Matthew P. Hare and Colin Rose Department of Biology University of Maryland THE BENEFITS AND CONSEQUENCES OF RESTORATION USING SELECTIVELY-BRED, DISEASE-TOLERANT OYSTERS

Talk Outline Rationale behind supportive breeding using artificially-selected oyster strains –pros and cons Risks are now predictable Modeling impacts of supportive breeding –Inbred broodstock – a critical factor Recommendations

The Experts Weighed In, 2000

Supportive Breeding Goals and Impacts Increase population size –limit early mortality in hatchery, then release juvenile “seed” oysters Hatchery broodstock and restoration seed represent a genetically bottlenecked subset of population Genetic diversity summarized by inbreeding effective population size, N e

Consensus Points from Allen & Hilbish 2000 “stocking programs [supportive breeding] will be important…” for restoration success “Diseases…are a major limitation” for restoration “Continued use of selected disease resistant stocks is warrented…” Benefits –Genetic measurement of restoration efficacy –Disease tolerance  greater longevity of seed oysters –“genetic rehabilitation”, infusing desirable alleles Risks –Increase overall inbreeding –Decrease genetic variation –Lower mean fitness of population “Effective population size of wild populations is an essential parameter to predict genetic effects, but is unknown”

Broodstock Sources and Numbers of Seed Planted in Virginia Supportive Breeding T. Leggett, Chesapeake Bay Foundation 3.7x10 7 Oysters Planted

Risks of Supportive Breeding Can severely reduce total N e total N e with % hatchery contribution x: 1 x 2 (1-x) 2 N e(tot) N e(hatchery) N e(wild) No estimates for these parameters in 1999 when ‘genetic rehabilitation’ recommended ― = ― + Ryman & Laikre 1991

Great Wicomico River,

Predicted Consequences Wang & Ryman 2001 Closed hatchery line N e(wild) = 1500 –95% CI =  –Rose et al % contribution from supportive breeding in 2002, Great Wicomico, VA –Hare et al –5% contribution graphed –N (census)  annually Hare & Rose in prep.

Effective Population Size – Hatchery WILD oysters collected in DElaware BaY and exposed to disease = DEBY strain Disease tolerant oysters selected, = “PRIMARY” DEBY line 6 generations of selection Hatchery amplification spawn broodstock from primary line create lots of DEBY juveniles plant these “seed” oysters annual restoration broodstock

Effective Population Size – Hatchery WILD oysters collected in DElaware BaY and exposed to disease = DEBY strain Disease tolerant oysters selected, = “PRIMARY” DEBY line 6 generations of selection Hatchery amplification spawn broodstock from primary line create lots of DEBY juveniles “seed” oysters plant these “seed” oysters annual restoration broodstock

BEFORE Wild population n = 300 AFTER hatchery amplification of DEBY strain n = 96 seed oysters Loss of Alleles, locus 2j24 Allele

Effective Population Size - Hatchery Population bottlenecks generate ephemeral correlations among alleles at unlinked genes –gametic phase disequilibrium Magnitude of correlations depends on bottleneck N e Waples 1991 method; N b(LD) = 8 microsatellite loci, binned into biallelic data n Wild Primary LCR02 DEBY GWR02 DEBY LCR04 DEBY LD(28) N b(LD) % CI x (r 2 – 1/S)

Effective Population Size - Hatchery Waples 1991 method 8 microsatellite loci, binned into biallelic data n Wild Primary LCR02 DEBY GWR02 DEBY LCR04 DEBY LD(28) N b(LD) % CI

Effective Population Size - Hatchery Waples 1991 method 8 microsatellite loci, binned into biallelic data n Wild Primary LCR02 DEBY GWR02 DEBY LCR04 DEBY LD(28) N b(LD) % CI

Consequences of Supportive Breeding Closed hatchery line N e(hatchery) = 5 Initial reduction in Ne of 75 – 95% Recovery is slower than implied here, assumes constantly growing census N Hare & Rose in prep.

What’s wrong with small N e ?? No problem with longstanding small N e Problems caused by N e Severity of problems depends on genetic load –8 to 14 highly deleterious recessives per genome in Pacific oyster, C. gigas NeNe

Inbreeding Depression in Oysters Common view: high fecundity buffers oysters from inbreeding depression –High early mortality allows ‘purging’ of load Correct view: even slight inbreeding causes measurable reduction in fitness-related traits Evans et al Aquaculture 230: families, n = 402

Recommendations I Two of three motivations for using selected strains were speculative, still no data on DEBY fitness in restoration setting Spawn wild oysters and use procedures that  N e(hatchery) Continue use of DEBY oysters only in rivers where genetic monitoring can be used to test efficacy of changing planting strategies

Recommendations II There is no empirical justification for using DEBY x wild broodstock crossings –Speculative benefits –Disables genetic monitoring of restoration –Known inbreeding risks still apply

Collaborators Department of Biology & Horn Point Laboratory, University of Maryland Virginia Institute of Marine Science College of William and Mary, Virginia C. Rose K. Paynter D. Meritt S.K. Allen, Jr. M.D. Camara R. Carnegie M. Luckenbach K.S. Reece

with help from… Maryland Oyster Recovery Partnership Charlie Frentz Virginia Chesapeake Bay Foundation Rob Brumbaugh Tommy Leggett VA Marine Resources Division Jim Wesson VIMS: Cheryl Morrison Wendy Ribeiro Missy Southworth Oyster Disease Research Program, NOAA, Sea Grant Hare Lab, UMD: Jenna Murfree Paulette Bloomer Natasha Sherman Gang Chen Maria Murray Peter Thompson Safra Altman Kristina Cammen Andrew Ascione Ninh Vu Katie Shulzitski