Meeting Abstract
Seasonal variation in environmental conditions such as temperature, food availability, and likelihood of disease influence an organism’s investment in costly physiological processes such as immune function and reproduction. Most temperate zone organisms use changes in day-length (photoperiod) as an initial predictive cue to time physiological investments to coincide with optimal environmental conditions such as peak food availability and benign temperatures. Red crossbills Loxia curvirostra are temperate zone songbirds that time reproduction to coincide with booms in conifer seeds, their preferred food resource, often in extreme environmental conditions. In this experiment, to determine if changes in photoperiod and/or food availability affected investment in innate immunity, crossbills were exposed to either long day-lengths (LD) or short day-lengths (SD) for six weeks before experiencing a 20% food reduction for a period of 10 days or continuing on an ad-libitum diet. Additionally, the acute phase response was induced by injecting lipopolysaccharide (LPS) both before and after diet change. Liver, spleen, and gonadal tissues were taken from sacrificed birds 22 days post experimental end. At this time, all birds had access to ad-libitum food but remained on the same experimental photoperiod. LDs decreased cytokine interleukin (IL)-10 mRNA expression in the liver and IL-4 and IL-6 expression in the spleen, but increased total testes volume in males. Birds that had been LPS challenged and kept on SDs had lower IL-4 and higher toll-like receptor (TLR)-4 expression in the liver. Effects of treatments on cytokine and reproductive physiology were determined by GLMs and AICc to assess weight and fit of all models.
