EVIDENCE OF CHLOROPLAST CAPTURE AND POLLEN-MEDIATED GENE FLOW IN PENSTEMON SECT PELTANTHERA (SCROPHULARIACEAE)

Restriction-site variation of chloroplast DNA was used to assess hypotheses of diploid hybrid speciation in Penstemon sect. Peltanthera where P. spectabilis is a putative stabilized hybrid of P. Centranthifolius and P. grinnellii, and P. clevelandii is a purported hybrid derivative of P. centranthifolius and P. spectabilis. Based on restriction-site mapping, cpDNA haplotypes were determined for hypothesized parental species and P. spectabilis and P. clevelandii. The distribution of nuclear and organellar DNA markers among populations of P. spectabilis and P. clevelandii were evaluated to determine whether the observed patterns result from diploid hybrid speciation, or from introgression. Nuclear markers of P. centranthifolius were found in several populations of P. grinnellii, P. spectabilis, and P. clevelandii; whereas chloroplast haplotypes of P. centranthifolius were found in only two populations of P. grinnellii. We suggest that the patterns of introgression observed for sect. Peltanthera result predominantly from pollen-mediated gene flow, with hummingbirds the most likely vector. A comparison of the phylogenetic trees based on cpDNA vs. nuclear restriction data reveals that at least one chloroplast-capture event has occurred in Penstemon sect. Peltanthera.