Evolutionary dynamics of a tropical wetland species, the black mangrove, Avicennia germinans (L.) L. (Avicenniaceae)

The black mangrove, Avicennia germinans (L.) L. (Avicenniaceae), is one of the main components of mangrove ecosystems in the Americas and West Africa. The potential for long-distance dispersal is high in A. germinans because of its crypto-viviparous seed and water-dispersed propagule that floats and remains viable for more than three months in salt water. Mangroves are susceptible to frosts and depend for establishment on protected, low-energy coastal environments. Therefore, mangrove populations may have been unfavorably affected by late Quaternary changes in climate and sea level. I used phylogenetic and population genetic analyses to reconstruct the biogeography of A. germinans. Analyses presented are consistent with extinction and recolonization of black mangrove populations at northern latitudes. Low divergence and low diversity estimates in Atlantic South American and West African A. germinans populations are consistent with recent trans-Atlantic long-distance-dispersal after major extinctions.; Despite the capability for long-distance dispersal of A. germinans, the detailed assessment of genetic structure in the East Pacific, presented in Chapter 2, shows strong structure and a lack of gene-flow between adjacent areas. Barriers to dispersal created by sea-surface circulation patterns and density dependent processes likely limit the genetic exchange between East Pacific populations.; The Pacific Coast of Central America is a region of high diversity for a number of different genetic markers. I investigated the hypothesis that hybridization with a Central America-restricted species, Avicennia bicolor Standl., enhanced diversity in A. germinans. I failed to detect any ongoing hybridization between these two species. Nevertheless, I detected evidence of ancient introgression of the nuclear ribosomal internal transcribed spacer (ITS) region. This hybridization event likely took place in northern Central America during the Pleistocene. Analyses presented in Chapters 2 and 3 show that an introgressant lineage of A. germinans recolonized northward to Mexico and southward to central Costa Rica and northern Panama. This introgressant lineage came into secondary contact with another lineage that was likely maintained in a refugium in the Panama Gulf.; I discuss the implications of historical population change and genetic differentiation patterns on the conservation and management of A. germinans and mangrove ecosystems in the region.