Body temperature, evaporative water loss and resting metabolic rate data for six southern African bats

1. The microsites that animals occupy during the rest phase of their
circadian activity cycle influence their physiology and behaviour, but
relatively few studies have examined correlations between interspecific
variation in thermal physiology and roost microclimate. Among bats, there
is some evidence that species exposed to high roost temperatures (Troost)
possess greater heat tolerance and evaporative cooling capacity, but the
small number of species for which both thermal physiology and roost
microclimate data exist mean that the generality of this pattern remains
unclear. 2. Here, we test the hypothesis that bat heat tolerance and
evaporative cooling capacity have co-evolved with roost preferences. We
predicted that species occupying roosts poorly buffered from high outside
environmental temperature exhibit higher heat tolerance and evaporative
cooling capacity compared to species inhabiting buffered roosts in which
Troost remains well below outside conditions. 3. We used flow-through
respirometry to investigate thermoregulation at air temperatures (Ta)
approaching and exceeding normothermic body temperature (Tb) among six
species with broadly similar body mass but differing in roost microclimate
(hot versus cool roosts). We combined these data with empirical
measurements of Troost for each study population. 4. Hot-roosting species
tolerated Ta ~4 °C higher than cool-roosting bats before the onset of loss
of coordinated locomotion and non-regulated hyperthermia. The evaporative
scope [i.e., ratio of maximum evaporative water loss (EWL) to minimum
thermoneutral EWL] of hot-roosting species (16.1 ± 2.4) was
substantially higher than that of cool-roosting species (5.9 ±
2.4). Maximum evaporative cooling capacities (i.e., evaporative heat loss
/ metabolic heat production) of hot-roosting species were > 2,
while the corresponding values for cool-roosting species were ≤1. 5. The
greater heat tolerance and higher evaporative cooling capacity of
hot-roosting species compared with those occupying cooler roosts reveal
variation in bat evaporative cooling capacity correlated with roost
microclimate, supporting the hypothesis that thermal physiology has
co-evolved with roost preference.