Genetic impact of intensive rearing practices in Genetic impact of intensive rearing practices in oyster hatcheries: oyster hatcheries:

selective processes and loss of genetic variabilityselective processes and loss of genetic variability

Nicolas Taris, Christopher Sauvage Nicolas Taris, Christopher Sauvage andand

Pierre Pierre BoudryBoudry

Laboratoire IFREMER de Génétique et Pathologie, 17390 La Tremblade

C. gigasC. gigas life cyclelife cycle

SpatLarvae

~20 jours

Settlement

Metamorphosis

Fertilization

Adults

G. C. Williams 1975

Stages Survival

+++++++++++

+

+++++

++““elmelm--oyster model”oyster model”

Specific

selective

presures

in

hatcheries

(i.e. domestication) ? ?

(2) Hatcheries

French production ~ 900 millions

(2003)

(1) Natural recruitment in the wild27000 t

41000 t

8000 t

38000 t

7000 t

7000 t Méditerranée

Arcachon-Aquitaine

Poitou-Charentes

Pays de Loire

Bretagne Nord et Sud

Normandie

Different larval development strategies

?

Different larval development strategies

?

Ernande et al., 2003

H2 significantly ≠

0

Genetic correlation significantly positive

Genetic correlation significantly negative

Larval traits Metamorphic traits

Survival

Growth

Developmentrate

Size at settlement

Sucess at metamoprphosis

Spat weight

Growth

Weight after settlement

survival

Post-metamorphictraits

Two extreme “strategies “ :

• High larval growth rate and larval size at settlement but low settlement success, growth and survival after settlement

• Lower larval growth rate and larval size at settlement but higher settlement success, growth and survival after settlement

Main objective :

Evaluate

the potential

impact of common

rearing

praticies

in oyster hatcheries

(culling, high

temperature…) on genetic

diversity

at

larval

stage

Method

:

Study

the genetic

components of larval

growth

and

survival

usinga mixed-family

approach

and

microsatellite-based

parentage analysis

Main objective :Main objective :

Evaluate

the potential

impact of common

rearing

praticies

in oyster hatcheries

(culling, high

temperature…) on genetic

diversity

at

larval

stage

MethodMethod

::

Study

the genetic

components of larval

growth

and

survival

usinga mixed-family

approach

and

microsatellite-based

parentage analysis

(1)

Selective

sieving

(«

culling

»)

(2)

Temperature26°C 20°C

Studied

effectsStudiedStudied

effectseffects

X

125 150 175

femelle

mâle

descendant

Mixed-family

ApproachMixedMixed--familyfamily

ApproachApproach

Male Female

A5

A1

A2

A9

A1 A5 A2 A9A1 A2offspring

Microsatellites-based parentage analysis

Common practice in hatcheries: culling of the slow growing (i.e. small) larvae by sieving

C.V. of larval

diameter

0

2

4

6

8

10

12

14

3 5 7 9 11 13 15 17 19 20 21 22 23 24 25 26 27 28 29 30 31

Settlement

date

Sieved

population control

(1)(1)

EffectEffect

of of cullingculling

Parentage analysis

in the progeny

of a 3 females

x 10 males factorial

cross

A172 178 22 179 103 144 82 89 164 175

40

30

20

10

B

172 178 22 179 103 144 82 89 164 175

40

30

20

10

172 178 22 179 103 144 82 89 164 175

Mâlesmales

C

40

30

20

10

(1)(1)

EffectEffect

of of cullingculling

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

Settlement

dates

Sam

pling

A B C

Sam

pling

Sam

pling

Nb

of lar

vae

read

y to

set

tle

Sieved

population

control

(1)(1)

EffectEffect

of of cullingculling

0102030405060708090

100

0 5 10 15 20 25 30

A B C

Ne (as % of the initial maximal value)

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

Date de fixation

Echantillonnage

A B C

Echantillonnage

Echantillonnage

(2)(2)

EffectEffect

of of temperaturetemperature

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

Sam

pling

Dia

mèt

r e m

axim

um

20°C 26°C

-3

-2

-1

0

1

2

3

4

5

6

7

1 2 3 4 5 6 7 8 9 10 11 12

0102030405060708090

100

1 2 3 4 5 6 7 8 9 10 11 12

(2)(2)

EffectEffect

of of temperaturetemperature

Mean

hatching

% / males

(24h post fertilization)

Observed male reproductive

success at D22 / expected at

24h

SurvivalSurvivalSurvival

(2)(2)

EffectEffect

of of temperaturetemperature

Reaction norm larval diametre/temperature per family

210

220

230

240

250

260

270

20°C 26°C

GrowthGrowthGrowth

Male

Female

MaleMale

FemaleFemale

nsnsns

nsnsns

p<0.05p<0.05p<0.05

p<0.05p<0.05p<0.05

First

conclusions Selective

pressures related

to common

hatchery

practices :

-

effect

of culling

on genetic

diversity

-

effect

of temperature

: Survival: GxE

interaction

Growth: GxE

interaction