Meeting Abstract
An organism’s investment in costly physiological processes such as immune function is often variable and fluctuates in response to environmental and physiological changes in order to maximize fitness. The red crossbill Loxia curvirostra is a reproductively flexible songbird that times reproduction to coincide with booms in conifer seed abundance, an erratically available food resource. Consequently, environmental factors can have strong effects on crossbill physiological investment patterns across the annual cycle. Data from free-living crossbills have demonstrated that, like many vertebrates, investment in immunity varies by season and food abundance and ambient temperature likely contribute significantly to these patterns. However, it is difficult to disentangle the effects of food availability and temperature from photoperiodic changes in the field samples. To overcome this limitation, we examined how changes in photoperiod and food availability affect investment in innate immunity and the acute phase response in captive crossbills. Birds were separated into four treatments and exposed to long or short day lengths (16L: 8D; 8L:16D, respectively) for six weeks before continuing on an ad-libitum diet or experiencing a 20% food reduction for 10 days. Additionally, we induced an acute phase response in all birds both prior to and post diet change. Innate immune function was measured throughout the experiment to assess baseline levels, effects of photoperiod alone, and the possible interaction of photoperiod and food availability via hemolysis-hemagglutination, haptoglobin and microbial killing assays as well as utilizing differential white blood cell counts. Photoperiod and food treatment effects on immunity will be analyzed using GLMMs and AICc to assess weight and fit of all models.
