Meeting Abstract
Birds deposit various immune compounds into their eggs that protect developing offspring. Infection risk may influence variation in deposition, but this has rarely been addressed in natural systems. We collected eggs and bacterial samples from tree swallow nests across the species range to investigate how characteristics of the nest microbiome relate to levels of egg yolk antibodies. Using next-generation sequencing of the 16S rRNA gene, we provide an in-depth look at the biogeography of avian-associated bacteria at a large geographic scale. Nest microbiomes were dominated by Proteobacteria, Actinobacteria, and Bacteroidetes, with the number of operational taxonomic units per sample ranging from 130 to 873. We found no evidence for a latitudinal species gradient, nor did we find any relationships between microbiota and longitude or elevation. As expected, phylogenetic distances between bacterial communities were smaller within sites than between sites. In contrast, the effect of geographic distance was weaker than expected, suggesting that nests provide similar microhabitat conditions that vary less than the environments in which they lie. In accordance with our predictions, preliminary analyses indicate a positive relationship between yolk antibody levels and nest bacterial richness across sites. To our knowledge, this is the first study to document a positive relationship between transgenerational immune investment and the diversity of bacteria in a wild host environment. Our results suggest that nest microbiota have the potential to influence important life history stages where microbe-host interactions are particularly intensive.
