Hybrid origins and F1 dominance in the free-floating, sterile bladderwort, Utricularia australis f. australis (Lentibulariaceae)

Abandonment of sexual reproduction is a well-known characteristic in aquatic plants, while the causes, levels, and consequences of sterility are often unknown. Utricularia australis f. australis (Lentibulariaceae) is a free-floating, sterile bladderwort distributed widely in temperate and tropical regions. Experimental crosses in cultivated conditions, AFLP analysis, and cpDNA haplotypes of natural populations clearly demonstrated that U. australis f. australis originates from the asymmetric hybridization between two parental taxa: U. australis f. tenuicaulis (mostly as female) and U. macrorhiza (mostly as male). No post-F(1) hybrids were detected using the additive patterns of AFLP bands combined with the observation of extensive sterility in U. australis f. australis. Recurrent hybridizations and subsequent perpetuation by asexual reproduction were demonstrated by the unique, but monomorphic, AFLP genotypes observed in each U. australis f. australis population. Hybrids and parental species did not coexist, implying the superiority of the hybrid U. australis f. australis in certain environmental conditions. It remains unclear whether populations of U. australis f. australis are maintained by colonizing propagules or as relicts of past hybridization events.