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.

Ontogeny of pronounced female-biased sexual size dimorphism in the Malaysian cat gecko (Aeluroscalabotes felinus: Squamata: Eublepharidae): a test of the role of testosterone in growth regulation.

Species differences in the effect of male gonadal androgens on male growth are considered a possible mechanism allowing shifts in magnitude and even direction of sexual size dimorphism (SSD) in squamate reptiles. According to the bipotential growth regulation hypothesis, the androgen testosterone (T) enhances male growth in species with male-biased SSD and conversely inhibits male growth in males of female-larger species. In the present study, we describe the ontogeny of the pronounced female-biased SSD and report the effect of T on growth via hormonal manipulations in males and females of the Malaysian cat gecko (Aeluroscalabotes felinus). In accord with the predictions of the bipotential growth regulation hypothesis, growth was inhibited by replacement of T in castrated males. Additionally, exogenous T inhibited growth of females to male-typical levels. Nevertheless, male castration alone did not significantly affect growth, contrary to the prediction of the bipotential growth regulation hypothesis, which contradicts the generality of this hypothesis. Application of exogenous T to females can interfere with normal ovarian function. Therefore, although not directly tested in this study, we suggest that ovarian effects on the ontogeny of SSD in A. felinus are consistent with our results. The development of SSD is a function of differential growth between the sexes, and potential sex-specific growth regulation in both males and females should be taken into account as possible proximate mechanisms responsible for SSD.

Neither male gonadal androgens nor female reproductive costs drive development of sexual size dimorphism in lizards.

Sexual size dimorphism (SSD) is an extensively studied phenomenon in animals, including reptiles, but the proximate mechanism of its development is poorly understood. The most pervasive candidates are: (1) androgen-mediated control of growth, i.e. a positive effect of gonadal androgens (testosterone) on male growth in male-larger species, and a negative effect in female-larger species; and (2) sex-specific differences in energy allocation to growth, e.g. sex with larger reproductive costs should result in smaller body size. We tested these hypotheses in adults of the male-larger lizard Paroedura picta by conducting castrations with and without testosterone implants in males and manipulating reproductive status in females. Castration or testosterone replacement had no significant effect on final body length in males. High investment to reproduction had no significant effect on final body length in intact females. Interestingly, ovariectomized females and females with testosterone implants grew to larger body size than intact females. We did not find support for either of the above hypotheses and suggest that previously reported effects of gonadal androgens on growth in male lizards could be a consequence of altered behaviour or social status in manipulated individuals. Exogenous testosterone in females led to decreased size of ovaries; its effect on body size may be caused by interference with normal ovarian function. We suggest that ovarian factors, perhaps estrogens, not reproductive costs, can modify growth in female lizards and may thus contribute to the development of SSD. This hypothesis is largely supported by published results on the effect of testosterone treatment or ovariectomy on body size in female squamates.

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.