Genetic effect of domestication Genetic effect of domestication selective pressures on Pacific oyster selective pressures on Pacific oyster

at larval stageat larval stage

N. Taris, C. Sauvage, B. N. Taris, C. Sauvage, B. ErnandeErnande*, *, P. BoudryP. Boudry

Laboratoire de Génétique et Pathologie, La Tremblade Laboratoire de Génétique et Pathologie, La Tremblade –– FranceFrance* Laboratoire Ressources Halieutiques, Avenue du G* Laboratoire Ressources Halieutiques, Avenue du Géénnééral de Gaulle, B.P. 32, 14520 ral de Gaulle, B.P. 32, 14520 PortPort--enen--BessinBessin, France, France

larvi 2005 Ghent University, Belgium september 5 - 8, 2005

Crassostrea gigas life cycle

Williams 1975

Stages Survival

++++++++++++++

+

+++++++++

+++++

The “elmThe “elm--oyster model”oyster model”

High fecundity and high mortality at early stages

Can specific rearing practices (culling) and/or environmental conditions (high temperature) lead to a specific genetic

adaptation in C. gigas larvae ?

Which consequences of such a life history strategy for hatchery production ?

☺ Few genitors needed for mass production of juveniles☺ Culling (size selection)

Low effective population size (Hedgecock et al., 1992)Risks of rapid loss of genetic variability and inbreeding in

closed populations

Ernande et al., 2003 Larval traits Metamorphic traits

Survival

Growth

Developmentrate

Size at settlement

Sucess at metamoprphosis

Spat weight

Growth

Weight after settlement

Survival

Post-metamorphic traits

H2 significantly ≠

0

Genetic correlation significantly positive

Genetic correlation significantly negative

Genetic variability of early life traits in C. gigas ?

- limited number of families- no family replicates - a single environment

Mixed-family approachOne set of 3 PCR-multiplexed markers allowing efficient parental assignment of larvae (Taris et al., 2005)

125 150 175

female

male

offspring

- More families- Homogeneous rearing conditions- G x E ?

X

1. Effect of culling

Crossing of 3 females x 10 males with equal gametic contribution within each sex

- 50%

Progressive culling fromday 4 to day 15

Control

culled population Control

Number of pediveliger larvae

0

10 000

20 000

30 000

40 000

50 000

60 000

70 000

20 21 22 23 24 25 26 27 28 29 30 31Days

after

fertilization

1.1 Phenotypic effect of culling 50% of the smallest larvae

Limited effect on yield:-30 % of ready-to-settle larvae (higher survival of fast growing larvae)-15 % of spat (higher settlement success of fast growing larvae)

Coefficient of variation of larval length

0

2

4

6

8

10

12

14

16

1 3 6 8 10 13 15 17 20Days

after

fertilization

20 21 22 23 24 25 26 27 28 29 30 31

Sampling

B

Sampling

Sampling

1.2 Genetic effect of culling

0

10

20

30

40

50

M7 M9 M1M10 M4 M5 M2 M3 M6 M8

males

D20

8.26.3

Ne =

D25

D28

0

10

20

30

40

50

M7

M9

M1

M10 M4

M5

M2

M3

M6

M8

0

10

20

30

40

50

M7 M1 M4 M2 M6

12.315.2 15.9

The effect of culling on genetic diversity is mediated through its effects on the timing of settlement

26°C 20°C

X

2. Effect of temperature

Crossing of 4 females x 12 males with equal gametic contribution within each sex

Individual measurements of larvae prior to genotyping

Estimation of hatching rate at day 1

50

100

150

200

250

300

350

400

1 3 6 8 10 13 15 17 20 22 24 27 29 30 31 33 80-28

-24

-20

-16

-12

-8

-4

0

4

8

12

16

leng

th(µ

m) l

arva

l she

ll

20°C 26°C

Larval stage

Time after fertilization (days)

settlement cohorts

early late

Spat

early late

2.1. Phenotypic effect & sampling

-15

-10

-5

0

5

10

15

(No

- Na)

