Mating system adaptation in populations of Centaurea cyanus L.

Abstract : 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.