Daily Torpor in Free‐Ranging Rock Elephant Shrews,Elephantulus myurus: A Year‐Long Study

Abstract

Under laboratory conditions, rock elephant shrews, Elephantulus myurus, use daily torpor under both short and long photoperiod acclimation. However, use of heterothermy often differs under field and laboratory conditions. We investigated the use of torpor in free-ranging elephant shrews from May 2001 to May 2002. The elephant shrews were capable of daily torpor throughout the year, with torpor most prevalent during winter. We recorded two torpor bouts during early summer (November). We recorded a total of 467 torpor bouts during the year. The mean torpor minimum body temperature (Tbmin) for the whole year was 15.3 degrees +/-4.4 degrees C, and the mean bout length was 8.6+/-3.5 h. These values were in the range expected for daily heterotherms. However, there was some marginal overlap with hibernation characteristics; a few torpor bouts were longer than 24 h in duration, and Tbmin decreased below 10 degrees C. Torpor was highly correlated with low ambient temperature and photoperiod. Torpor was also correlated with invertebrate abundance after controlling for photoperiod effects. During the year in which this study was conducted, the rainfall was 14% below long-term average. Historical rainfall records show that summer rainfall during strong El Nino years is up to 40% below the long-term average. During these drought years, the frequency of summer torpor may be higher, highlighting the need for long-term physiological data in free-ranging animals.

Timing of the daily temperature cycle affects the critical arousal temperature and energy expenditure of lesser long-eared bats

“…Selection of poorly insulated rest sites is not uncommon among bats and appears particularly common in solitary roosting males (Kurta and Kunz, 1988;Kurta et al, 1989;Bronner et al, 1999;Chruszcz and Barclay, 2002;Kunz and Lumsden, 2003;Lausen and Barclay, 2003;Turbill et al, 2003b;Turbill, 2006a;Turbill, 2006b). A number of heterothermic mammals also prefer rest sites that receive direct solar radiation, which increases the amplitude of heating of shelter T a during the day (Vaughan and O'Shea, 1976;Humphrey et al, 1977;Hosken, 1996;Kerth et al, 2001;Geiser et al, 2002;Mzilikazi et al, 2002;Mzilikazi and Lovegrove, 2004). By co-ordinating torpor and normothermy with the daily T a cycle, small species like N. geoffroyi can exploit the high T a provided in thermally unstable roosts to minimise the energetic cost of arousal and a period of normothermy during the rest phase.…”

A New Comparative Metric for Estimating Heterothermy in Endotherms

“…To emphasize the flexibility of the HI approach, we made no attempt to standardize the period analyzed. Data are from Kortner and Geiser (1998), Park et al (2000), Mzilikazi and Lovegrove (2004), Munro et al (2005), Mzilikazi et al (2006), and Hetem et al (2009). possible way to compare heterothermy between adults and juveniles is with the minimum T b . However, this may miss important temporal patterns, such as the time spent below T b-opt .…”

Seasonal changes in thermogenesis of a free-ranging afrotherian small mammal, the Western rock elephant shrew (Elephantulus rupestris)

“…This conclusion, however, may be biased by the fact that the majority of studies have focused on thermoregulation in mammals of the northern hemisphere. In addition, several species of the southern hemisphere from diVerent mammalian orders have already been shown to display torpor and hibernation (Bozinovic et al 2004;Dausmann et al 2004;Geiser 2007;Geiser and Körtner 2010;Lovegrove and Genin 2008;Mzilikazi and Lovegrove 2004;Stawski et al 2009), suggesting that they may also beneWt from NST for arousal. In order to fully understand the plasticity of NST and its signiWcance in the evolution of thermoregulatory patterns in mammals, it is therefore important to study the magnitude by which cold-induced adaptive NST from BAT is recruited in species from diVerent mammalian subgroups and geographical regions.…”