Fecundity Selection and the Evolution of Reproductive Output and Sex-Specific Body Size in the Liolaemus Lizard Adaptive Radiation

Fecundity is a primary component of fitness. Theory predicts that the evolution of fecundity through increased brood size results from fecundity selection favouring larger female size to accommodate more offspring and to store more energy. This is expected to generate asymmetric selection on body size between the sexes, ultimately driving evolution of female-biased sexual size dimorphism. Additionally, it has been predicted that the intensity of fecundity selection increases when the opportunities for reproduction are reduced by the limiting thermal effects of increasing latitude-elevation (i.e. decreasing environmental temperatures) on the length of the reproductive season. This later factor would be particularly strong among ectotherms, where reproduction is heavily temperature-dependent. However, this integrative perspective on reproductive evolution by fecundity selection has rarely been investigated. Here, we employ a comparative approach to investigate these predictions in Liolaemus, a prominent lizard radiation. As expected, Liolaemus reproductive output (i.e. offspring number per reproductive episode) increases predictably with increasing female size. However, contrary to predictions, we found that increased fecundity does not translate into female-biased SSD, and that combined latitude-elevation does not impose a detectable effect on fecundity. Finally, our allometric analyses reveal that SSD scales with body size, which supports the occurrence of Rensch's rule in these lizards. We discuss the evolutionary implications of our results, and the assumptions of the investigated hypotheses.