Abstract:
Thermoregulation and energy metabolism of the pouched mouse (Saccostomus campestris) was studied to establish how this species copes with different climatic conditions throughout its broad distribution in southern Africa. Nine burrows excavated at four localities in South Africa each contained a single nesting chamber, at least 200mm below ground, in which variation in temperature was minimal. Not all of the burrows contained bedding material or caches of food and there was no direct effect of photoperiod, temperature or locality on nest-building or food-hoarding behaviour in captivity which indicated that these activities do not respond to seasonal or geographical changes in climate. However, males and females were observed collecting seeds throughout the year in the wild, presumably to minimise the amount of time spent foraging outside their burrows where thermoregulatory costs and predation risks are higher. There was a multiple correlation between body size and a variety of climatic factors which was largely due to a positive correlation with rainfall. These geographical differences in body size appeared to be heritable and might represent an adaptation to reduce the energy requirements of pouched mice living in arid/semi-arid environments where food availability is low. Although there were significant differences in energy metabolism between pouched mice from nine localities, their resting metabolism was not correlated to local climatic conditions, possibly because they do not experience geographical variation in temperature when they are at rest inside their nests. Nevertheless, they do experience some seasonal and geographical differences in ambient temperatures because they are active above ground at night when cold temperatures necessitate an increase in thermoregulatory heat production. This might explain why pouched mice display seasonal changes in heat production while animals from cooler localities exhibit a higher capacity for heat production than those from warmer areas. The significance of a correlation between locality temperature and the duration of spontaneous daily torpor remains unclear, because torpor was only observed at temperatures below those usually recorded within their burrows. It therefore appears that pouched mice are able to survive under a wide variety of climatic conditions because their semi-fossorial lifestyle allows them to avoid most unfavourable temperatures. At the same time they also display ecotypic differences in body size, heat production and torpor which help them cope with geographical variation in food availability and nocturnal temperatures which they cannot escape.
