Data from: Morph-specific artificial selection reveals a constraint on the evolution of polyphenisms

Theory predicts that the evolution of polyphenic variation is facilitated
where morphs are genetically uncoupled and free to evolve towards their
phenotypic optima. However, the assumption that developmentally plastic
morphs can evolve independently has not been tested directly. Using
morph-specific artificial selection, we investigated correlated evolution
between the sexes and male morphs of the bulb mite Rhizoglyphus echinopus.
Large ‘fighter’ males have a thick and sharply terminating pair of legs
used to kill rival males, while small ‘scrambler’ males have unmodified
legs, and search for unguarded females, avoiding fights. We selected on
the relative leg width of only the fighter male morph, tracked the
evolutionary responses in fighters and the correlated evolutionary
responses in scramblers and females that were untouched by direct
selection. Fighters diverged in relative leg thickness after six
generations; assaying scramblers and females at the ninth generation we
observed correlated responses in relative leg width in both. Our results
represent strong evidence for the evolution of intraspecific phenotypic
diversity despite correlated evolution between morphs and sexes,
challenging the idea that male morphs are genetically uncoupled and free
to independen- tly respond to selection. We, therefore, question the
perceived necessity for genetic independence in traits with extreme
phenotypic plasticity.

理论预测，当不同形态（morphs）在遗传上解耦且可自由向其表型最优状态进化时，多态变异（polyphenic variation）的进化会得到促进。然而，发育可塑性（developmentally plastic）形态可独立进化这一假设尚未得到直接验证。通过形态特异性人工选择（morph-specific artificial selection），我们研究了球螨Rhizoglyphus echinopus的性别间及雄性形态间的关联进化（correlated evolution）。体型较大的“战斗型”（fighter）雄性拥有一对粗壮且末端锋利的足，用于杀死竞争对手；而体型较小的“竞配型”（scrambler）雄性足未发生特化，通过搜寻未受守护的雌性来繁殖，避免争斗。我们仅针对战斗型雄性形态的相对足宽进行选择，追踪了战斗型雄性的进化响应，以及未受直接选择的竞配型雄性和雌性的关联进化响应。经过六代选择后，战斗型雄性的相对足厚度出现分化；在第九代对竞配型雄性和雌性进行检测时，我们观察到两者的相对足宽均出现了关联响应。我们的结果为种内表型多样性（intraspecific phenotypic diversity）的进化提供了有力证据——尽管形态与性别间存在关联进化，这一发现挑战了“雄性形态在遗传上解耦且可独立响应选择”的观点。因此，我们对“具有极端表型可塑性（extreme phenotypic plasticity）的性状需具备遗传独立性”这一普遍认知的必要性提出质疑。