High population differentiation and genetic variation in the endangered Mexican pine Pinus rzedowskii (Pinaceae)

Pinus rzedowskii is an endangered pine species from Michoacan (central Mexi co), which has been previously reported from only three localities. Classif ied within the subgenus Strobus, it exhibits intermediate morphological cha racters between subgenera Strobus and Pinus. We analyzed genetic aspects th at could shed light on the Evolution and conservation of this species. The genetic structure of nine populations was examined using 14 isozyme loci. P inus rzedowskii has a relatively high level of genetic variation with 46.8% of the loci assayed being polymorphic, a total of 35 alleles, and a mean h eterozygosity per population of 0.219. We calculated 'Wright's F-ST,, stati stic to estimate gene flow indirectly and to evaluate whether or not there was genetic structuring among populations. We found a marked differentiatio n among populations (F-ST,, = 0.175) and significant inbreeding (F-IS,, = 0 .247). No pattern of isolation by distance was found. We also constructed a dendrogram, based on a genetic distance matrix to obtain an overview of th e possible historical relationships among populations. Finally, we found a convex relationship between the genetic distance among populations and the number of ancestral lineages, suggesting that demographically this species has not been at risk recently. Although endangered, with small and fragment ed populations, P. rzedowskii shows higher levels of genetic Variation than other conifer species with larger populations or similar conservation stat us.