Résumé
Describing and explaining the geographic within-species variation in
phenotypes (“phenogeography”) in the sea over a species distribution range
is central to our understanding of a variety of eco-evolutionary topics.
However, phenogeographic studies that have a large potential to
investigate adaptive variation are overcome by phylogeographic studies,
still mainly focusing on neutral markers. How genotypic and phenotypic
data could covary over large geographic scales remains poorly understood
in marine species. We crossed 75 noninbred sires (five origins) and 26
dams (two origins; each side of a hybrid zone) in a factorial diallel
cross in order to investigate geographic variation for early survival and
sex ratio in the metapopulation of the European sea bass (Dicentrarchus
labrax), a highly prized marine fish species. Full-sib families (N =
1,950) were produced and reared in a common environment. Parentage
assignment of 7,200 individuals was performed with seven microsatellite
markers. Generalized linear models showed significant additive effects for
both traits and pleiotropy between traits. A significant nonadditive
genetic effect was detected. Different expression of traits and distinct
relative performances were found for reciprocal crosses involving
populations located on each side of the main hybrid zone located at the
Almeria-Oran front, illustrating asymmetric reproductive isolation. The
poor fitness performance observed for the Western Mediterranean population
of sea bass is discussed as it represents the main source of seed hatchery
production, but also because it potentially illustrates nonadaptive
introgression and maladaptation.