Adams, Danielle MargretTo understand the myriad effects of sexual selection in the evolution and diversification of life, we must investigate variation within and among diverse animal taxa. Here, I study sexual selection in phyllostomid bats (Family Phyllostomidae), a diverse radiation comprised of 216 species that vary widely in their social behavior and roosting ecology, but whose mating behavior is largely unknown. First, I investigate whether socio-ecological traits predict variation in the intensity of sexual selection among phyllostomid species. In the absence of behavioral data, I use measures of sexual dimorphism as an indicator of precopulatory sexual selection and testes size as a proxy for postcopulatory competition. Taking a phylogenetic approach, I find that roosting aggregation size, but not roost structure permanence, explains family-wide variation in both pre- and postcopulatory sexual selection. Next, I examine the distribution of extra-group paternity in a single species, Phyllostomus hastatus, whose social mating system of female-defense polygyny has been well described. Through molecular parentage assignment of 241 offspring from three wild colonies in Trinidad, West Indies, I find that most harem-holding males are unable to monopolize mating in their social groups, resulting in paternity by extra-group males. Furthermore, variation in the rate of extra-group paternity is associated with harem male body condition as well as the composition of the female group. Finally, I investigate the variation in a male-specific chemical signal found in P. hastatus, which has been implicated in male-male competition and female choice of this species. Results show that in addition to individual variation, harem males have significantly different chemical profiles from males found roosting in all-male groups (bachelors). Through the examination of both family-wide and species-specific patterns, we can broaden our understanding of how sexual selection has contributed to the diversity within the Phyllostomidae.enDissertationBiology