Nicieza A G
Division of Environmental and Evolutionary Ecology, Graham Kerr Building, Institute of Biomedical and Life Sciences, Glasgow University, Glasgow G12 8QQ, UK, , , , , , GB.
Oecologia. 2000 Jun;123(4):497-505. doi: 10.1007/s004420000343.
Age and size at metamorphosis are two important fitness components in species with complex life cycles. In anurans, metamorphic traits show remarkable phenotypic plasticity, especially in response to changes in growth conditions. It is also possible that the perception of risk directly determines changes in larval period and the size of metamorphs. This study examines how the perception of predation risk affects the timing of and size at metamorphosis in common frogs (Rana temporaria). I raised tadpoles at two risk levels (fish-conditioned water or unconditioned water) crossed with the availability or lack of food at night (all tadpoles had food available in the day). Tadpoles reacted to chemical cues from predatory fish by decreasing activity. A novel behavioural result was a predation×food interaction effect on refuge use, which also accounted for most of the predator main effect: predation risk only caused increased refuge use in the night-starved treatment. Despite these behavioural modifications, the perception of predation risk did not affect growth rate and mass at metamorphosis in a simple way: the effects of food regime on growth and size at metamorphosis were dependent on the level of predation risk as revealed by significant predation×food interaction effects. Tadpoles who had food withheld at night metamorphosed at the smallest size, suggesting a negative relationship between size at metamorphosis and refuge use. Tadpoles raised in fish-conditioned water had longer larval periods than those in unconditioned water, but these differences were significant only if food was available at night. These results conflict with the hypotheses that tadpoles should reduce their larval period or growth rates (and hence metamorphose at a smaller size) as the risk of predation increases. In contrast to predation risk, food availability strongly affected the length of the larval period: night-starved tadpoles metamorphosed relatively early with or without fish stimulus. Thus, early metamorphosis resulted from periods of low food availability, but not from a heightened "perceived risk" of predation. This example counters the hypothesis of acceleration of the developmental rate (which shortens the time to metamorphosis) as a mechanism to escape a risky environment.
在具有复杂生命周期的物种中，变态时的年龄和体型是两个重要的适合度组成部分。在无尾两栖类动物中，变态特征表现出显著的表型可塑性，尤其是对生长条件变化的响应。捕食风险的感知也有可能直接决定幼体期的变化以及变态幼体的大小。本研究探讨了捕食风险的感知如何影响普通青蛙（欧洲林蛙）变态的时间和大小。我将蝌蚪饲养在两种风险水平下（有捕食者鱼类条件的水或无捕食者条件的水），并与夜间食物的有无进行交叉处理（所有蝌蚪在白天都有食物）。蝌蚪通过减少活动来对来自捕食性鱼类的化学信号做出反应。一个新的行为结果是捕食×食物对避难所使用的交互作用效应，这也解释了捕食者的主要效应：捕食风险仅在夜间饥饿处理中导致避难所使用增加。尽管有这些行为改变，捕食风险的感知并没有以简单的方式影响变态时的生长速率和体重：食物供应方式对变态时生长和大小的影响取决于捕食风险水平，这通过显著的捕食×食物交互作用效应得以体现。夜间食物被扣留的蝌蚪变态时体型最小，这表明变态时的体型与避难所使用之间存在负相关关系。在有捕食者鱼类条件的水中饲养的蝌蚪比在无捕食者条件的水中饲养的蝌蚪幼体期更长，但这些差异仅在夜间有食物时才显著。这些结果与蝌蚪应随着捕食风险增加而缩短其幼体期或生长速率（从而以较小的体型变态）的假设相矛盾。与捕食风险相反，食物供应强烈影响幼体期的长度：无论有无鱼类刺激，夜间饥饿的蝌蚪变态相对较早。因此，早期变态是由食物供应不足期导致的，而不是由捕食风险的“感知增加”导致的。这个例子反驳了发育速率加速（缩短变态时间）作为逃避危险环境机制的假设。
