Isozyme variability in Gambusia under different ecological conditions.

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.