Metabolic, Immune, and Reproductive Responses to an Immune Challenge in the Pygmy Rattlesnake (Sistr
Department of Biological and Allied Health Sciences
Fairleigh Dickinson University
Madison, New Jersey, USA
Lind, Craig M.
Department of Natural Sciences and Mathematics Stockton University
Galloway, New Jersey, USA
Farrell, Terence M.
Department of Biology
DeLand, Florida, USA
A growing body of literature supports the notion that mounting an immune response is energetically costly, and that energetic tradeoffs associated with increased immune activity may have fitness consequences via negative sublethal effects on host growth and reproduction. Nevertheless, relatively few studies have examined energy allocation tradeoffs mediated by immune system activation in reptiles, and direct documentation of a metabolic response to immune challenge in reptiles is largely lacking. Furthermore, it is currently unknown how reproductive condition influences the metabolic response to immune challenge in reptiles. We measured the effect of a lipopolysaccharide (LPS) challenge on resting metabolic rate (RMR) and immune function in male, non-reproductive female, and pregnant female Pygmy Rattlesnakes (Sistrurus miliarius) from central Florida. We measured RMR (as CO2 production rate) before and after treatment (LPS injection or vehicle control) via flow-through respirometry, and quantified immune response as change in plasma bactericidal ability (BA) and change in heterophil:lymphocyte (H:L) ratio before and after treatment. After parturition, we also compared live litter mass between LPS-challenged and control pregnant females. We found that LPS challenge caused a significant increase in mean RMR of males and non-reproductive females, but did not significantly affect RMR of pregnant females. Furthermore, we found that the effects of LPS challenge on immune response varied between measures of immune activity. Pairwise comparisons indicated that LPS decreased mean BA of pregnant females relative to non-reproductive individuals. In contrast, LPS significantly increased mean H:L ratio regardless of reproductive condition. Finally, we documented a significant reduction in mean live litter mass associated with LPS challenge, suggesting a possible negative effect of mounting an immune response on fitness despite the absence of a measurable metabolic response to LPS in pregnant females.