Comparative biology of salinity discrimination in crocodilians and the possible role of the integument

grantor: University of TorontoThis study investigated the mechanisms underlying salinity discrimination in crocodilians. The results are as follows: (1) In crocodilians, the capacity for salinity discrimination has a phylogenetic component. All crocodylids tested discriminated between salinities and did not drink hyperosmotic sea water. In alligatorids, however, only individuals collected in an estuarine area were capable of salinity discrimination. (2) The salinity discrimination organ of the estuarine crocodylid, 'Crocodylus porosus', is not located in the mouth. Dehydrated crocodiles discriminate very precisely between salinities and do not drink hyperosmotic sea water when they are immersed in it. However, they drink strongly hyperosmotic sea water when it is dripped directly onto their tongues. Crocodiles must therefore have a salinity discrimination organ on another part of the body. (3) Crocodylids, but not alligatorids have sensory organs on their post-cranial scales. The morphology and ultrastructure of pits on the scales of 'C. porosus' was studied using SEM, TEM, and light microscopy. Their structure is consistent with a sensory function. Physiological study will be required to determine whether their function is mechanosensory or chemosensory.M.Sc