The Evolution of Viviparity in Amphibians: A Study of Homoplasy

胎生--繁殖的活的方式，而不是产卵--在许多动物的谱系中独立进化。 因此，这是趋同进化的结果，相同的特征发生在没有共同祖先的类群中，这些祖先具有该特征（同质性）。 两栖动物的胎生有许多不同的表达方式，包括卵黄被吸收后，内部受精卵保留在输卵管中，或没有母体营养，输卵管内相残，外部受精卵保留在母亲背部的皮肤中，等等。 本研究计画将探讨胎生发生的机制，比较1）父母卵巢、输卵管、皮肤与相关产卵物种的特征，以阐明“妊娠”维持的效果; 2）不同胎生模式的分类群与相关产卵物种的胚胎发育模式;（3）胚胎发育的滞留方式，包括形态学上测定的激素底物，（4）发育中幼体的营养方式，（5）胎生种幼体与近缘卵生种幼体比较的变态特征，（6）胚胎发育的营养方式，（7）胚胎发育的营养方式，（8）胚胎发育的营养方式，（9）胚胎发育的营养方式。（6）“怀孕”的时间长短以及分娩的环境和生理线索。 这项研究将是第一个考虑同源性进化机制的研究，而不是简单地记录这种进化模式的实例。

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.