Résumé
Flowering time divergence can be a crucial component of reproductive
isolation between sympatric populations but few studies have quantified
its actual contribution to the reduction of gene flow. In this study, we
aimed at estimating pollen-mediated gene flow between cultivated sunflower
and a weedy conspecific sunflower population growing in the same field,
and at quantifying how it is affected by the weeds’ flowering time. For
that purpose, we extended an existing mating model by including a temporal
distance (i.e. flowering time difference between potential parents) effect
on mating probabilities. Using phenological and genotypic data gathered on
the crop and on a sample of the weedy population and its offspring, we
estimated an average hybridization rate of approximately 10%. This rate
varied strongly from 30% on average for weeds flowering at the crop
flowering peak to 0% when the crop finished flowering, and was affected by
the local density of weeds. Our result also suggested the occurrence of
other factors limiting crop-to-weed gene flow. This level of gene flow and
its dependence on flowering time might influence the evolutionary fate of
weedy sunflower populations sympatric to their crop relative.