Dispersal limitations and population genetic structure of two mangroves in the neotropics

In this study I focused on mangrove forests as a model system to understand the role of historical and contemporary forces in shaping local and regional patterns of genetic diversity. Mangroves have a very important ecological role in tropical coastal areas; however they are disappearing at an alarming rate. Therefore, a better understanding of historical and contemporary patterns of gene flow is critical for their conservation. Here, I focused on the two most widespread mangrove species in the Neotropics: red mangrove (Rhizophora mangle) and black mangrove (Avicennia germinans) and to address the following questions (1) what is the evolutionary history of the Rhizophora genus in Neotropics? (2) Does R. mangle show evidence of long-distance dispersal across its geographic range of distribution? Is this pattern similar to the pattern previously described for A. germinans? And (3) how do life-history characteristics of A. germinans and R. mangle affect Spatial Genetic Structure (SGS) at local scales? I found the evolutionary history of Rhizophora genus in Neotropics resulted very complex. Genetic data support ancient and ongoing introgressive hybridization between R. mangle and R. racemosa, at both sides of CAI and when these two sister species are in sympatry. Apparently, the final closure of the Central American Isthmus (CAI) represents the most important geologic event in the evolutionary history of Rhizophora because generated strong divergence between Oceans without evidence of secondary gene flow across this barrier. In consequence Caribbean/Atlantic and East Pacific Ocean basins have been evolving independently since the Pliocene. In addition, similar to previously reported in A. germinans, there is long-distance dispersal (LDD) of R. mangle within Oceans. Extreme LDD is occurring between West Africa and South America, across the Atlantic Ocean. Nevertheless, R. mangle populations have strong geographic structure within each Ocean basin indicating that cooling events and sea-level fluctuations in late Tertiary and Quaternary contract and expand populations several times generating strong structure. Finally, I found stronger fine-scale SGS in A. germinans than R. mangle suggesting that pollen and propagule dispersal is more restricted in A. germinans and that recruitment in riverine and fringe forest favor R. mangle over A. germinans.