15N enrichment of lizard uric acid and feces: Implications for physiological ecology.
Hatch, Kent*,, Tschudy, Jessica,
ABSTRACT- Stable isotopes are used by animal physiological ecologists to determine such things as dietary sources, migration, and trophic levels. Attempts have been made to use 15N values as indicators of body condition as well. The assumption is that proteins are 15N enriched during anabolism whereas nitrogenous wastes are 15N depleted relative to diet. Catabolism then only further enriches the tissues as 15N depleted urates are excreted. However, this model is based, in part, on two studies of ureotylic mammals (cattle and camelids) that showed 15N depletion of urea relative to diet. Because of their small size and ease with which uric acid can be collected, lizards are logical system to use to test the hypothesis that, across taxa, nitrogenous wastes are 15N depleted relative to diet. Based two studies, one of 15 side-blotched lizards (Uta stansburiana), and a second of 6 side-blotched lizards and 8 American anoles (Anolis anolis, we show that nitrogenous wastes are 15N depleted across taxa. We also discovered a difference in 15N between the side-blotched lizards and the American anoles. While the uric acid samples showed no difference, the feces samples of side-blotched lizards had a significantly higher 15N/14N ratio when compared to the feces of anoles. Finally, we show that water deprivation increased the 15N/14N in uric acid.
Key words: stable isotopes, nitrogen, lizards, water deprivation
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