Break-out Session Questions relating to Genetics

1. Break-out Session Questions relating to Genetics • What are the best uses for disease resistant strains (DRS) of oysters? • originally intended for aquaculture • new and improved? • Can we define a policy for the use of disease resistant strains?

2. Background 1999 Workshop: Genetic considerations for hatchery-based restoration of oyster reefs Allen & Hilbish 2000 • Disease perceived as primary obstacle • DRS seed oysters tentatively proposed as part of the solution: • Higher survivorship could provide greater reproductive output • Supplementation with DRS may increase population frequency of alleles related to disease resistance (“genetic rehabilitation”)

3. Numbers of oysters planted on restoration reefs in Virginia 1996 - 2006 data from T. Leggett, CBF

4. Supportive Breeding • Captive breeding • Minimize early mortality of juveniles • Release juveniles into wild • Genetic impact from single generation of supportive breeding: • Ne= genetically effective population size • x = proportional contribution of hatchery bred oysters to recruitment

5. Recent Findings Wild oysters with disease tolerance exist in enzootic areas of Chesapeake Bay Carnegie & Burreson submitted Chesapeake oyster metapopulation biophysical models suggest source-sink connections North et al. submitted genetic isolation by distance indicates low connectivity Rose & Hare 2006 Within Chesapeake tributaries, oyster Ne~ 103 Rose & Hare 2006

6. Recent Findings, cont. DEBY strain oysters are severely bottlenecked genetically, Nb~ 3 Hare & Rose submitted Inbreeding depression can be severe First cousin matings reduce average oyster weight by 8% (C. gigas; Evans et al. 2004) Great Wicomico recruitment in 2002 proportion attributable to 2002 DEBY seed oysters (3/4 million) was ~ 5% Hare et al. 2006

7. Recent Findings, cont. Model Initial wild tributary Ne = 420 % contribution from seed oysters = 5% Using closed line, expect 74% reduction in Ne of supplemented population Hare & Rose submitted Wild brood stock Nb= 25 Closed line Nb = 5 Wild brood stock Nb = 2.5

8. Disease is primary obstacle, need short cut Finding disease-resistant standing stock not practical most will be highly susceptible DRS seed may increase frequency of alleles related to disease resistance (“genetic rehabilitation”) Can’t avoid hatchery bottlenecks even with wild broodstock Long-term restoration goal, precautionary approach DRS are inbred Inadvertent hatchery selection lowers fitness in wild Supplementation with DRS depresses overall Ne compromising adaptive potential Balancing Risks

9. Recommendations • Where long-term restoration goals are primary: • do not use artificially-selected DRS • do not try to select for an improved restoration oyster • use ‘local’ wild broodstock Short term goals: • Put-and-take If DRS desirable, make triploid seed to prevent reproductive contribution • Aquaculture use DRS triploids • Restoration monitoring in restricted areas use artificially selected DRS to enable crucial genetic monitoring of restoration efficacy

10. Recommendations, cont. • Minimize hatchery bottlenecks • as many pair crosses as possible • target is Nb = 10 – 25 • don’t reuse wild broodstock • Monitor hatchery bottlenecks • 50 seed oysters sufficient to genetically measure Nb from a spawn

11. Stan Allen Jens Carlsson Ryan Carnegie Jan Cordes Anu Frank-Lawale Don ‘Mutt’ Meritt Colin Rose Jim Wesson And for additional comments by Mark Camara Pat Gaffney Dennis Hedgecock Kim Reece Thanks to Genetic Working Group

13. Change in total Ne expected from a single generation of supportive breeding(Ryman & Laikre 1991 model)

14. Annual changes in census size and total Ne resulting from sustained supportive breeding ( Wang and Ryman [2001] models I and II)

15. Annual changes in census size and total Ne Model I Model II Initial Ne 1500 Initial Ne 420

16. The reduction in average number of alleles over time in 100 simulated populations experiencing a one time change in Ne from 1500 to150