The joint effect of micro- and macro-climate on the thermoregulation and heat dissipation of two African mole-rat (Bathyergidae) sub-species, Cryptomys hottentotus mahali and C. h. pretoriae

Wallace, Kyra M. E. , van Jaarsveld, Barry , Bennett, Nigel C. , Hart, Daniel W.

2021-07-01 JOURNAL OF THERMAL BIOLOGY 2021   99(卷), null(期), (null页)

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The effect of the macro- and micmclimate on small mammal thermoregulation in the past has been studied independently instead of investigating the dual effect of both the components. This study addresses this dearth in knowledge by exploring the dual effect of both micro- and macro-climate on the thermoregulatory responses of two subterranean rodent species belonging to the family Bathyergidae, namely the more arid dwelling Mahali mole-rat (Cryptomys hottentotus mahali) and less arid dwelling Highveld mole-rat (C. h. pretoriae). Open flow through respirometry was used to quantify resting metabolic rates (RMR), evaporative water loss (EWL), core body temperature (Tb), the ratio between the evaporative heat loss and metabolic heat production (EHL/MHP: evaporative cooling capacity) and conductance (C-dry) over a range of increasing ambient temperatures (T-a; 20-42 degrees C). Furthermore, RMR, EWL, T-b, EHL/MHP and C-dry were measured at the mole-rat's thermal maxima (43 degrees C). At cooler temperatures, the arid-dwelling C. h. mahali possesses a broader thermoneutral zone (similar to 5 degrees C; 27.2-32.1 degrees C), while C. h. pretoriae possess a single thermoneutral point (33.6 degrees C). This is in response to the greater selection pressure to conserve energy in the more arid regions inhabited by C. h. mahali. Contrastingly, at hotter temperatures, there were no significant thermoregulatory differences in EWL, EHL/MHP or C-dry responses between the two sub-species, as expected due to the limitations bestowed by the buffered microclimates (burrow systems). Thus, neither macro-climate, nor micro-climate singularly moulds the thermoregulatory adaptations, but rather, it appears to be a combined effect from both climates. Other small endotherms may share this dual response, and therefore, it is crucial to incorporate the effect of both macro- and microclimates into future climate models when determining the ecological capabilities and persistence of a species.