Meeting Abstract
68.4 Sunday, Jan. 6 Acute Phase Immune Responses along a Life History Gradient ADELMAN, J.S.*; HAU, M.; Princeton University; Princeton University jsadelma@princeton.edu
Life history theory posits a trade-off between reproductive effort and self-maintenance. While prior studies have investigated this trade-off among populations using immune function as a proxy for self-maintenance, few have considered the acute phase response, likely the most costly immune defense. This rapid, systemic response includes synthesis of defensive proteins, fever, and sickness behavior, specifically anorexia and lethargy. These symptoms come at a high cost in terms of time, energy, and nutrients, making this response the most likely type of immune function to trade-off with other costly activities, such as reproductive effort. We studied the acute phase response in song sparrows (Melospiza melodia) in the western United States, along a latitudinal gradient in reproductive effort as measured by clutch size and breeding season length. We predicted that birds in southern populations, with lower clutch sizes and longer potential breeding seasons, would devote fewer physiological resources to reproductive effort than birds in northern populations. Therefore, southern birds should retain more resources for self-maintenance and mount more robust acute phase responses. At three sites (33° N, 46° N, and 60° N) we induced an acute phase response with lipopolysaccharide (LPS), a non-pathogenic bacterial cell wall component. We assessed sickness behavior as a lack of response to song playback at 6 and 24 hours post injection. At 6 hours, all LPS treated birds were less likely to respond than controls (log-linear analysis, odds ratio=.02, p=.01). At 24 hours, only LPS injected birds at the southernmost site were less likely to respond (odds ratio=.01, p=.04). These results suggest that all birds mounted sickness behavior, but, consistent with our predictions, this response was most severe in populations exhibiting lower reproductive effort.
