Touchon Justin C, Worley Julie L
Department of Biology, Vassar College, 124 Raymond Avenue, Poughkeepsie, NY 12604, USA Department of Biology, Boston University, 5 Cummington Mall, Boston, MA 02215, USA
Biology Department, Portland State University, 1719 SW 10th Avenue, Portland, OR 97201, USA.
Proc Biol Sci. 2015 Jun 7;282(1808):20150376. doi: 10.1098/rspb.2015.0376.
Laying eggs out of water was crucial to the transition to land and has evolved repeatedly in multiple animal phyla. However, testing hypotheses about this transition has been difficult because extant species only breed in one environment. The pantless treefrog, Dendropsophus ebraccatus, makes such tests possible because they lay both aquatic and arboreal eggs. Here, we test the oviposition site choices of D. ebraccatus under conflicting risks of arboreal egg desiccation and aquatic egg predation, thereby estimating the relative importance of each selective agent on reproduction. We also measured discrimination between habitats with and without predators and development of naturally laid aquatic and arboreal eggs. Aquatic embryos in nature developed faster than arboreal embryos, implying no cost to aquatic egg laying. In choice tests, D. ebraccatus avoided habitats with fish, showing that they can detect aquatic egg predators. Most importantly, D. ebraccatus laid most eggs in the water when faced with only desiccation risk, but switched to laying eggs arboreally when desiccation risk and aquatic predators were both present. This provides the first experimental evidence to our knowledge that aquatic predation risk influences non-aquatic oviposition and strongly supports the hypothesis that it was a driver of the evolution of terrestrial reproduction.
在水中之外产卵对于向陆地过渡至关重要，并且在多个动物门类中反复进化。然而，检验关于这种过渡的假说一直很困难，因为现存物种只在一种环境中繁殖。无裤树蛙（Dendropsophus ebraccatus）使得此类检验成为可能，因为它们既产水生卵也产树栖卵。在此，我们在树栖卵干燥风险和水生卵被捕食风险相互冲突的情况下，测试了无裤树蛙的产卵地点选择，从而估计每种选择因素对繁殖的相对重要性。我们还测量了有无捕食者的栖息地之间的辨别能力以及自然产下的水生卵和树栖卵的发育情况。自然界中的水生胚胎比树栖胚胎发育得更快，这意味着产水生卵没有代价。在选择测试中，无裤树蛙避开有鱼的栖息地，表明它们能够察觉到水生卵捕食者。最重要的是，当仅面临干燥风险时，无裤树蛙大多在水中产卵，但当干燥风险和水生捕食者同时存在时，它们会转而在树上产卵。据我们所知，这提供了首个实验证据，证明水生捕食风险会影响非水生环境中的产卵行为，并有力地支持了水生捕食风险是陆地繁殖进化驱动力这一假说。
