Trends Towards Non-Aquatic and Direct Development in Frogs

Abstract

T HE study of the life-cycle of the Amphibia Salientia has been relatively L neglected compared to other aspects of work upon them, such as taxonomy. This can only be attributed to the circumstance that most herpetologists interested in frogs live in the temperate zones of the world, where the species are relatively few and fairly uniform as to life history. In the tropical and sub-tropical belts the number of forms is considerably increased and a greater variety of life history obtains. There, visiting or resident naturalists have discovered a number of exceptions to the rule of spawning in water and undergoing a free-swimming larval stage before metamorphosis into adult shape. Not the least striking, and probably the best known, is that of the genus Pipa in which the female carries her eggs in individual chambers in the dorsal tegument, out of which the young hatch as minute adults (Maria Sybille von Merian, 1705; see Werner, 1912; Laurenti, 1768; Wyman, 1854; Sclater, 1895; Barlett, 1896). Many other exceptions have been described since. Some of them exemplify apparently simple methods of parental care for the young. Male Dendrobates and Phyllobates, for instance, transport their tadpoles on their backs (Wyman, 1857, 1859; Kappler, 1885; 1887; Cope, 1887; Smith, 1887; Boulenger, 1895; Ruthven and Gaige, 1915; Dunn, 1924, 1926, 1931, 1940, 1941; Eaton, 1941; Breder, 1927, 1946). The female Leptodactylus ocellatus guards her very immature tadpoles (Fernandes, 1921). Other changes are more radical, such as the development of the larvae of Rhinoderma darwinii in the vocal sac of the male (Espada, 1872; Howes, 1888; Buerger, 1905; Krefft, see Werner, 1912; and Pflaumer, 1934). Information on these and similar facts is largely scattered in papers on species from diverse zoological regions. There have been relatively few attempts to carry out systematic observations in the same place, over long periods, a method which, though slow and somewhat dependent on chance, is the most likely to uncover other unusual and perhaps intermediate life histories.