Behavioral Adaptations

Behavioral Adaptations

Overview of Water Conservation in Kangaroo Rats

Kangaroo rats have evolved a unique ability to survive in arid, low productivity areas by reducing their water and energetic needs. These adaptations include adaptations of the urinary systems, morphological adaptations of other body systems, and various behavioral adaptations. In order to understand how these rodents have developed these adaptations, it is important to understand the problems facing kangaroo rats with respect to water loss.

Kangaroo rats live in arid environments, where rainfall is seasonal and sparse. These xeric environments have little primary production, and most of the available food sources (seeds and grains) contain little moisture. These conditions require the rodents to survive long periods with little to no water and sparse food resources. Furthermore, temperatures often reach up to 42.5 ° C during the day, putting additional stress on the animals’ conservation of water. Such conditions are particularly difficult on an endotherm, which generally must maintain higher metabolisms than ectotherms and therefore have higher water and energetic needs.

Metabolic Water Production

Often the only source of water available to Kangaroo Rats is water is metabolic water. Metabolic water is the water produced as a by product of the Krebs cycle, where glucose is converted into ATP and water. While metabolic water is normally a small input in an organisms overall water balance, Kangaroo Rats have developed such efficient water conservation that they are able to survive entirely on metabolic water.

Types of Water Loss

Mammals such as the kangaroo rat experience water loss in several different ways. The two main mechanisms by which water loss occurs are evaporative water loss and loss from waste excretion.

Evaporative Water Loss

• Evaporative water loss occurs both in the lungs during respiration, and on any external surfaces that are not completely dry.

Waste Excretion

• Water is required during urine formation in order to remove nitrogenous wastes formed during physiological processes. Also, water is lost during the elimination of feces, as the feces must contain some moisture in order to pass through the intestinal tract of the animal.

Mechanisms of Water Conservation

While Kangaroo rats are not able to eliminate these water losses, they are able to reduce them to a sufficient level where they can maintain an acceptable water balance.

Humidity Regulation

• Water lost through lung respiration cannot be avoided, since moist surfaces must be in contact with air to allow for diffusion of oxygen, but kangaroo rats are able to reduce evaporative water loss by remaining in relatively moist burrows.

Reduction of External Surface Evaporation

• Kangaroo rats have eliminated sweat glands and panting, and use behavior and dwellings to control temperature.
• Kangaroo rats have been shown to develop an oily coat on their fur, which helps to reduce water loss from the epidermal surfaces (Schmidt-Nielsen, 1950).

Urine Concentration

• Physiological and anatomical adaptations of the kidneys have allowed for kangaroo rats to produce very concentrated urine, reducing the amount of water they must use to eliminate wastes.