Matthew P. Hare and Colin Rose Department of BiologyUniversity 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, Ne

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

0.0E+00

2.0E+06

4.0E+06

6.0E+06

8.0E+06

1.0E+07

1.2E+07

1.4E+07

1.6E+07

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Year

Oysters Planted

Buyback Hatchery Selected DEBY cross 3.7x107

Oys

ters

Pla

nted

Risks of Supportive Breeding

• Can severely reduce total Ne

total Ne with % hatchery contribution x:

1 x2 (1-x)2

Ne(tot) Ne(hatchery) Ne(wild)

• No estimates for these parameters in 1999 when ‘genetic rehabilitation’ recommended

― = ― + Ryman & Laikre 1991

Great Wicomico River, 2002

http://www.vims.edu/mollusc/cbope/vabasin.htm

Predicted Consequences

• Wang & Ryman 2001• Closed hatchery line• Ne(wild) = 1500

– 95% CI = 422 - – Rose et al. 2006

• 5-10% contribution from supportive breeding in 2002, Great Wicomico, VA– Hare et al. 2006– 5% contribution graphed– N(census) annually

Hare & Rose in prep.

N e(wild) = 1500

0

200

400

600

800

1,000

1,200

1,400

1,600

0 1 2 3 4 5 6 7 8 9 10

Generation

Ne-Inbreeding

Ne - Hatchery = 50 Ne-Hatchery = 5

Ne(wild) initial = 420

0

100

200

300

400

500

600

0 1 2 3 4 5 6 7 8 9 10

Generation

Ne-Inbreeding

Ne - Hatchery = 50 Ne-Hatchery = 5

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 juvenilesplant 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 juvenilesplant these “seed” oysters“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 Ne

• Waples 1991 method; Nb(LD) =

• 8 microsatellite loci, binned into biallelic data

n 300 48 100 82 100 Wild Primary LCR02 DEBY GWR02 DEBY LCR04 DEBY

LD(28) 0 5 9 11 23Nb(LD) 5.76 4.69 3.80 4.8695% CI 3.05 2.66 2.17 2.77 

10.27 7.50 6.04 7.73

1

3 x (r2 – 1/S)

Effective Population Size - Hatchery

• Waples 1991 method• 8 microsatellite loci, binned into biallelic data

n 300 48 100 82 100 Wild Primary LCR02 DEBY GWR02 DEBY LCR04 DEBY

LD(28) 0 5 9 11 23Nb(LD) 5.76 4.69 3.80 4.8695% CI 3.05 2.66 2.17 2.77 

10.27 7.50 6.04 7.73

Effective Population Size - Hatchery

• Waples 1991 method• 8 microsatellite loci, binned into biallelic data

n 300 48 100 82 100 Wild Primary LCR02 DEBY GWR02 DEBY LCR04 DEBY

LD(28) 0 5 9 11 23Nb(LD) 5.76 4.69 3.80 4.8695% CI 3.05 2.66 2.17 2.77 

10.27 7.50 6.04 7.73

Consequences of Supportive Breeding

• Closed hatchery line• Ne(hatchery) = 5

• Initial reduction in Ne of 75 – 95%

• Recovery is slower than implied here, assumes constantly growing census N

Hare & Rose in prep.

N e(wild) = 1500

0

200

400

600

800

1,000

1,200

1,400

1,600

0 1 2 3 4 5 6 7 8 9 10

Generation

Ne-Inbreeding

Ne - Hatchery = 50 Ne-Hatchery = 5

Ne(wild) initial = 420

0

100

200

300

400

500

600

0 1 2 3 4 5 6 7 8 9 10

Generation

Ne-Inbreeding

Ne - Hatchery = 50 Ne-Hatchery = 5

What’s wrong with small Ne ??

• No problem with longstanding small Ne

• Problems caused by Ne

• Severity of problems depends on genetic load– 8 to 14 highly deleterious recessives per

genome in Pacific oyster, C. gigas

Ne

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. 2004

Aquaculture 230:89-98

40 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 Ne(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 BrumbaughTommy Leggett

VA Marine Resources DivisionJim Wesson

VIMS: Cheryl MorrisonWendy RibeiroMissy 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