Differential landscape effects on the fine-scale genetic structure of populations of a montane conifer from central Mexico

Abstract

Isolation by distance and isolation by adaptation can be difficult to differentiate, particularly in long-lived species in which overlapping evolutionary processes operate at different spatial and temporal scales. Hypotheses related to this interplay between gene flow, genetic drift, and selection were tested in Abies religiosa (Pinaceaea) populations around the Ajusco Volcano (central Mexico) under a landscape genetic framework and using markers from two genomes differentially dispersed by pollen and seed. We sampled 240 individuals around the volcano and genotyped them with 394 amplified fragment length polymorphisms (AFLPs) and three chloroplast microsatellites (cpSSRs). Genetic variation was correlated with ecological factors and geography, and putative candidates for local adaptation were pinpointed with three complementary approaches. Candidates were used to generate predictive models and to evaluate the relative contribution of ecological and geographical distances to genetic differentiation. Genetic diversity was high, and populations were structured in four (AFLPs) and two (cpSSRs) genetic groups, respectively. The 12 nuclear variants retained as candidates explained over 70% of the total genetic variance; the relative contribution of environmental and geographic distances ratio indicated that their spatial distribution was mostly accounted for by environmental differences among sites (aE/aD = 3.26). Such genetic structure combined with the convulse history of the Ajusco Volcano suggest a metapopulation-like dynamics over which disruptive selection is acting. Such differences should be taken into account by management programs, which should no longer consider the study site as a single homogeneous population.