Data from: Eversion and withdrawal of an intromittent organ before sexual maturation prepares male beetles for copulation

Some species of criocerine beetles have a hyper-elongated part of the intromittent organ called a flagellum. In resting position, the flagellum is stored in a specialized internal sac in the intromittent organ. This specialized state of the flagellum and internal sac is indispensable during copulation for flagellar insertion into the female spermathecal duct for sperm transfer. However, the morphogenesis of the flagellum does not generate the active state of the flagellum; rather, the flagellum is generated in an inactive and completely coiled state. After eclosion, males of Lema coronata evert and withdraw the internal sac multiple times before sexual maturation, without mounting a female. This behavior serves to uncoil the flagellum and guide it into the active state with the aid of surface structures on the internal sac. A closely related species, Lema dilecta, also has a long flagellum and undergoes the same behavior to place the flagellum in the active position. However, some other species of criocerine beetles with much shorter flagella can attain the active state without exhibiting this behavior. Based on a previously proposed phylogenetic tree, we discuss the evolutionary history of the hyper-elongation of the flagellum and associated behavior.部分沟胫叶甲亚科（Criocerinae）甲虫的交配器官（intromittent organ）带有一段被称为鞭毛（flagellum）的极度延长结构。静息状态下，该鞭毛收纳于交配器官内的特化内囊（internal sac）中。这种鞭毛与内囊的特化状态，在交配过程中对鞭毛插入雌性受精囊管（spermathecal duct）以完成精子传输（sperm transfer）不可或缺。然而，鞭毛的形态发生（morphogenesis）并不会直接产生活性状态的鞭毛，而是以无活性且完全卷曲的状态完成生成。冠毛守瓜（Lema coronata）的雄性个体在羽化（eclosion）后、达到性成熟（sexual maturation）前，会多次外翻并收回内囊，且未发生攀附雌虫（mounting a female）的行为。该行为可借助内囊表面的结构解开鞭毛卷曲，使其转变为活性状态。近缘物种双斑守瓜（Lema dilecta）同样具有长鞭毛，且会通过同类行为将鞭毛调整至活性位置。但另有部分鞭毛极短的沟胫叶甲亚科甲虫，无需展现此类行为即可使鞭毛进入活性状态。基于此前提出的系统发育树（phylogenetic tree），本文探讨了鞭毛极度延长现象及其伴随行为的演化历程。