Overview on
selective breeding and genetic
improvement in bivalve shellfish
Pierre Boudry
Laboratoire de Génétique et Pathologie
17390 La Tremblade
France
[email protected]
www.ifremer.fr
Aquaculture of bivalves (FAO, 2001)
¾ World production :
¾ European production :
800
700
600
500
(Tm X 1000)
400
300
200
100
0
Oysters
Mussels
Scallops
Clams,
Cockles
Two possible sources of seed
(1) natural settlement (native or introduced species)
larvae
(2) hatchery propagation
Adults
spat
Genetic improvement of bivalves ?
Ploidy manipulations:
- triploids
- tetraploids
(4n x 2n = 3n)
1
Selective breeding:
- heritability estimates
- genetic correlations and trade-offs
- mass versus familly-based selection
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
2
3
4
5
Triploidy : a “single step” improvement
Re-allocation of energy from reproduction to
maintenance and growth in triploid oysters
Weight (g)
Comparison of 3n et 2n hatchery spat relative to
naturally recruited seed
90
Wild spat
80
Hatchery 3n
Hatchery 2n
70
60
50
40
collection
of wild
spat
30
20
spat
produced
in
hatchery
Nov
Aug
May
Feb
Nov
Aug
May
Feb
Nov
Aug
May
Feb
Nov
Aug
0
May
10
CREAA
¾ Nell, J.A. (2002). Farming triploid oysters. Aquaculture 210: 69-88
How to produce triploid bivalves ?
1) Chemical treatment of fertilized eggs using
Cytochalasine B or 6-DMAP
successfully applied on oysters, pearl oysters, mussels...
How to produce triploid bivalves ?
2) Tetraploid x diploid = 100 % triploid
• Tetraploid oysters first obtained in 1994
• Production and maintenance of tetraploids is
rather difficult : confinement, chromosome set instability
Chromosome number variation in 4n x 4 n progenies :
38
3%
38
10%
28
3630
3%
38 3%3%
7%
33
3%
41
20%
32
7%
34
3%
29
10%
39
10%
39
17%
40
97%
40
100%
Tetraploids
40
77%
Aneuploids
40
47%
30
80%
Triploids
Selective breeding of oysters
¾ U.S.A. : yield
x WRAC: « Crossbreeding » and heterosis
x MBP (http://www.hmsc.orst.edu/projects/mbp)
disease resistance
xVIMS
xRutgers University
¾ Australia: Growth
xCSIRO
¾ New Zeland: Growth
xCawthron Institute
¾ France : Stress and disease resistance
xIfremer
Mass (individual) selection
¾ Targeted traits : growth, disease resistance
xBonamiosis resistance in O. edulis (Naciri- Graven et al., 1998; Culloty et al., 2001)
xGrowth in S. commercialis (Nell et al., 2000)
¾ Main constrain : rapid loss of genetic variability
¾low number of effective parents (e.g. Launey et al., 2001)
¾high variance in reproductive success (Boudry et al., 2002)
Stages
Survival
+++++++++++
+++++
++
+
Microsatellite-based parentage analysis
5 females x 5 male cross :
A1
A2
A5
A9
Male
A1 A5
Offspring Female
A1 A2
A2 A9
Females
F1
F2
F3
F4
F5
M2
Males
M3
M4
M5
0.6
1.5
1.5
2.1
0.0
5.7
0.0
0.9
3.9
1.5
0.9
7.2
0.0
0.3
0.6
0.0
0.9
1.8
3.0
11.4
21.4
21.1
8.7
65.7
1.8
2.7
7.8
5.7
1.5
19.6
5.4
16.9
35.2
30.4
12.0
100.0
M1
Microsatellite-based genetics of larval traits
270
Reaction norm larval diametre/temperature per family
260
250
240
230
220
210
20°C
Male
Male
26°C
ns
ns
p<0.05
p<0.05
ns
ns
p<0.05
p<0.05
Female
Female
Family-based genetics and selective breeding
Relative performance of (many) families
reared under common conditions to
estimate their genetic value
Maturation
Male
1
Fertilization
Larval rearing
F
e
m
a
l
e
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
2
3
4
Male
5
6
7
