DODD, RICHARD S.1* and ZARA AFZAL-RAFII2. 1Department Environmental Science Policy and Management, University of California Berkeley, CA 94720, U.S.A; 2CNRS UMR 6100, Universite d'Aix-Marseille III, Marseille, France. - Genetic differentiation and adaptation in the mangrove Avicennia germinans L.
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