Penstemon centranthifolius

Abstract: Diploid hybrid speciation remains a central issue in plant evolutionary biology. Here we test hypotheses of diploid hybrid speciation and introgressive hybridization in Penstemon section Peltanthera where P. spectabilis is a purported hybrid derivative species of the progenitors P. centranthifolius and P. grinnellii, and P. clevelandii is regarded as a hybrid derivative of P. centranthifolius and P. spectabilis. Forty-five populations representing P. centranthifolius (subsection Centranthifolii); P. spectabilis, P. clevelandii, P. grinnellii, P. palmeri in subsection Spectabiles; and P. xparishii (a purported hybrid between P. centranthifolius and P. spectabilis) were examined for allozyme differentiation. Penstemon centranthifolius has highfrequency allozymes at seven isozyme loci that differentiate it from species in subsection Spectabiles, whereas no genetic markers are detected that reliably differentiate species within Spectabiles. Because our data reveal that P. centranthifolius is genetically distinct compared to species in Spectabiles, we conclude that a recent hybrid origin of P. spectabilis and P. clevelandii with P. centranthifolius as a progenitor is not supported. Bidirectional gene flow and introgression between P.

Abstract: Penstemon spectabilis is a putative stabilized diploid hybrid of P. centranthifolius and P. grinnellii. It is morphologically intermediate, and all three species have different pollinators. Penstemon centranthifolius and P. spectabilis have been proposed as parents of P. clevelandii, which is purportedly isolated by ecological factors. Although hybridization between the proposed parental species has been reported, hybrid swarm formation has not been observed and introgression is purported to be minimal. We tested hypotheses of diploid hybrid speciation and introgression among these species based on rDNA restrictionsite and length variation for 56 populations within and outside of the hybrid complex. Unambiguous molecular markers clearly differentiated P. centranthifolius, P. grinnellii, and P. spectabilis, whereas P. spectabilis and P. clevelandii had the same rDNA type. The P. centranthifolius rDNA type was found in some populations of P. spectabilis and P. clevelandii, but there was no evidence of the additive profile documented for other recent diploid hybrid species. In contrast, the rDNA profile of P. x parishii had a completely additive profile of its proposed parental species P. centranthifolius and P. spectabilis. Ribosomal DNA markers for P. grinnellii were restricted to populations within the species and were not found in any population of P. spectabilis. Our data did not support hybrid-speciation hypotheses, but were in accord with allozyme data that provided evidence for introgression between P. centranthifolius and P. grinnellii, P. spectabilis and P. clevelandii. These results were used to propose criteria to differentiate ancient diploid hybrid speciation from patterns of introgression.

Abstract: Flower size dimensions, colour, and nectar quantities potentially account for differences in pollinator species between Penstemon centranthifolius (Benth.) Benth. (tubular, red, nectar-rich, hummingbird pollinated) and Penstemon spectabilis Thurber (wide, purple, nectar-poor, hymenopteran pollinated). For this study, floral characters and pollinator attraction were measured for the two species, F1 hybrids, and backcrosses. Floral dimensions, nectar characters, and color spectra combined in the hybrids in a largely linear fashion, consistent with an interpretation of net additive gene expression. In other words, the changes from one pollination syndrome to another appeared to be quantitative. There were some deviations from linearity, but not so much as to obscure the linear effect. Generally, backcrosses were not more variable than F1 hybrids or pure parents. Hummingbirds preferred P. centranthifolius over P. spectabilis. The strength of this preference varied by year, and the birds did not respond to hyb...

Abstract: Hybrid speciation has played a significant role in the evolution of angiosperms at the polyploid level. However, relatively little is known about the importance of hybrid speciation at the diploid level. Two species of Penstemon have been proposed as diploid hybrid derivatives based on morphological data, artificial crossing studies, and pollinator behavior observations: Penstemon spectabilis (derived from hybridization between Penstemon centranthifolius and Penstemon grinnellii) and Penstemon clevelandii (derived from hybridization between P. centranthifolius and P. spectabilis). Previous studies were inconclusive regarding the purported hybrid nature of these species because of a lack of molecular markers sufficient to differentiate the parental taxa in the hybrid complex. We developed hypervariable nuclear markers using inter-simple sequence repeat banding patterns to test these classic hypotheses of diploid hybrid speciation in Penstemon. Each species in the hybrid complex was genetically distinct, separated by 10–42 species-specific inter-simple sequence repeat markers. Our data do not support the hybrid origin of P. spectabilis but clearly support the diploid hybrid origin of P. clevelandii. Our results further suggest that the primary reason diploid hybrid speciation is so difficult to detect is the lack of molecular markers able to differentiate parental taxa from one another, particularly with recently diverged species.