Desiccation resistance in dung-feeding Scarabaeinae

Abstract

The desiccation resistance of seventeen species of southern African dung-feeding Scarabaeinae is investigated. The species occur in a wide range of habitats including the Namib desert, savanna, grassland and valley bushfeld. It was found that the three apterous species, two from the Namib desert and one from Addo, have the highest resistance to desiccation. The principal mechanism promoting desiccation resistance is a reduced rate of water loss. Other factors that influence desiccation resistance are large body size, diel activity and the behavioural ecology of the species; telecoprids are more resistant to desiccation than the para- and endocoprids. The analyses were repeated excluding the apterous species. This indicated that habitat has an important influence on desiccation resistance. Of the macropterous species, two small species, one from the Namib desert and the other from the Orange Free State grassland, are the most resistant to desiccation. The principal mechanism promoting desiccation resistance is an increased tolerance to low body water levels. The resistances of the remaining species are influenced by their size, activity periods and ecological strategies. Experiments to investigate osmoregulatory ability and the influence of temperature on water balance were done on four selected species - an apterous and a macropterous species from the desert biome and a similar pair from the savanna biome. Based on the thermal biology of the species it was found that their resistances to desiccation are optimal at the temperatures at which they are active in the field, and that the apterous species from both biomes are the most resistant to desiccation. The savanna species recover water faster than the desert species, but the desert species have a stable source of water in the moist layer beneath the dune surface. The macropterous species are able to produce water by metabolising lipids, but they have very poor haemolymph osmoregulatory capabilities. The apterous species in contrast are less able to produce water by metabolising lipids but they have excellent haemolymph osmoregulatory capabilities. These adaptations are closely related to the pedestrian and flying modes of foraging employed by the beetles.