A 3-year study of color polymorphism in a population of boreal chorus frogs revealed that nearly all characteristics studied con- cerning the composition of the population were similar to those of an idealized population. The sex ratio was 1 : 1, there was no evidence of interaction between color phenotype and sex, and mating was random with respect to color phenotypes. Changes in the frequency of background colors did not follow any detectable pattern, while changes in the frequen- cy of spot colors did. The frequency of green-spot genotypes and pheno- types was lowest in juveniles, somewhat higher in yearlings, and highest in adults. Individuals having the highest coefficients of survival in the aquatic phase were brown-spotted, but were green-spotted in the terres- trial phase. Spot color polymorphism in the population is probably balanced. It is conceivably maintained by differential selection pressures in the aquatic and terrestrial phases of the life cycle.
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Terry Matthews (1971) studied this question.
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