Positive selection on secretory and structural components of salivary glands within the ecologically diverse bat family Phyllostomidae
Abstract The leaf-nosed bats (Phyllostomidae) are outliers among chiropterans with respect to the unusually high diversity of dietary strategies within the family. Salivary glands, owing to their functions and high ultrastructural variability among lineages, are proposed to have played an important role during the phyllostomid radiation. Salivary gland secretory products directly interact with food materials and pathogens which can provide selective interactions. To identify genes underlying salivary gland functional diversification, we sequenced submandibular gland transcriptomes from phyllostomid species representative of divergent dietary strategies. From the assembled transcriptomes, we identified and tested 3,266 single gene orthologs and identified 57 evolving under positive selection. All enriched gene ontology terms were related to defense against other organisms and the cell membrane/extracellular environment. Based on GO annotation, many of the defense-related loci under selection form secretory products. Salivary glands perform a complex array of tasks, and we identified positive selection on additional proteins bound to membranes and in the extracellular environment with multiple functions. Although illuminating exact function is difficult, results suggest that regulatory release of secretory products, not the products themselves, is disproportionately shaped by positive selection on coding sequence. Identified instances of selection on such cellular components may help explain the ultrastructural variability of salivary glands previously documented.