Meeting Abstract
Sexually transmitted infections have been suggested as major costs of sexual reproduction, but the mechanisms underlying transmission have been largely overlooked. Testosterone is a hormone that mediates several aspects of reproduction, including the number of sexual contacts. Therefore, testosterone has the potential to affect sexually transmitted infections, either indirectly by behaviors that increase contact rates and potential exposures to cloacal pathogens, or directly by altering immune function. We investigated the relationship between plasma testosterone levels and cloacal bacterial diversity and community composition in tropical populations of male Zonotrichi capensis in Ecuador. We collected cloacal swabs to assess their bacterial communities using Illumina amplicon sequencing of the 16S rRNA gene. There was a positive correlation between testosterone levels and bacterial phylogenetic diversity. Contrary to our expectations, high and medium testosterone individuals had bacterial communities that were more similar to each other than to low testosterone individuals. Finally, looking at several groups of potential avian pathogenic bacteria, the relative abundance of Chlamydiae was positively correlated with testosterone levels. Two nonexclusive explanations for these results are that testosterone is mediating sexual contact rates and thus the acquisition of more bacterial strains, or that testosterone is directly altering immune function and bacteria become established more easily. Overall, increased exposure to sexually transmitted pathogens in the form of cloacal bacteria can constitute a strong selective pressure for the modulation of testosterone levels.