HalfSib
1
HalfSib
2
F
e
m
a
l
e
HalfSib
3
HalfSib
4
HalfSib
5
HalfSib
6
Setting
Pediveliger larvae
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
8
9
10
Male
11
12
13
HalfSib
7
HalfSib
8
F
e
m
a
l
e
HalfSib
9
HalfSib
10
HalfSib
11
HalfSib
12
Nursing
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
14
15
16
17
17
HalfSib
13
HalfSib
14
HalfSib
15
HalfSib
16
HalfSib
17
Field testing
HalfSib
18
Family-based selective breeding programs
ŠMolluscan Broodstock Program (MBP): selection for yield
http://www.hmsc.orst.edu/projects/mbp
Family-based selective breeding programs
Š“WRAC” : development of inbreed lines and crossbreeding
http://hmsc.oregonstate.edu/projects/wrac/
Selective breeding experiment on spat survival
First summer
field testing
nursery
Field testing
(second summer)
G0 parents
Autumn 2000
Spring 2001
G1
Field testing G1
(first summer)
Nursery G1
Selected G1 for G2s
Summer 2001
Autumn 2001
Field testing G1 Field testing G1 Field testing G2 Nursery G2
(second summer) (second summer) (first summer)
Summer 2002
Parents for G3s
Autumn 2002
BDV
RA
Ronce
Field testing G2 Field testing G2 Field testing G3
(second summer) (second summer) (second summer)
Nursery G3
Summer 2003
G1 half-sib families: mortality in the field
100
Set
BDV
80
RA
60
Mortality (%)
(ns)
Ronce
(p<0.01)
Family(set)
22%
Site (p<0.01)
40
46%
14%
20
Replicate (ns)
Set*Site
21%
0
14
8
4
7
16
5
(ns)
Site*Family(Set)
(p<0.01)
3
13 17
12
Male
1
2
11
18
15
9
10
error
h² = 0.81 ± 0.29
Dégremont, 2003
Second generation (G2SD): divergent selection
70
mortality (%)
60
50
Selected ‘good’ HS
40
Selected ‘bad’ HS
30
20
10
Low selected group ‘S’
4
Male
Family
4
7
14
F4-15
F4-16
F7-25
F7-26
7
14
15
14
16
17
10
M
9
M
15
M
18
M
11
2
2
Male
18
19
20
21
22
23
M
High selected group ‘R’
Family
F4-15 F4-16 F7-25 F7-26 F14-54 F14-55
13
M
1
M
12
M
M
17
13
3
M
M
5
M
7
16
M
M
4
M
8
M
M
14
0
24
F14-54
F14-55
+ Controls : 2N and 3N
2
9
15
F2-5
9
15
F2-8 F9-35 F9-36 F15-57 F15-58
F2-5
1
2
5
6
F2-8
3
4
7
8
F9-35
9
10
F9-36
11
12
F15-57
F15-58
G2SD: Summer mortality in Brittany (RA)
90
Mortality (%)
80
‘S’ :
‘R’ :
43 %
7%
60
2N control :
24 %
50
3N control :
7%
70
p < 0.0001
40
30
20
10
0
Z
L
P
F
C
A
D
A
B
M
J
X
U
W
T
Q
Family
S > T2n > T3n = R
A
C
R
D
S
I
Y
H
A
N
K
G2SD: Response to selection for survival
on growth and yield
16
14
weight (g)
12
10
Growth
8
6
ns
4
2
0
R
10
S
T3N
c
8
yield (%.d-1)
T2N
b
bc
a
6
Yield
4
***
2
R² = 0.94
0
R
S
T2N
T3N
How to breed selected polyploids ?
2n males
(non selected)
4n males
(non selected)
Mortality :
2n control females
‘R’ 2n females
‘S’ 2n females
3n R
3n S
3n
2n
36 %
58 %
50 %
48 %
3n R < 2n = 3n = 3n S
How to genetically improve tetraploids ?
¾Production of new 4n stock from genetically improved 2n
¾Direct selection of 4n
¾Combined selection of 4n and 2n on their 3n progeny
¾Introgression of selected traits from diploids to tetraploids :
2n x 4n CB (PB2 inhibition gives 4n)
2n x 4n CB (PB1 inhibition gives 4n)
McCombie et al., in press
Conclusions:
Until now, relatively limited impact on production
Concerns about the interaction with the environment
Genetically improved bivalves can be developed, assuming
hatchery production is feasible and profitable, so that money
can be invested in selective breeding programs
Combined selective breeding and polyploidy is complex but
promising
www.ifremer.fr