Genetic divergence among Mexican populations of red mangrove (Rhizophora mangle): geographic and historic effects

Abstract

The Panamanian Isthmus uplifted about 3.5 million years ago, isolating plant and animal populations distributed in what today are the Pacific and Atlantic coasts. The red mangrove, Rhizophora mangle, is one of those species in which gene flow was interrupted by this geological phenomenon. Here, we measure the extent of genetic divergence among Mexican populations of R. mangle, both between and within coasts, and explore the evolutionary processes responsible for their genetic structure. Fourteen populations of R. mangle were sampled and individuals were screened for multi-locus genotypes using isozymes. We detected a marked genetic differentiation among populations (Fst = 0.287) and high inbreeding (Fis = 0.428) in R. mangle. Inferred gene flow among populations of the Atlantic coast (Nm = 0.738) was lower than that observed among the Pacific populations (Nm = 3.174). As indicated by the low values of gene flow (Nm = 0.433), and by the presence of alleles restricted to Pacific populations, the two coasts are isolated from each other. Gene flow does not follow the expectation of the model of isolation by distance, and reflects a complex pattern of migration among populations. The loss of one allele is documented for the northernmost population on the Pacific coast. Our results suggest that genetic drift may have played a major role in the population differentiation of red mangrove found in this study.