Chloroplast evolution in the Pinus montezumae complex: A coalescent approach to hybridization

This study addresses the evolutionary history of the chloroplast genomes of two closely related pine species, Pinus hartwegii Lindl. and P. montezumae Lamb (subsect. Ponderosae) using coalescent theory and some of the statist ical tools that have been developed from it during the past two decades. Pi nus hartwegii and P. montezumae are closely related species in the P. monte zumae complex (subsect. Ponderosae) of Mexico and Central America. Pinus ha rtwegii is a high elevation species, whereas P. monrezumae occurs at lower elevations. The two species occur on many of the same mountains throughout Mexico. A total of 350 individuals of P. hartwegii and P. montezumae were c ollected from Nevado de Colima (Jalisco), Cerro Potosi (Nuevo Leon), Iztacc ihuatl/Popocatepetl (Mexico), and Nevado de Toluca (Mexico). The chloroplas t genome of P. hartwegii and P. montezumae was mapped using eight restricti on enzymes. Fifty-one different haplotypes were characterized; 38 of 160 re striction sites were polymorphic. Clades of most parsimoniously related chl oroplast haplotypes are geographically localized and do not overlap in dist ribution, and the geographically localized clades of haplotypes include bot h P. hartwegii and P. montezumae. Some haplotypes in the clades occur in on ly one of the two species, whereas other haplotypes occur in both species. These data strongly suggest ancient and/or ongoing hybridization between P. hartwegii and P. montezumae and a shared chloroplast genome history within geographic regions of Mexico.