HARMS, Heidi K.*; BOWDEN, Rachel M.; TUCKER, John K.; Illinois State University; Illinois State University; Illinois Natural History Survey: Seasonal, sex-, and age-related variation in serum immunoglobulin levels in the red-eared slider turtle

The immune system of ectothermic vertebrates fluctuates seasonally, being sensitive to both environmental and hormonal cues. Low immunocompetence often occurs during the winter and the mating season, when energy and resources are directed away from the immune system towards self-maintenance and reproduction, respectively. Additionally, variation in male and female reproductive biology, as well as ontogenetic changes in resource allocation may lead to variation in immune function. We examined seasonal, sex-, and age-related variation in serum immunoglobulin (Ig) levels in the red-eared slider turtle (Trachemys scripta elegans). Serum samples were obtained monthly from March to September from both sexually immature and mature males and females trapped from a natural population. Using protein gel electrophoresis, we separated the five main classes of serum proteins (albumin, alpha-1, alpha-2, beta, and gamma) based on their electrical charge and size. Because Ig�s are present mostly in the gamma class (and are referred to as gamma globulins), we were able to determine changes in the relative proportions of Ig in serum by examining changes in the gamma globulins. In general, across both sexes, levels of circulating gamma globulins increase seasonally, and sexually mature individuals have higher levels than immature individuals. We also detected sex-specific variation in the levels of gamma globulins across the sampling period. These patterns suggest that ontogeny and reproductive cycles do influence at least some components of immune function in turtles.