Résumé
Cultivated plants have been molded by human-induced selection, including manipulations of the mating system in the twentieth century. How these manipulations have affected realized parameters of the mating system in freely evolving cultivated populations is of interest for optimizing the management of breeding populations, predicting the fate of escaped populations and providing material for experimental evolution studies. To produce modern varieties of sunflower (Helianthus annuus L.), self-incompatibility has been broken, recurrent generations of selfing have been performed and male sterility has been introduced. Populations deriving from hybrid-F1 varieties are gynodioecious because of the segregation of a nuclear restorer of male fertility. Using both phenotypic and genotypic data at 11 microsatellite loci, we analyzed the consanguinity status of plants of the first three generations of such a population and estimated parameters related to the mating system. We showed that the resource reallocation to seed in male-sterile individuals was not significant, that inbreeding depression on seed production averaged 15-20% and that cultivated sunflower had acquired a mixed-mating system, with ∼50% of selfing among the hermaphrodites. According to theoretical models, the female advantage and the inbreeding depression at the seed production stage were too low to allow the persistence of male sterility. We discuss our methods of parameter estimation and the potential of such study system in evolutionary biology.
L’apparition et le maintient de divergences adaptatives entre populations occupant des niches écologiques différentes dépend de l’importance relative de la sélection et de l’effet homogénéisant des flux de gènes. Chez les plantes à reproduction sexuée, les flux de gènes entres groupes d’individus géographiquement proches, peuvent être réduit du fait de divergences phénologiques (i.e., date du pic de floraison, étendue et intensité de la période de floraison...) favorisant les croisements entre individus à floraison synchrone (« temporal assortative mating», Fox 2003). En dépit de son impact sur l’évolution et l’adaptation des populations l’effet des divergences phénologiques sur les flux de gènes a rarement quantifié