Structural mouthpart interaction evolved already in the earliest lineages of insects

Abstract

In butterflies, bees, flies and true bugs specific mouthparts are in close contact or even fused to enable piercing, sucking or sponging of particular food sources. The common phenomenon behind these mouthpart types is a complex composed of several consecutive mouthparts which structurally interact during food uptake. The single mouthparts are thus only functional in conjunction with other adjacent mouthparts, which is fundamentally different to biting-chewing. It is, however, unclear when structural mouthpart interaction (SMI) evolved since this principle obviously occurred multiple times independently in several extant and extinct winged insect groups. Here, we report a new type of SMI in two of the earliest wingless hexapod lineagesDiplura and Collembola. We found that the mandible and maxilla interact with each other via an articulatory stud at the dorsal side of the maxillary stipes, and they are furthermore supported by structures of the hypopharynx and head capsule. These interactions are crucial stabilizing elements during food uptake. The presence of SMI in these ancestrally wingless insects, and its absence in those crustacean groups probably ancestral to insects, indicates that SMI is a groundplan apomorphy of insects. Our results thus contradict the currently established view of insect mouthpart evolution that biting-chewing mouthparts without any form of SMI are the ancestral configuration. Furthermore, SMIs occur in the earliest insects in a high anatomical variety. SMIs in stemgroup representatives of insects may have triggered efficient exploitation and fast adaptation to new terrestrial food sources much earlier than previously supposed.

Functional morphology of parasitic isopods: understanding morphological adaptations of attachment and feeding structures inNerocilaas a pre-requisite for reconstructing the evolution of Cymothoidae

“…The other should concern the mouthparts. Although it has been suggested that especially insects represent extreme cases of evolutionary derived mouthparts ( Blanke et al , 2015 ), we should also expect strong modification representing true adaptations in cymothoiids. In an evolutionary framework those representatives of Cymothoidae should be most interesting as they are considered to represent less strongly derived forms.…”

The Early Evolution of Biting–Chewing Performance in Hexapoda

“…Further distal at the caudal side of the mandible, there is an impression into which a stud of the stipes fits. This stud can articulate with the mandible during the simultaneous mouthpart movement of the mandibles and maxillae (Blanke et al 2015b). Further disto-medial is a mandibular hump which articulates with parts of the endoskeleton (Hofmann 1908;Koch 2001).…”

“…obs) suggest more forceful adduction capabilities in Diplura compared to Collembola. As in Collembola, the dipluran mandible shows several interactions with parts of the gnathal pouch, endoskeletal elements, or parts of the maxilla which are currently debated regarding their homology (Koch 2000(Koch , 2001Blanke et al 2015b;Blanke and Machida 2015;Koch 2016). The proximal part of the mandible is formed like a pointed tip and fits into a sclerotized part of the gnathal pouch.…”

Surface contrast enhancement of integumentary structures in X‐ray tomography

“…The acquisition of accurate three-dimensional (3D) morphological data is a crucial prerequisite for many taxonomic, functional, comparative and developmental studies (Jones et al 2009;Akkari et al 2015;Blanke et al 2015;Parapar et al 2017;Schachner et al 2017). Micro-computed tomography (lCT) accordingly has developed into a standard technique in biology for capturing internal and external information in 3D (Holdsworth & Thornton, 2002).…”