Historical and contemporary factors affect the genetic diversity and structure of Laguncularia racemosa (L.) Gaertn, along the western Atlantic coast

Abstract Laguncularia racemosa (L.) Gaertn (Combretaceae) is one of the eight tree mangrove species of the Atlantic-Caribbean-Eastern Pacific region (AEP). This species is widely distributed throughout the Americas, Caribbean and the West Coast of Africa. Understanding genetic structure allows us to elucidate the main historical and contemporary mechanisms that influenced the distribution of natural populations. The aim of the present study was to evaluate the genetic diversity and genetic structure in populations of L. racemosa in the western Atlantic coast. Seven loci of nuclear microsatellites were used to genotype 102 individuals in eight populations. Laguncularia racemosa populations presented a hierarchical island model of genetic structure most likely resulting from propagule dispersal mediated by coastal superficial climatological circulation (Near-Surface Ocean Currents). Moreover, equatorial populations presented greater genetic variability than the tropical and subtropical populations, possibly related to the existence of refuges in the equatorial region during the last glacial period, followed by stepping-stone recolonization of tropical and subtropical mangroves in the Holocene.