Introgressive hybridization in Pinus montezumae lamb and Pinus pseudostrobus lindl. (pinaceae):: Morphological and molecular (cpSSr) evidence

Pinus pseudostrobus and Pinus montezumae are closely related species. They belong to the subsection Ponderosae, with a wide geographical distribution in Mexico and Central America. Morphological, biochemical, and anatomical information suggests that these species can form hybrids in natural populations. In this study, molecular (chloroplast microsatellites) and morphological markers were studied in 13 natural populations of these species to test the existence of introgressive hybridization, infer its dynamics, and describe the phylogeographic structure of the populations. Using analytical methods of population genetics, as well as Bayesian inference and coalescent approach, we show that putative hybrid populations are more similar to P. pseudostrobus than to P. montezumae and that these populations had the highest estimates of morphological and genetic variation. Furthermore, a greater introgression rate was observed from P. montezumae to putative hybrid and P. pseudostrobus populations. We showed that genetic structure as well as introgression dynamics of populations could be the result of colonization events, historical expansion, and isolation by distance. Our results suggest the existence of three independent lineages (P. pseudostrobus, P. montezumae, and putative hybrid) that have coexisted and diversified during the past 11-27 million years as well as the possible origin of evolutionary new lineages through repeated introgressive hybridization combined with lineage sorting of ancestral polymorphisms.