Isozyme variability in Gambusia under different ecological conditions.
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Eight stations under different ecological conditions were sampled at Clear Creek in Texas, U.S.A 321 individuals of mosquitofish, Gambusia, were taken. Samples were electrophoresised using horizontal starch-gel electrophoresis similar to the system described by Poulik (1957) and modified by Beckman and Johnson(1964). Ten enzymes were studied, 2 of which were not used for analysis, 3 were found to be monomorphisis without inter- and intraspecies variation, and 5, encoded by 8 loci and 25 alleles, were used for analysis. Allele frequencies and genetic distance were calculated. In 321 individuals, there are 2 populations of the endemic species G. heterochir and 8 populations of the more cosmopolitan species G. affinis. These 2 species were shown to be genetically distinct. Moreover, a stable hybrid swarm was observed between them. The more generalized species, G. affinis, has a greater number of alleles at loci ES-1, PGI-1 and PGI-2 than the specialist, G. heterochir. The allele frequencies of the various sample areas and the genetic distances versus meter distance form dam break were figured.