Nonadaptive microbiota in molluscivore pupfish
We found enrichment of the families Rhodobacteraceae andPlanctomycetacia within the molluscivore gut from both lake populations (Figure 5). However, these families have no clear role in anything related to mollusc digestion or even increased levels of protein, lipids, or chitin in the diet (due to some molluscivores specializing on ostracods during periods of abundance). Taxa from these taxonomic group are known to be found within aquatic environments (Simon et al. 2017; Yilmaz et al. 2016). Marine Rhodobacteraceae have a key role in biogeochemical cycling, make up about 30% of bacterial communities in the pelagic environment, and generally have a mutualistic relationship with eukaryotes providing vitamins to these groups (Simon et al. 2017). Both families are known for aquatic cellulose-decomposing taxa (Ringø et al. 2016; Kim et al. 2016), which suggests this microbiome shift may help more with macroalgae digestion rather than molluscs, despite previous observations that macroalgae forms the largest component of the generalist pupfish diet in the hypersaline lakes of San Salvador Island, Bahamas (Martin and Wainwright 2013).