Seasonal Variation in Metabolism and Immunity in the Rubber Boa (Charina bottae)
Department of Biological and Allied Health Sciences
Fairleigh Dickinson University
Madison, NJ USA
As part of ongoing research examining seasonal variation in resting and activity metabolism in a laboratory population of Rubber Boas (Charina bottae), we investigated potential seasonal changes in the thermal sensitivity of innate immune performance. We sought to test two competing hypotheses: 1) that immune performance would be down-regulated during artificial hibernation as an energy conservation strategy; or 2) that immune performance would be enhanced, especially at lower acute temperatures, to compensate for the otherwise suppressive effects of low temperature on ectotherm immune function. We quantified the bacteria-killing ability of plasma as a function of acute temperature (7, 16, and 25°C) during the simulated active season and artificial hibernation in a repeated-measures design (n = 7 individuals). In addition, we conducted differential leukocyte counts via light microscope inspection of blood smears prepared during the simulated active season and artificial hibernation. We found that plasma bacteria-killing ability was significantly affected by season, acute temperature, and snake body mass. After adjusting for the positive effect of body mass on plasma bacteria-killing ability via ANCOVA, bactericidal activity was uniformly depressed across all sampled acute temperatures during artificial hibernation, relative to the simulated active season. Within each season, plasma bacteria-killing ability increased with increasing acute temperature. Snakes also exhibited a significant increase in the relative number of heterophils and a significant decrease in the relative number of lymphocytes during artificial hibernation. Observed variation in immune parameters will be discussed in the context of seasonal and individual variation in resting metabolic rate and aerobic capacity.