Daily torpor in a pregnant dunnart ('Sminthopsis macroura' Dasyuridae: Marsupialia)

Mammalian reproduction is an energetically expensive process. In addition to normal energetic costs for maintenance, locomotion and thermoregulation, reproduction requires energy expenditure to acquire and process nutrients, produce milk, and transferring nutrients to growing offspring with the consequent increase in metabolic rate (MR) (Farmer 2003). Torpor in heterothermic mammals, on the other hand, results in an overall reduction of energy expenditure and is characterised by a pronounced fall in body temperature and MR (Geiser and Ruf 1995). For most mammals, these different energetic, and also hormonal, demands appear to require a temporal sequence of reproduction and torpor within the yearly schedule and thus, torpor usually occurs during the non-reproductive season (Goldman et al. 1986; Barnes 1996; Stamper et al. 1998; Mzilikazi and Lovegrove 2002). Not surprisingly then, there is a widely held view that torpor and reproduction in mammals are mutually exclusive processes.