Mating system of yellow starthistle (Centaurea solstitialis), a successful colonizer in North America

Abstract

The mating system of Centaurea solstitialis L. was investigated in relation to its colonization of North America. A preliminary investigation of its reproductive biology suggested that the species is a pollinator-dependent outbreeder, and probably self-incompatible. Quantitative analysis of the mating system parameters was performed using progeny arrays assayed for nine allozyme markers. Multilocus outcrossing rates (t(m)) ranged from 0.948 to 0.990 among eight populations. Moderate levels of biparental inbreeding (≃6 per cent apparent selfing) were detected in most populations. The correlation of outcrossed paternity within progeny arrays (r(p)) ranged from 0.05 to 0.64 among populations, indicating differences in modes of outcross pollination. A geographically marginal population, San Diego, showed the only significant parental inbreeding coefficient (F = 0.27), as well as highest r(p), suggesting microevolutionary changes of mating system following founder events. One other population exhibited significant variation of individual plant outcrossing rate, with a correlation of selfing within progeny arrays of r(s) = 0.65, indicating variation of self-incompatibility. Mating system variation in colonizing, self-incompatible species is valuable for understanding the evolution of self-incompatibility systems.