Mating system adaptation in populations of Centaurea cyanus L.
Résumé
Since the 50s, the agriculture intensification in Western Europe resulted in landscape homogenization
and reduction of habitat connectivity, which in turn caused a widespread decline of farmland biological diversity.
Centaurea cyanus is one of the declining “segetal species”. It is an annual and insect-pollinated
species with a self-incompatibility system. When the populations are small and fragmented, they may
extinct if the incompatibility system cannot evolve towards a compatibility system. A coexistence of
mixed mating system is also possible in a population.
In our study, we examined the ability of C. cyanus to produce seeds by autogamy. For this purpose,
three conditions were tested: 1) two plants in a cage with flies as pollinators to allow outcrossing;
2) one plant by cage with flies as pollinators to force free self fertilization; and 3) one capitulum
bagged by cage without flies to force self fertilization. The results confirmed that C. cyanus is an
insect-pollinated species that cannot produce seeds without pollinators. In most of the plants flower
fertilization was less than 1% under free self fertilization while some plants produced more than 6% of
seeds. Crossing by flies yielded 26% of fertilized flowers. Therefore, a low frequency of plants seemed
to be partially self-compatible. It could be an advantage for the conservation of small populations, but
it could change the genetic structure of the populations and modify their biology.