Genetic variability in Palaemonetes Pugio in habitats open and closed to migration



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Nine collections of the grass shrimp, Palaemonetes pugio, were made on Galveston Island to test the hypothesis that small populations show reduced genetic variability as a result of increased allele fixation due to random genetic drift. Four small ponds and five sites in or adjacent to the bay were sampled as representative of finite and infinite populations, respectively. Starch gel electrophoresis was used to analyze enzyme electromorphs encoded by seventeen loci. Four loci showed electromorph variation. Three measures of genetic variability were determined: percent polymorphism (P[overline]), the number of alleles per population for the polymorphic loci (n), and the average heterozygosity per locus (H[overline]). For all three measures, the four closed populations had values lower than or equal to the smallest value found among the open populations. These results are believed to support the hypothesis that population size can be an important determinant of genetic variability resulting in reduced variability in small populations.