Demographic history and the low genetic diversity in Dipteryx alata (Fabaceae) from Brazilian Neotropical savannas

Genetic effects of habitat fragmentation may be undetectable because they are generally arecent event in evolutionary time or because of confounding effects such as historicalbottlenecks and historical changes in species'' distribution. To assess the effectsof demographic history on the genetic diversity and population structure in theNeotropical tree Dipteryx alata (Fabaceae), we used coalescence analyses coupledwith ecological niche modeling to hindcast its distribution over the last 21 000years. Twenty-five populations (644 individuals) were sampled and all individuals weregenotyped using eight microsatellite loci. All populations presented low allelic richnessand genetic diversity. The estimated effective population size was small in allpopulations and gene flow was negligible among most. We also found a significant signal ofdemographic reduction in most cases. Genetic differentiation among populations wassignificantly correlated with geographical distance. Allelic richness showed a spatialcline pattern in relation to the species'' paleodistribution 21 kyr BP(thousand years before present), as expected under a range expansion model. Our resultsshow strong evidences that genetic diversity in D. alata is the outcome of thehistorical changes in species distribution during the late Pleistocene. Because of thishistorically low effective population size and the low genetic diversity, recentfragmentation of the Cerrado biome may increase population differentiation, causingpopulation decline and compromising long-term persistence.