Insect mandibles—comparative mechanical properties and links with metal incorporation
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A number of arthropod taxa contain metals in their mandibles (jaws), such as zinc, manganese, iron, and calcium. The occurrence of zinc and its co-located halogen chlorine have been studied in relation to the mechanical properties and shown to be linked in a direct fashion with increasing concentration. Hardness along with elastic modulus (stiffness) has also been linked to zinc and halogen concentration in some marine polychaete worms. The metal appears to be incorporated within the biological matrix, possibly bonding with proteins. However, the comparative advantage of metal inclusion has not been tested. It is possible that without metals, alternative mechanisms are used to achieve hardness of equal value in similar ‘tools’ such as mandibles. This question has direct bearing on the significance of metal hardening. In the present article, we compare across mandibles from six termite species, including samples with major zinc concentration, minor manganese, and no metals. Nanoindentation, electron microscopy, and electron microanalysis are used to assess metal concentration, form, and mechanical properties. The data demonstrate that termite mandibles lacking metals when fully developed have lower values for hardness and elastic modulus. Zinc is linked to a relative 20% increase in hardness when compared with mandibles devoid of metals. The similar transition metal, manganese, found in minor concentrations, is not linked to any significant increase in these mechanical properties. This raises the question of the function of manganese, which is as commonly found in insect mandibles as zinc and often located in the same mandibles.
KeywordsCoptotermes Mastotermes Cryptotermes Isoptera Young’s modulus
We gratefully acknowledge supply of some termite samples from Dr Michael K. Rust, Department of Entomology, UCR, Riverside, USA; Dr B. Peters, Queensland Department of Primary Industries and Fisheries; and Mrs Rachel Hancock Narangbar, Queensland, Australia. HH is grateful for experimental assistance by Mr. B. L. Wang at the University of Queensland, Brisbane, Australia. The experiments comply with the current laws of the country in which they were performed.
- Fontaine AR, Olsen N, Ring RA, Singla CL (1991) Cuticular metal hardening of mouthparts and claws of some forest insects of British Columbia. J Entomol Soc Brit Columbia 88:45–55Google Scholar
- Goldstein J, Newbury DE, David C, Joy DC, Lyman CE, Echlin P, Lifshin E, Sawyer LC, Michael JR (2003) Scanning electron microscopy and x-ray micronalysis, 3rd edn. Kluwer, New YorkGoogle Scholar
- Hillerton JE, Vincent JFV (1982) The specific location of zinc in insect mandibles. J Exp Biol 101:333–336Google Scholar
- Hillerton JE, Reynolds SE, Vincent JFV (1982) On the indentation hardness of insect cuticle. J Exp Biol 96:45–52Google Scholar
- Newbury DE (1991) Standardless quantitative electron-excited x-ray microanalysis by energy-dispersive spectrometry: what is its proper role. Microsc Microanal 4:585–597Google Scholar
- Schofield RMS (2001) Metals in cuticular structures. In: Brownell P, Polis G (eds) Scorpion biology and research. Oxford University Press, Oxford, pp 234–256Google Scholar
- Schofield R, Lefevre H (1989) High concentrations of zinc in the fangs and manganese in the teeth of spiders. J Exp Biol 144:577–581Google Scholar
- Yoshimura T, Kagemori N, Sugiyama J, Kawai S, Sera K, Futatsugawa S, Yukawa M, Imazeki H (2005) Elemental analysis of worker mandibles of Coptotermes formosanus (Isoptera: Rhinotermitidae). Sociobiology 45:255–259Google Scholar