An individual’s early-life environment and phenotype often influence its traits and performance as an adult. We investigated whether such ‘carryover effects’ are associated with alternative, environmentally-induced phenotypes (‘polyphenism’), and, if so, whether they influence the evolution of polyphenism. To do so, we studied Mexican spadefoot toads, Spea multiplicata, which have evolved a polyphenism consisting of two, dramatically different forms: a carnivore morph and an omnivore morph. We sampled both morphs from a fast-drying and a slow-drying pond and reared them to sexual maturity. Larval environment (pond) strongly influenced survival as well as age and size at metamorphosis and sexual maturity; i.e. environment-dependent carryover effects were present. By contrast, larval phenotype (morph) did not affect life-history traits at sexual maturity; i.e. phenotype-dependent carryover effects were absent. These results are consistent with theory, which suggests that by amplifying selective trade-offs in heterogenous environments, environment-dependent carryover effects might foster the evolution of polyphenism. At the same time, by freeing selection to refine a novel phenotype without altering the existing form, the absence of phenotype-dependent carryover effects might enable polyphenism to evolve in the first place. Generally, carryover effects might play an underappreciated role in the evolution of polyphenism.

中文翻译：

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残留效应和多态性的演变

一个人的早期生活环境和表型通常会影响其成年后的特征和表现。我们调查了这种“残留效应”是否与环境诱导的其他表型（“多态性”）相关联，如果存在，是否影响了多态性的演变。为此，我们研究了墨西哥黑脚蟾蜍Spea multiplicata，已经发展出一种由两种截然不同的形式组成的多态性：食肉动物变体和杂食动物变体。我们从快干和慢干的池塘中采样了这两种变体，并将它们饲养到性成熟状态。幼体环境（池塘）在变态和性成熟时对生存以及年龄和大小有很大影响；即存在与环境有关的残留效应。相比之下，幼虫表型（形态）在性成熟时不会影响生活史特征。即没有表型依赖性的残留效应。这些结果与理论相符，该理论表明，通过扩大异构环境中的选择性权衡，依赖环境的残留效应可能会促进多态性的进化。同时，通过释放选择来精制新的表型而不改变现有形式，不存在依赖表型的残留效应可能使多态性首先发展。通常，残留效应可能在多态性的进化中起不到充分的作用。