Data from: Spatially heterogeneous selection in nature favors phenotypic plasticity in anuran larvae

Theory holds that adaptive phenotypic plasticity evolves under spatial or temporal variation in natural selection. I tested this prediction in a classic system of predator-induced plasticity: frog tadpoles (Rana temporaria) reacting to predaceous aquatic insects. An outdoor mesocosm experiment manipulating exposure to Aeshna dragonfly larvae revealed plasticity in most characters: growth, development, behavior, and external morphology. I measured selection by placing 1927 tadpoles into enclosures within natural ponds; photographs permitted identification of the survivors 6–9 days later. Fitness was defined as a linear combination of growth, development, and survival that correlates with survival to age 2 in another anuran species. In enclosures with many predators, selection favored character values similar to those induced by exposure to Aeshna in mesocosms. The shift in selection along the predation gradient was strongest for characters that exhibited high predator-induced plasticity. A field survey of 50 ponds revealed that predator density changes over a spatial scale relevant for movement of individual adults and larvae: 17% of variation in predation risk was among ponds separated by tens to thousands of meters and 81% was among sites ≤10m apart within ponds. These results on heterogeneity in the selection regime confirm a key tenant of the standard model for the evolution of plasticity.

理论认为，适应性表型可塑性（adaptive phenotypic plasticity）是在自然选择的空间或时间异质性条件下演化形成的。本研究以经典的捕食者诱导表型可塑性（predator-induced plasticity）系统为研究对象，即林蛙（Rana temporaria）蝌蚪对捕食性水生昆虫的响应模式。我们开展了一项操控晏蜓（Aeshna）蜻蜓幼虫暴露水平的室外中宇宙（mesocosm）实验，结果显示多数性状均存在可塑性：包括生长、发育、行为与外部形态。本研究将1927只蝌蚪放置于自然池塘的围隔（enclosure）中开展选择实验，并于6至9天后通过照片识别存活个体。适合度以生长、发育与存活的线性组合进行定义，该组合与另一无尾两栖类（anuran species）个体存活至2龄的存活情况具有相关性。在捕食者密度较高的围隔中，自然选择所青睐的性状值与中宇宙实验中晏蜓诱导产生的性状值相一致。沿着捕食压力梯度（predation gradient）发生的选择偏移，在表现出高捕食者诱导可塑性的性状中最为显著。对50个池塘的野外调查（field survey）显示，捕食者密度的空间变化尺度与成体及幼体的移动范围相匹配：17%的捕食风险变异存在于相隔数十至数千米的池塘之间，而81%的变异存在于单个池塘内相距≤10米的样点之间。本研究中关于选择模式（selection regime）异质性的结果，验证了表型可塑性演化标准模型的核心要义。