Table_S2_matrix_for_pairwise_correlations.xls from Computational biomechanics changes our view on insect head evolution

Despite large-scale molecular attempts, the relationships of the basal winged insect lineages dragonflies, mayflies and neopterans, are still unresolved. Other data sources, such as morphology, suffer from unclear functional dependencies of the structures considered, which might mislead phylogenetic inference. Here, we assess this problem by combining for the first time biomechanics with phylogenetics using two advanced engineering techniques, multibody dynamics analysis and finite-element analysis, to objectively identify functional linkages in insect head structures which have been used traditionally to argue basal winged insect relationships. With a biomechanical model of unprecedented detail, we are able to investigate the mechanics of morphological characters under biologically realistic load, i.e. biting. We show that a range of head characters, mainly ridges, endoskeletal elements and joints, are indeed mechanically linked to each other. An analysis of character state correlation in a morphological data matrix focused on head characters shows a highly significant correlation of these mechanically linked structures. Phylogenetic tree reconstruction under different data exclusion schemes based on the correlation analysis unambiguously supports a sistergroup relationship of dragonflies and mayflies. The combination of biomechanics and phylogenetics as it is proposed here could be a promising approach to assess functional dependencies in many organisms to increase our understanding of phenotypic evolution.

尽管已开展大规模分子研究，基部有翅昆虫支系（蜻蜓、蜉蝣与新翅类）的演化关系仍未得到明确解析。其他数据源（如形态学数据）存在所考察结构的功能关联性模糊的问题，这可能误导系统发育推断。本研究首次将生物力学与系统发育学相结合，采用两种先进工程技术——多体动力学分析（multibody dynamics analysis）与有限元分析（finite-element analysis），客观鉴定了传统上用于论证基部有翅昆虫演化关系的昆虫头部结构的功能关联。通过构建精度前所未有的生物力学模型，我们能够在符合生物学现实的载荷条件（即咬合过程）下探究形态特征的力学机制。研究证实，一系列头部特征（主要包括脊突、内骨骼结构与关节）确实存在机械关联性。对聚焦头部特征的形态学数据矩阵开展特征状态相关性分析后发现，这些机械关联的结构呈现出高度显著的相关性。基于相关性分析制定的不同数据排除方案进行的系统发育树重建结果，明确支持蜻蜓与蜉蝣构成姊妹群的结论。本研究提出的生物力学与系统发育学融合方法，有望成为评估众多生物类群功能关联性的有效路径，从而加深我们对表型演化的认知。