Hybrid zones in Rhododendron subsection Taliensia

Abstract

The investigation of hybrid zones has proven to be one of the most promising approaches to advance our understanding of species barriers, and to elucidate evolutionary processes involved in speciation. Due to the improvement of molecular techniques it will soon be possible to investigate the genetic composition of non-model species in much greater detail, and also include species that defy investigation using controlled laboratory conditions. To be able to draw further reaching conclusions about the generality of certain evolutionary factors, it is crucial to investigate a wide spectrum of organisms differing in traits, life histories and relatedness. This study investigates patterns of hybridisation between two pairs of closely related species in the genus Rhododendron. AFLP data for 346 loci, from twelve populations in total comprising 390 individuals, were obtained. Additionally, the abundance of three alkane components in the leaf waxes of 115 individuals was determined. For the species pair R. clementinae and R. roxieanum low levels of recent hybridisation were found, however, the wax composition of R. roxieanum var. cucullatum suggests historical introgression. Two types of hybrid zones were found for R. aganniphum and R. phaeochrysum, one mainly comprising F1 individuals, and the other frequent backcrosses to R. aganniphum. Furthermore, evidence for genomic incompatibilities at several loci for the two species will be presented, and hybrid identity of R. aganniphum var. avorufum and R. phaeochrysum var. agglutinatum is suggested.