OVIDUCT STRUCTURE AND FUNCTION AND REPRODUCTIVE MODES IN AMPHIBIANS

The structure and function of the oviducts of members of the three Ord ers of the Class Amphibia (Anura, frogs and toads; Urodela, salamander s and newts; Gymnophiona, caecilians) are well described for only a fe w species. Further, the majority of such descriptions relate only to t emperate species that breed in water, lay their eggs there, and have f ree-living larvae, the presumed ancestral condition of oviparity. Many species of amphibians have derived reproductive modes. Such modes inc lude breeding terrestrially and arboreally, making foam nests, parenta l transport of eggs and/or tadpoles, direct development (copulating on land, laying the eggs in terrestrial sites, fully metamorphosed juven iles hatching, obviating the free-living larval stage). Other derived modes are ovoviviparity (developing embryos retained in the oviducts, born at a diversity stages of development, no maternal nutrition in ad dition to yolk) and viviparity (oviductal retention of developing youn g, maternal nutrition after yolk is resorbed, young born as fully meta morphosed juveniles). The amphibian oviduct is regionally differentiat ed to secrete varying numbers of layers of material around each egg, w hich function in fertilization, etc.; it is responsive to endocrine ou tput and environmental mediation during the reproductive cycle; and it maintains developing embryos in some members of all three orders, som e with oviductal epithelial secretion of nutrients. However, little is known of the structure-function relationships of the oviduct in speci es with derived reproductive modes. A comparison of oviduct morphology , function, endocrinology, ecology and phylogeny in amphibians with di verse reproductive modes suggests a number of highly productive avenue s of investigation. J. Exp. Zool. 282:477-506, 1998. (C) 1998 Wiley-Li ss, Inc.