|
|
|
Abstracts
Workgroup: Frontiers in Disease Research
Evaluation of inherent and induced thermal-tolerance in protection of oyster populations from summer mortality caused by Dermo infection and thermal stress
Principal Investigator(s):
Fu-Lin E. Chu, Virginia Institute of Marine Science, College of William and Mary, chu@vims.edu
Funding Period: 10/ 01/01 to present
Increased Dermo and MSX proliferation coupled with thermal stress may be dually responsible for high oyster mortalities in the summer and fall months. Heat shock proteins (hsps) are known to protect organisms at the cellular level from thermal or other environmental stress. Heat shock proteins are also believed to play a role in protecting many animals from pathogenic insult and to be involved in immune functions and host-pathogen interactions, in addition to conferring tolerance to thermal and other environmental stresses. Induced hsp expression may increase tolerance to diseases by reducing the stress of high temperatures associated with seasonal parasitic bouts, direct protection from the effects of parasitism, or both.
In this project we are examining the roles of thermotolerance and heat shock proteins in resistance to Dermo in the eastern oyster. Our objectives are to 1. characterize the heat shock protein (hsp) expression in Chesapeake Bay natural disease resistant (Tangier sound, CTS) and susceptible (Rappahannock River, CRB) stocks identified via our previous project (VA-OD-99-3/5-29456), 2. compare the thermal tolerances and hsp expression in disease resistant and susceptible stocks, 3. compare in situ seasonal hsp expression in these oyster stocks, and 4. determine whether induced hsp expression confers tolerance to thermal stress and P. marinus. In earlier experiments we found that heat shock protein expression remained elevated over controls (oysters maintained at ambient temperature) for up to two weeks following a sublethal heat shock. Exposure of oysters to sublethal heat shock increases tolerance to a subsequent lethal heat treatment (induced thermal tolerance). We are currently testing whether induced thermal tolerance and associated hsp expression confers enhanced tolerance to parasitic stress in oysters challenged with isolated P. marinus. We are also examining intraspecific variation in thermal tolerance and hsp expression among genetically distinct oyster stocks. Initially, we compared thermal tolerance (LT50) between two oyster stocks found previously to be Dermo resistant (CTS and Oyster Bayou, LA - LOB). Both stocks were identical in age and reared under identical conditions. Thermal tolerance was higher in CTS oysters than LOB oysters, although hsp levels were similar. Changes in hsp isoform expression are being examined to resolve how isoform variation may affect total hsp levels. Our previous results show that two constitutive isoforms are present in gill tissue of eastern oysters. A third inducible isoform has been observed by other scientists' studies of west coast C. gigas and C. virginica, so further investigation in hsp expression patterns is warranted. Seasonal variation in hsp expression is also being compared among Dermo resistant (F2 CTS and XB) and susceptible (F2 CRB) oyster stocks deployed in the field. Initial results show little variation in hsp levels despite distinct differences in survival among these stocks. High survivorship occurred in the F2 CTS and XB stocks despite high Dermo infection. Survival in F2 CTS and XB oysters were similar to each other and their respective parental stocks, suggesting that Dermo resistance is heritable. The F2 CRB stocks experienced high mortality, identical to the F1 CRB stock.
IMPACTS and/or BENEFITS:
As shown by the results from this on-going project, resistance to Dermo is heritable as patterns of survival are retained from F1 to F2 generations in CTS stock. Oyster stocks from this and earlier research are presently being utilized in the selective breeding program at VIMS and by commercial aquaculture enterprises (Middle Peninsula Aquaculture and Chesapeake Bay Aquaculture), but little is known about how these oysters respond to natural stress. The interaction of thermal stress and parasitism can significantly affect oysters' survival. Heat shock proteins may be a key component in oysters' tolerance to thermal and parasitic stress. Improving the stress tolerance of disease resistant oysters may lead to development of improved oyster strains for both aquaculture and restoration purposes. Our research will identify mechanisms involved in stress tolerance in oysters, which will aid strain development. Results from this project have applications to both the hatchery and grow out stages of oyster aquaculture production, which could result in combining strain selection with optimal culture techniques to maximize aquaculture yields. Results from this project will be presented at the 2003 National Shellfisheries Association meeting, and will be prepared for publication.
PROJECT PUBLICATIONS:
Encomio, V.G.; Chu, F.L.E. The Role of Heat Shock Proteins in Tolerance to Parasitic Stress in the Eastern Oyster, Crassostrea virginica. National Shellfisheries Association Annual Meeting, April 13-17, 2003, New Orleans, USA (upcoming invited presentation)
![[Maryland Sea Grant]](../mdsg_logo.gif){kind=logo}
![[NOAA]](../noaa_logo.gif){kind=logo}
![[Virginia Sea Grant]](../vasg_logo.gif){kind=logo}