Population Genomic Consequences of Seastar Wasting Disease for the Ochre Seastar During the 2013 Outbreak
Campuses: UCM, UCSC
PI(s): Dawson, Raimondi
Background: In 2013, sea star wasting disease (SSWD) swept through Pisaster ochraceus populations from Baja California, Mexico to southern Alaska, causing major mortality throughout the region (Hewson et al. 2014). We captured this event in a pair of long-term ecological-genetic studies, one in southern California and one in northern California, which documented median 90% mortality coast-wide but location-specific heterogeneity in the mortality rate (range 51% to 96%). From all locations, we have ethanol-preserved tissue from specimens collected according to a random sampling protocol from both immediately before and after the mass mortality. Moreover, all individuals were categorized as ‘healthy’, ‘diseased’, or ‘recovering’; in addition, we have a dozen samples of ‘healthy’, ‘diseased’, or ‘recovering’ P. ochraceus preserved in RNAlater. All collections are ongoing. These samples therefore permit rigorous analyses of the population genomic consequences of the SSWD outbreak on a site-by-site basis and also coast-wide, and further allow genome-wide association studies of loci under selection and identification of those that may have conferred increased resistance to the disease.
Approach: We propose a four-part study.  We have developed ddRAD analyses for P. ochraceus but have yet to genotype the specimens described above; we plan to genotype all specimens from immediately before (n = 290) and after (n = 1037) the outbreak.  To sequence the exomes of ‘healthy’, ‘diseased’, and ‘recovering’ specimens using RNAseq (n ≈ 60).  To sequence the exomes of ‘healthy’, ‘diseased’, and ‘recovering’ specimens using RNAseq (n ≈ 60).  To generate a reference genome against which to map ddRAD and RNAseq loci.
Resources: Awards from Sea Grant and NSF supported field collections, a graduate student researcher, and development of ddRAD and genotyping of P. ochraceus from before the outbreak. Funding from National Parks ($12K) is supporting genotyping of 288 P. ochraceus from after the outbreak from National Park locations. The project involves catalyst co-PI Mike Dawson (UCM) and associated faculty Pete Raimondi (UCSC) and establishes a new collaboration with UCSB’s Gretchen Hofm.