Hybridization, coexistence, and possible reproductive interference between native Oxalis corniculata and alien O. dillenii in Japan.
Hybridization with alien species can affect the reproduction and persistence of native species. Native Oxalis corniculata and alien O. dillenii are distributed in human-made habitats in Japan, and they coexist with their putative hybrid. We examined the origin of the putative hybrid and the possibility of introgression and reproductive interference between these species by analyzing their morphological, cytological, genetic, and reproductive characteristics. The flower morphology of the putative hybrid was similar to the alien species. The chromosome complement and the amount of nuclear DNA of the putative hybrid were intermediate between the two species. Genotyping of the nuclear ITS region showed the putative hybrid was invariably heterozygous for native and alien alleles. Haplotyping of the chloroplast trnS-trnG region showed that 22 and four hybrids had their maternal origin in the alien and native species, respectively. The ovules of the putative hybrid were sterile. When pollen of the putative hybrid was applied to flowers of the parental species, the fruit set was very low, suggesting that their pollen is only marginally viable. Based on these results, we conclude that the putative hybrid is an F1 hybrid between native and alien Oxalis species. The hybrid is virtually sterile, indicating that hybridization led to a waste of gametes and may result in reproductive interference between the two parental species. The capacity for selfing and/or asexual reproduction may weaken reproductive interference between the species; alternatively, their apparent coexistence may be maintained by dispersal from different parental habitats.