Haemolymph osmolality and thermal hysteresis activity in 17 species of arthropods from sub-Antarctic Marion Island

Abstract.

In this paper, we present measurements of haemolymph osmolality for individuals from 17 species of arthropods on Marion Island, including a mite, a spider, Collembola, Psocoptera, Coleoptera, Diptera and Lepidoptera. This is the largest such survey for a Southern Hemisphere habitat. We also screened these species for thermal hysteresis activity, and show that the lepidopteran Embryonopsis halticella has a haemolymph thermal hysteresis agent that imparts approximately 0.2°C of thermal hysteresis. This low level leads us to conclude that, in this mild habitat, it may have a role in preventing nucleation, rather than directly acting to depress the freezing point of whole caterpillars. Haemolymph osmolalities were generally concordant with published values for the groups examined. With the exception of Isotomurus cd. palustris acclimated at 5 and 10 °C, we found no statistical evidence of acclimation altering the haemolymph osmolality for any of the arthropods investigated.