Allozyme evidence for the hybrid origin of Desmodium humifusum (Fabaceae)

摘要

Desmodium humifusum, one of the rarest members of the New England flora, always occurs with two conspecifics, D. paniculatum and D. rotundifolium, and a hybrid origin for D. humifusum has been proposed. Protein (allozyme) electrophoresis was used to test this hypothesis. Allozyme data demonstrated that the extant D. humifusum populations totaled eight genetic individuals rather than the 100+ previously estimated. The Rogers genetic similarity between the putative parental species was 0.797 and they were fixed for different alleles at a single locus, Tpi-1. All but one individual of D. humifusum were heterozygous at this locus, combining alleles unique to both of the putative parental species. Desmodium humifusum exhibited excess heterozygosity (relative to Hardy-Weinberg expectations), in sharp contrast to the consistent heterozygote deficiency in the parental species. Desmodium humifusum consists of both F, interspecific hybrids, as well as later-generation hybrids; introgression between the parental species was not obvious.