Selective breeding for disease resistance in Crassostrea virginica

1. Selective breeding for disease resistance in Crassostrea virginica Patrick Gaffney University of Delaware

2. VIMS Two diseases plague C. virginica US EPA MSX Haplosporidium nelsoni DERMO Perkinsus marinus

3. Can we develop dual-disease resistant C. virginica capable of restoring decimated Atlantic coast populations? • Does the species exhibit natural variation in disease resistance? • Can selective breeding enhance disease resistance? • How good are existing selected strains?

4. MSX was first observed in 1957 in Delaware Bay, where it caused 90-95% mortalities. In 1959 it was found in Chesapeake Bay. Subsequent surveys showed it to occur from North Carolina to Cape Cod, and more recently, from Florida to Maine. It appears to be a recent arrival that may have come from C. gigas. Ewart & Ford 1993

5. Dermo has been observed from the Gulf of Mexico to the lower Chesapeake Bay since the 1940s. Range extension northward occurred during the warm, dry 1980s. Ewart & Ford 1993

6. http://vertigo.hsrl.rutgers.edu/climate.html

7. Can we develop dual-disease resistant C. virginica capable of restoring decimated Atlantic coast populations? • Does the species exhibit natural variation in disease resistance? • Can selective breeding enhance disease resistance? • How good are existing selected strains?

8. Gulf oysters are generally more susceptible to MSX Calvo 2002 CrossBreed CrossBreed

10. MSX tolerance increased over time in Delaware Bay oysters Haskin & Ford 1979

11. Bushek 1994

12. At two Louisiana grow-out sites, Chesapeake Bay stocks showed consistently heavier Dermo infections than local oysters (Shawn Stickler, VIMS, unpubl.)

13. (CrosBreed) (CrosBreed) Atlantic oysters are more susceptible to Dermo than Louisiana oysters when grown in Atlantic waters. Calvo et al. 2002

14. Conclusion: wild populations show regional genetic differences in MSX and Dermo susceptibility • Gulf oysters are more tolerant of Dermo, less tolerant of MSX • Atlantic oysters are less tolerant of Dermo, more tolerant of MSX • Northeastern Atlantic populations are most sensitive to Dermo

15. Can we develop dual-disease resistant C. virginica capable of restoring decimated Atlantic coast populations? • Does the species exhibit natural variation in disease resistance? • Can selective breeding enhance disease resistance? • How good are existing selected strains?

16. 100 B B B B B B B B J B J J B J B J SUS 80 J F H J B H F H J H B H F J G1 B H 60 J H F J F H G3 F J G5 H 40 J F F H H J F H F F H 20 H F B F F F J H 0 J H B F ONE TWO THREE FOUR FIVE YEAR OF EXPOSURE Cumulative mortality over five years of continuous exposure to MSX disease pressure PERCENT MORTALITY S. Ford, unpubl.

17. 100 J J SECOND FIFTH UNSELECTED GENERATION J J GENERATION J J 80 J J J 60 J 40 J J J 20 J 0 J J J 0 1 2 3 4 0 1 2 3 4 5 0 1 2 3 4 5 Cumulative and annual mortality patterns during selection for resistance to MSX disease Percent Mortality Year of Exposure

18. Survival and growth over one season of a 6th generation selected strain compared to an unselected strain, both starting with the same number at the same age and size. S. Ford, unpubl.

19. Conclusion: Oysters can be selected for resistance to MSX • Improved survival - highly selected stocks have essentially no mortality caused by the disease during the first 2-3 years (until they reach market size) • They still become infected and eventually die with MSX disease, but only after 5-6 years rather than 5-6 weeks • Selected oysters can restrict the development of lethal infections

20. Oyster lines selected fordual disease resistance • CrosBreed: Delaware Bay origin, long selected for MSX and (since 1992) Dermo resistance • WHS: hybrid between NE and DB selected lines • DEBY: Delaware Bay origin, selected for dual disease resistance in lower York River, VA • NE-1: Long Island origin, selected for both MSX and (since 1980) Dermo resistance • NE-3: Long Island strain selected for MSX, Dermo and JOD resistance • NE-2: NE-1 x NE-3 hybrid

21. CrosBreed (Cooperative RegionalOyster Selective Breeding Project) • GOAL: develop oyster lines with resistance to both MSX and Dermo • Strategy: create synthetic lines by crossing MSX-resistant Rutgers lines, followed by mass selection for Dermo resistance

22. Origins of CROSBreed • Inbred MSX-resistant HSRL lines crossed in 1992 to restore vitality • Four lines of Delaware Bay origin (selected plus wild stock), one from northeast (selected plus wild stock) • Dramatic improvement in performance and survival • Dermo exposure 1992 onwards

23. CROSBreed objectives • Evaluate performance of new synthetic lines across environments (common-garden design) • Dual disease challenge to begin selective breeding program for dual disease-resistant lines • Make strains available for commercial use and remediation

24. In the first generation (XB2), MSX levels were low. In the next generation, XB lines showed lower levels of MSX than Louisiana or Virginia oysters.

26. In the first generation, CrosBreed lines had better survival than wild local oysters, except in Maryland, a low salinity, low disease site.

27. In the second generation, CrosBreed oysters showed superior survival compared to wild oysters.

28. CROSBreed summary • MSX resistance superior to VA, LA oysters but similar to Delaware Bay • Dermo resistance superior to Delaware Bay but not clearly better than LA or VA oysters • Survival in NJ superior to local wild oysters and LA oysters • Survival in VA superior to DB and LA oysters, comparable to local oysters.

29. DEBY • F1 generation began in 1987 with wild Delaware Bay oysters spawned at VIMS • selection for dual disease resistance at disease enzootic site (lower York River) through F2 (1991), F3 (1993), F4 (1997) generations

30. Originally, lines selected for increased tolerance of MSX showed greater Dermo susceptibility than wild stocks (Burreson 1991)

33. Calvo et al. 2002

34. Calvo et al. 2002

35. DEBY summary • Dermo resistance greater than local wild oysters, not clearly better than LA oysters • MSX resistance better than LA, but not clearly better than local oysters – test inadequate due to low MSX pressure • Survival markedly better than local or LA stocks

36. BEOS (Breeding and Evaluation of Oyster (Crassostrea virginica) Strains selected for resistance to MSX, Dermo and JOD) • Three selected stocks (NE-1, NE-2, NE-3) plus a standard disease-susceptible line and local control • grow-out at four sites (Cape May NJ, Cape Shore NJ, Clinton CT, Cape Cod MA) • Evaluation of growth, mortality, disease levels (MSX, Dermo, JOD)

38. Selected lines show improved resistance to MSX only when MSX pressure is high (Ford et al. unpubl.)

40. BEOS summary • Selected lines show lower Dermo levels at all sites • MSX levels generally low except in CT, where selected lines were less infected • Superior survival of selected lines at all sites

41. General Conclusions • Selection for increased disease resistance/tolerance works • Selected lines are not disease resistant, but can survive and grow to market size despite infection • Selective breeding programs will continue to make incremental gains, particularly if intraspecific genetic diversity is tapped – but will “non-native” C. virginica be acceptable?