A comparative study of heat production and thermoregulation in two sympatric gerbils (gerbillus gerbillus and g. pyramidum)

Two species of gerbils, Gerbillus gerbillus and G. pyramidum, coexist in the dunes of the Northern Negev. While the distribution in Israel of G. pyramidum is restricted to the Coastal Plain dunes (as far north as the Yarkon River) and Northern Negev dunes, G. gerbillus is also distributed in the dunes of the Arava Rift Valley and Makhtesh Ramon. central Negev Highlands. A comparative study of heat production, thermoregulation, and daily body temperature rhythm was carried out on individuals of both species that had been acclimated to an ambient temperature (T.) of 28 °C and a photoperiod regime of 12L:12D. The results reveal that G. gerbillus is better adapted than G. pyramidum to cope with extremely hot habitats due to three characteristics: (1) its lower critical point is higher, (2) it can increase its body temperature within the thermoneutral zone, and (3) its minimal overall thermal conductance (C) is higher. Nonshivering thermogenesis (NST), measured as a response to a noradrenalin injection, is higher in G. gerbillus than in G. pyramidum. The greater ability of G. gerbillus to increase NST may be a compensation for its high C values. The daily rhythm of body temperature, (T b) has a different pattern in the two species studied. As both species are nocturnal, it is suggested that during the dark phase G. pyramidum has periods of inactivity while G. gerbillus can remain active throughout the night.