Urates of colubroid snakes are different from those of boids and pythonids

Abstract

Uricotelic species, such as squamate reptiles, birds and insects, effectively eliminate nitrogen as uric acid in a solid form commonly called urates. Observations made over a decade suggested that the voided urates produced by colubroids (modern snake species) exhibit remarkable differences from those of boids and pythons (ancient snake species). Here, we compare the urates generated by eight captive snake species fed the same diet. Although all fresh urates were wet at the time of excretion, those produced by modern snakes dried to a powdery solid, whereas those of ancient species dried to a rock-hard mass that was tightly adherent to surfaces. Powder X-ray diffraction and infrared spectroscopy analyses performed on voided urates produced by five modern and three ancient snakes confirmed their underlying chemical and structural differences. Urates excreted by ancient snakes were amorphous uric acid, whereas urates from modern snakes consisted primarily of ammonium acid urate, with some uric acid dihydrate. These compositional differences indicate that snakes have more than one mechanism to manage nitrogenous waste. Why different species use different nitrogen-handling pathways is not yet known, but the answer might be related to key differences in metabolism, physiology or, in the case of ancient snakes, the potential use of urates in social communication.

An Improved Model for Biogenic Ammonium Urate

“…7−9 Reptiles are also not immune from developing pathogenic ammonium urate deposits 10,11 even though some routinely excrete excess nitrogen in that solid form. 12 Crystallographic data on biogenic ammonium urate are limited, in part because the crystals are poorly formed and rarely pure. Obtaining large synthetic ammonium urate single crystals is also difficult, such that most previous studies have relied on powder X-ray diffraction (PXRD) data.…”

“…Urolithiasis, the formation of renal calculi, is a common medical condition that affects humans as well as other animals. , Such physiologic deposits can have a range of chemical compositions, the frequencies of which vary across different species. Though infrequently identified in humans, ammonium urate stones are quite common in some canine breeds (e.g., Dalmatians), , felines, and managed bottlenose dolphins. − Reptiles are also not immune from developing pathogenic ammonium urate deposits , even though some routinely excrete excess nitrogen in that solid form …”