The significance of the moult cycle to cold tolerance in the Antarctic collembolan Cryptopygus antarcticus

Research into the ecophysiology of arthropod cold tolerance has largely focussed on those parts of the year and/or the life cycle in which cold stress is most likely to be experienced, resulting in an emphasis on studies of the preparation for and survival in the over-wintering state. However, the non-feeding stage of the moult cycle also gives rise to a period of increased cold hardiness in some microarthropods and, as a consequence, a proportion of the field population is cold tolerant even during the summer active period. In the case of the common Antarctic springtail Cryptopygus antarcticus, the proportion of time spent in this non-feeding stage is extended disproportionately relative to the feeding stage as temperature is reduced. As a result, the proportion of the population in a cold tolerant state, with low supercooling points (SCPs), increases at lower temperatures. We found that, at 5 degrees C, about 37% of the population are involved in ecdysis and exhibit low SCPs. At 2 degrees C this figure increased to 50% and, at 0 degrees C, we estimate that 80% of the population will have increased cold hardiness as a result of a prolonged non-feeding, premoult period. Thus, as part of the suite of life history and ecophysiological features that enable this Antarctic springtail to survive in its hostile environment, it appears that it can take advantage of and extend the use of a pre-existing characteristic inherent within the moulting cycle.