On Dorsal Prothoracic Appendages in Treehoppers (Hemiptera: Membracidae) and the Nature of Morphological Evidence

Abstract

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.

A hymenopterists’ guide to the Hymenoptera Anatomy Ontology: utility, clarification, and future directions

“…Biodiversity, host-parasite biology, collections digitization, genomics, ecology, evolutionary developmental biology (evo-devo), invasive species evaluation, agro-ecosystem management and biological control (to name just a few) as well as those aspects of society impacted by these all rely on the correct interpretation of anatomical structures (e.g., Mikó et al 2012). The core mechanism by which one can reference the HAO, URIs, is implementable now via simple URI tables.…”

“…During its short life, the potential utility of the HAO has already begun to emerge (e.g., Mikó et al 2012, Johnson and Musetti 2011, Kawada 2011, Talamas et al 2011, Vilhelmsen et al 2010, Mikó and Deans 2009, Deans and Kawada 2008, Yoder 2007. Here we attempt to clarify recurrent issues, with the goal of facilitating continued adoption of the HAO.…”

“…Here we introduce an alternative, table-based format that facilitates reference to existing anatomical concepts within the HAO. Examples exist in Johnson and Musetti 2011, Mikó et al 2012, and Talamas et al 2011. In its simplest format the table only requires two columns: a term and a URI.…”

Evolutionary phenomics and the emerging enlightenment of arthropod systematics

“…A simple solution is to append one's publication with a glossary of terms, explicitly defined using genus differentia (Smith 2005). Some insect systematists, Talamas et al (2011) and Mikó et al (2012) for example, have started doing this in the form of a table that also includes links (Uniform Resource Identifiers or URIs) to anatomical concepts in the Hymenoptera Anatomy Ontology (Yoder et al 2010) and, in some cases, to phenotypic qualities in the Phenotype Quality Ontology (PATO; Mungall et al 2010) (see Seltmann et al 2012 for a description of the process).…”

“…Since dissections are inherently dissociative (not inevitably destructive), visualisation and imaging of the specimens are highly recommended in different phases of the mining process. Vilhelmsen et al (2010) and Mikó et al (2007Mikó et al ( , 2012, provide examples of how dissections and subsequent observations of internal soft-tissue features can inform character concepts.…”