Allen Cerisse E, Beldade Patrícia, Zwaan Bas J, Brakefield Paul M
Institute of Biology, Leiden University, PO Box 9516 2300 RA Leiden, The Netherlands.
BMC Evol Biol. 2008 Mar 26;8:94. doi: 10.1186/1471-2148-8-94.
There is spectacular morphological diversity in nature but lineages typically display a limited range of phenotypes. Because developmental processes generate the phenotypic variation that fuels natural selection, they are a likely source of evolutionary biases, facilitating some changes and limiting others. Although shifts in developmental regulation are associated with morphological differences between taxa, it is unclear how underlying mechanisms affect the rate and direction of evolutionary change within populations under selection. Here we focus on two ecologically relevant features of butterfly wing color patterns, eyespot size and color composition, which are similarly and strongly correlated across the serially repeated eyespots. Though these two characters show similar patterns of standing variation and covariation within a population, they differ in key features of their underlying development. We targeted pairs of eyespots with artificial selection for coordinated (concerted selection) versus independent (antagonistic selection) change in their color composition and size and compared evolutionary responses of the two color pattern characters.
The two characters respond to selection in strikingly different ways despite initially similar patterns of variation in all directions present in the starting population. Size (determined by local properties of a diffusing inductive signal) evolves flexibly in all selected directions. However, color composition (determined by a tissue-level response to the signal concentration gradient) evolves only in the direction of coordinated change. There was no independent evolutionary change in the color composition of two eyespots in response to antagonistic selection. Moreover, these differences in the directions of short-term evolutionary change in eyespot size and color composition within a single species are consistent with the observed wing pattern diversity in the genus.
Both characters respond rapidly to selection for coordinated change, but there are striking differences in their response to selection for antagonistic, independent change across eyespots. While many additional factors may contribute to both short- and long-term evolutionary response, we argue that the compartmentalization of developmental processes can influence the diversification of serial repeats such as butterfly eyespots, even under strong selection.
自然界中存在着惊人的形态多样性，但谱系通常表现出有限的表型范围。由于发育过程产生了推动自然选择的表型变异，它们很可能是进化偏差的来源，促进了一些变化而限制了其他变化。尽管发育调控的转变与不同分类群之间的形态差异相关，但尚不清楚潜在机制如何影响在选择作用下种群内进化变化的速率和方向。在这里，我们聚焦于蝴蝶翅膀颜色图案的两个与生态相关的特征，即眼斑大小和颜色组成，它们在一系列重复的眼斑中呈现出相似且强烈的相关性。尽管这两个特征在种群内表现出相似的静态变异和协变模式，但它们在潜在发育的关键特征上存在差异。我们针对成对的眼斑进行人工选择，使其颜色组成和大小发生协同（协同选择）或独立（拮抗选择）变化，并比较这两个颜色图案特征的进化响应。
尽管起始种群在所有方向上最初具有相似的变异模式，但这两个特征对选择的响应方式却截然不同。大小（由扩散诱导信号的局部特性决定）在所有选定方向上都能灵活进化。然而，颜色组成（由组织对信号浓度梯度的响应决定）仅在协同变化的方向上进化。在拮抗选择下，两个眼斑的颜色组成没有独立的进化变化。此外，单个物种内眼斑大小和颜色组成的短期进化变化方向上的这些差异与该属中观察到的翅膀图案多样性是一致的。
两个特征对协同变化的选择都能快速响应，但它们对眼斑间拮抗、独立变化的选择响应存在显著差异。虽然许多其他因素可能对短期和长期进化响应都有贡献，但我们认为，即使在强选择下，发育过程的区室化也会影响蝴蝶眼斑等系列重复结构的多样化。
