Adaptation to harshness is fundamentally different from the adaptive stress response: Results from a 20‐year‐long case study in African striped mice

Abstract Animals are adapted to cope with harsh environments. Understanding these adaptations is crucial to assessing species resilience to global change. Harsh environments are characterised by persistent and long‐lasting factors that threaten homeostasis and survival, such as reduced food and water availability, seasonal cold or heat. We review two decades of field studies exploring how African striped mice ( Rhabdomys pumilio ) are adapted to harshness in the Succulent Karoo semi‐desert, which is characterised by hot, dry and food‐restricted summers and moist, benign winters. Striped mice adapted to harshness via multiple behavioural and physiological mechanisms, which reduce energy consumption and increase water retention. These mechanisms include social flexibility, communal huddling, sun‐basking, reducing activity, a broad range of blood glucose regulation, decreased levels of metabolic hormones and decreased resting metabolic rate. Together, these mechanisms lead to an overall reduction of daily energy expenditure during harsh summers. This harshness response contrasts with the physiological stress response, which is characterised by increased energy expenditure to overcome the stress via the secretion of catecholamines and glucocorticoids. In contrast, the harshness response is characterised by reduced levels of glucocorticoids and allows endurance of the harsh conditions. We conclude that the harshness response is fundamentally different from the stress response.