We analyzed patterns of complexity and simplicity in holometabolan insects using parsimony and maximum-likelihood. By contrast with other groups of arthropods (and most other groups of animals), insects have undergone a stepwise process of structural simplification in their evolution. The megadiverse Holometabola are characterized mainly by structurally simplified larvae, which differ strongly from the adults in their morphology and usually also in their life habits. Although smaller groups such as Neuropterida have largely maintained their structural complexity in adults and immature life stages, a series of reductions occurred with the appearance and diversification of Coleopterida, Mecopterida and especially Antliophora. Parasitic Strepsiptera or fleas display conspicuous patterns of reduction in different life stages and body regions, and high degrees of simplification also occur in groups with short-lived adults. Larvae living in moist substrates display far-reaching structural simplifications and also morphological uniformity, especially in the species-rich Diptera, but also in other groups. Liquid feeding leads to correlated simplifications and innovation of adult head structures, especially of the mouthparts. Functional or anatomical dipterism leads to an optimization of the flight apparatus in most holometabolous groups, which is correlated with reductions in one of the pterothoracic segments, and coupled (e.g. by hamuli), partly reduced or transformed wings (e.g. halteres). In flightless groups, the pterothoracic skeleto-muscular apparatus is strongly simplified. In the abdomen of adult females a stepwise reduction of the lepismatoid ovipositor occurs. By contrast, the male genital apparatus often undergoes an extreme diversification. Our evaluations revealed a highly correlated complexity between larval and adult stages.

中文翻译：

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大型多样性全变态动物（昆虫纲）的形态简化和创新模式

我们使用简约法和最大似然法分析了全变态昆虫的复杂性和简单性模式。与其他节肢动物群（和大多数其他动物群）相比，昆虫在进化过程中经历了结构简化的逐步过程。大型多样性全变态动物的主要特征是结构简化的幼虫，它们在形态上与成虫有很大不同，而且通常在生活习惯上也有很大不同。尽管神经翅目等较小的群体在成年和未成熟的生命阶段很大程度上保持了它们的结构复杂性，但随着鞘翅目、长翅目，尤其是角翅目的出现和多样化，发生了一系列的减少。寄生链翅目或跳蚤在不同的生命阶段和身体区域表现出明显的减少模式，高度简化也发生在短命成年人的群体中。生活在潮湿基质中的幼虫表现出深远的结构简化和形态均匀性，特别是在物种丰富的双翅目中，但在其他群体中也是如此。液体喂养导致成人头部结构的相关简化和创新，尤其是口器。功能性或解剖学上的双翅目导致大多数全代谢组中飞行装置的优化，这与翼胸节之一的减少相关，并且耦合（例如通过hamuli），部分减少或转化的机翼（例如halteres）。在不能飞行的群体中，翼胸骨骼肌肉装置被强烈简化。在成年雌性的腹部，鳞片状产卵器逐渐减少。相比之下，男性生殖器经常经历极端多样化。我们的评估揭示了幼虫和成虫阶段之间高度相关的复杂性。