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

Abstract

SUMMARYSexual 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.

Bearded ladies: females suffer fitness consequences when bearing male traits

“…We expected that these costs could take two forms: (i) since badges act as sex-identifiers [11], males may preferentially court females lacking badges and (ii) since badges result from high levels of plasma testosterone (in males and females; [10]), they may indicate low female fecundity associated with high testosterone in females (e.g. [13]). …”

Variability in vertebral numbers does not contribute to sexual size dimorphism, interspecific variability, or phenotypic plasticity in body size in geckos (Squamata: Gekkota: Paroedura)

“…Several species from the genus Paroedura are endangered or even critically endangered (Bora et al., ; Raxworthy et al., ). Nevertheless, the male‐larger Madagascar ground gecko ( Paroedura picta ) has become an emerging laboratory reptile model because of its extremely rapid reproduction for a reptile and relatively easy care (e.g., Kubička & Kratochvíl, ; Kubička, Starostová, & Kratochvíl, , ; Kubička, Schořálková, Červenka, Kratochvíl, ; Schořálková, Kratochvíl, & Kubička, ; Starostová et al., ; Starostová, Angilletta, Kubička, & Kratochvíl, ; Starostová, Kubička, Golinski, & Kratochvíl, ; Starostová, Gvoždík, & Kratochvíl, ). For these reasons we used it for a series of manipulative experiments to investigate the control and correlates of growth, sexual size dimorphism, and body size.…”

“…Body size and structural growth is generally believed to be negatively affected by energy limitation and should therefore also be negatively affected by high expenditure due to other energetically demanding processes. However, we discovered that snout‐vent length (SVL) and structural growth in P. picta was unaffected by manipulations of food intake under nutrient conditions allowing continuous reproduction (Kubička & Kratochvíl, ), by energy allocation to reproduction in females (Kubička et al., ; Starostová et al., ), by tail regrowth after tail autotomy (Starostová et al., ), and by castration in males (Kubička, Starostová, & Kratochvíl, ; Starostová et al., ). We suggest that these results can be explained by a simple hierarchical rule of resource allocation followed by the geckos, where the allocation to structural growth and body size have priority over investment in all other energy expenditures.…”

“…This hierarchical rule would to a large extent buffer the effect of energy limitation on growth and structural body size (Kubička & Kratochvíl, ). On the other hand, body size of fully grown geckos, or their asymptotic body size estimated from growth curves, was affected by the removal of ovaries (positive effect) or the supplementation of exogenous estradiol (negative effect) to females, suggesting that SSD is influenced by ovarian hormones (Kubička et al., ; Starostová et al., ). Notably, testicular, not ovarian, hormones were previously suggested to control growth and thus SSD in other lizard lineages (Cox & John‐Alder, ; Cox, Stenquist, & Calsbeek, ; Pollock, Feigin, Drazenovic, & John‐Alder, ).…”

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)

“…Among lizards, the expression of sexually dimorphic morphology and behaviors are associated with elevated levels of androgens present in reproductively active males (Cox et al, 2005;Crews et al, 1978;Golinski et al, 2014;Crews, 1999, 2000;Rhen et al, 2005;Sinervo et al, 2000;Tokarz, 1986;Weiss and Moore, 2004;Woolley et al, 2004, but see Kubička et al, 2013;Starostová et al, 2013;Sanger et al, 2014). Studies have also demonstrated that chemical or pheromonal cues play an important role in social interactions of several species of reptiles, including the eublepharid gecko E. macularius, such as for the identification of conspecifics and distinguishing between the sexes (Brillet, 1993;Cooper and Steele, 1997;Greenberg, 1943;Mason and Gutzke, 1990;Shine et al, 2002;reviewed in Houck, 2009;Martin and Lopez, 2011; but see Hews et al, 2011).…”