Why are defensive toxins so variable? An evolutionary perspective
Why are defensive toxins so variable? An evolutionary perspective
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为什么防御性毒素变化如此之大？
DOI：
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发表时间：
2012
影响因子：
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通讯作者：
T. Sherratt
中科院分区：
文献类型：
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作者：
M. Speed;G. Ruxton;J. Mappes;T. Sherratt
动物、植物和微生物广泛使用防御性毒素来威慑天敌。这种防御的一个重要特征是毒素的数量和存在的特定防御化学物质的特征都不同。在这里，我们评估了进化和生态学对猎物种群中毒素多样性持续存在的解释，从文献中收集了一系列解释，并增加了新的假设。我们从三个方面考虑毒素多样性：(1)在其他有毒的猎物种群中的一定比例的个体中没有毒性(自动仿制)；(2)同一种群中个体内毒素数量的广泛差异；(3)化学防御的化学成分的差异。对于这些现象中的每一种，我们都为变异的持久性确定了不同的进化解释。一种重要的一般性解释是多样化(依赖于频率或密度)选择，在这种选择中，随着猎物种群中毒性绝对丰度或相对丰度的增加，毒性成本增加或其效益减少。第二类主要的解释是，毒性分布的变化本身是非适应性的。这一解释的一种应用要求捕食者的行为不受猎物种群内化学防御水平或轮廓的变化影响，并且在种群内发现的不同数量或形式的毒素之间没有成本差异。最后，动物的生态和生活史可能会使一些关于毒素变异的一般预测成为可能。例如，对于只以未成熟形式获得毒素的动物(如寄主植物上的毛毛虫)，我们可能预计成年后毒性会下降(或至少没有变化)。相比之下，当毒素也是在成年过程中获得时，例如，我们可能会期待相反的情况，即年轻人比老年人有更少的时间获得毒性。我们得出的一个主要结论是，有充分的理由认为防御性毒素的物种内变异不仅仅是生态噪音。相反，有许多令人信服的进化假说可以解释和预测猎物毒性的变化。
Defensive toxins are widely used by animals, plants and micro‐organisms to deter natural enemies. An important characteristic of such defences is diversity both in the quantity of toxins and the profile of specific defensive chemicals present. Here we evaluate evolutionary and ecological explanations for the persistence of toxin diversity within prey populations, drawing together a range of explanations from the literature, and adding new hypotheses. We consider toxin diversity in three ways: (1) the absence of toxicity in a proportion of individuals in an otherwise toxic prey population (automimicry); (2) broad variation in quantities of toxin within individuals in the same population; (3) variation in the chemical constituents of chemical defence. For each of these phenomena we identify alternative evolutionary explanations for the persistence of variation. One important general explanation is diversifying (frequency‐ or density‐dependent) selection in which either costs of toxicity increase or their benefits decrease with increases in the absolute or relative abundance of toxicity in a prey population. A second major class of explanation is that variation in toxicity profiles is itself nonadaptive. One application of this explanation requires that predator behaviour is not affected by variation in levels or profiles of chemical defence within a prey population, and that there are no cost differences between different quantities or forms of toxins found within a population. Finally, the ecology and life history of the animal may enable some general predictions about toxin variation. For example, in animals which only gain their toxins in their immature forms (e.g. caterpillars on host plants) we may expect a decline in toxicity during adult life (or at least no change). By contrast, when toxins are also acquired during the adult form, we may for example expect the converse, in which young adults have less time to acquire toxicity than older adults. One major conclusion that we draw is that there are good reasons to consider within‐species variation in defensive toxins as more than mere ecological noise. Rather there are a number of compelling evolutionary hypotheses which can explain and predict variation in prey toxicity.