PS 4-59 - Limited genetic connectivity of aquatic invertebrate communities in Grand Canyon tributaries revealed using environmental DNA metabarcoding

Abstract: The spatial distribution of genetic diversity in river networks reflects the complex influences of landscape and environmental factors on the evolutionary and demographic histories of aquatic organisms. While the dispersal ability of every species is different, barriers to dispersal such as stream network configuration, flow regime variation, inhospitable terrestrial landscapes, and anthropogenic alterations have the potential to influence community-wide patterns of genetic diversity. The interplay of hydrologic and topographic connectivity in stream networks allows for several competing models of genetic connectivity, namely the stream hierarchy model, the headwater model, and the Death Valley model, although it is unclear how these models hold up across entire communities. Environmental DNA (eDNA) metabarcoding presents a promising method for studying genetic connectivity and dispersal of entire communities without reliance on representative species. In the Grand Canyon ecosystem, the mainstem Colorado River collects numerous small, canyon-bound tributaries that contain distinct invertebrate communities. Using eDNA metabarcoding, we tested for community-wide patterns of genetic diversity among Grand Canyon tributaries. We collected eDNA samples from the Colorado River and its tributaries within Grand Canyon and performed metabarcoding sequencing on a short region of the aquatic invertebrate COI fragment. Applying strict denoising and filtering algorithms to this dataset of aquatic invertebrate genetic sequences, we extracted exact sequence variants (ESVs; analogous to haplotypes) before clustering into operational taxonomic units (OTUs; analogous to species). We identified 1,201 ESVs across 448 OTUs, with 148 OTUs comprised of multiple haplotypes. These genetically diverse OTUs were predominantly found in tributary habitats, indicating that the isolated and canyon-bound tributaries of Grand Canyon harbor greater genetic diversity across many aquatic invertebrate species. A large portion of haplotypes were only found in a single tributary habitat, suggesting possible support for the Death Valley model of genetic connectivity, which predicts high genetic isolation due to limited aquatic and terrestrial dispersal capabilities. Further work will incorporate AMOVA analysis to identify specific landscape and environmental variables that influence the distribution of genetic diversity in Grand Canyon aquatic invertebrate species. Ultimately, these findings will shed light on the impact of landscape barriers on genetic diversity and dispersal in Grand Canyon aquatic communities. A greater understanding of the genetic connectivity of these communities will help inform efforts to protect biodiversity in light of severe anthropogenetic impacts on the Grand Canyon ecosystem in the last decade.