Experimental Consequences of Low Temperatures on Caiman latirostris Inmune and Endocrine Systems

PARACHU MARCO MV; SIROSKI PA; MOLEÓN MS; JAHN GA; REYES S; PIETROBON EO

Santa Fe

Workshop; 25th Working Meeting of the Crocodile Specialist Group (CSG/SSC/IUCN); 2018

Crocodile Specialist Group (CSG/SSC/IUCN)

Low temperatures have an inhibitory effect on animal metabolism, causing organisms to respond with physiological mechanisms to reestablish their homeostatic condition. Corticosterone is a glucocorticoid synthesized and secreted under stress conditions in order to stabilize metabolic functions and maintain the immune response of individuals. This hormone depends on the same metabolism for its synthesis, so if the latter descends to very low levels the organism is unable to synthesize it and, therefore, generate a regulatory response. For ectothermal animals, such as crocodiles, the release of corticosterone is the main compensatory response against the decrease in metabolism in low temperature conditions, but for a certain threshold of temperature the organism is unable to continue its synthesis and the metabolism ceases. In Caiman latirostris tolerance range and corticosterone blood levels at low temperatures are unknown. The objective of this study was to determine the lowest temperatures in which the concentration of corticosterone is maintained at adequate levels to maintain a stable metabolism and immunological parameters. Thus, 6 hatchlings and 6 juvenile were exposed consecutively to decreasing 3 temperatures during 24hr each: 25°C (baseline and control), then to 17°C and lasts 8°C. Blood samples were taken from all animals to measure corticosterone plasma concentrations. In addiction total and differential white blood cell count, natural antibody titers and complement system activity were measured. Results showed a total white blood cell count and natural antibodies titers were significantly lower in juveniles exposed at 8°C compared to control and 17°C. Activity of complement system was lower at control and 8°C. Similarly, proportion of heterophils increased significantly between temperatures control and 17°C, and decreased between 17°C and 8°C. There was no significant change in immunological parameters of hatchling between control and 17°C. The results of corticosterone are processing to the date. For both groups of treatment, the period of 24 hours at 17°C did not produce a change in the immunological parameters, this may be due to the action of corticosterone. On the other hand, the period at 8°C generated a decrease in the immunological parameters in juveniles even death in some hatclings, which may be related to the inability to continue synthesizing corticosterone due subsequently stopping metabolic activities.