Sexual selection and sex ratios in Anolis lizards

Biased sex ratios, or unequal numbers of males and females in a population, can alter the intensity of sexual selection by enhancing competition for mates, and thus may affect the evolution of reproductive strategies. Studies of sex ratio variation across a clade provide an opportunity to examine the morphological or behavioral consequences of different levels of sexual selection. We examined sex ratio variation, using phylogenetic comparative methods, across a diverse clade of terrestrial vertebrates, the Anolis lizards. Across a sample of 14 species in 21 localities, we found remarkable bidirectional variation in sex ratios across the Anolis clade: males are more common in some populations and females in others. However, we find no evidence that sex ratio bias is associated with sexual size dimorphism, a proxy for sexual selection. Nor do we find an association of sex ratio bias with ecological niches (i.e. ecomorphs), which vary in sexual selection pressures and mating systems. The observed inter-specific variation in sex ratio suggests that a balance of different, possibly opposing, factors, including sex-specific dispersal and mortality rates, may play a role in determining population sex ratio.