Energy Metabolism and Evaporative Water Loss in the European Free‐Tailed Bat and Hemprich’s Long‐Eared Bat (Microchiroptera): Species Sympatric in the Negev Desert

Abstract

We compared the thermoregulatory abilities of two insectivorous bat species, Tadarida teniotis (mean body mass 32 g) and Otonycteris hemprichii (mean body mass 25 g), that are of different phylogenetic origins and zoogeographic distributions but are sympatric in the Negev Desert. At night, both were normothermic. By day, both were torpid when exposed to ambient temperatures (T(a)) below 25 degrees Celsius, with concomitant adjustments in metabolic rate (MR). Otonycteris hemprichii entered torpor at higher T(a) than T. teniotis, and, when torpid, their body temperatures (T(b)) were 1 degrees -2 degrees Celsius and 5 degrees -8 degrees Celsius above T(a), respectively; MR was correspondingly reduced. At night, the lower critical temperature of T. teniotis was 31.5 degrees Celsius, and that of O. hemprichii was 33 degrees Celsius. Mean nocturnal thermoneutral MR of T. teniotis was 37% greater than that of O. hemprichii. At high T(a), evaporative water loss (EWL) increased markedly in both species, but it was significantly higher in T. teniotis above 38 degrees Celsius. In both species, the dry heat transfer coefficient (thermal conductance) followed the expected pattern for small mammals, by day and by night. Total EWL was notably low in normothermic and torpid animals of both species, much lower than values reported for other bats, indicating efficient water conservation mechanisms in the study species. Comparing thermoregulatory abilities suggests that O. hemprichii is better adapted to hot, arid environments than T. teniotis, which may explain its wider desert distribution. By both standard and phylogenetically informed ANCOVA, we found no differences in basal metabolic rate (BMR) between desert and nondesert species of insectivorous bats, substantiating previous studies suggesting that low BMR is a characteristic common to insectivorous bats in general.

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

“…Whereas EWL in T. mauritianus and S. petrophilus increased very rapidly at higher T a , a pattern similar to that observed in Mops condylurus ) and a number of other species (e.g., Marom et al 2006), EWL in N. thebaica began increasing at lower T a , increased more gradually, and reached a maximum value far lower than those of M. condylurus or T. mauritianus (Figure 3). These differences in thebaica increased rapidly, and reached 45 °C at T a ≈ 39 °C, with several individuals dying at this T a .…”

“…The maximum T b s of our species were also considerably higher than those of Tadarida teniotis and Otonycteris hemprichii at T a = 40 °C (Marom et al 2006) and Pipistrellus pipistrellus at T a ≈ 38 °C (Genoud and Christe 2011).…”

“…Maximum T b during heat exposure in M. condylurus was 43 °C , and to the best of our knowledge this remains the highest T b recorded to date in a bat. In contrast, T b in 4 two species sympatric in the Negev Desert never exceeded 40 °C, even at T a ≈ 40 °C (Marom et al 2006). …”

“…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 ).…”

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).…”