Species traits and local environmental conditions often correspond strongly. This correspondence may arise due to ecological species sorting, where dispersal and competitive species replacement determine composition. The correspondence may also arise due to local adaptation of resident species, where natural selection acts on existing genetic variation to determine genetic composition. As a result of the traditional separation of ecological and evolutionary timescales, methods that incorporate community composition, spatial descriptors, environmental gradients, as well as population genetic differentiation are lacking. Our goal was to expand on existing variation partitioning methods to explore the relationship between spatial isolation, community composition, and local adaptation. We then worked to apply these methods to a survey of zooplankton communities and Daphnia pulex population genetics in southwest Michigan ponds. We surveyed zooplankton in a pond metacommunity in southwest Michigan. For each pond, we surveyed environmental characteristics and zooplankton community composition. We also isolated D. pulex clones from each pond, placed them in a common garden assay of growth rate, and analyzed them at 12 microsatellite markers. This array of community, environmental, and genetic (both neutral and quantitative) information, combined with spatial descriptors of each pond, served as a test for our variance decomposition methods.
Results/Conclusions
Our method provides a novel way of incorporating population genetic differentiation with spatial and environmental patterns. Existing population genetic methods can ascribe genetic differentiation to space (isolation by distance) or environment (selection and common garden experiments), but are less straightforward for interpreting environment-space interactions. By incorporating this new method with contemporary community ecology metrics that partition species composition with environment and space, we were able to determine the degree of local adaptation and community composition that correspond to environmental conditions and spatial isolation. Our data indicate that D. pulex population differentiation has no clear relationship with environmental factors. We went further by determining whether zooplankton community composition interferes with D. pulex local adaptation. We believe that datasets with environmental, spatial, community, and genetic information, analyzed by our variance decomposition method, are crucial to continuing to merge the studies of ecology and evolution. Our data also indicate that community composition and local adaptation are not independent processes.
