Isolation by distance or by resistance? Gene flow patterns of Pinus hartwegii in a highly human-damaged forest, in central Mexico

Spatial genetic structure is the result of evolutionary and demographic processes that can be affected by historical and recent environmental changes. Pinus hartwegii is distributed in the highest areas of the Mexican mountains (>3400 m a.s.l.); most of its populations in central Mexico have been destroyed by anthropogenic activities. This research assessed the gene flow patterns of P. hartwegii in La Malinche National Park (LMNP), a Natural Protected Area severely affected by land use changes and forest extraction. Ten chloroplast microsatellites loci were used to determine the genetic diversity and spatial genetic structure of P. hartwegii. Genetic structure was studied using an Analysis of Molecular Variance and a Discriminant Analysis of Principal Components. Spatial genetic structure was evaluated by a Mantel test. Moreover, isolation by distance, and by resistance to land-use changes, and to elevation were analyzed through a partial Mantel test, based on Reciprocal Causal Modeling, and with Maximum Likelihood Population Effects models. Moran’s Eigenvector Maps were used to determine genetic neighborhoods. An effect of distance and elevation on spatial genetic structure of Pinus hartwegii in LMNP was detected, likely explained by pollen movement patterns, limited seed dispersal, and microenvironmental selection during germination. This information is of great value for the conservation of the species and the remaining populations in the park and other temperate forests in central Mexico.