Modifications of oogenesis and development in marsupial frogs

Abstract:

In this review, we compare oogenis and the early development strategies of certain egg-brooding tree frogs with X. laevis. Egg-brooding tree frogs belong to the family Hylidae and include 7 genera. In egg-brooding tree frogs without pouches, eggs are exposed to the external environment, while in eggbrooding tree frogs with pouches, called marsupial frogs, eggs are totally protected inside a closed pouch, with the exception of some species of Fritziana, in which the pouch remains open during incubation (del Pino, 1980; Duellman and Gray, 1983). Comparison of morphological and reproductive characteristics, as well as the immunological comparison of albumins suggest that egg-brooding tree frogs without pouches represent older lineages than marsupial frogs (Duellman and Hoogmoed, 1984; Scalan et al. 1980); Wassersug and Duellman, 1984). The lineages leading to egg-brooding tree frogs without pouches (Stefania, Hemiphractus and Cryptobatrachus) last shared a common ancestor with the marsupial frogs genus Gastrotheca some 40-60 million years ago. Within the genus Gastrotheca, the high Andean lineages, such as Gastrotheca riobambae, are recent and have the most complex reproductive adaptations. The groups of high Andean species evolved within the last 2-10 million years. Marsupial frogs of the genus Flectonotus do not show immunological cross-reactivity with other egg-brooding marsupial frogs (Scalan et al. 1980). Most egg-brooding tree frogs live in the humid forest of tropical South America and Panama and their limited availability restricts investigation. In spite of this limitation, we have been able to observe developmental aspects in nearly 40 to the 60 decribed species by the analysis of museum-preserved specimens (del Pino, 1980; del Pino and Escobar, 1981; del Pino and Humphries, 1978). Methods used for the developmental study of marsupial frogs were explained by Elinson et al. (1989). Our work has centered on the adaptations of the marsupial frog Gastrotheca riobambae, a frog that produces advanced tadpoles and occurs with relative abundance in the northern inter-Andean region of Ecuador (Duellman and Hillis, 1987). In addition, we have studied certain aspects of oogenesis and development in Flectonotus pygmaeus, a marsupial frog from Venezuela that gives birth to advanced tadpoles (Duellman and Maness, 1980). For other species, only limited comparisons were possible. The unusual modifications of egg-brooding tree frogs demonstrate that amphibian oogenesis and early development possess great flexibility to adapt to the variety of environments in which frogs have deposited their eggs during the course of evolution.

Año de publicación:

1989

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