatal development of the urogenital tract in juvenile Eastern Fence Lizards (Sceloporus undulatus) to better understand the mechanisms underlying the ontogeny of sexual differentiation in reptiles. We examined gonads, mesonephric kidneys and ducts (male reproductive tract primordia), paramesonephric ducts (oviduct primordia), sexual segments of the kidneys (SSKs), and hemiphalluses to determine which structures were sexually dimorphic independent of T treatment and which structures exhibited sexually dimorphic responses to T. To better understand tissue-level responsiveness to T treatment, we also characterized androgen receptor (AR) expression by immunohistochemistry. At approximately 4 months after hatching in control animals, gonads were well differentiated but quiescent; paramesonephric ducts had fully degenerated in males; mesonephric kidneys, mesonephric ducts, and SSKs remained sexually undifferentiated; and hemiphalluses could not be everted in either sex. Exogenous T caused enlargement, regionalization, and secretory activity of the mesonephric ducts and SSKs in both sexes; enlargement and regionalization of the oviducts in females; and enlargement of male hemipenes. The most responsive tissues exhibited moderate but diffuse staining for AR in control lizards and intense nuclear staining in T-treated lizards, suggestive of autoregulation of AR. The similarity between sexes in the responsiveness of the mesonephric ducts and SSK to T indicates an absence of sexually dimorphic organizational effects in these structures prior to treatment, which was initiated approximately 2 months after hatching. In contrast, the sex-specific responses in oviducts and hemipenes indicate that significant organization and/or differentiation had taken place prior to treatment.

Development of male-larger sexual size dimorphism in a lizard: IGF1 peak long after sexual maturity overlaps with pronounced growth in males

Squamate reptiles have been considered to be indeterminate growers for a long time. However, recent studies demonstrate that bone prolongation is stopped in many lizards by the closure of bone growth plates. This shift in the paradigm of lizard growth has important consequences for questions concerning the proximate causes of sexual size dimorphism. The traditional model of highly plastic and indeterminate growth would correspond more to a long-term action of a sex-specific growth regulator. On the other hand, determinate growth would be more consistent with a regulator acting in a sex-specific manner on the activity of bone growth plates operating during the phase when a dimorphism in size develops. We followed the growth of males and females of the male-larger Madagascar ground gecko (Paroedura picta) and monitored the activity of bone growth plates, gonad size, levels of steroids, expression of their receptors (AR, ESR1), and expression of genes from the insulin-like growth factor network (IGF1, IGF2, IGF1R, and IGF2R) in livers. Specifically, we measured gene expression before the onset of dimorphic growth, at the time when males have more active bone growth plates and sexual size dimorphism was clearly visible, and after a period of pronounced growth in both sexes. We found a significant spike in the expression of IGF1 in males around the time when dimorphism develops. This overexpression in males comes long after an increase in circulating testosterone levels and sexual maturation in males, and it might be suppressed by ovarian hormones in females. The results suggest that sexual size dimorphism in male-larger lizards can be caused by a positive effect of high levels of IGF1 on bone growth. The peak in IGF1 resembles the situation during the pubertal growth spurt in humans, but in lizards, it seems to be sex-specific and disconnected from sexual maturation.

Characterizing seasonal transitions: Breeding-like morphology and behavior during the late non-breeding season in green anole lizards

Seasonally breeding animals, such as green anole lizards (Anolis carolinensis), allow for the examination of the control of reproduction during different reproductive states. During the breeding season, the gonads are large and reproductively active. Following the breeding season, gonads regress and become less active, and the lizards enter a refractory period where breeding is inhibited. After this stage, a post-refractory period occurs during which the lizards are still in a non-breeding state, but environmental changes can trigger the onset of breeding. However, it is unclear what causes these changes in reproductive state and we hypothesized that this may be due to alterations in gonadotropin-releasing hormone (GnRH) signaling. The present study aimed to identify morphological and behavioral differences in GnRH- and saline-injected refractory and post-refractory male anoles when housed under the same non-breeding environmental conditions. We found that post-refractory anoles had increased testicular weight, recrudescence, sperm presence, and reproductive behavior, with no impact of GnRH injection. Renal sex segment size and steroidogenic acute regulatory protein (StAR) mRNA levels did not differ among groups, indicating that testosterone levels likely had not increased in post-refractory lizards. Post-refractory anoles in this study were beginning to transition towards a breeding state without exposure to changing environmental conditions, and GnRH was not necessary for these changes. These data reveal a complex interaction between the activation of breeding, changing environmental conditions, and the underlying physiology regulating reproduction in seasonally breeding lizards. Future studies are needed to further elucidate the mechanisms that regulate this relationship.

