Rattlesnakes Must Drink: Meal Consumption Does Not Improve Hydration State.

Water is critical to survival, yet free-standing water is often rare in deserts and seasonally dry environments. Thus, many dry-adapted species utilize either metabolic (that produced from metabolism) or dietary (that found in food) water to meet their hydric needs. It is suspected that desert reptiles can fulfill their hydric needs solely through dietary water intake. However, food consumption does not improve the hydration state of Gila monsters (Heloderma suspectum), a binge-feeding desert lizard, and meal consumption by snakes leads to increased voluntary drinking. Therefore, we predicted that meal consumption would not improve hydration state in dehydrated western diamondbacked rattlesnakes (Crotalus atrox). We found no significant difference in the change in plasma osmolality between moderately dehydrated snakes that consumed a meal and those that did not. In fact, snakes that received a meal reached severe dehydration more than a week sooner than snakes that did not receive a meal. Additionally, consuming a meal when severely dehydrated did not reduce plasma osmolality, whereas severely dehydrated snakes provided with water ab lib. returned to a normosmotic state. These results provide the most convincing evidence that carnivorous desert reptiles likely rely on free-standing water to fulfill their hydric needs. These species have thus had to adapt to sporadic water availability through minimizing water loss and tolerating considerable variation in plasma osmolality.