Insect Museum, Department of Entomology, North Carolina State University, Raleigh, North Carolina, United States of America.
PLoS One. 2012;7(1):e30137. doi: 10.1371/journal.pone.0030137. Epub 2012 Jan 17.
A spectacular hypothesis was published recently, which suggested that the "helmet" (a dorsal thoracic sclerite that obscures most of the body) of treehoppers (Insecta: Hemiptera: Membracidae) is connected to the 1st thoracic segment (T1; prothorax) via a jointed articulation and therefore was a true appendage. Furthermore, the "helmet" was interpreted to share multiple characteristics with wings, which in extant pterygote insects are present only on the 2nd (T2) and 3rd (T3) thoracic segments. In this context, the "helmet" could be considered an evolutionary novelty. Although multiple lines of morphological evidence putatively supported the "helmet"-wing homology, the relationship of the "helmet" to other thoracic sclerites and muscles remained unclear. Our observations of exemplar thoraces of 10 hemipteran families reveal multiple misinterpretations relevant to the "helmet"-wing homology hypothesis as originally conceived: 1) the "helmet" actually represents T1 (excluding the fore legs); 2) the "T1 tergum" is actually the anterior dorsal area of T2; 3) the putative articulation between the "helmet" and T1 is actually the articulation between T1 and T2. We conclude that there is no dorsal, articulated appendage on the membracid T1. Although the posterior, flattened, cuticular evagination (PFE) of the membracid T1 does share structural and genetic attributes with wings, the PFE is actually widely distributed across Hemiptera. Hence, the presence of this structure in Membracidae is not an evolutionary novelty for this clade. We discuss this new interpretation of the membracid T1 and the challenges of interpreting and representing morphological data more broadly. We acknowledge that the lack of data standards for morphology is a contributing factor to misinterpreted results and offer an example for how one can reduce ambiguity in morphology by referencing anatomical concepts in published ontologies.
最近发表了一个引人注目的假说，该假说表明叶蝉的“头盔”（一个覆盖身体大部分的背部胸板）通过关节连接到第一胸节（T1；前胸），因此是真正的附肢。此外，“头盔”被解释为与翅膀具有多个共同特征，而在现存的翼节昆虫中，翅膀仅存在于第二（T2）和第三（T3）胸节。在这种情况下，“头盔”可以被认为是一种进化上的新奇事物。尽管有多种形态学证据支持“头盔”-翅膀同源假说，但“头盔”与其他胸板和肌肉的关系仍不清楚。我们对 10 个半翅目科的典型胸部的观察揭示了与最初设想的“头盔”-翅膀同源假说相关的多种误解：1）“头盔”实际上代表 T1（不包括前腿）；2）“T1 背板”实际上是 T2 的前背部区域；3）“头盔”和 T1 之间的假定关节实际上是 T1 和 T2 之间的关节。我们的结论是，在叶蝉科中，T1 上没有背部、关节的附肢。尽管叶蝉 T1 的后扁平、角质化外突（PFE）与翅膀具有结构和遗传属性，但 PFE 在半翅目昆虫中广泛分布。因此，该结构在叶蝉科中的存在并不是该分支的进化新奇事物。我们讨论了叶蝉 T1 的这种新解释以及更广泛地解释和表示形态数据所面临的挑战。我们承认缺乏形态学数据标准是导致结果误解的一个因素，并提供了一个如何通过参考已发表本体论中的解剖学概念来减少形态学歧义的示例。
