Vonesh James R, Warkentin Karen M
Department of Biology, Boston University, Boston, MA 02215, USA.
Ecology. 2006 Mar;87(3):556-62. doi: 10.1890/05-0930.
Predation risk can cause organisms to alter the timing of life history switch points. Theory suggests that increased risk in an early life stage should select for switching earlier and smaller, while increased risk in the subsequent stage should select for switching later and larger. This framework has frequently been applied to metamorphosis in amphibians, with mixed results. Few studies examining the effect of larval predation risk on metamorphosis have observed the predicted pattern, and no studies, to our knowledge, have examined the effect of increased risk during and after metamorphosis on the timing of this switch point. Here we examine the effect of larval and post-metamorphic predation risk on metamorphosis in the red-eyed treefrog, Agalychnis callidryas. We raised tadpoles in the presence or absence of cues from caged water bugs fed larvae and cues from spiders fed emerging metamorphs. Water bugs are effective larval predators, while spiders are poor larval predators but prey on metamorphs. Furthermore, since spiders forage on the water surface it is possible that tadpoles could assess future risk from this predator. Predators induced opposite shifts in life history. Tadpoles emerged smaller and less developed in response to water bugs, but later and larger in response to spiders. Interestingly, predator effects on larval duration were not independent; tadpoles delayed emerging in response to spiders, but only in the absence of water bugs.
捕食风险会导致生物体改变生活史转换点的时间。理论表明，生命早期阶段风险增加应选择更早且更小的转换，而后续阶段风险增加则应选择更晚且更大的转换。这一框架经常被应用于两栖动物的变态过程，结果不一。很少有研究考察幼体捕食风险对变态的影响时观察到预测模式，据我们所知，没有研究考察变态期间及之后风险增加对这个转换点时间的影响。在这里，我们研究了幼体和变态后捕食风险对红眼树蛙（Agalychnis callidryas）变态的影响。我们在有或没有来自喂食幼体的笼养水蝽的线索以及来自捕食刚变态个体的蜘蛛的线索的情况下饲养蝌蚪。水蝽是有效的幼体捕食者，而蜘蛛是较差的幼体捕食者，但会捕食刚变态个体。此外，由于蜘蛛在水面觅食，蝌蚪有可能评估来自这种捕食者的未来风险。捕食者导致了生活史的相反变化。蝌蚪因水蝽而出现时体型更小且发育程度更低，但因蜘蛛而出现得更晚且体型更大。有趣的是，捕食者对幼体持续时间的影响并非独立；蝌蚪因蜘蛛而延迟出现，但仅在没有水蝽的情况下如此。
