Thermoregulation in the Angolan Free‐Tailed BatMops condylurus: A Small Mammal That Uses Hot Roosts

Abstract

The Angolan free-tailed bat (Mops condylurus) uses roosts that often exceed 40 degrees C, an ambient temperature (Ta) that is lethal to many microchiropterans. We measured the physiological responses of this species at Ta's from 15 degrees to 45 degrees C. Torpor was commonly employed during the day at the lower Ta, but the bats generally remained euthermic at night, with a mean body temperature (Tb) of 35.2 degrees C. Metabolic rate reflected the pattern of Tb, increasing with falling Ta at night but decreasing during the day. Metabolic rate and evaporative losses were lower in torpid than in euthermic bats. Body temperature increased at each Ta >35 degrees C and was 43 degrees C at Ta of 45 degrees C. At Ta of 40 degrees C bats increased dry thermal conductance and evaporative heat loss compared to lower Ta. At 45 degrees C dry thermal conductance was lower than at 40 degrees C and evaporative heat loss was 132% of metabolic heat production. At high Ta there was only a slight increase in metabolic rate despite the employment of evaporative cooling mechanisms and an increase in Tb. Collectively our results suggest that M. condylurus is well suited to tolerate high Ta, and this may enable it to exploit thermally challenging roost sites and to colonise habitats and exploit food sources where less stressful roosts are limiting.

Interspecific variation in thermoregulation among three sympatric bats inhabiting a hot, semi-arid environment

“…These data reveal the variation in heat tolerance that can exist within sympatric species occurring at a single site, and reiterate the importance of factors other than climate in determining a taxon's thermoregulatory capacity. One such variable may be phylogeny; several authors have noted pronounced heat tolerance in members of the Molossidae (Licht and Leitner 1967a;Maloney et al 1999), and the greater heat tolerance of S. petrophilus is qualitatively consistent with this idea.…”

“…We then examined whether this index of heat tolerance is correlated with the extent to which roosts are buffered from high outside T a , using the difference between maximum T roost and maximum T a as an indication of the thermal buffering of a specific roost site. We used data for Mops condylurus Maloney et al 1999), Myotis yumanensis, Antrozous pallidus and Tadarida brasiliensis (Licht and Leitner 1967a;Licht and Leitner 1967b), and the three species examined in the 14 present study. We recognize that these indices are overly simplistic quantifications of variables that are in reality determined by a host of complex interactions between abiotic and physiological variables, and intend this merely as a preliminary analysis aimed at developing a hypothesis to be tested in future studies.…”

“…Like other small endotherms, bats rapidly increase EWL under hot conditions (Herreid and Schmidt-Nielsen 1966;Maloney et al 1999;Marom et al 2006). In one of the few detailed examinations of how bats cope with very high T roost , M. condylurus roosting under a corrugated iron roof in eastern South Africa were found to dissipate up to 132 % of metabolic heat production via EWL ).…”

“…However, the latter values are based on bats roosting in relative mild thermal conditions, and dehydration rates are likely to be far higher in very hot roosts. In M. condylurus, for instance, total EWL on a very hot day estimated from a T roost profile was equivalent to 44 % of body mass, leading Maloney et al (1999) to conclude that the bats must have selected cooler microsites within the roost and/or reduced heat gain by clustering together. Data on acute dehydration tolerance limits for bats experiencing very high roost temperatures are lacking.…”

Partitioning of Evaporative Water Loss into Respiratory and Cutaneous Pathways in Wahlberg's Epauletted Fruit Bats (Epomophorus wahlbergi)

“…In bats, evaporation may constitute 80%-85% of overall water flux (Studier 1970;Arad and Korine 1993;Bassett et al 2009) and has particular thermoregulatory significance for insectivorous species roosting in hot microsites (Maloney et al 1999;Marom et al 2006;Cory Toussaint and McKechnie 2012). Relatively little is known about rates of respiratory evaporation versus cutaneous evaporation in bats (Bassett et al 2009), particularly compared with birds, where it is well established that the relative importance of REWL and CEWL for thermoregulation at air temperatures (T a ) approaching and exceeding T b varies widely among orders (Wolf and Walsberg 1996;Tieleman and Williams 2002;McKechnie and Wolf 2004).…”