Integumental buffering in an alpine grasshopper

Authors

  • Timothy C. Hawes

    Corresponding author
    1. Asian University, Banglamung, Thailand
    2. Department of Zoology, University of Otago, Dunedin, New Zealand
    • Correspondence: Dr Timothy Hawes, Asian University, Banglamung, Chonburi 20260, Thailand. Tel.: +66 38 253 700; e-mail: timothyhawes@hotmail.com

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Abstract

In most freeze tolerant insects, the tolerance of the formation of internal body ice is arrived at by a two-step process: (S-1) a period of supercooling of the body fluids that is followed by (S-2) the freezing event. To date, the necessity of S-1 remains to be questioned seriously. The present study reports evidence that S-1 may be almost completely substituted or superseded in large-bodied insects by integumental buffering. In the New Zealand alpine grasshopper Sigaus australis Hutton, there is a substantial difference between external and body core temperatures at the moment when internal ice nucleation is registered. Using the invagination of the pleural suture as a nondetrimental proxy for the core and the sclerotized postnotum as a measure of surface temperature, comparisons of the temperature of crystallization (Tc) show a highly significant difference (P < 0.001; Kolmogorov–Smirnov test). Proxy core Tc values are in the range from −0.11 to −4.78 °C compared with the range of −4.1 to −14.2 °C in external proxy Tc values. Although a thermal lag may sometimes be quietly assumed in measurements of Tc, a temperature differential of this size (approximately 6 °C), which is equivalent to the entire supercooling potential of many freeze tolerant insects, is of particular note. These findings have wider application to other large-bodied insects with similarly well-developed integumental protection.

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