Determining the Effects of Serial Injections of Pregnant Mare Serum Gonadotropin on Plasma Testosterone Concentrations, Testicular Dynamics, and Semen Production in Leopard Geckos (Eublepharis macularius)

Reptiles are highly susceptible to anthropogenic activities as a result of their narrow geographical ranges and habitat specialization, making them a conservation concern. Geckos represent one of the mega-diverse reptile lineages under pressure; however, limited assisted reproductive technologies currently exist for these animals. Exogenous pregnant mare serum gonadotropin (PMSG) has been found to exhibit follicle stimulating hormone-like action and has been routinely used to alter reproductive hormones of vertebrates in assisted reproductive protocols. The purpose of this study was to determine the effects of serial injections of 20 IU and 50 IU PMSG on circulating testosterone concentrations, testicular dynamics, and semen production in a model species of gecko. Twenty-four captive-bred, adult, male leopard geckos (Eublepharis macularius) were divided into three treatment groups and administered a once-weekly injection of either PMSG or saline for a total of nine weeks. Ultrasonographic testicular measurements, electrostimulation for semen collection, and venipuncture were performed on days 0, 21, 42, and 63. Right unilateral orchidectomies and epididymectomies were performed in all animals on day 63; tissues were submitted for histopathology. PMSG treated geckos had significantly higher testicular volumes and weights, spermatozoa motility, and spermatozoa concentrations compared with controls. However, there were no significant differences in testosterone concentrations by treatment or time. Under the conditions outlined, PMSG is effective at stimulating spermatogenesis and increasing testicular size, but not effective at increasing testosterone concentrations in the leopard gecko between October-December in the Northern hemisphere.

Clinical Reptile Behavior

Reptile behavior varies widely among the approximately 11,000 species of this class. The authors' objective is to allow practitioners to discriminate between normal and abnormal behaviors in reptiles. Some of the most common reasons for presentation of behavioral issues are discussed, including hyperactivity, self-mutilation, biting, repetitive behaviors, and postural abnormalities. Medical problems and suboptimal husbandry causing abnormal behaviors should be ruled out by attending veterinarians. Addressing behavior issues involves determining a differential diagnosis through a systematic approach, which then allows implementation of necessary environmental changes including enrichment, developing plans for behavior modification and biomedical training, and medication when appropriate.

Little if any role of male gonadal androgens in ontogeny of sexual dimorphism in body size and cranial casque in chameleons

Proximate control of the development of sexual dimorphism is still hotly debated in reptiles. In some squamates, many male-typical exaggerated traits including body size were assumed to be controlled by masculinization by male gonadal androgens. We performed a manipulative experiment to test the importance of this mechanism in the development of pronounced sexual differences in body size and size of head casque in the chameleon Chamaeleo calyptratus. Castrated males attained male-typical body size highly deviating from the body size of control females. Ontogenetic allometries of casque size on head length revealed that sexes depart considerably in casque growth later in the ontogeny; however, castrated males still follow male-typical casque growth. Paradoxically, exogenous testosterone led in females to slight increase of casque size, which might reflect interference with the feminizing effects of female gonadal hormones. The results in males strongly suggest that masculinization by male gonadal androgens during growth is not required for the development of sexual dimorphism in body size and casque size in the chameleon. The ontogeny of sexually dimorphic body size and exaggerated traits in at least some squamates is likely controlled by other proximate mechanism, possibly by feminization by ovarian hormones.

