The phasmatodean tree of life: resolving evolutionary patterns of diversity and disparity in a mesodiverse insect lineage

杆状和叶状昆虫是大型陆生食草性节肢动物的中观多样性谱系，主要分布在热带和亚热带。它们通常是夜间活动的，表现出非凡的伪装密码形式，模仿植物的不同部分，如树枝、树皮和树叶，以欺骗肉眼上的捕食者。该属包括约3100个现存描述的物种，是研究进化生物学中重要问题的模式系统，如物种形成、无性进化、形态特征的丧失和恢复、分支多样化，或者更准确地说，在地理孤立的情况下重复适应辐射。直到最近，树枝和树叶昆虫才脱颖而出，成为最后的昆虫目之一，没有强有力的更高水平的系统发育假说。我们基于广泛的转录和Sanger序列数据的最新分子研究现在已经解决了这些昆虫的早期进化，并证实了现有的多样性是最近令人惊讶的快速辐射的结果。我们全面的时间校准的系统发育分析是基于从1200多个分类群中选择的最大系统发育覆盖率的数据-超过已知物种多样性的三分之一。该树提供了进化框架，用于(I)追踪全球历史生物地理学，(Ii)评估物种形成和灭绝的速度，以及(Iii)重建祖先特征状态和关键特征的转换，这些特征涉及适应性辐射并对多样性产生影响。这些特征包括飞行能力和相关结构的存在，如翅膀和眼窝，身体的大小和形状，颧骨附着结构和无性繁殖的能力。然而，对于一些没有转录组数据的关键进化谱系，我们的分析仍然产生了相互矛盾的系统发育假说。然而，所概述的研究问题的强有力的进化情景只能从可靠的系统发展史中推断出来。为了实现这一目标，我们将扩大我们的研究，并应用进一步的系统基因组学方法，该方法基于对200种精心挑选的树枝和树叶昆虫的选定外显子的靶标丰富。该项目的目的是显著提高我们对以前被忽视的昆虫群体中跨越空间和时间的适应性分支多样性的理解。

Stick and leaf insects, or Phasmatodea, are a mesodiverse lineage of large terrestrial herbivorous arthropods with predominantly tropical and subtropical distribution. They are usually nocturnal and exhibit remarkable forms of masquerade crypsis, imitating various parts of plants, such as twigs, bark and leaves to deceive visually hunting predators. Phasmatodea comprises ~3100 extant described species and serves as a model system to address important questions in evolutionary biology, such as speciation, evolution of asexuality, loss and regain of morphological traits, and clade diversification or, more precisely, repeated adaptive radiations in geographic isolation. Until recently, stick and leaf insects stood out as one of the last remaining insect orders without a robust higher-level phylogenetic hypothesis. Our latest molecular studies based on extensive transcriptomic and Sanger sequence data have now resolved the early evolution of these insects and corroborate the finding that the extant diversity is the result of a surprisingly recent rapid radiation. Our comprehensive temporally calibrated phylogenetic analysis is based on data selected for maximum phylogenetic coverage from over 1200 taxa – more than one third of the known species diversity. The tree provides the evolutionary framework for (i) tracing the global historical biogeography of phasmatodeans, (ii) assessing rates of speciation and extinction, and (iii) reconstructing ancestral character states and transformations of crucial traits that are involved in adaptive radiations and have an effect on diversification. These traits comprise flight capability and the presence of associated structures such as wings and ocelli, body size and form, tarsal attachment structures and the capacity for asexual reproduction. Yet, for some crucial evolutionary lineages of which no transcriptomic data is available our analyses still produce conflicting phylogenetic hypotheses. However, robust evolutionary scenarios for the outlined research questions can only be inferred from a reliable phylogeny. To reach this goal, we will expand our studies and apply a further phylogenomic approach, which is based on target enrichment of selected exons for 200 carefully chosen informative species of stick and leaf insects. The project is designed to significantly advance our understanding of adaptive clade diversification across space and time in a previously neglected group of insects.