Rafting in Antarctic Collembola

Darwin was an early exponent of the importance of 'occasional means of dispersal' in accounting for the present-day distribution of plants and animals. This study examined the implications of capture on the water surface of meltwater and seawater for the local and long-range dispersal of Antarctic springtails. Individuals of the maritime Antarctic collembolan Cryptopygus antarcticus, were floated on tap water and seawater at 0, 5 and 10 degrees C. LT(50)s on seawater were 34 (10 degrees C), 65 (5 degrees C) and 75 (0 degrees C) days. On tap water, LT(50)s were 69 (10 degrees C), 126 (5 degrees C) and 239 (0 degrees C) days. Less than 20% escaped from the water surface. A significantly greater proportion of springtails moulted on tap water and viable offspring were produced on both tap water and seawater. Comparison across treatments of survival of moulting and non-moulting individuals found significantly greater survival in moulting animals for three of the treatment combinations. It is suggested that moult exuviae facilitate survival on the water film through the simultaneous provision of a flotation aid and a source of nourishment - that is, an 'edible raft'. A separate experiment measuring changes in haemolymph osmolality over time on tap water and seawater at 2 and 5 degrees C found significant differences in all treatments. Causes of mortality are discussed in relation to osmoregulatory failure and starvation.