| Abstract |
Most nearshore brachyuran crabs of the northern Gulf of Mexico have been treated as
conspecifics of those in warm-temperate Carolinian waters on the southeastern Atlantic coast
of North America. However, historical physiographic constraints appear to have periodically
restricted gene flow between northern Gulf populations and sibling Atlantic coast populations,
and contemporary disjuncture of ranges often persists across south Florida. The present examination
of intertidal complexes has centered on grapsid crabs presently assigned to Sesarma
reticulatum and ocypodid crabs assigned to Uca minax, 2 species in which we have observed
marked variations in coloration over their distributional range. Genetic differentiation between
populations has been assayed by allozyme electrophoresis, and resultant data have been evaluated
with F-statistics and cluster analysis of genetic distance. Allozyme divergence between
Gulf and Atlantic populations of the S. reticulatum complex is at levels previously reported
for speciated populations, while that between trans-Floridian populations of U. minax is much
less pronounced. In both species, minimal divergence can be measured between 2 widely
separated Atlantic coast sample localities that were compared, while more complex grades of
differentiation are evident between sample localities compared within the northern Gulf of
Mexico. Trans-Floridian divergence of populations for both of these species is compatible with
models for periods of contact and subsequent isolation of Gulf and Atlantic stocks during and
since peak glacial advances in North America. Less conspicuous patterns of genetic differentiation
between sample localities within the northern Gulf of Mexico may reflect a history of
glacial and postglacial alluvial events which resulted in contemporary physiography of northern
Gulf estuaries. |
