Received: 15 January 2018 Revised: 19 March 2018 Accepted: 23 March 2018 DOI: 10.1002/jez.2159 RESEARCH ARTICLE Variability in vertebral numbers does not contribute to sexual size dimorphism, interspecific variability, or phenotypic plasticity in body size in geckos (Squamata: Gekkota: Paroedura) Lukáš Kratochvíl 1 Lukáš Kubiˇ cka 1 Martin Vohralík 1 Zuzana Starostová 2 1 Department of Ecology, Faculty of Science, Charles University, Prague 2, Czech Republic 2 Department of Zoology, Faculty of Science, Charles University, Prague 2, Czech Republic Correspondence Lukáš Kratochvíl, Department of Ecology, Faculty of Science, Charles University, Viniˇ cná 7, Prague 2, 12844 Czech Republic. Email: lukas.kratochvil@natur.cuni.cz Funding information Grantová Agentura, Univerzita Karlova, Grant/Award Number: GAUK 363715; Grantová Agentura ˇ Ceské Republiky, Grant/Award Num- ber: GA16-24619S Abstract Body size is a fundamental trait correlated with nearly every aspect of animal life. It is influenced by numerous genetic and non-genetic factors. Despite its central importance, proximate mecha- nisms of intra- and interspecific variability in body size are still not well understood even in such a largely studied group as reptiles. For our study, we concentrated on the gecko species Paroedura picta. We investigated whether differences in sexual size dimorphism and in final and asymptotic snout-vent length (induced by a range of incubation and rearing temperatures) are correlated with differences in the number of presacral vertebrae. Moreover, we tested whether changes in this number were associated with evolutionary changes in sexual size dimorphism and body size in the genus Paroedura. We found that the variation in the number of presacral vertebrae is very limited both intra- and interspecifically, ranging between 26 and 28 vertebrae with most individuals pos- sessing the modal number of 27. We conclude that changes in the number of vertebrae do not con- tribute to developmental plasticity or evolutionary changes in body size nor, in contrast to some other squamate lineages, to sexual size dimorphism. KEYWORDS axial skeleton, body size, developmental plasticity, reptile, sexual size dimorphism, temperature- size rule 1 INTRODUCTION Body size is a fundamental trait correlated with nearly every aspect of animal life. It is influenced by numerous genetic and non-genetic factors. Despite its central importance and decades of research, prox- imate mechanisms of intra- and interspecific variability in body size are still not comprehensibly understood even in well-studied groups, such as reptiles. Our long-term goal is to contribute to the understand- ing of the processes responsible for variability in body size in reptiles using comparative studies combined with manipulative experiments in geckos, with particular focus on the genus Paroedura. This genus currently contains 18 described species of diverse morphology and ecology from Madagascar and the Comoro archipelago (Schönecker, 2008; Uetz, Freed, & Hošek, 2018). Species of the genus Paroedura vary greatly in body size. The smallest species P. androyensis weighs only up to 2 g, whereas its sister species P. picta (Jackman et al., 2008) can grow to more than 35 g. From the distribution of body sizes across the phylogeny of the genus Paroedura it can be expected that both the largest and the smallest body sizes are derived states within the genus. The genus Paroedura includes male-larger, monomorphic, and female-larger species and sexual size dimorphism (SSD) changes systematically with body size across the species (Starostová, Kubi ˇ cka, & Kratochvíl, 2010). Males are evolutionary more variable in body size than females and male-biased SSD tends to increase with increasing body size among species. Thus, the genus as a whole follows the trend known as Rensch's rule (Abouheif & Fairbairn, 1997; Fairbairn, 1997; Fairbairn, Blanckenhorn, & Székely, 2007; and references therein). Several species from the genus Paroedura are endangered or even critically endangered (Bora et al., 2011; Raxworthy et al., 2011). Nev- ertheless, 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., Kubiˇ cka & Kratochvíl, 2009; Kubiˇ cka, Starostová, & Kratochvíl, 2012, 2015; Kubiˇ cka, Schoˇ rálková, ˇ Cervenka, Kratochvíl, 2017; Schoˇ rálková, Kratochvíl, & Kubiˇ cka, 2018; Starostová et al., 2010; Starostová, Angilletta, Kubiˇ cka, & Kratochvíl, 2012; Starostová, Kubiˇ cka, Golinski, & Kratochvíl, 2013; Starostová, Gvoždík, & Kratochvíl, 2017). For these reasons we used it for a series of manipulative experiments to investi- gate the control and correlates of growth, sexual size dimorphism, and body size. J. Exp. Zool. 2018;1–6. c  2018 Wiley Periodicals, Inc. 1 wileyonlinelibrary.com/journal/jez