Adaptive Traits in Desert Ungulates Under Thermal Stress

Abstract

Desert ungulates inhabiting the hyperarid zones of the Arabian Peninsula, Sahara, and Central Asian deserts face extreme thermal environments characterised by ambient temperatures exceeding 45degC, solar radiation loads of 800-1,000 W/m2, and chronic water restriction, yet maintain core body temperatures within physiologically tolerable limits through a suite of morphological, physiological, and behavioural thermoregulatory adaptations that are among the most extreme documented in terrestrial mammals. This study quantified adaptive thermoregulatory traits in four desert ungulate species -- Arabian oryx (Oryx leucoryx), dromedary camel (Camelus dromedarius), dorcas gazelle (Gazella dorcas), and sand gazelle (Gazella subgutturosa) -- using implanted biologgers recording core body temperature (T(b)) at 15-minute intervals (n = 84 individuals; 6-24 months per individual), combined with GPS-linked ambient temperature sensors, infrared thermography of surface temperature distribution, and haematological sampling for heat shock protein (HSP70) and osmolality indicators of hydration status. Core body temperature heterothermy amplitude (T(b) range over 24 hours) ranged from 2.8 +- 0.4degC (dorcas gazelle; low heterothermy) to 6.4 +- 0.8degC (dromedary camel; extreme heterothermy). T(b) was significantly correlated with ambient temperature (r = +0.84, p < 0.001) and hydration status (r =-0.72, p < 0.001). HSP70 expression (plasma concentration ng/mL) was significantly elevated in dehydrated individuals across all four species (dehydrated: 48.4 +- 12.4 vs. hydrated: 18.4 +- 6.4 ng/mL; t = 8.42, p < 0.001). Behavioural thermoregulation (shade-seeking, activity restriction) reduced T(b) by 1.2-2.8degC relative to predicted T(b) without behavioural adjustment. Climate projections under SSP5-8.5 by 2070 indicate mean ambient temperature increases of 3.8-4.2degC in the study areas, which when applied to the T(b)-ambient temperature regression functions predict that all four species will experience T(b) exceeding their documented thermal tolerance limits (40.5-42.0degC) for significantly longer daily periods, identifying behavioural thermoregulation capacity as the key trait determining climate change vulnerability in desert ungulate populations.