Developmental Features Influencing Color Polymorphism in Chorus Frogs

Publisher Website
Google Scholar
Abstract
Montane populations of chorus frogs, P. triseriata, near Chambers Lake, Larimer County, Colorado [USA] exhibit dorsal color polymorphism. Previous studies showed that these color morphs are under genetic control and that phenotypic frequencies may be affected by natural selection. Developmental features of 2 color morphs, green vs. brown dorsal colors, were examined to postulate selective mechanisms that might be affecting the polymorphism. The features examined were adult female size, egg size, egg number, rate of early embryogenesis, rate of development to metamorphosis, juvenile growth rate and juvenile survival. No differences were found between the green and brown morphs with respect to adult female size, egg diameter, number of eggs per female or juvenile survival. No differences in rate of early embryogenesis, through the beginning of tail fin circulation, were detected among offspring of a variety of matings involving green and brown frogs. Differences were detected on continuing the developmental trials through metamorphosis. Offspring from green females metamorphosed earlier than those from brown females. Regression analyses indicate this difference to be a maternal effect, which is not related to paternal phenotype or to the ultimate color phenotype of the resulting frogs. Green juveniles were slightly larger at metamorphosis than browns and grew at a slightly faster rate than browns during a 30 day postmetamorphic period, resulting in 30 day green juveniles that were significantly larger than 30 day browns. Color polymorphism in chorus frog populations may be affected by a complex of selection pressures. The existence or relative importance of these pressures in natural populations were not determined.