Data from: A test of the "flexible stem" model of evolution: ancestral plasticity, genetic accommodation, and morphological divergence in the threespine stickleback radiation

If an ancestral stem group repeatedly colonizes similar environments, developmental plasticity specific to that group should consistently give rise to similar phenotypes. Parallel selection on those similar phenotypes could lead to the repeated evolution of characteristic ecotypes, a property common to many adaptive radiations. A key prediction of this "flexible stem" model of adaptive radiation is that patterns of phenotypic divergence in derived groups should mirror patterns of developmental plasticity in their common ancestor. The threespine stickleback radiation provides an excellent opportunity to test this prediction because the marine form is representative of the ancestral stem group, which has repeatedly given rise to several characteristic ecotypes. We examined plasticity of several aspects of shape and trophic morphology in response to diets characteristic of either the derived benthic or limnetic ecotypes. When marine fish were reared on alternative diets, plasticity of head and mouth shape paralleled phenotypic divergence between the derived ecotypes, supporting the flexible stem model. Benthic and limnetic fish exhibited patterns of plasticity similar to the marine population; however, some differences in population means were present, as well as subtle differences in shape plasticity in the benthic population, indicating a role for genetic accommodation in this system.

若某一祖先支干类群（ancestral stem group）反复定殖于相似环境，该类群特有的发育可塑性（developmental plasticity）应会持续催生相似的表型（phenotypes）。对这些相似表型的平行选择，可促成特征性生态型（ecotypes）的反复演化——这亦是诸多适应性辐射（adaptive radiations）共有的特性。适应性辐射的“灵活支干”（flexible stem）模型的核心预测为：衍生类群的表型分化模式，应与其共同祖先的发育可塑性模式相匹配。三刺棘鱼（threespine stickleback）适应性辐射为验证该预测提供了绝佳契机，因其海洋种群代表了该祖先支干类群，且该类群已反复演化出多种特征性生态型。本研究针对衍生的底栖（benthic）与浮游（limnetic）生态型特有的饮食条件，检测了体形与营养形态学（trophic morphology）多个维度的可塑性。当以不同饮食饲喂海洋棘鱼时，其头部与口部形态的可塑性与衍生生态型间的表型分化高度吻合，为灵活支干模型提供了支持。底栖与浮游棘鱼展现出的可塑性模式与海洋种群相似，但种群均值存在一定差异，且底栖种群的形态可塑性还存在细微区别，这表明遗传容纳（genetic accommodation）在该系统中发挥了作用。