Castillo Laura P, Hatch Kent A
151 WIDB, Brigham Young University, Provo, UT 84602, USA.
Rapid Commun Mass Spectrom. 2007;21(24):4125-8. doi: 10.1002/rcm.3305.
Previous studies suggest that a nutritional/energetic state may be determined from the delta(15)N-values of an animal's tissues. It has been hypothesized that if an animal is in a negative nutritional/energetic balance, (15)N will be retained by the tissues preferentially and (14)N preferentially excreted. Over time, this should cause enrichment of the delta(15)N-values of the tissues. Tests of this hypothesis have met with mixed results. To date, these studies have focused on endotherms. Few studies have considered the effects of fasting on the (15)N/(14)N ratios of substrates from ectotherms. We hypothesized that the delta(15)N-values of tail tissue and uric acid of fasted lizards would increase over time, while that of the fed lizards would remain the same. We fasted five side-blotched lizards (Uta stansburiana) and five green anoles (Anolis carolinensis) for 14 days. At the same time we fed six side-blotched and four green anoles ad libitum. All lizards were given water ad libitum. During this period, we collected uric acid from each lizard daily and tail tissue on the first day of the study and on the last day of the study. We found the the delta(15)N-values of uric acid of fasted lizards at the end of the study were (15)N-enriched compared with that of the control lizards in both species, probably due to a shift in amino acid source pools during fasting. However, we found no difference between treatment and controls in the delta(15)N-values of the tails.
以往的研究表明，动物组织的δ(15)N值可用于确定营养/能量状态。据推测，如果动物处于负营养/能量平衡状态，组织会优先保留(15)N，而优先排泄(14)N。随着时间的推移，这会导致组织的δ(15)N值升高。对这一假设的测试结果不一。迄今为止，这些研究主要集中在内温动物上。很少有研究考虑禁食对外温动物底物的(15)N/(14)N比率的影响。我们假设，禁食蜥蜴的尾部组织和尿酸的δ(15)N值会随时间增加，而喂食蜥蜴的该值将保持不变。我们将5只侧斑蜥蜴（犹他蜥）和5只绿安乐蜥禁食14天。同时，我们让6只侧斑蜥蜴和4只绿安乐蜥随意进食。所有蜥蜴都可随意饮水。在此期间，我们每天收集每只蜥蜴的尿酸，并在研究第一天和最后一天收集尾部组织。我们发现，在研究结束时，两种禁食蜥蜴的尿酸δ(15)N值均比对照蜥蜴的(15)N值富集，这可能是由于禁食期间氨基酸源库发生了变化。然而，我们发现处理组和对照组尾部的δ(15)N值没有差异。
