Parasite load in salt marsh amphipods

Located on the northeastern coast of Massachusetts, the Plum Island Ecosystem (PIE) – Long Term Ecological Research Network (LTER) serves as a model system for studying long-term ecosystem level responses of high salt marsh communities to large-scale nutrient additions across scales of space and time.

The ubiquitous saltmarsh cordgrass (Spartina alterniflora) dominates the high marsh vegetation community across nitrogen enriched and control creeks. Accordingly, studies at the PIE LTER have shown that the density and biomass of Spartina alterniflora and macroinvertebrate communities in the Spartina habitat were significantly greater in the creeks enriched with nitrogen fertilizer, than in reference creeks (Johnson 2011). Previous studies also suggest invertebrate density and biomass increased with nitrogen enrichment as well (Bertness et al. 2008, Johnson and Fleeger 2009, Wimp et al. 2010).

Focusing on the addition of nitrogen to a northeast American salt marsh, we aim to dissect the levels of diversity that exist among a parasitic trematode (Levinseniella byrdii), its second intermediate host (Orchestia grillus), and among L. byrdii within a single O. grillus. Using a double-digest restriction associated DNA (ddRAD) sequencing, we aim to: 1) Pioneer a partial draft de novo genome for each previously unsequenced species, 2) Characterize genetic diversity of the amphipod O. grillus and its associated trematode L. byrdii, 3) Compare genetic diversity within and between two naturally-occurring O. grillus populations exposed to different levels of nitrogen, 4) Characterize variation in trematode load and intraspecific diversity within each trematode population, 5) Evaluate genomic differences between infected and uninfected amphipods.

Previous sequencing work on trematodes infecting amphipods has taken the form of targeted sequencing to address a specific hypothesis (Keeney et al, 2007.) Less work has been done to apply the full power of next generation sequencing to host/parasite interactions in a habitat. To this end, we will sequence whole amphipod samples--including trematode parasites. We hope to extract information about: parasitic load and diversity within each amphipod and amphipod and trematode population structure of as measured by SNPs.

We hypothesize that increased nitrogen fertilization will be a driving force for genetic differentiation between the amphipods at each site. This study will be the first to characterize diversity across the genome of Orchestia grillus and the first to assess genome-wide diversity in any Levinseniella species.