High variance in
reproductive success of the Pacific oyster (Crassostrea gigas,
Thunberg) revealed by microsatellite-based parentage analysis of
multifactorial crosses
P.
Boudry, B. Collet, F. Cornette, V. Hervouet, F. Bonhomme-2002
Aquaculture, 204(3-4): 283-296
Abstract:
Marine bivalves are known to have small Ne/N
ratios, both in wild and hatchery-propagated populations. This has been
interpreted as the consequence of a high variance in reproductive success.
However, how much of this variance could be attributed to pre-zygotic
reproductive factors or to post-zygotic selection was not yet estimated. To
estimate the relative effect of these factors, we have conducted a parentage
analysis on two 5×5 outbred crosses of Pacific oyster, Crassostrea gigas,
using a single microsatellite marker. This was made possible by the high
polymorphism encountered at this locus and careful selection of progenitors
according to their genotypes. Results show large variance in parental
contributions at various developmental stages, leading to a strong reduction
of experiment-wide effective population sizes. Segregation distortions
fluctuating with time were also observed. Our results show that the observed
variance in reproductive success can be attributed to three main factors:
gamete quality, sperm-egg interaction and differential viability among
genotypes. The comparison of two kinds of crosses, where sperm competition
was allowed or not, allowed us to estimate a 20% decrease of the effective
population size under sperm competition. A further decrease was observed
from larval to juvenile stages. Taken together, the observed gametic,
zygotic and genetic effects warn against using too limited a number of
progenitors in breeding programmes.
(Laboratoire
IFREMER de Génétique Aquaculture et Pathologie, BP133, 17390 La Tremblade,
France, Tel.: +33-5-4636-9836; fax: +33-5-4636-3751, e-mail : pboudry@ifremer.fr)