Abstract
Rapid environmental changes are challenging for endothermic species because they have direct and immediate impacts on their physiology by affecting microclimate and fundamental resource availability. Physiological flexibility can compensate for certain ecological perturbations, but our basic understanding of how species function in a given habitat and the extent of their adaptive scope is limited. Here we studied the effect of acute, experimental microclimate change on the thermal physiology of two populations of the widespread Malagasy bat, Macronycteris commersoni. Populations of this species are found roosting under contrasting conditions, i.e., in a constant hot and humid cave or below foliage unprotected from fluctuations in ambient conditions. We exposed free-ranging individuals of each population to the respective opposite condition and thus to novel microclimate within an ecologically realistic scope while measuring metabolic rate and skin temperature. Cave bats in forest setting had a limited capacity to maintain euthermia to the point that two individuals became hypothermic when ambient temperature dropped below their commonly experienced cave temperature. Forest bats on the other hand, had difficulties to dissipate heat in the humid cave set-up. The response to heat, however, was surprisingly uniform and all bats entered torpor combined with hyperthermia at temperatures exceeding their thermoneutral zone. Thus, while we observed potential for flexible compensation of heat through “hot” torpor, both populations showed patterns suggestive of limited potential to cope with acute microclimate changes deviating from their typically occupied roosts. Our study emphasizes that intraspecific variation among populations could be misleading when assessing species’ adaptive scopes, as variation may arise from genetic adaptation, developmental plasticity or phenotypic flexibility, all of which allow for compensatory responses at differing time scales. Disentangling these mechanisms and identifying the basis of variation is vital to make accurate predictions of species’ chances for persisting in ever rapidly changing habitats and climates.
Highlights
Rapid environmental alteration has an immediate impact on the ecological stability of habitats and their inhabitants
Individuals were torpid for more than 70% of the total measurement duration despite several arousals within 24 h. They were euthermic for an average of only 19 ± 14 min at a time and never > 57 min (Figure 1A). This was in clear contrast to the torpor pattern observed in the native population as only 60% of native cave bats entered torpor and for a much smaller fraction of the total measurement duration (26%; Table 1; W = 1, P < 0.001)
We found no difference in resting MR (RMR) between the two populations (Table 1; t22.8 = 0.497, P = 0.624) but torpid MR (TMR) was lower in the forest bats exposed to cave conditions than the native cave population (Table 1; W = 91, P = 0.010)
Summary
Rapid environmental alteration has an immediate impact on the ecological stability of habitats and their inhabitants. Many endotherms living in unpredictable or highly seasonal habitats or those that are widespread and face heterogeneous environmental conditions, have evolved considerable flexibility in traits associated with thermal maintenance, and these may vary among and within populations (e.g., Stawski and Geiser, 2010; Glanville et al, 2012; Noakes et al, 2016; van Jaarsveld et al, 2021). Populations inhabiting arid habitats often have lower water turnover rates and mechanisms to retain water more efficiently than their conspecifics from more mesic habitats (e.g., Klüg-Baerwald and Brigham, 2017; Cooper et al, 2018; Gearhart et al, 2020). Quantifying such intraspecific variation can aid our understanding of the physiological compensatory capacity of a species and its general ecological resilience
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