Abstract:
Under climate change, increasing air temperature average and variability pose substantial thermal
challenges to animals. While plasticity in thermoregulatory traits could potentially attenuate this
impact, whether thermal acclimatisation can occur quickly enough to track weather variability in hot
climates is unknown in any endotherm, and sex differences have never been tested. We investigated
acclimatisation responsiveness of male and female wild zebra finches to short-term (< 2 weeks)
summer temperature fluctuations in the Australian desert. Hotter weather before respirometry trials
triggered a typical acclimatisation response (especially at chamber temperature Tchamb
≥ 40). However,
acclimatisation occurred remarkably rapidly: metabolic rate responded within just one day, while
body temperature (
Tb) and evaporative cooling capacity (EHL/MHP) were best predicted by weather
on the trial day; whereas evaporative water loss responded more slowly (1 week). Nonetheless, rapid
acclimatisation only occurred in males, and females had higher Tb
and lower EHL/MHP than males,
potentially increasing hyperthermia risk. Furthermore, acclimatisation did not translate into greater
acute heat tolerance (i.e. ability to tolerate Tchamb
= 46 °C). Our results therefore reveal surprisingly
rapid acclimatisation and even anticipatory adjustments to heat. However, with no changes in acute
heat tolerance, and in females, phenotypic flexibility may provide only limited buffering against the
detrimental impact of heatwaves.
