High genetic variability in an ecologically variable vertebrate, Bufo viridis

Allozymic variation in proteins encoded by 26 loci was analyzed electrophoretically in 517 specimens of green toads from 11 populations from Israel and one population from Vis Island in the Adriatic Sea. Genetic variation in this toad is the highest yet reported in any vertebrate. All three genetic parameters, mean number of alleles per locus (Ā), mean proportion of loci polymorphic per population ( {Mathematical expression}), and mean number of heterozygous loci per individual ( {Mathematical expression}), are very high (Ā=1.65, range 1.38-2.04; {Mathematical expression}=0.423, range .346-0.615; {Mathematical expression}=0.133, range 0.108-0.159). Central and marginal mainland populations are only slightly more variable than desert isolates, but much more variable than the Vis Island population. Genetic similarity is very high between mainland populations ( {Mathematical expression}=0.951, range 0.93-0.97). Frequencies of two alleles (Icd-1^c and Tf^a) are correlated with an ecological gradient of increasing aridity. Regulatory enzymes appeared to contribute more to overall polymorphism than non-regulatory enzymes. The genetic variation observed suggests that selection for heterozygosity as an adaptive strategy is operating in the ecologically variable environment in which green toads live.