Genetic population structure of red mangrove (Rhizophora mangle L.) along the northwestern coast of Mexico

This study contributes to our understanding of population genetic diversity and connectivity in the red mangrove of northwestern Mexico. We evaluated the population genetic structure and the patterns of gene flow of the red mangrove, Rhizophora mangle, along the northwestern coast of Mexico. We analyzed samples taken from the northern Pacific distribution range limit, discuss the main mechanisms that probably have shaped the current genetic composition. The results show significantly reduced genetic diversity in northern populations, which can be attributed to very low effective population size, inbreeding, and high environmental pressure at distribution margins. Private alleles were found to be present at very low frequency on both the Pacific coast of Baja California and inside the Gulf of California, which suggests heterogeneity in genetic composition. Although we detected gene flow that was apparently associated with marine currents, we believe that the Baja California peninsula and the convergence of marine currents at the mouth of the Gulf of California are acting as effective barriers that limit gene flow. Cluster analysis supports this hypothesis, showing two main areas of genetic composition (inside and outside the Gulf of California). These findings were confirmed by significant genetic differentiation (FST = 0.26; RST = 0.50) between these regions; the findings also show that R. mangle presents low genetic diversity at margins without a random distribution and is present in at least two genetic population units along the northwestern Mexican coast.