eastern Florida Bay. Over the whole bay, where shrimp are present, they appear to be 
most abundant in shallow water, either near-key or bank habitat. 
1982 
Bert, T. M. (1985) Geographic variation, population biology, and hybridization in Menippe 
mercenaria and evolution in the genus Menippe in the southwestern North Atlantic Ocean. 
Ph.D. Dissertation. Yale University, New Haven, CT. 305 pp. 
Electrophoretically detectable variation in 40 proteins, color morphology, and field 
studies involving trapping and SCUBA diving were used to determine the evolutionary 
relationships of crabs of the genus Menippe (Xanthidae) in the south eastern United 
States. Correlation of the patterns of geographic variation in genotype and phenotype 
with the geological record and estimated times of divergence indicated that the 
observed patterns are the product of the influence of Late Cenozoic changes in climate 
and geology. Both allele frequencies (= genotype) and color morphology (= phenotype) 
showed that one of the species, M. mercenaria, is actually a taxonomic supergroup, 
composed of two taxa (designated semispecies). One (the western Gulf form) is 
distributed from northwest Florida westward through Texas. The second ranges, in its 
pure form, through the Florida peninsula from northwest to east central Florida, and in 
North Carolina. The taxa hybridize in two discrete regions - in the Gulf of Mexico 
(northwest Florida) and in the Atlantic Ocean (east central Florida to South Carolina). 
The Atlantic hybrid zone was formed prior to the closure of the seaway across north 
Florida connecting the Gulf of Mexico and the Atlantic, and the northwest Florida zone 
at some time subsequent to that closure. The northwest Florida hybrid zone is narrow, 
exhibits a strong concurrent clinal shift in both allele frequencies ( = genotype) and 
color pattern ( = phenotype). The zone has definable deficits of hybrids in general, and 
of particular hybrid phenotype-genotype combinations. The structure and dynamics of 
the zone can be attributed to (1) its location in an ecological transition zone, and at the 
parapatric junction of the ranges of the two parent taxa, (2) partial assortative mating 
due to different habitat preferences of the two taxa, and (3) post-mating selection 
against particular genotype-phenotype forms. The northwest Florida hybrid zone is 
characteristic of hybrid zones that persist through evolutionary long periods of time 
with relatively little change. The Atlantic hybrid zone is broad and has a unique 
geographical pattern of allele frequencies and color morphology. The greatest variation 
in color pattern is seen where the zone is thought to have originated (Georgia), and no 
animals within the zone are phenotypically identical to either parental form. Allele 
frequencies never completely shift from one parental type to the other but remain close 
to those of the form inhabiting peninsular Florida. The strongest shifts in allele 
frequencies occur in east central Florida and South Carolina, to the south and north or 
the origin of the zone. The structure and dynamics of the Atlantic hybrid zone can be 
attributed to: (1) its ancient age; (2) the absence of a pronounced ecotone throughout 
the zone; (3) greater habitat overlap than is seen between the two taxa in the 
northwest Florida hybrid zone; (4) location of the hybrid zone in relation to the range of 
the two parental taxa; and (5) numerical and genetic swamping of the western Gulf 
taxon by the peninsular Florida taxon. Hybridization in Menippe illustrates that multiple 
instances of hybridization between the same two species can result in very different 
morphological configurations of the zones themselves, and possibly even in different 
resolutions of the hybridization event, depending upon the environmental context in 
which hybridization occurs and stage of divergence of the two hybridizing taxa. 
Sampling in Florida Bay took place in 1982 north of Marathon. 
1982 0 
Beccasio, A. D., N. Fotheringham, A. E. Redfield, and et al. (1982) Gulf coast ecological 
inventory: user’s guide and information base. Biological Services Program, US Fish and 
Wildlife Service, Washington, DC. 191 pp. 
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