Assessment of hybridization and introgression in lava-colonizing Hawaiian Dubautia (Asteraceae: Madiinae) using RAPD markers.

Hybridization between Dubautia ciliolata and D. scabra occurring on a mosaic of lava flows of 1855 and 1935 on the island of Hawai'i was examined using random amplified polymorphic DNA (RAPD) markers. The RAPD data indicate that D. ciliolata plants, nearly restricted to the 1855 lava flow, contain higher levels of genetic variation than do D. scabra plants occurring on the 1935 lava flow. Seventy-one markers were specific to D. ciliolata and 60 to D. scabra; 40 of these were "constant" (found in all individuals) in one or the other species. Hybrids sampled were determined to represent F(1), filial hybrids beyond the F(1), and backcross progeny. All backcrosses were unidirectional with D. ciliolata acting as the recurrent parent. No hybrid, including an artificially produced F(1), had all 40 constant markers, suggesting that at least some loci for these markers were heterozygous in the parents. However, several hybrids exhibited a loss of many of the species markers, suggesting that they were later filial hybrid generation plants. The apparent occurrence of unidirectional introgression at the study site may be providing D. ciliolata plants with genetic plasticity to colonize the new lava flow previously occupied only by D. scabra.