FURTHER GENETIC ANALYSES OF A HYBRID ZONE BETWEEN LEOPARD FROGS (RANA PIPIENS COMPLEX) IN CENTRAL TEXAS

Abstract

Additional animals were collected from a previously described hybrid zone between two species of leopard frogs. The material now includes 1,054 specimens collected over a five-year period. The new and the original data were reanalyzed using two multilocus techniques: an analysis of linkage disequilibrium (Hill, 1975); and an analysis of the variance of the distribution of individual heterozygosities (Brown et al., 1980). An analysis of cline shape (Barton and Hewitt, 1983) also was performed. The zone appears to be stable in position. There are major year-to-year changes in allele frequencies, but these do not show concordant patterns between localities. This is probably the result of local stochastic factors. The shapes and position of clines at five loci are similar. Multilocus analysis shows the greatest disequilibrium values in the center of the zone. The ratio of observed to expected variance of individual heterozygosity is also largest in the central localities. Analysis of a single cohort during a three-month period that included both the larval and post-metamorphic stages shows a strong shift in genotypes. The froglet population had more animals with parental genotypes and fewer hybrid combinations. This probably is a result of differential mortality due to developmental incompatibilities when hybrids begin to metamorphose. We compare the usefulness of the two multilocus analytical techniques and make recommendations about collecting procedures for future studies of hybrid zones.