Data from: Drosophila wing modularity revisited through a quantitative genetic approach

To predict the response of complex morphological structures to selection it is necessary to know how the covariation among its different parts is organized. Two key features of covariation are modularity and integration. The Drosophila wing is currently considered a fully integrated structure. Here we study the patterns of integration of the Drosophila wing and test the hypothesis of the wing being divided into two modules along the proximo-distal axis, as suggested by developmental, biomechanical and evolutionary evidence. To achieve these goals we perform a multilevel analysis of covariation combining the techniques of geometric morphometrics and quantitative genetics. Our results indicate that the Drosophila wing is indeed organized into two main modules, the wing base and the wing blade. The patterns of integration and modularity were highly concordant at the phenotypic, genetic, environmental, and developmental levels. Besides, we found that modularity at the developmental level was considerably higher than modularity at other levels, suggesting that in the Drosophila wing direct developmental interactions are major contributors to total phenotypic shape variation. We propose that the precise time at which covariance-generating developmental processes occur and/or the magnitude of variation that they produce favour proximo-distal, rather than anterior-posterior, modularity in the Drosophila wing.

若要预测复杂形态结构对自然选择的响应，需明确其不同组分间的协变（covariation）模式是如何组织的。协变的两个核心特征为模块化与整合性。当前学界普遍认为果蝇翅（Drosophila wing）为完全整合的结构。本研究以果蝇翅为对象，探究其整合模式，并验证由发育学、生物力学及进化生物学证据所提出的“翅沿近-远轴（proximo-distal axis）划分为两个模块”这一假说。为达成上述研究目标，本研究结合几何形态测量学（geometric morphometrics）与数量遗传学（quantitative genetics）技术，开展多层级协变分析。研究结果表明，果蝇翅确实可划分为两个主要模块：翅基（wing base）与翅片（wing blade）。表型、遗传、环境及发育各层级下的整合模式与模块化模式均高度一致。此外，本研究发现发育层级的模块化程度显著高于其他层级，这表明果蝇翅中直接的发育互作是整体表型形状变异的主要来源。我们提出，产生协变的发育过程发生的精准时序，以及/或其所产生的变异幅度，共同促使果蝇翅演化出近-远轴方向而非前-后轴（anterior-posterior）方向的模块化结构。