UC San Diego

Biotic interactions, including those on the microscopic level, are important contributors to adaptive evolution. This includes the host- associated microbiome, which is crucial for many aspects of their hosts’ biology. However, the role of the microbiome in their hosts’ adaptation to ecological niches remains largely unknown. Threespine stickleback represent a good model system to address this question. Notably, there is substantial variation in freshwater stickleback trophic ecology associated with lake size; populations in small lakes mainly feed on littoral invertebrates from the lake sediment (benthic prey) and populations in large lakes mainly feed on pelagic zooplankton (limnetic prey). Populations from intermediate-sized lakes feed on a mix of benthic and limnetic prey. The evolution of trophic divergence along the benthic-limnetic axis as a result of repeated freshwater colonization allows the study of gut microbiome dynamics in response to varying environmental conditions. The goal of this project is to analyze the relationships between trophic ecology and morphological traits, as well as gut microbiome diversity, in order to examine patterns in the gut microbiome which might reflect niche specialization by threespine stickleback. Specifically, we hypothesized that populations from intermediate-sized lakes have the highest degree of gut microbiome diversity. Though two morphological traits correlate with the trophic ecology of lake size, there was minimal pattern in variation between gut microbiome diversity measures and the trophic ecology proxy or morphological data. Further study may improve our understanding of how a host, its gut microbiome, and the environment interact during the adaptation to different ecological niches.