School of Life Sciences, Arizona State University, Tempe, AZ 85287-4601, USA.
J Exp Biol. 2013 Apr 15;216(Pt 8):1439-47. doi: 10.1242/jeb.080895.
Many xeric organisms maintain water balance by relying on dietary and metabolic water rather than free water, even when free water may be available. For such organisms, hydric state may influence foraging decisions, since meal consumption is meeting both energy and water demands. To understand foraging decisions it is vital to understand the role of dietary water in maintaining water balance. We investigated whether meal consumption was sufficient to maintain water balance in captive Gila monsters (Heloderma suspectum) at varying levels of dehydration. Gila monsters could not maintain water balance over long time scales through meal consumption alone. Animals fed a single meal took no longer to dehydrate than controls when both groups were deprived of free water. Additionally, meal consumption imparts an acute short-term hydric cost regardless of hydration state. Meal consumption typically resulted in a significant elevation in osmolality at 6 h post-feeding, and plasma osmolality never fell below pre-feeding levels despite high water content (~70%) of meals. These results failed to support our hypothesis that dietary water is valuable to Gila monsters during seasonal drought. When considered in conjunction with previous research, these results demonstrate that Gila monsters, unlike many xeric species, are heavily reliant on seasonal rainfall and the resulting free-standing water to maintain water balance.
许多耐旱生物通过依赖饮食和代谢水来维持水分平衡，而不是自由水，即使自由水可能可用。对于这些生物来说，水合状态可能会影响觅食决策，因为进食既满足能量需求又满足水分需求。为了理解觅食决策，了解饮食水在维持水分平衡中的作用至关重要。我们调查了在不同脱水水平下，圈养的希拉毒蜥（Heloderma suspectum）是否通过进食就能维持水分平衡。希拉毒蜥不能仅通过进食来长期维持水分平衡。当两组动物都被剥夺自由水时，只吃一顿饭的动物比对照组脱水的时间更长。此外，无论水合状态如何，进食都会带来急性短期的水合成本。进食后 6 小时，通常会导致渗透压显著升高，尽管食物的含水量很高（约 70%），但血浆渗透压从未低于进食前的水平。这些结果与我们的假设相矛盾，即饮食水在季节性干旱期间对希拉毒蜥有价值。当与之前的研究结合考虑时，这些结果表明，希拉毒蜥与许多耐旱物种不同，它们严重依赖季节性降雨和由此产生的自由水来维持水分平衡。