Influence of temperature, size and confinement on testosterone and corticosterone levels in breeding male spined toads (Bufo spinosus)

Winter breeding amphibians opportunistically engage in reproductive behaviour when environmental conditions become favourable. In such explosive breeding systems, males strongly compete for reproductive females. Although most research has been oriented on species in which males use mating calls to attract females, many high-density explosive breeding amphibians do not rely on mating calls. In such systems, larger and stronger males are thought to have significant advantages to access reproductive females. Testosterone (T) is expected to increase with the physical attributes that facilitate access to females, while increased corticosterone levels (CORT) are needed to sustain the energetic requirements associated with mating behaviour. In this study, we investigated how environmental temperature, and body size influence testosterone and corticosterone in males of an explosive winter-breeding species with low investment in mating call, the spined toad (Bufo spinosus). We found that both baseline CORT and T were positively correlated with environmental temperature. Interestingly, despite a remarkable range of variation in CORT and T, there was no evidence that either hormone was correlated with body size. Finally, we found no effect of confinement (13 h of captivity) on circulating CORT and T levels. This suggests that breeding male toads may be relatively insensitive to stress in order to maintain reproductive effort during their short mating period. Future studies should investigate both the influence of the phenology of breeding and the social interactions on these hormonal levels.

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.

Sex hormones and the development of sexual size dimorphism: 5α-dihydrotestosterone inhibits growth in a female-larger lizard (Sceloporus undulatus)

Sexual differences in adult body size [sexual size dimorphism (SSD)] and color (sexual dichromatism) are widespread, and both male- and female-biased dimorphisms are observed even among closely related species. A growing body of evidence indicates testosterone can regulate growth, thus the development of SSD, and sexual dichromatism. However, the mechanism(s) underlying these effects are conjectural, including possible conversions of testosterone to estradiol (E₂) or 5α-dihydrotestosterone (DHT). In the present study, we hypothesized that the effects of testosterone are physiological responses mediated by androgen receptors, and we tested two specific predictions: (1) that DHT would mimic the effects of testosterone by inhibiting growth and enhancing coloration, and (2) that removal of endogenous testosterone via surgical castration would stimulate growth. We also hypothesized that females share downstream regulatory networks with males and predicted that females and males would respond similarly to DHT. We conducted experiments on eastern fence lizards (Sceloporus undulatus), a female-larger species with striking sexual dichromatism. We implanted Silastic^® tubules containing 150 µg DHT into intact females and intact and castrated males. We measured linear growth rates and quantified color for ventral and dorsal surfaces. We found that DHT decreased growth rate and enhanced male-typical coloration in both males and females. We also found that, given adequate time, castration alone is sufficient to stimulate growth rate in males. The results presented here suggest that: (1) the effects of testosterone on growth and coloration are mediated by androgen receptors without requiring aromatization of testosterone into E₂, and (2) females possess the androgen-receptor-mediated regulatory networks required for initiating male-typical inhibition of growth and enhanced coloration in response to androgens.

Physiological and behavioral effects of exogenous corticosterone in a free-ranging ectotherm

In the face of global change, free-ranging organisms are expected to experience more unpredictable stressors. An understanding of how organisms with different life history strategies will respond to such changes is an integral part of biodiversity conservation. Corticosterone (CORT) levels are often used as metrics to assess the population health of wild vertebrates, despite the fact that the stress response and its effects on organismal function are highly variable. Our understanding of the stress response is primarily derived from studies on endotherms, leading to some contention on the effects of chronic stress across and within taxa. We assessed the behavioral and hormonal responses to experimentally elevated stress hormone levels in a free-ranging, arid-adapted ectotherm, the Southern Pacific rattlesnake (Crotalus helleri). Plasma CORT was significantly elevated in CORT-implanted snakes 15days after implantation. Implantation with CORT did not affect testosterone (T) levels or defensive behavior. Interestingly, we observed increased defensive behavior in snakes with more stable daily body temperatures and in snakes with higher plasma T during handling (tubing). Regardless of treatment group, those individuals with lower baseline CORT levels and higher body temperatures tended to exhibit greater increases in CORT levels following a standardized stressor. These results suggest that CORT may not mediate physiological and behavioral trait expression in arid-adapted ectotherms such as rattlesnakes.

