Water balance and osmoregulation in weevil larvae (Coleoptera: Curculionidae: Brachycerinae) from three different habitats on sub-antarctic Marion Island

Summary

Ectemnorhinine weevils are the most successful group of beetles in the sub-antarctic region, which is undoubtedly due partly to the ability of these weevils to tolerate a wide variety of abiotic conditions. In the laboratory, larvae of three species of ectemnorhinine weevils, from three diverse habitats on Marion Island, were exposed to desiccating conditions and to water of two different salinities to elucidate the physiological basis of their ability to tolerate various abiotic conditions. In the desiccation experiment, the supralittoral Palirhoeus eatoni (C.O. Warerhouse) larvae lost water faster than larvae of the “inland” epilithic species, Bothrometopus randi Jeannel, and could not fully replenish lost water by drinking. However, larvae of P. eatoni showed greater osmoregulatory ability than the latter species when exposed to hypoand hypcrosmotic conditions. The detritus-dwelling larvae of Ectemnorhinus similis C.O. Waterhouse showed rates of water loss similar to those of the B. randi larvae in the desiccation experiment, but took longer to replace lost water by drinking. All three species showed little change in haemolyrnph water activity despite approximately 28% reduction in water content during desiccation. These physiological responses seem to reflect an equilibrium between the species and their environments which may be considered an adaptation (sensu Coddington 1988) in the case of B. randi, but which appears to be a result of phylogenetic constraint in E. similis. P. eatoni's status as a “marine” weevil is confirmed.