GENETIC DIFFERENTIATION OF TEXAS GULF-COAST POPULATIONS OF THE BLUE-CRAB CALLINECTES-SAPIDUS

Allelic frequencies at three polymorphic, enzyme-encoding gene loci (G OT-2, EST-1, EST-2) were determined for Callinectes sapidus (Rathbun) megalopae and adults sampled along the Texas coast of the Gulf of Mexi co. Significant temporal and spatial variation was observed at all thr ee loci. Primary findings included: (1) megalopal allelic frequencies often differed significantly from those observed among neighboring adu lt populations; (2) larval allelic frequencies appeared to vary season ally, with populations showing sharp differences in the summer months but tending to be more homogeneous in winter; (3) allelic frequencies among adult populations were significantly heterogeneous, but only one locus (EST-2) showed significant temporal variation; (4) juvenile and adult crabs sampled within one bay showed no size-specific difference s in allelic frequencies. The spatial heterogeneity in allelic frequen cies suggests that inter-population gene flow is not sufficient to ove rcome population differentiation resulting from genetic drift and/or n atural selection. Temporal variation in larval allelic frequencies sug gests seasonal changes in larval source populations which may result f rom population differences in spawning season or developmental times o r from seasonal changes in coastal current patterns.