Ovarian control of growth and sexual size dimorphism in a male-larger gecko

Sexual size dimorphism (SSD) reflects sex-specific solutions to the allocation of energy among growth, reproduction and survival; however, the proximate mechanisms behind these solutions are still poorly known even in vertebrates. In squamates, sexual differences in body size used to be attributed to direct energy allocation to energetically demanding processes, largely to reproduction. In addition, SSD is assumed to be controlled by specific endogenous mechanisms regulating growth in a sex-specific manner, namely masculinization by male gonadal androgens or feminization by ovarian hormones. We performed a manipulative growth experiment in females of the male-larger gecko Paroedura picta in order to test the reproductive cost hypothesis, the male androgen hypothesis and the ovarian hormone hypothesis. Specifically, we investigated the effect of total ovariectomy, prepubertal ovariectomy, unilateral ovariectomy, and total ovariectomy followed by exogenous estradiol, dihydrotestosterone or testosterone treatment, on female growth in comparison to males and reproductively active females. The present results and the results of our previous experiments do not support the hypotheses that SSD reflects direct energy allocation to reproduction and that male gonadal androgens are involved. However, all lines of evidence, particularly the comparable growth of reproducing intact and unilaterally ovariectomized females, were concordant with the control of SSD by ovarian hormones. We suggest that feminization of growth by female gonadal hormones should be taken into consideration as an endogenous pathway responsible for the ontogeny of SSD in squamates.

Reptile Soft Tissue Surgery

The surgical approach to reptiles can be challenging. Reptiles have unique physiologic, anatomic, and pathologic differences. This may result in frustrating surgical experiences. However, recent investigations provided novel, less invasive, surgical techniques. The purpose of this review was to describe the technical aspects behind soft tissue surgical techniques that have been used in reptiles, so as to provide a general guideline for veterinarians working with reptiles.

Endogenous control of sexual size dimorphism: Gonadal androgens have neither direct nor indirect effect on male growth in a Madagascar ground gecko (Paroedura picta)

Changes in the effect of gonadal androgens on male growth are considered as a possible mechanism allowing shifts in magnitude and even direction of sexual size dimorphism in vertebrates, particularly squamate reptiles. Positive effects of gonadal androgens on male growth were found in several male-larger species of lizards. Contrastingly, we document that in the male-larger Madagascar ground gecko (Paroedura picta) gonadal androgens do not affect male growth under constant thermal conditions. However, the absence of a thermal gradient might prevent the potential indirect effect of gonadal androgens on growth via the influence of circulating hormones on an individual's thermoregulation and hence metabolic rate. In order to study this, we monitored the growth and body temperature of socially isolated sham-operated and castrated males of the same species in a thermal gradient. We also compared the oxygen consumption and activity between the treatment groups in the open field to test the effect of gonadal hormones on these traits potentially affecting growth. Even under a thermal gradient we found no effect of gonadal androgens on growth rate or final body dimensions. Castration also did not significantly affect oxygen consumption or activity in the open field test. Together with our previous findings, we can exclude both the direct effect of male gonadal androgens on the ontogeny of sexual size dimorphism via the influence on the growth axis, and the indirect influence of gonadal androgens acting on the ontogeny of SSD through the effect on thermoregulation, metabolic rate and activity.

The complete mitochondrial genome of the Madagascar ground gecko Paroedura picta (Squamata: Gekkonidae)

We sequenced the complete mitochondrial genome of the Madagascar ground gecko Paroedura picta (Squamata: Gekkonidae). The mitogenome is 17 220 base pairs long and conforms to the typical vertebrate gene composition and arrangement, i.e. 13 protein-coding genes, 22 tRNA genes, 2 ribosomal RNA genes and 1919 bp long control region. We reconstructed phylogenetic relationships of P. picta and representatives of nine other genera from the family Gekkonidae and calculated mean p-distances for all 13 protein-coding mitochondrial genes. The lowest mean p-distances were found in cytochrome oxidase subunit I and III genes (COI and COIII) indicating their usefulness for elucidating deeper phylogenetic relationships.

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.