![[Haskin Shellfish Research Laboratory]](http://njaes.rutgers.edu/_common/images/subheads/haskin.gif "[Haskin Shellfish Research Laboratory]"){kind=small}
Identify possible phenotypic and genotypic differences
in oysters from putative refugia and high-disease areas
Ecology of Infectious Diseases |
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Collaborative Research: Field and Modeling Studies in Support of
Understanding Disease Resistance in Estuarine Populations and Response to Climate Change
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Producing oysters in a hatchery. Inset shows juvenile oysters to be deployed for testing. |
Oysters from potential disease refugia, which have not experienced selective mortality, should be both genotypically and phenotypically different from oysters in high disease regions that have experienced mortality. We have collected oysters from sites in both regions of Delaware Bay for analysis. Genotyping determines whether oysters from the potential refugia can be genetically differentiated from those in enzootic sites. Phenotypic differences, such as high infection prevalence and intensity and high mortality in offspring from refugia parents, compared to those from enzootic sites, imply that refugia from disease selection do exist in the Bay.
Genotypic differences
- Twenty-three microsatellite markers were used to identify genotypic differences within the bay. Significant deviation from Hardy-Weinberg equilibrium was observed at many loci and in several or all populations, possibly due to null-allelism and the Wahlund effect.
- Preliminary data reveal that the upper-Bay and tributary populations (Leipsic River, Hope Creek, and Cohansey River) are genetically distinct from those in the main portion of the Bay. It is possible that the Delaware Bay axis populations are well-mixed; however the tributaries may be self-recruiting and remain genetically distinct.
Phenotypic differences
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Oysters from different sites were spawned in the hatchery and their offspring exposed to MSX and Dermo infections. Phenotypic differences were assessed as infection prevalence and intensity, and oyster mortality.
“Delaware Bay sites sampled to identify genotypic and phenotypic differences in oysters from putative refugia and known disease areas. 1 – Hope Creek Bed; 2 – Round Island Bed; 3 - Cohansey River; 4 – Leipsic River; 5 – New Beds; 6 – Cape Shore Lab (natural set).
- Preliminary data indicate that oysters from the very low salinity regions, including tributaries, acquired somewhat more and heavier MSX infections than did those from higher salinity regions, but they did not become as heavily infected as did susceptible control oysters from outside the Bay. There were few measurable differences in the levels of Dermo infections among different Bay groups.
- These data are consistent with the genotype differences and with comparisons of disease levels in low-salinity, putative “refugia” with those in high-salinity regions. It appears that some of the low-salinity sites are refuges from MSX disease, but not from Dermo disease and that oysters in these refuges are genetically distinct from those in other sites.