Genetic analysis of natural hybrids between endemic and alien Rubus (Rosaceae) species in Hawai`i

Abstract

A population of putative hybrids between the endemic Rubus hawaiensis and naturalized R. rosifolius was discovered in KValley, on the island of Maui in the Hawaiian archipelago. The goal of this study was to molecularly characterize this natural hybridization event, investigate the mode of hybridization, and determine the male fertility of the hybrid individuals. Both morphological and RAPD marker data indicate that the putative hybrid individuals are the progeny of R. rosifolius and R. hawaiensis. All 39 hybrid individuals sampled had the chloroplast DNA haplotype of R. rosifolius. Thus hybridization appears to be asymmetric, with R. rosifolius acting as the maternal parent. All hybrid individuals assessed for pollen stainability were sterile, and there was no evidence of backcrossing to either parent. This result suggests that hybrids are of the first filial generation and that variation among hybrids reflects differences within the parental populations. Sympatric populations of R. hawaiensis and R. rosifolius occur on four islands and six additional alien species of Rubus are naturalized and sympatric with R. hawaiensis in Hawai'i. Further investigation is merited to assess whether hybridization may pose a threat to the long term viability of R. hawaiensis. This study highlights the increasing frequency and negative consequences of native-alien hybridization and the importance of maintaining active alien species control programs in the Hawaiian Islands.