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J. Exp. Biol. 216 (10): 1872-1880

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

Zuzana Starostová1, Lukás Kubicka2, Alison Golinski3, and Lukás Kratochvíl2,*

1 Faculty of Science, Charles University in Prague, Department of Zoology, Vinicná 7, CZ-128 44 Praha 2, Czech Republic
2 Faculty of Science, Charles University in Prague, Department of Ecology, Vinicná 7, CZ-128 44 Praha 2, Czech Republic
3 Graduate Program in Endocrinology and Animal Biosciences, Rutgers University, 84 Lipman Drive, New Brunswick, NJ 08901, USA

* Author for correspondence (lukas.kratochvil{at}natur.cuni.cz)

AUTHOR CONTRIBUTIONS

All authors participated in the design of the study and execution of the experiments. Data were analyzed and the first draft of the manuscript was prepared by L.K., L.K. and Z.S. All authors edited and approved the final version of the manuscript.

Received for publication 24 August 2012. Accepted for publication 28 January 2013.

Abstract: 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.

Key Words: gecko • growth • life history • phenotypic plasticity • reproductive investment • trade-off

Abbreviations: D, limit of y • SSD, sexual size dimorphism • SVL, snout–vent length • y, ln(actual SVL/SVL at the time of hatching) • {lambda}, length of the lag phase of growth in days • μmax, relative maximum growth rate (day–1)

THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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