/ 10

0

81 160 9 164

J22 20°C

J22 26°C

J30 20°C

Observed maternal contributions relative to mean hatching rate at

Day 1

females

2.2. Variance of female reproductive success

males

Observed paternal contributions relative to mean hatching rate at

Day 1

2.2. Variance of parental reproductive success

-4

-2

0

2

4

6

8

10

(N

o-

Na

)/

10

0

2 55 71 89 168 180

J22 20°CJ22 26°CJ30 20°C

70

90

110

130

150

170

190

210

230

250

270

1 3 6 8 10 13 15 17 20 22 24 27 29 30 31 33

20°C 26°C

male ***

female

***

male ***

female

***

male *

female

nsle

ngth

(µm

)

Time after fertilization (days)

2.2. Variance of parental reproductive success

-10

-5

0

5

10

15

20

25

30

2 40 55 58 71 74 89 90 168 179 180 199

(No-

Na)

/100

Significantly different contributions between early and late cohorts at 20°C (same result at 26°C)

Late cohort 20°C

Early cohort 20°C

-10

-5

0

5

10

15

20

25

30

2 40 55 58 71 74 89 90 168 179 180 199

Early cohort 20°C

Early cohort 26°C

(No-

Na)

/100 Significantly different

contributions between early cohorts at 20°C and 26°C (same result for the late cohort)

2.3. Paternal contributions at day 80 (spat)

Reaction norm larval diametre/temperature per family

210

220

230

240

250

260

270

20°C 26°C

Male

Female

MaleMale

FemaleFemale

nsnsns

nsnsns

p<0.05p<0.05p<0.05

p<0.05p<0.05p<0.05

2.2. « G x E » interaction on larval size

9

9,5

10

10,5

11

11,5

12

12,5

13

13,5

14

cohortes précoces cohortes tardives

20°C26°C

Early cohorts Late cohorts

2.4. Effect of temperature during larval rearing on spat growth

Rearing conditions: • 24°C• no culling

2 x 2

Wild broodstockHatchery broodstock

7 generations of breeding Loss in allele diversity ≈

70%

Loss in heterozygosity ≈

20%

3. Selection for fast growing larvae in hatcheries ?

HatcheryH x WW x HWild

HatcheryH x WW x HWild

3.1. Larval growth

89

113

138

150

175

199

230

85

105

125

145

165

185

205

225

245

265

3 6 8 10 13 15 17

days

after

fertilization

diam

eter

(µm

)

HatcheryH x WW x HWild

3.2. Larval survival

42

57

62

51

30

40

50

60

70

80

90

100

3 6 8 10 13 15 17 20days

after

fertilization

% s

urvi

val

Settlement success (%):

Hatchery 90.7 > HxW 78.1 > Wild 72.3 > WxH 68.7

0

10 000

20 000

30 000

40 000

50 000

60 000

70 000

80 000

90 000

22 24 26 28 30 32

jours après fécondation

effe

ctifs

péd

ivél

igèr

esHatchery

H x WW x HWild

3.3. Timing to reach the pediveligere stage and settlement success

C.V. of larval length

0102030405060708090

100

100 115 130 145 160 175 190 205 220 235 250 265 280 295

Wild progeny

Inbred

larvae

?

0102030405060708090

100

100 115 130

145

160 175 190

205

220 235 250

265

280

295

205 μm 225 μm **

Hatchery progeny

Distribution of larval length at Day 15

3.4. Within progeny variation for larval size

HatcheryH x WW x HWIld

0

5

10

15

20

25

30

3 6 8 10 13 15 17

Days

after

fertilization

coef

ficie

ntof

var

iatio

n

ConclusionsConclusionsMethodology

- As individual tagging is impossible at early life stages, marker-based parentage analysis of mixed families represents an efficient tool to study genetic variability of larval traits.Selection at larval stage

- Significant differences are observed between progenies, confirming the existence of genetic variation for several traits.

- Temperature influences the expression of genetic variability for growth and survival and therefore is likely to increases the genetic effect of culling.

- Intensive rearing practices can lead to the selection of faster growing / higher settlement larvae, despite inbreed depression.

Thanks