Thermal biology of the fossorial rodent Ctenomys fulvus from the Atacama desert, northern Chile

The Andean tuco-tuco, Ctenomys fulvus (Rodentia: Ctenomyidae) inhabits one of the most arid regions of the world, the Salar de Atacama, Northeast of A ntofagasta, Chile (23 degrees 17'06 "S, 68 degrees 05'43 "W; 2.240 m.a.s.l) . We found that a stable microclimate in burrows, a low evaporative water l oss (EWL), and a diet of roots (59% water content) are the main factors tha t permit the survival of this fossorial species in harsh desert conditions. Large circadian variation in T-a was observed above ground. Daily DeltaT(a ) (T-a max - T-a min) = 37.9 +/- 0.2 degreesC in summer and in winter. In c ontrast, circadian variation of T-a inside the burrows was only 5.8 +/- 0.5 degreesC in the same seasons. Relative humidity (RH) was 1.9-3.1% during t he day, increasing to maximum values of 27% at night and early morning. Ins ide the burrows RH was higher and quite stable, ranging between 53.1 and 65 %, independent of the time of day and season. EWL, measured between 10 and 25 degreesC, was low (1.26 mg/g h), and a moderate increase of 13-20% was o bserved at higher temperatures. The low EWL may prevent dehydration. Howeve r, because of the low heat loss capability, animals became hyperthermic (0. 8-1.6 degreesC) in dry air at T-a = 30-35 degreesC. As T-a during afternoon normally exceeded 35 degreesC, the microclimate of burrows provided the on ly way to avoid the lethal effects of hyperthermia. (C) 2000 Elsevier Scien ce Ltd. All rights reserved.