Genetic structure, phylogeography and potential distribution modeling suggest a population expansion in the mesquite Prosopis laevigata since the last interglacial

Abstract

Patterns of genetic and phylogeographic structure and recent population history of plant species in the Mexican arid zones have been scarcely investigated. Prosopis laevigata is the most widely spread species of mesquite in Mexico, with extensive populations in the arid and semiarid zones of the central and northern plateaus and scattered presence in southern Mexico. We evaluated the genetic and phylogeographic structure of this species to infer its recent demographic history. We genotyped six nuclear microsatellite loci and sequenced the psbA3´-trnH chloroplast DNA (cpDNA) region in individuals from 21 populations covering the whole distribution of the species. Nuclear genetic diversity was moderately high (HE = 0.527), and genetic differentiation was moderate (FST = 0.16). A positive correlation between genetic diversity and latitude was observed. The cpDNA analyses indicated a lack of phylogeographic structure in P. laevigata (GST = 0.090, NST = 0.101; P = 0.497). Historical demography statistics indicated a population expansion supported by a skyline plot analysis, the star-like shape of the haplotype network, and the unimodal shape of the mismatch distribution. Ecological niche modeling suggested a contracted distribution into west-central Mexico during the Last Interglacial (~ 140 Ka), followed by an expansion in both northwards and southwards directions in the Last Glacial Maximum (~ 22 Ka), which continued in the mid-Holocene (~ 6 Ka) and the present. Results are congruent with a recent population growth and colonization of newly opened arid zones by P. laevigata populations. This pattern is consistent with the high capacity of colonization of nutrient-poor areas, high germination rates and resistance to drought reported for Prosopis species.