Evolutionary ecology of separate sexes: Causes and consequences of sex differences in morphology, behavior, and life history

As a consequence of anisogamy, females and males are expected to have sex-specific optima for morphological, behavioral and life history traits. Selection acting differently on the same traits in both sexes has pushed towards these sex-specific optima and driven the evolution of sex differences in morphology, reproductive strategy, behavior, and life history. The great diversity in sexual dimorphism that has evolved across species is a testament to the effects of independent evolution of males and females. However, despite the assumption of sex-specific evolutionary dynamics, many phenomena central to evolutionary ecology, such as costs of reproduction, aggressive interactions, selection, and life-history evolution, have often been studied with a focus limited to a single sex. The lack of between-sex comparisons of these phenomena has left outstanding questions as to how often the same evolutionary dynamics are operating in both sexes and how sex differences in selection may shape the evolutionary trajectories of separate sexes within a species. In Chapters 1-3 of this dissertation, I test theoretical predictions related to costs of reproduction, aggressive behavior, and selection with approaches that make direct comparisons between females and males using experimental manipulations, behavioral assays, and mark-recapture methods in wild populations of brown anole lizards (Anolis sagrei). In Chapter 1, I use an experimental manipulation of reproductive investment to show that, despite their dramatically different forms of reproductive investment, females and males pay comparable costs of reproduction in the common currencies of energy storage and parasitism. In Chapter 2, I test the assumption that males are categorically more aggressive than females in territorial polygynous species and find no sex difference in the likelihood that males or females will attack a territorial intruder and that females actually have a shortened latency to attack as compared to males. In Chapter 3, I test the hypothesis that sexually antagonistic selection develops over ontogeny and find that natural selection on body size is similar for females and males during the earliest part of the juvenile life stage, but that selection on body size diverges coincident with the onset of sexual maturity. In Chapter 4, I test across 82 lizard species for evolutionary consequences of sex-specific selection acting on life-history traits in the context of intralocus sexual conflict. Chapter 4, both provides a clear demonstration of the tradeoff between survival and reproduction and shows that sexual conflict can shape life history evolution by demonstrating a correlation between sexual size dimorphism and residual variation in survival around the central life-history tradeoff. Specifically, I find that the degree of sexual size dimorphism correlates with residual survival such that female-larger species have lower survival than would be predicted by reproductive effort, while male-larger species tend to have greater levels of annual survival than would be predicted by reproductive effort.