Integumental buffering in an alpine grasshopper

Abstract

AbstractIn 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 The present study reports evidence that S‐1 may be almost completely substituted or superseded in large‐bodied insects by integumental buffering.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.