PDF(Pubmed)
Abstract：
Among vertebrates, nearly all oviparous animals are considered to have either obligate aquatic or terrestrial oviposition, with eggs that are specialized for developing in those environments. The terrestrial environment has considerably more oxygen but is dry and thus presents both opportunities and challenges for developing embryos, particularly those adapted for aquatic development. Here, we present evidence from field experiments examining egg-laying behavior, egg size, and egg jelly function of 13 species of Central and South American treefrogs in the genus Dendropsophus, which demonstrates that flexible oviposition (individuals laying eggs both in and out of water) and eggs capable of both aquatic and terrestrial development are the likely factors which enable the transition from aquatic to terrestrial reproduction. Nearly half of the species we studied had previously undescribed degrees of flexible oviposition. Species with obligate terrestrial reproduction have larger eggs than species with aquatic reproduction, and species with flexible reproduction have eggs of intermediate sizes. Obligate terrestrial breeding frogs also have egg masses that absorb water more quickly than those with flexible oviposition. We also examined eight populations of a single species, Dendropsophus ebraccatus, and document substantial intraspecific variation in terrestrial oviposition; populations in rainy, stable climates lay fewer eggs in water than those in drier areas. However, no differences in egg size were found, supporting the idea that the behavioral component of oviposition evolves before other adaptations associated with obligate terrestrial reproduction. Collectively, these data demonstrate the key role that behavior can have in facilitating major evolutionary transitions.
摘要：
在脊椎动物中，几乎所有产卵动物都被认为具有专性水生或陆生产卵，专门在这些环境中发育的卵。陆地环境有相当多的氧气，但干燥，因此给胚胎发育带来了机遇和挑战。特别是那些适应水生发展的。这里,我们提供了来自田间试验的证据，检查产卵行为，鸡蛋大小,以及Dendropsophus属的13种中美洲和南美洲树蛙的卵果冻功能，这表明灵活的产卵（个体在水中和水中产卵）和能够同时进行水生和陆生发育的卵是使从水生繁殖过渡到陆生繁殖的可能因素。我们研究的几乎一半的物种具有先前未描述的柔性产卵程度。具有专性陆地繁殖的物种比具有水生繁殖的物种具有更大的卵，具有灵活繁殖的物种具有中等大小的卵。独立的陆地繁殖青蛙的卵团也比具有灵活产卵的青蛙更快地吸收水分。我们还检查了单个物种的八个种群，ebraccatus，并记录了陆地产卵的大量种内变异；多雨的种群，与干燥地区相比，稳定的气候在水中产卵较少。然而,没有发现鸡蛋大小的差异，支持以下观点：产卵的行为成分在与专性陆地繁殖相关的其他适应之前发展。总的来说，这些数据证明了行为在促进重大进化转变中的关键作用.
