Evolution of proboscis musculature in Lepidoptera

Abstract

Abstract. The suctorial proboscis of adult Lepidoptera represents a key morphological innovation that enabled these insects to gain access to new food sources. In the ancestral condition of the lepidopteran proboscis only extrinsic galeal muscles are present in the basal joint region. The presence of additional muscles (i.e., the intrinsic galeal muscles) is regarded as a morphological novelty of the Myoglossata that evolved after the galeae were modified to form suctorial mouthparts. The present comparative investigation of the galeal anatomy in representatives of all major taxa revealed that the intrinsic galeal muscles are derived from the basal galeal musculature. In the examined Neopseustoidea, Exoporia, Nepticuloidea, Incurvarioidea, and Tischerioidea all galeal muscles have their origin in the stipes-galea joint and/or in the proximal region of the galea. Two muscle units form the basal galeal musculature of the joint region and one to three longitudinal muscles extend into the galea lumen. Multiple intrinsic galeal muscles, of which both the origin and attachment sites are markedly distal from the basal joint region are regarded as a groundplan autapomorphy of the Ditrysia. Some slightly oblique muscles may occur along the lateral wall; these were lost in species with extremely slender galeae. In most investigated Obtectomera two series of intrinsic galeal muscles occur; these are the (1) oblique lateral intrinsic galeal muscles, which are arranged one upon the other along the lateral proboscis wall and (2) the median intrinsic galeal muscles, which run more or less longitudinally along the ventral wall. Oblique muscle arrangement probably evolved in concert with the functional demands of a long lepidopteran proboscis. A likely evolutionary pathway to account for the serial arrangement of galeal muscles is propo sed.

A molecular phylogeny for the oldest (nonditrysian) lineages of extant Lepidoptera, with implications for classification, comparative morphology and life‐history evolution

“…The monophyly of the latter, the ‘tongue moths’, has never been seriously questioned, and it is supported by an impressive syndrome of structural specializations of the adult head. The transformation of the generalized galeae into the coilable proboscis/tongue initially took place with surprisingly little modification of the maxillary musculature (Kristensen, ; Krenn & Kristensen, ). In contrast, the physical properties of the proboscis wall (with cuticle elasticity enabling nonmuscle‐aided recoil), as well as details of its specialized surface configuration such as the linking mechanism (Krenn & Kristensen, ; Kristensen et al , ), have in eriocraniids, acanthopteroctetids and lophocoronids a remarkable similarity, which surely reflects the acquisition of these specializations in the stem lineage of Glossata (node 8).…”

Adaptations for nectar-feeding in the mouthparts of long-proboscid flies (Nemestrinidae: Prosoeca)

“…Walters, Albert & Zacharuk (1998) described similar sensillae in butterflies as bimodal contact‐chemo‐mechano sensillae. A great morphological variety of sensilla have evolved in context with nectar‐feeding in Lepidoptera (Krenn & Kristensen, 2002; Krenn, 2010). Such a diversity of sensilla is generally not known from dipteran proboscides and, similarly, the sensilla equipment of the labella in Prosoeca was inconspicuous compared to butterflies.…”

Structure of the lepidopteran proboscis in relation to feeding guild

“…Studies of the lepidopteran proboscis have produced a mix of functional, structural, and positional terminology (Eastham and Eassa, ; Hepburn, ; Kingsolver and Daniel, ; Krenn, ; Walters et al, ; Krenn and Mühlberger, ; Krenn and Kristensen, ; Petr and Stewart, ; Zaspel et al, ; Monaenkova et al, ; Lehnert et al, ). We, therefore, explicitly define the terms that we use.…”