Osmoregulation of Crocodiles in Everglades National Park
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Material Information

Title:
Osmoregulation of Crocodiles in Everglades National Park Report T-599
Creator:
South Florida Natural Resources Center/South Florida Research Center, Everglades National Park
William A. Dunson
Place of Publication:
Homestead
Florida
Publisher:
National Park Service, U.S. Department of the Interior
Publication Date:

Notes

Abstract:
It is possible that the survival rate of hatchling C. acutus in Florida Bay is low and is associated with osmoregulatory problems caused by high salinities near nest sites. Crocodiles show few physiological specializations for life in saline waters in comparison with marine snakes and turtles. Wild C. acutus hatchlings have a plasma osmotic pressure near 330 mOsm, a typical level for vertebrates. The osmotic pressure of the cloacal fluid of wild caught C. acutus was equal to or less than that of the plasma. The solid portion of the cloacal fluid was mainly uric acid, and contained 1.3 to 450 times more K than Na. The highest levels of these ions were 1111 and 222 ymoles/g dry weight respectively, normal values for carnivorous reptiles. Thus it appears that K is excreted in both the fluid and solid portions of the "urine," whereas Na is conserved. The analysis of Na fluxes of small C. acutus submerged in sea water (35 ppt) is complicated by the presence of a sizeable compartment that turns over quite rapidly. There is a second compartment with a long turnover time (T1/2 of efflux 29-156 days). I assume that the slow compartment represents the true long-term rate of exchange with sea water. Na influx (11.5 yrnoles/lOOg h) and efflux (2.3 ~moles/lOOg h) were both quite low, although the influx did exceedtheefflux. Thus a net uptake of about 10 ymoles Na/100g h may occur. No passage of Na across small pieces of keratin was observed after one day. It appears that the skin is virtually impermeable to Na, as is the case with most aquatic reptiles. In some plasma samples taken during the first two weeks of life, Na was atypically low, but in others it is near normal (about 150 mM). This discrepancy was not found in plasma samples from mangrove snakes (Nerodia fasciata compressicauda) taken and analyzed under identical conditions. The indication that there may be a 1Ja deficiency in some recent hatchlings is supported by the extremely low Na concentrations of cloacal fluid (12-21 mM). In some, but not all cases, C1 and K were much,higher than Na. The relationships between snout vent length (L), body weight (W), and surface area (A) are as follows: A = 1.1550~1.~~~~; W = 0.0263~~-9730. The head-neck, tail, legs and body regions each account for about one fourth of the total area. After hatching, crocodiles seek out cool, moist, terrestrial microclimates by entering crab holes and wave-cut crevices, or by hiding in clusters of mangrove roots. It might appear that this behavior is advantageous for small crocodiles in avoiding the loss of body weight (about 1.7%/day) that occurs when fasting and immersed in 100% sea water. Such is not the case since a similar amount of evaporativewater loss occurs i n a i r at 30°C and 96.5% relative humidity. This is several times the loss of the mangrove snake living in the same habitat. It appears that this obligatory water loss is normally counterbalanced by feeding. When fed -- ad lib. and kept in an aquarium divided into land and water portions, small (100-480g) crocodiles maintain weight at salinities up to at least 17.5 ppt (50% sea water). ( English )

Record Information

Source Institution:
Florida International University
Holding Location:
South Florida Natural Resource Center
Rights Management:
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Resource Identifier:
I 29.95:T-599 ( sudoc )