Hoverman Jason T, Relyea Rick A
Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
Ecology. 2007 Mar;88(3):693-705. doi: 10.1890/05-1697.
Inducible defenses allow prey to modulate their phenotypic responses to the level of predation risk in the environment and reduce the cost of constitutive defenses. Inherent in this statement is that prey must alter their phenotypes during development in order to form these defenses. This has lead many ecologists and evolutionary biologists to call for studies that examine developmental plasticity to provide insights into the importance of development in controlling the trajectories of trait formation, the integration of phenotypes over ontogeny, and the establishment of developmental windows for trait formation and reversal. By moving away from studies that focus on a single point in development, we can obtain a more complete understanding of the phenotypic decisions and limitations of prey. We exposed freshwater snails (Helisoma trivolvis) to environments in which predatory water bugs (Belostoma flumineum) were always absent, always present, or added and removed at different points in development. We discovered that snails formed morphological defenses against water bugs. Importantly, after the initial induction of defenses, snails showed similar developmental trajectories as snails reared without predators. Further, the snails possessed wide developmental windows for inducible defenses that extended past sexual maturity. However, being induced later in development appeared to have an associated cost (i.e., decreased shell thickness) that was not found when water bugs were always present. This epiphenotype (i.e., new shell formation as an extension of the current shell) suggests that resource limitation plays an important role in responses to temporal variation in predation risk and may have critical ecological costs that limit the benefits of the inducible defense. Lastly, the ability of snails to completely reverse their defenses was limited to early in ontogeny due to the constraints associated with modular growth of shell material. In sum, we demonstrate that taking a developmental perspective is extremely valuable for understanding the ecology of inducible defenses.
可诱导防御使猎物能够根据环境中的捕食风险水平调节其表型反应，并降低组成型防御的成本。这句话的内在含义是，猎物必须在发育过程中改变其表型才能形成这些防御。这使得许多生态学家和进化生物学家呼吁开展研究，以检验发育可塑性，从而深入了解发育在控制性状形成轨迹、个体发育过程中表型的整合以及性状形成和逆转的发育窗口建立方面的重要性。通过摆脱专注于发育中单个点的研究，我们可以更全面地理解猎物的表型决策和局限性。我们将淡水蜗牛（三旋膀胱螺）置于不同环境中，在这些环境中捕食性水蝽（美洲巨田鳖）始终不存在、始终存在，或者在发育的不同阶段添加和移除。我们发现蜗牛形成了针对水蝽的形态防御。重要的是，在最初诱导出防御后，蜗牛表现出与未接触捕食者的蜗牛相似的发育轨迹。此外，蜗牛具有广泛的可诱导防御发育窗口，该窗口延伸至性成熟之后。然而，在发育后期受到诱导似乎会带来一种相关成本（即壳厚度减小），而当水蝽始终存在时并未发现这种情况。这种表观型（即作为当前壳的延伸形成新壳）表明资源限制在对捕食风险时间变化的反应中起着重要作用，并且可能具有关键的生态成本，限制了可诱导防御的益处。最后，由于与壳物质模块化生长相关的限制，蜗牛完全逆转其防御的能力仅限于个体发育早期。总之，我们证明从发育角度出发对于理解可诱导防御的生态学极具价值。
