Sex-based population structure of ectoparasites from Neotropical bats

The structure and composition of populations may be molded by multiple evolutionary and ecological mechanisms, with natural selection affecting sex ratios as well as the distributions of each sex throughout the environment. To address sex-based aspects of population structure, I evaluated sex ratios, co-occurrence of the sexes, correlations of abundance of the sexes, and dispersion of individuals of each sex for each of 34 host–ectoparasite associations from Paraguayan bats. Of the 34 host–ectoparasite associations, 23 exhibited positive co-occurrence, 27 exhibited positive correlation of abundances, three exhibited male sex bias, one exhibited female sex bias, 27 had clumped distributions of males, and 26 had clumped distributions of females. No associations exhibited negative co-occurrence, negative correlation of abundance, or hyperdispersed males or females. There was no evidence for sexual segregation, sex-based niche partitioning, or intrasexual selection in any host–ectoparasite association. Previously proposed mechanisms (e.g. pre-partum sex bias, local mate competition, or mortality from host grooming) fail to explain observed patterns of sex bias. For ectoparasites of hosts that occupy permanent roost sites, sex-specific behaviour related to reproduction may make females more susceptible to off-host predation, and less likely to be present in samples from bats captured away from the roost. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107, 56–66.