Embryological evidence substantiates the subcoxal theory on the origin of pleuron in insects

Yuta Mashimo,Ryuichiro Machida

doi:10.1038/s41598-017-12728-2

Abstract

The lateral body plate pleuron is a significant structure in insects that contributes to the development and elaboration of wings and limbs (appendages). Although the pleuron is thought to originate from the proximal-most appendicular segment, the subcoxa, details remain unclear, and the morphological boundary between the dorsal body plate tergum and appendage (BTA) has not been clearly specified. Employing low-vacuum scanning electron microscopy (SEM) and the nano-suit method for SEM, we followed, in detail, the development of the thoracic segments of the two-spotted cricket Gryllus bimaculatus and succeeded in clearly defining the BTA. This study demonstrates the subcoxal origin of the pleuron, suggests the tergal origin of spiracles, and reveals that the wing proper originates exclusively from the tergum, whereas the wing hinge and direct muscles may be appendicular in origin, suggesting the dual origin (i.e., tergal plus appendicular origin) of wings.

Highlights

Insects are the most successful group of animals, with one million known species at present, and their megadiversity has attracted researchers’ attention
Are spiracles derived from the subcoxa or are they tergal in origin? Such confusion may be due to the lack of reliable embryological evidence, as previously described by Matsuda9 “It is clear ... that workers, including the present writer, have tended to indulge in speculations, extending and modifying the subcoxal theory, without really looking for reliable developmental facts in support.”
We followed the detailed formation of the pleuron throughout development in the two-spotted cricket Gryllus bimaculatus to provide a sound basis for discussions on the subcoxal theory and related issues

Summary

Introduction

Insects are the most successful group of animals, with one million known species at present, and their megadiversity has attracted researchers’ attention. This study reveals that the true pleural suture forms during the final developmental stage when the nymphal cuticle is secreted.

Results

Conclusion