Interspecific hybridization and introgression in Schiedea salicaria and S. menziesii and implications for sexual dimorphism

Gene flow among adjacent populations of two different species and their putative hybrids has implications for allelic variation in all three groups, which could affect the evolution of breeding systems in some plant species.In the case of interspecific hybridization between two Schiedea species, both woody shrubs in the mountains of Maui, the genetic relationship between putative hybrids and the parental populations is largely unknown.The two species possess different breeding systems: Schiedea salicaria is gynodioecious while Schiedea menziesii is hermaphroditic, although some females have been detected in greenhouse-grown progeny of S. menziesii.We suspect there is an open pathway for gene flow through which the male sterility allele found in S. salicaria could possibly be passed to S. menziesii through a natural hybrid zone.To detect discernable maternal gene flow, chloroplast microsatellite markers were developed at five loci to genetically characterize populations of the two species and the putative hybrids.Thirteen different haplotypes were observed across the five loci.Each haplotype was observed in only one of the three groups, suggesting strong sub-population structure with no recent maternal gene flow.The genetic patterns observed give indication of unidirectional pollination allowing for the possibility of nuclear gene flow through the pollen to pass along the male sterility allele.