The mangrove Avicennia germinans L. is found along tropical and sub-tropical coastlines of the Atlantic coasts of Africa and America, the Caribbean and the Pacific coast of America from Mexico to Peru. It has been assumed that mangrove species are dispersal specialists, long distance migration being relatively facile by ocean currents. However, our recent biochemical data (foliar cuticular hydrocarbons) have indicated population structure suggesting that even between relatively geographically close populations, migration may be infrequent. We have compared the biochemical population structure with genetic structure using AFLP molecular analyses of genomic DNA. A total of 349 polymorphic bands from 4 primer sets were scored. Estimated population differentiation ranged from FST = 0.379 assuming a panmictic model for these dominant markers to GST = 0.285 assuming complete inbreeding. The Central American Isthmus accounted for the greatest genetic differentiation among populations that included 4 from West Africa, 3 from French Guiana, 2 from Guadeloupe, 1 from Florida and one from the Pacific coast of Mexico. Two populations from French Guiana were anomalous, clustering closely with African populations, which raises the question of possible transport of propagules by French shipping. Mantel correlations for the biochemical and molecular databases were significant and the biochemical data were also correlated with climatic variables. Partial Mantel correlations indicated a significant climate effect after removal of the phylogenetic effect. This supports our earlier work suggesting genetic adaptation of cuticular chemistry to environmental stress.

Key words: adaptation, Avicennia germinans, genetic differentiation, mangrove