Water Balance and Arginine Vasotocin in the Cocooning FrogCyclorana platycephala(Hylidae)

Abstract

It is well established that forming a cocoon, for frog species capable of doing so, markedly reduces evaporative water loss; however, the capacity of cocooned frogs to maintain hydration during extended estivation is not well understood. The combined effects of long-term estivation and water loss were examined in the cocoon-forming species Cyclorana platycephala by assessing the hydration state of the frogs throughout a 15-mo estivation period. Frogs lost mass throughout the 15-mo period to a maximum of 36%+/-6.5% of their initial standard mass. Plasma osmolality reached maximal levels by the ninth month of estivation at 487 mOsm kg(-1) and then remained stable to the fifteenth month of estivation. Urine osmolality continued to increase to the fifteenth month of estivation, at which point plasma and urine concentrations were isosmotic. The use of bladder water to counter losses from circulation was indicated by the relatively slow rate of increase in plasma osmolality with mass loss and the progressive increase in urine osmolality. For estivating frogs, evidence was found for a possible threshold relationship between plasma osmolality and plasma arginine vasotocin (AVT) concentration. After estivation, plasma AVT concentrations decreased markedly after 15-mo estivators were placed in water for 2 h, suggesting that high levels of AVT may not be integral to rapid rehydration in this species.

Metabolic and Kidney Diseases in the Setting of Climate Change, Water Shortage, and Survival Factors

“…The water-holding frog (Cyclorana platycephala) of the Sandy Desert of Australia, for example, stores so much water that it may double its weight. 8 These frogs were a favorite source of water for the Tiwi people during hot summers. Some frogs live 5 years without drinking water, which is because they utilize water stored in their bladders and also generate water during the metabolism of fat.…”

“…Some frogs live 5 years without drinking water, which is because they utilize water stored in their bladders and also generate water during the metabolism of fat. 7,8 The giant tortoise of the Galapagos Islands stores water in their urinary bladder. After rain, the tortoise voids their bladder urine (which contains urea and other waste products) and drinks copiously to refill their bladder with fresh water.…”

Regulation of skeletal Muscle Glycolysis During Dehydration in the Aestivating African Clawed Frog, Xenopus Laevis

“…Cocoon forming frogs such as Neobatrachus and Cyclorana present an interesting example of metabolic rate control as they become a closed system once they form their cocoon out of epidermal layers that are shed during aestivation (Cartledge et al, 2007). Survival of aestivation in this case is dependent on large bladders, dehydration tolerance and metabolic rate depression (Reynolds et al, 2011).…”

“…When the soil surrounding them in their burrows dries to a point where the influx of water across their skin is negative, these frogs form cocoons from multiple layers of shed skin, which reduces their evaporative water loss by 0.8% to 38% compared to non-cocooned rates (Cartledge et al, 2006). Once formed however, they must be able to survive on their internal energy reserves and manage waste accumulation without the ability to excrete potentially harmful accumulations (Cartledge et al, 2007).…”

“…This compares with the water-holding cocoon-forming frogs that can have bladder reserves with a holding capacity of 50% of their body mass at the start of aestivation and that are slowly reduced over time. By utilizing the water reserve in the bladder, cocooned frogs are able to keep plasma osmolality low during aestivation (Cartledge et al, 2007). Similarly, the spadefoot toads, which can hold 30% of their body mass as bladder water, or other terrestrial anurans such as Bufo cognatus that can store up to 45% of their body mass in their bladder, use this water to help maintain osmotic balance under seasonally dry conditions.…”