Completely engaged three-dimensional mandibular gear-like structures in the adult horned beetles: reconsideration of bark-carving behaviors (Coleoptera, Scarabaeidae, Dynastinae)

By

Ichiishi, Wataru
Shimada, Shinpei
Motobayashi, Takashi
Abe, Hiroaki

Type

Article

Date of Publication

2019

Original Publication

ZooKeys

Volume

813

Pages

89--110

Subjects

beetle bark-carving behavior gear-

Contributed by

Pensoft Publishers

Language

English

Published by

Sofia, Bulgaria Pensoft Publishers

Identifiers

DOI: https://doi.org/10.3897/zookeys.813.29236

 

Abstract

Adult horned beetles (Coleoptera, Scarabaeidae, Dynastinae) such asTrypoxylusdichotomus(Linnaeus, 1771) exhibit bark-carving behaviors to feed on tree sap, in part by using small projections of the clypeus. However, in the present experiments, adult horned beetles (T.dichotomusandDynasteshercules(Linnaeus, 1758)) used their mandibles and not the projections of the clypeus to carve bark. Our findings show the presence of completely engaged mandibular interlocking, gear-like surface structures in molar areas that guide mandible opening and closure, and lead to completely synchronous movements of adult horned beetle mandibles. Three-dimensional shapes of these mandibular gear-like structures are complex and remained in contact after the death of a beetle. Moreover, adult horned beetles often performed bark-carving behaviors using only the mandible of one side, suggesting that the primary role of the mandibular gear-like structure is to prevent breakage of the mandible by transmitting load from one mandible to the other. Among the 22 Dynastinae and 16 other beetle species examined (not Dynastinae), the gear-like structure was found in all the Dynastinae species and in no other species.