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12 semble diesel fuel . Unfortunately, the I In the light of the rapid progress made The lesson here, however, is that the named species does not grow in cooler within the past five years in eukaryotic thermal conditions under which our climates. Calvin12 has suggested that the gene expression, and indeed in the en­ present thermoregulatory taxonomy has genes for biosynthesis of sesquiterpenes gineering of entire metabolic pathways been developed are irrelevant to these 13 from Copaifera be transferred to species in prokaryotic organisms , these semi­ animals, because they never ( or hardly such as Euphorbia lathyris, a fuel­ natural alternatives to semiconductor­ ever) experience ambient temperatures 4 producing plant which can be grown in based solar cells could appear in the not below 28 °C in their burrows . So arid regions of the United States. Like­ so distant future. D althou~h they are technically poikilo­ wise, one might imagine that eukaryotic therms , their body temperature never algae could be modified to produce more Thomas E. Mal/ouk is in the Department of falls below 28 °C. hydrogenase, and to bind CO2 less effec­ Chemistry and Biochemistry, University of The naked mole rat therefore provides tively at normal partial pressures. Texas, Austin, Texas 78712, USA. an . exception to the rule that resting mammals have an effective system for 1. O'Regan, B. & Gratzel, M. Nature 353, 737-740 8. Roffia, S. et al. J. electroanal. Chem. 302, 157-171 endothermic thermoregulation. How­ (1991). (1991). 2. Fujishima, A. & Honda, K. Nature 238, 37-38 (1972). 9. Hashimoto, K., Hiramoto, M. & Sakata, T. Chem. Phys. ever, it is not simply a degenerate 3. Abrahams, I. L. et al. New J. Chem. 11, 157 (1987). Lett. 148, 215 220 (1988). mammal in this respect, but has prob­ 4. Gerischer, H. Photochem. Photobiol. 16, 243 (1972). 10. Bolton, J. R.. Strickler, S. J. & Connolly, J. S. Nature ably sacrificed a redundant physiology 5. Spitler, M. T. & Calvin, M. J. chem. Phys. 66, 4294- 315. 495-500 (1985). 4305 (1977). 11. Greenbaum, E. in Photochemical Energy Conversion for some other adaptive benefit. It may 6. Spitler, M. T. & Parkinson, B. A. Langmuir 2, 549-553 (eds Norris, J. R. Jr & Meisel, D.) 184--195 (Elsevier, be that reduced metabolic rates lower (1986). New York, 1989). 7. Amadelli, R., Argazzi, R., Bignozzi. C. A. & Scandola, F. 12. Calvin, M. J. chem. Ed. 64, 335-336 (1987). the possibility of overheating in an en­ J. Am. chem. Soc. 112, 7099-7103 (1990). 13. Bailey, J. E. Science 252, 1668-1675 (1991). closed and humid burrow. Or perhaps PHYSIOLOGY------~ the energetic savings on abandoning en­ dothermy are crucial to balancing the energy budget in a food-scarce habitat. Cold facts and naked truth Either way these animals offer new opportunities for the study of hypother­ Andrew R. Cossins mia in mammals because, unlike every other mammal, body temperature can be THAT curious mammal, the naked mole developed subcutaneous fat layer. The set at any desired level, at least in the 1 rat, subject of a recent biography , is skin is loosely folded over the surface short term, as it can in poikilotherms. even odder than it had seemed. Writinf and possesses only a few whiskers, main­ This convenience may be also appre­ in the Journal of Thermal Biology , ly around the snout. It lacks sweat ciated in studies of cold preservation Buffenstein and Yahav report that the glands but is nevertheless highly perme­ of transplantation organs, where tissue animal is unable to regulate its body able to water. The absence of an effec­ may suffer from hypothermia in vivo. temperature and instead displays all the tive insulation layer, together with the Experimental biology is littered with characteristics of a poikilotherm. animals' small size and low Not so long ago there were only two basal metabolic rate, were types of animal, warm-blooded (birds thought to restrict their ther­ and mammals) and cold-blooded (the moregulatory capacity and rest). This simple classification became they were commonly re­ confused by the discovery of warm­ garded as poorly regulating 6 blooded insects and reptiles, and of homoeotherms . periodic hypothermia in small mam­ However, it is now clear mals3. Nevertheless, until now mammals that they also lack another and birds could still be characterized by fundamental attribute of the their high resting metabolic rates, an small homeothermic mam­ effective surface insulation and high mal, an effective mechanism body temperatures in the cold. for increasing the production The naked mole rat, Heterocephalus of metabolic heat in the glaber, is found only in the tropical, cold. One obvious mani­ Naked mole rat: new insights into hypothermia semi-arid zones of north-east Africa, festation of this property is where it lives in a complex of poorly an ability to elevate body temperature examples of unusual creatures providing ventilated, subterranean burrows. Food above a cool ambient temperature, but insight into fundamental biological pro­ is sparse and foraging through the bur­ Buffenstein and Yahav show that the cesses. So, for the naked mole rat, row is an activity that dominates the body temperature of the naked mole rat opportunity knocks. D energy budget. On the other hand, the is only slightly (0.5 °C) above ambient burrows are thermally very stable at over the range 12-37 °C. Another test of Andrew R. Cossins is in the Department of 28-32 °C but with a high humidity and thermogenic potential is an animal's in­ Environmental and Evolutionary Biology, Uni• the potential for low levels of oxygen creased rate of oxygen consumption ( and versity of Liverpool, PO Box 14 7, Liverpool 4 L69 3BX, UK. and high levels of carbon dioxide • The heat production) when transferred to the animals have a complex social structure. cold via the rapid activation of brown 1. Sherman, P. W., Jarvis, J. & Alexander, R. D. (eds) The They live in subterranean colonies of adipose tissue. Buffenstein and Yahav Biology of the Naked Mole-Rat (Princeton University 60-100 individuals, with a strict division show that oxygen consumption is in fact Press, 1991). 2. Buffenstein, R. & Yahav, S. J. Thermal Biol. 16, 227- of labour extending even to the provi­ greatly reduced in the cold. 232 (1991). 5 sion of a single breeding female • They This lack of thermogenic potential 3. Cossins, A. R. & Bowler, K. Temperature Biology of often rest together in large huddles up to separates naked mole rats even from Animals (Chapman & Hall, London, 1987). 4. Bennet, N. B. et al. S. Afr. J. Zoo/. 3, 189-195 (1988). four animals deep. hibernating mammals of similar size, 5. Jarvis, J. U. M. Science 212, 571-573 (1981). The most notable features from a their production of metabolic heat being 6. Withers, P. C. & Jarvis, J. U. M. Comp. Biochem. Physiof. 66A, 215--219 (1980). thermoregulatory point of view are a more than compensated for by high rates 7. IUPS Thermal Commission Pf/iigers Arch. ges. Physiol. 2 complete absence of fur and a poorly of evaporative and conductive cooling • 410, 567-587 (1987). NATURE · VOL 353 · 24 OCTOBER 1991 699 © 1991 Nature Publishing Group