Uricotélisme

Uricotelism is an excretory strategy observed in some animal species where the primary nitrogenous waste product excreted is uric acid. This mode of excretion is particularly advantageous in arid or terrestrial environments because uric acid is a virtually insoluble compound with very low toxicity. This allows animals to conserve water by excreting their waste in a semi-solid, paste-like form, rather than as a dilute solution.

Animals that are uricotelic, such as birds, reptiles, and many insects, typically excrete uric acid along with feces. This is often achieved through a specialized renal system that actively reabsorbs water and essential ions, concentrating the nitrogenous waste into a highly concentrated form. The metabolic cost of synthesizing uric acid from ammonia is higher than for urea or ammonia, but this is offset by the significant water savings.

The evolution of uricotelism is considered a key adaptation that enabled vertebrates to colonize dry land and birds to develop flight. By minimizing water loss through excretion, these animals can survive in environments where water is scarce. The exact mechanisms of uric acid excretion can vary between different groups of uricotelic animals, reflecting their diverse evolutionary histories and physiological adaptations.