A 1ST ESTIMATION OF THE MATING SYSTEM OF ONOPORDUM-ILLYRICUM (L) AND ITS RELEVANCE TO THE INVASION OF AUSTRALIA

We tested the hypothesis that the breeding system of an invasive weed is altered following invasion using Onopordum illyricum (L.), a self-c ompatible insect-pollinated monocarpic perennial of mediterrenean orig in, which has invaded Australia. Our results, obtained by the analysis of the genetic composition of progeny of individual plants of an Aust ralian population, suggest that this species has an intermediate outcr ossing rate (t = 0.57) in its area of introduction. This mixed mating system seems to be stable, since the estimates obtained by other techn iques assuming equilibrium, are very close. Furthermore the mating sys tem of this species has apparently not changed during invasion, since estimates of the outcrossing rates of French populations are similar t o that of the Australian population (t = 0.52). The mixed mating syste m of this species, may have contributed to its invasive capacity, as s elfing allows avoidance of demographic hazards, and outcrossing would promote the generation of novel genotypes allowing adaptation to novel environmental conditions.