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The mechanisms of osmoregulation have been characterized extensively in crustaceans, with studies expanding to investigate gene expression during salinity transfers in the last ~10 years. A current meta-analysis by lab member Justin C. Havird supports individual studies showing the up-regulation of multiple ion transporters and supporting enzymes during salinity transfer, which acts to transport ions across the gills (Havird et al., 2013). However, these studies have mainly focused on brachyurans (crabs) of marine ancestry that migrate into bays and estuaries. Anchialine shrimp present an opportunity to expand these studies to both a novel taxonomic and ecological niche. Anchialine habitats are landlocked coastal ponds and caves with subterranean influences from both the ocean and freshwater aquifer. The animals that live in these habitats therefore have to cope with salinities that fluctuate continuously due to tides, rainfall, and vertical salinity stratification in the habitat. Moreover, anchialine shrimp are primarily from the family Atyidae, which has an undisputed freshwater ancestry and likely invaded anchialine habitats from streams. To begin to characterize osmoregulatory adaptations in anchialine organisms, Justin has been studying the endemic Hawaiian atyid Halocaridina rubra. Preliminary results suggest classic crustacean osmoregulatory mechanisms like up-regulation of ion transporters during salinity change do not characterize H. rubra.

Although preliminary results from H. rubra are intriguing, it is unclear if the unusual patterns observed extend to other anchialine crustaceans or are specific to H. rubra. In this context, the Evolutionary Ecology Program within the Division of Environmental Biology at the National Science Foundation (NSF) has generously funded Justin's doctoral research for the next two (2) years to describe osmoregulatory processes in H. rubra in greater detail and compare them with anchialine shrimp species from the Ryukyus Islands in Southern Japan. Specifically, Caridina rubella, Metabetaeus minutus, Antecaridina lauensis, and Halocaridinides trigonophthalma will be investigated, which have varying degrees of relatedness to H. rubra and represent at least three (3) independent invasions of anchialine habitats. The main goal of this project is to use high-throughput transcriptome shotgun sequencing (RNA-Seq) to examine gene expression across the entire gill transcriptome during salinity transfers in these species. This research will further our limited understanding of the molecular basis of the evolution of euryhalinity and address convergent evolution in response to similar natural selection pressures. More information on this project can be found on its NSF award page (NSF-DEB #1311500).

This project represents a collaborative effort with Japanese researchers at the University of the Ryukyus and Justin was generously awarded a fellowship from the NSF's East Asia and Pacific Summer Institutes (EAPSI) Program (NSF-IIA #1309694) to collaborate with Drs. Yoshihisa Fujita and Michio Hidaka.

Previous work from Justin's dissertation in The Santos Lab has focused on the response of H. rubra to invasive poeciliid fishes in Hawaiian anchialine habitats (Havird et al., 2013) as well as the role grazing by H. rubra plays in maintaining microbial diversity in anchialine habitats (in conjunction with the Lab's currently funded anchialine microbial project). For more information on Justin's research, see his Sigma-Xi Student Research Showcase video.

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