Genetic variation in constant environments.

Allozymic variation in proteins encoded by 32 gene loci was analyzed electrophoretically in 64 specimens from 6 localities representing 2 species of the spadefoot toads Pelobates syriacus and P. cultripes from Israel and Portugal, respectively. Out of the 32 loci examined, Esterase-1 was the only locus that proved strongly polymorphic in all 6 localities and in the 2 species. The pattern of genetic variation in Pelobates is best explained by the environmental variability model. Selection for homozygosity as an adaptive strategy seems to operate in the relatively constant and narrow subterranean niche.