Viviparity-live-bearing modes of reproduction, rather than egg-laying-has evolved independently in lineages of many animals. It therefore is a consequence of convergent evolution, with the same feature occurring in taxa that do not share a common ancestor that bears the trait (homoplasy). Viviparity in amphibians has many different expressions of these independent evolutions including retention of the internally fertilized ova in the oviducts with our without maternal nutrition after yolk is resorbed, intraoviductal cannibalism, retention of externally fertilized ova in the skin of the mother's back, and others. This research program will investigate the mechanisms by which viviparity has arisen by comparing 1) features of parental ovaries, oviducts, and skin with those of related species that are egg-layers to elucidate the effects of 'pregnancy' maintenance; 2) patterns of development of embryos of taxa with different modes of viviparity and with related egg-laying species; 3) modes of retention of the developing embryos, including the hormonal substrate as measured morphologically; 4) modes of nutrition of the developing young; 5) the features of metamorphosis of the young of viviparous species as compared with those of related egg-layers; and 6) length of 'pregnancy' and the environmental and physiological cues for birth. The study will be one of the first to consider mechanisms by which homoplasy has evolved, rather than simply documenting instances of such patterns of evolution.
