OBSERVATIONS ON THE DEVELOPMENT OF UNUSUAL MELANIZATION OF LEOPARD FROG VENTRAL SKIN

The ontogeny of ventral pigmentation of two species of leopard frog, R ana pipiens and R. chiricahuensis, was examined by light microscopy an d transmission electron microscopy to reveal how the unusual melanisti c ventral pigmentation of R. chiricahuensis is achieved at the cellula r level. Ventral skin of R. pipiens is always white. Ventral skin of a dult R. chiricahuensis is white when frogs are background-adapted to a white substrate, but ventral skin becomes nearly as dark colored as t he dorsal skin when frogs darken in response to a black background. Sk in samples from tadpoles of both species, newly metamorphosed frogs, a nd adult frogs were analyzed for chromatophore composition and distrib ution. Ventral skin of R. pipiens larvae, newly metamorphosed frogs, a nd adults and of R. chiricahuensis larvae was white due to abundant ir idophores and no melanophores. Melanophore density in the ventral inte gument of R. chiricahuensis was 9.1 +/- 2.8/mm2 in newly metamorphosed frogs and 87.0 +/- 4.8/MM2 in adult frogs. Pigment within ventral mel anophores migrated during physiological color change during background adaptation.