Osmoregulatory mechanisms of the Australian freshwater crocodile, Crocodylus johnstoni , in freshwater and estuarine habitats

Abstract

Abstract. The estuary of the Limmen Bight River in Australia's Northern Territory is home to an unusual salt water-adapted population of the Australian `freshwater' crocodile, Crocodylus johnstoni. Crocodiles were captured from tidal reaches of the estuary ranging in salinity from 0.5-24 0 / 00 and from several permanent fresh water reaches more or less remote from saline waters. C. johnstoni is an effective osmoregulator in moderately saline waters and has osmoregulatory mechanisms very similar to its more marine-adapted relative, the estuarine crocodile Crocodylus porosus. Fasted C. johnstoni in brackish water appear to lose little sodium in cloacal urine, relying on their lingual salt glands for excretion of excess sodium chloride. The lingual glands show clear evidence of short-term and long-term acclimation to salt water. Like estuarine crocodiles, C. johnstoni drinks fresh water and will not drink sea water. Gross sodium and water fluxes in brackish water are very similar to those in other crocodilians, suggesting differences in integumental permeability are not a major influence on osmoregulatory differences between crocodilians. The data reinforce the hypothesis that crocodylids differ fundamentally from alligatorids in the structure and function of the renal-cloacal-salt gland complex and are of interest in current debate over the evolutionary and zoogeographical history of the eusuchian crocodilians.

Ecophysiological steps of marine adaptation in extant and extinct non‐avian tetrapods

“…Brackish feeding has been documented for at least three species of crocodile, the freshwater crocodile ( Crocodylus johnstoni ) (Taplin et al ., 1999), the broad‐snouted caiman ( Caiman latirostris ) (Grigg et al ., 1998), and the American alligator ( Alligator mississippiensis ) (Mazzotti & Dunson, 1984)], three species of turtles [the painted terrapin ( Batagur borneoensis ) (Davenport & Wong, 1986), the northern river terrapin ( B. baska ) (Dunson & Moll, 1980) and the pig‐nosed turtle ( Carettochelys insculpta ) (Groombridge & Wright, 1982)], and a mammal, the long‐tailed monkey ( Macaca fascicularis ) [Son, 2003; Malaivijitnond et al ., 2007; see also BBC Planet Earth documentary (http://www.bbc.co.uk/pressoffice/pressreleases/stories/2006/02_february/01/earth_firsts.shtml)].…”

Effects of temperature and salinity on body fluid dynamics and metabolism in the estuarine Diamond-backed Terrapin (Malaclemys terrapin)

“…Preference for low salinity drinking water is a common characteristic of turtles (Dunson and Moll, 1980; Table 2. Davenport and Wong, 1986;Davenport and Macedo, 1990), snakes (Lillywhite and Ellis, 1994;Lillywhite et al, 2008) and crocodilians (Taplin et al, 1999) that utilize brackish water or estuarine habitats. Discrimination in drinking water is an important behavioral component of water balance and osmoregulation for terrapins and other estuarine species, as the efficacy of salt glands in estuarine reptiles is much lower than that of fully marine forms (Dunson, 1970).…”

Technique for the collection of clear urine from the Nile crocodile (<i>Crocodylus niloticus</i>)

“…Schmidt-Nielsen and Skadhauge 27 used a relatively complicated method of collecting urine directly from the urinary papillae (urethral openings). However, it appears that the technique used most frequently by different researchers 16,17,20,22,23,25,26 is to insert a glass tube or any other suitable instrument through the cloacal opening or vent. By gently forcing these instruments forward, the uroproctodeal sphincter is opened, allowing urine to flow freely through the proctodeum and into a sample bottle.…”

“…Urine has been collected previously from the American alligator, 16,17,18 estuarine crocodile, 13,21,22,23,24 Australian freshwater crocodile (Crocodylus johnsoni), 25 Nile crocodile 19,20,24 and the broad-snouted caiman (Caiman latirostris). 26 Most of the collected urine samples were used for research projects that investigated osmoregulation in crocodilians.…”

“…26 Most of the collected urine samples were used for research projects that investigated osmoregulation in crocodilians. 13,20,21,22,23,24,25,26 Leslie and Spotila 20 collected urine from Nile crocodiles by inserting a blunt pair of stainless steel forceps through the cloacal opening. The technique used by Hopping 18 is described as catheterisation of the cloaca, but no detail is given.…”