Genetic structure and evolution of Avicennia Germinans and Rhizophora Mangle along Northwestern México

Mangrove forests in the Gulf of California, Mexico represent the northernmost populations along the Pacific coast. Today, these populations are relatively small, fragmented and poor in genetic diversity. We evaluated the population genetic structure and recent evolution of the red mangrove, Rhizophora mangle and the black mangrove, Avicennia germinans, along the northwestern coast of Mexico. Genetic diversity of both mangrove species showed a decreasing trend toward northern latitudes along the Pacific coast. The lowest levels of genetic diversity were found at the range limits around the Gulf of California and the outer Baja California peninsula. Lack of a strong spatial genetic structure in this area and recent northern gene flow in A. germinans suggest recent colonization of this species. On the other hand, lack of a signal of recent northern dispersal in R. mangle, despite the higher dispersal capability of this species, indicates a longer presence of populations, at least in the southern Gulf of California. We suggest that the longer history, together with higher genetic diversity of R. mangle at the range limits, likely provides a gene pool better able to colonize northwards under climate change than A. germinans.