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?

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”)

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

Supportive Breeding 1.Captive breeding 2.Minimize early mortality of juveniles 3.Release juveniles into wild Genetic impact from single generation of supportive breeding: N e = genetically effective population size x = proportional contribution of hatchery bred oysters to recruitment

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 N e ~ 10 3 Rose & Hare 2006

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

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

Balancing Risks 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 N e compromising adaptive potential

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

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

Thanks to Genetic Working Group 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

Population Number of pairwise locus comparisons (out of 28) with significant GD (p < ) Harmonic mean sample size, S Mean squared allelic correlation, r 2 N b (95% CI)NeNe Allelic richness Gene diversity Primary (1.6 – 4.7) a ab GWR02 DEBY (1.0 – 3.0) a a LCR02 DEBY (1.3 – 3.7) a a LCR04 DEBY (1.2 – 3.4) a a Wild LCR (45.3 – 135.7) b b Wild GWR (131.9 – 387.1) b b

Change in total N e expected from a single generation of supportive breeding (Ryman & Laikre 1991 model)

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

Annual changes in census size and total N e Model I Model II Initial N e 1500 Initial N e 420

The reduction in average number of alleles over time in 100 simulated populations experiencing a one time change in N e from 1500 to150