Adaptive developmental plasticity allows individuals to match their phenotype with their environment, increasing fitness where threats are inconsistently present. However, despite clear advantages of plasticity, adaptive traits are not ubiquitously nor infinitely plastic. Trade‐offs between benefits and costs or limits are therefore theoretically necessary to constrain the evolution of plastic responses. Systems in which extreme risk can be reliably detected are ideal for investigating trade‐offs, as even costly responses may be adaptive where risk is severe. Cane toads (Rhinella marina) are abundant in Australia and produce large clutches (frequently >10,000 eggs), but asynchronous breeding and rapid development result in variable larval densities within breeding pools. In the field, we found that cannibalism by older cohorts often reduces the survival of conspecific eggs and newly hatched pre‐feeding larvae (“hatchlings”) by >99%, as feeding larvae (“tadpoles”) use chemical cues from the relatively immobile hatchlings to locate and consume them. After hatchlings become free‐swimming, however, they cannot be cannibalized. Hatchlings can reduce this period of vulnerability by accelerating development when they detect cannibal cues. However, this developmental acceleration decreases initial tadpole mass, reduces subsequent survival, growth, and development, affects behavior, and compromises feeding structures. Reaction norms differ among clutches, and greater developmental acceleration is followed by greater impairment of larval function in plastic clutches, whereas nonresponsive clutches are unaffected by cue exposure. More plastic clutches ultimately exhibit both poorer performance and greater variation among siblings in exposed and (to a lesser degree) control treatments. Variation among clutches in tadpole viability is driven by differences in plasticity rather than phenotype; fitness reductions are linked to developmental acceleration, not rapid development per se. Clutches with intrinsically slow pre‐feeding developmental rates exhibit stronger acceleration (i.e., steeper reaction norms), but clutches with intrinsically rapid development reach invulnerable stages more quickly than those that accelerate development. As a result, high cannibalism risk may favor canalized rapid development rather than facultative developmental acceleration. Cannibalism plays an important role in the recruitment of this invasive species, and hatchling defenses against this threat demonstrate how the limits and costs associated with an inducible defense can favor canalized defenses over phenotypic plasticity.

中文翻译：

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折衷会影响可塑性的适应性价值：食人诱导的防御力增强会导致蟾蜍幼虫的成本增加

适应性发育可塑性使个体能够使其表型与环境相匹配，从而在不一致地存在威胁的情况下提高适应能力。然而，尽管可塑性有明显的优势，但适应性状并不是普遍存在的，也不是无限可塑性的。因此，从理论上讲，必须在收益与成本或限制之间进行权衡以限制可塑性响应的演变。可以可靠地检测到极端风险的系统是研究折衷方案的理想之选，因为即使在代价高昂的风险严重的情况下，即使是代价高昂的应对措施也可能是自适应的。甘蔗蟾蜍（莱茵利亚码头）在澳大利亚很丰富，并且会产出大型的离合器（通常> 10,000个卵），但是异步育种和快速发展导致了育种池内幼虫密度的变化。在野外，我们发现，同龄人的同类相食通常会使同种卵和刚孵出的幼体幼虫（“小鱼苗”）的存活率降低99％以上，因为幼虫（“ ta”）使用相对不动的化学线索孵化场来定位和食用它们。但是，在幼体自由游动后，就不能再吞食它们了。孵化时，孵化器可以通过检测食人鱼线索来加速发育，从而减少这一时期的脆弱性。但是，这种发育加速度会降低初始t的质量，降低其随后的存活，生长和发育，影响行为并损害饲喂结构。离合器之间的反应规范各不相同，并且更大的发展加速度会导致塑料离合器中幼虫功能的更大损害，而无响应的离合器则不受提示暴露的影响。最终，更多的塑料离合器在暴露和（较小程度的）对照处理中表现出较差的性能和兄弟姐妹之间更大的差异。es间存活力的差异是由可塑性而不是表型的差异驱动的。体能的降低与发展的加速有关，而不是与自身的迅速发展有关。本质上预喂发育速度较慢的离合器表现出较强的加速度（即，较陡的反应范数），但本质上较快发育的离合器比那些较快发育的离合器更快地进入无害阶段。作为结果，高的食人风险可能有利于快速发展，而不是兼职的发展加速。食人族在这种入侵物种的招募中起着重要作用，对这种威胁的孵化防御表明与诱导型防御相关的限制和成本如何比表型可塑性更有利于渠道化防御。