Chronic Water Restriction Leads to Body Mass Loss, Increased Urine Concentrations, and Reduced Evaporative Water Loss in Female Octodon degus, an Arid-Adapted Rodent.

AbstractRegions worldwide over the next few decades are projected to experience higher rates of drought, and animals will be faced with increasingly arid conditions. Understanding physiological effects of low water availability, such as impacts on metabolism and water loss, can further understanding of how animals will cope with aridification. Common degus (Octodon degus) are social rodents native to central Chile, an area that has been experiencing drought since 2010. Using a laboratory population of female degus, we subjected individuals to either (1) control conditions in which water was provided ad lib. or (2) a water-restriction regimen in which water allotments were decreased by 25% each week for 3 wk. Basal metabolic rate and evaporative water loss were estimated using flow-through respirometry before experimental manipulation and at the end of each week. We also collected urine samples, quantified daily food consumption, and weighed animals weekly. We found that body mass decreased significantly in water-restricted animals compared to in controls and that their capacity to concentrate urine increased significantly after 1 wk of water restriction. However, the rate of evaporative water loss did not decrease until the third week of water restriction. Thus, under conditions of low water availability in the absence of heat stress, female degus primarily limit urinary water loss and later decrease evaporative water loss, a strategy that may also be used by similar-sized mammals.