Genetic structure and mating systems of metallicolous and nonmetallicolous populations of Thlaspi caerulescens

) of NONMET populations was significantly higher compared to MET populations. Pollen/Ovule ratios were significantly higher in MET compared with NONMET populations. • These results suggest that NONMET populations of T. caerulescens are more self-fertile than their MET counterparts. This contrasts with earlier studies on other metal-tolerant species in which selfing rates were higher in MET populations. This pattern may be explained by the fact that both ecotypes are not in sympatry in the populations studied, and therefore reproductive isolation has not been selected to maintain the adaptations to metal-contaminated soils. In addition, higher selfing rates in NONMET populations may have evolved as a mechanism of reproductive assurance, because these populations generally are at low densities.