Fetal Maintenance and Its Evolutionary Significance in the Amphibia: Gymnophiona

Abstract

The oviducts of several species of caecilians are modified for maintenance of fetal development through metamorphosis. Nutrition is provided by secretions from epithelial cells of the duct. Nutritional demands on the parent are great. I t is concluded that the species-specific fetal dentition is functional in obtaining nutrition in the oviduct, in contrast to previous suggestions. This mode of viviparity is found in members of three of the four families of caecilians. Several species of amphibians are known to retain developing young in their oviducts and to give birth to fully metamorphosed juveniles. The majority of such amphibian species belong to the order Gymnophiona-the blind, limbless, elongate caecilians of the tropics. Several aspects of the reproductive biology of caecilians are correlated with the ability to bear living young. Members of all caecilian species practice internal fertilization and have a number of morphological and behavioral modifications to facilitate it (Barrio, 1969; Wake, 1968, 1970, 1972); females produce relatively few, but large and yolky eggs (Wake, 1968); oviducts are capable of great distention and of secretory activity (Wake, 1970). Study of the morphology of oviducts of pregnant and non-pregnant adult females and the way developing young are maintained in the oviducts, as well as analysis of the developmental morphology of the fetuses, has produced some new ideas about the mechanism of viviparity in caecilians. In addition, i t has necessitated review of previous ideas about caecilian fetal growth and nutrition. Morphology o f the Oviduct.-The gross morphology of the oviduct of several species, both viviparous and oviparous, has been described (Parker, 1956; Wake, 1970). A specimen of Dermophis mexicanus has more extensive epithelial proliferation than seen in other species. Three 'columns' of epithelium, one ventral, two lateral, f i l l the lumen of the duct, except for the space occupied by fetuses. The six 25 mm fetuses have gills, but yolk appears to be resorbed, or nearly so. General comments about the microanatomy of the ducts of two viviparous species, Gymnopis multiplicata and Scolecomorphus kirk i i were also presented by Wake ( 1970). Material is now available representing the non-pregnant Gymnopis multiplicata oviduct, pregnant and non-pregnant Dermophis, and the pregnant and non-pregnant ducts of Typhlonectes compressicauda. These agree in general with the descriptions by Parker (1956) and Wake (1970). In non-pregnant females of both species the duct is slender, 1-3 mm in external diameter. Projections of connective tissue and capillaries covered with epithelium fi l l the lumen of the duct. The histology of the oviduct has been examined in more detail in order to consider the characteristics of the epithelium, especially the secretory cells of pregnant females. The epithelium is a single cell layer thick, and virtually all cells are ciliated. Nuclei are large; the 1977 JOURNAL OF HERPETOLOGY 11(4):379-386 (379)