Meeting Abstract

P1.187  Friday, Jan. 4  Cooling and Hibernation Effects on Leukocyte Numbers in the Ornate Box Turtle Terrapene ornata ornata. BACHMAN, G; Univ. of Nebraska, Lincoln gbachman@unl.edu

Changes in circulating leukocyte numbers (heterophils or neutrophils, lymphocytes, and the ratio of these, H/L ratio) reflect immune system activity, stress, and seasonal effects. Winter can elevate the H/L ratio in endotherms due to seasonal increases in glucocorticoids although the H/L ratio decreases in hibernating mammals. In ectotherms, the H/L ratio may be elevated in winter. An elevated H/L in hibernating reptiles has been interpreted as an indication that hibernation is stressful. However the stress response includes changes that support increased metabolic rate, an impossibility in hibernating ectotherms. To begin to understand the functional role and potential causes of changes in leukocyte numbers in response to season and temperature in reptiles, I collected blood smears from active ornate box turtles in the field in summer, in hibernating captive turtles over winter, and from summer-active animals that had been cooled for 5 days to temperatures normally encountered only in winter. Smears were evaluated for the number of leukocytes per erythrocyte and the H/L ratio. Both winter and cold exposure in summer increased heterophil numbers, and because these dominated cell counts, total leukocyte counts were elevated in these samples. Lymphocyte counts are lower in hibernation than in summer , but cooling in summer did not alter lymphocyte numbers. H/L ratios were highest in winter and cooling in summer also significantly increased the ratio. Hematocrit did not differ between active and hibernating turtles. These results suggest that in this species, observed seasonal changes in leukocytes in circulation may be largely due to lowered body temperature, with either extended cold exposure or seasonal cues affecting only part of the leukocyte population.