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

Restriction-site variation of chloroplast DNA was used to assess hypot heses of diploid hybrid speciation in Penstemon sect. Peltanthera wher e P. spectabilis is a putative stabilized hybrid of P. Centranthifoliu s and P. grinnellii, and P. clevelandii is a purported hybrid derivati ve of P. centranthifolius and P. spectabilis. Based on restriction-sit e mapping, cpDNA haplotypes were determined for hypothesized parental species and P. spectabilis and P. clevelandii. The distribution of nuc lear and organellar DNA markers among populations of P. spectabilis an d P. clevelandii were evaluated to determine whether the observed patt erns result from diploid hybrid speciation, or from introgression. Nuc lear markers of P. centranthifolius were found in several populations of P. grinnellii, P. spectabilis, and P. clevelandii; whereas chloropl ast haplotypes of P. centranthifolius were found in only two populatio ns of P. grinnellii. We suggest that the patterns of introgression obs erved for sect. Peltanthera result predominantly from pollen-mediated gene flow, with hummingbirds the most likely vector. A comparison of t he phylogenetic trees based on cpDNA vs. nuclear restriction data reve als that at least one chloroplast-capture event has occurred in Penste mon sect. Peltanthera.