Adaptive variations in heat production within Gerbils (genus Gerbillus) from different habitats

Species of the genus Gerbillus are very common among the rodent fauna inhabiting arid zones and dune habitats in the palaearctic region. In Israel G. nanus is distributed in extreme arid areas, while G. allenbyi is common in coastal plain dune habitats, of mesic and semi-arid areas. Therefore, their distribution pattern is considered allopatric. Heat production, estimated by the oxygen consumption (Vo2), and body temperature (T_b) at various ambient temperatures were measured in both gerbils. The thermoneutral zone for G. allenbyi is between T_a=28-35° C ( {Mathematical expression}T_b=36.3-38.3° C) and for G. nanus is at T_a=33±1° C ( {Mathematical expression}, T_b=38.8° C). The {Mathematical expression} values at thermoneutrality are 75.7% and 50.6% respectively of the calculated values for rodents with a mean body weight of 35.3 g and 28.4 g. Nonshivering thermogenesis (NST) was measured in both species as the maximal response to an injection of noradrenaline (2.0 mg/Kg s.c.). NST magnitude was the same for both species. The results show that both gerbils are adapted to arid environments. The difference in the thermoneutral zones of the two species is discussed in terms of its adaptive nature.