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Functional transformation series and the evolutionary origin of novel forms: evidence from a remarkable termite defensive organ

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Title: Functional transformation series and the evolutionary origin of novel forms: evidence from a remarkable termite defensive organ
Authors: Kaji, Tomonari Browse this author
Keiler, Jonas Browse this author
Bourguignon, Thomas Browse this author
Miura, Toru Browse this author →KAKEN DB
Issue Date: 2016
Publisher: Wiley-Blackwell
Journal Title: Evolution and development
Volume: 18
Issue: 2
Start Page: 78
End Page: 88
Publisher DOI: 10.1111/ede.12179
PMID: 26766508
Abstract: The origins of evolutionary novelties are often deeply puzzling. They are generally associated with new functions that were absent in ancestors. The new functional configuration should arise via intermediate stages without any loss of function or impediment to the whole organism during the transitions. Therefore, understanding of the functional configurations of transitional states can shed light on how novel forms arise. Here we infer the evolutionary origin of a highly specialized termite defensive organ "nasus" where different functions overlap in different structural configurations at intermediate evolutionary stages to ensure that each phase is functional. Soldiers of a nasutitermitine termite use reconfigured mandibular muscles to squirt a viscous secretion from a nozzle-like head projection (the nasus). This contrasts sharply with the primitive defensive strategy where mandibles are used to bite. MicroCT observations of soldiers of Nasutitermes takasagoensis and of species with the ancestral state (Hodotermopsis sjostedti, Embiratermes neotenicus) revealed three different yet fully functional configurations in the transition from ancestral to novel state: (i) elevated hydrostatic pressure induced by contraction of mandibular muscles when biting gently oozes secretion from a gland; (ii) direct pressure on an enlarged gland arises from expansion of the mandibular muscles when biting; (iii) squirting in a piston-like manner by an inflated gland enveloped by highly modified mandibular muscles. Even a structure as exotic as the nasus therefore appears to have evolved with no loss of function at any stage. Such a functional approach, holds much promise for understanding the evolutionary origin of seemingly preposterous novel forms.
Rights: This is the peer reviewed version of the following article:, which has been published in final form at 10.1111/ede.12179. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
Type: article (author version)
Appears in Collections:環境科学院・地球環境科学研究院 (Graduate School of Environmental Science / Faculty of Environmental Earth Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 三浦 徹

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