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.

理论表明，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可塑性系统为研究对象，即欧洲林蛙（Rana temporaria）蝌蚪对捕食性水生昆虫的响应。本研究开展了一项野外中型实验围隔（outdoor mesocosm）实验，通过调控蝌蚪接触蜓属（Aeshna）蜻蜓幼虫的程度，发现多数性状均表现出可塑性：涵盖生长、发育、行为与外部形态四大维度。为量化自然选择压力，本研究将1927只蝌蚪放置于自然池塘的围栏样地中，6至9天后通过拍摄照片甄别存活个体。适合度（fitness）被定义为生长、发育与存活的线性组合，该组合与另一无尾两栖类（anuran）物种至2龄时的存活率相关。在捕食者密度较高的围栏样地中，自然选择所青睐的性状值与中型围隔实验中蜓属幼虫诱导产生的性状值高度一致。沿捕食压力梯度发生的选择偏移，在表现出强捕食诱导可塑性的性状上最为显著。对50个池塘的野外调查显示，捕食者密度的空间变化尺度与单个成体及幼体的活动范围相匹配：17%的捕食风险变异存在于相距数十至数千米的池塘之间，而81%的变异存在于单个池塘内间距≤10米的样点之间。上述关于选择模式异质性的研究结果，证实了可塑性演化标准模型的一项核心要义。