Contemporary patterns of genetic diversity of cedrela fissilis offer insight into the shaping of seasonal forests in eastern South America.

Abstract

We investigated how genetic diversity is distributed across the range of Cedrela fissilis, a tree species associated with seasonal neotropical forests, to gain insights into competing biogeographic scenarios that explain how disjunct distributions of these forests were shaped. A total of 250 samples were sampled from 18 sites across the species' range in Brazil and eastern Bolivia and genotyped with 10 microsatellite loci. An array of complementary methods-F statistics, analyses of molecular variance (AMOVA), and clustering analyses-assessed genetic diversity, population differentiation, and structure. Most of the genetic diversity (82.5%) was partitioned within populations, but about 12% was due to differences among groups of populations on either side of the Cerrado or located within the Cerrado; mean expected heterozygosity and mean observed heterozygosity were 0.821 and 0.704, respectively. The 250 samples were sorted into two Bayesian groups: one group for each side of the Cerrado. The populations showed varying levels of admixture, with the greatest admixture evident in populations located toward central Brazil. In C. fissilis, genetic diversity is structured according to geography: the Atlantic range and the Chiquitano range each harbor a genealogical lineage. Interfertility and varying levels of admixture between lineages provide strong evidence that the lineages evolved under geographic, but not genetic, isolation. Admixture is of recent origin, owing to population expansion. Cedrela fissilis shares this dual pattern of distribution of genetic diversity with other phylogenetically unrelated taxa that are typically associated with seasonal forests.