Patterns of annual and seasonal immune investment in a temporal reproductive opportunist

Abstract

AbstractHistorically, investigations of how organisms’ investments in immunity fluctuate in response to environmental and physiological changes have focused on seasonally breeding organisms that confine reproduction to seasons with mild environmental conditions and abundant resources. Consequently, knowledge of how harsh environmental conditions and reproductive effort may interact to shape investment in immunity remains limited. The red crossbill, Loxia curvirostra, is a songbird that can breed on both short, cold and long, warm days if conifer seeds are abundant. This species provides an ideal system to investigate the influence of environmental fluctuations, reproductive investment, and their potential interactions on patterns of immune investment. In this study, we measured inter- and intra-annual immune variation in crossbills across four consecutive summers (2010-2013) and multiple seasons within one year (summer 2011-spring 2012) to explore how physiological and environmental factors impact this immune variation. Overall, the data suggest that immunity varies seasonally, among years, and in response to environmental fluctuations in food resources, precipitation, and temperature, but less in response to physiological measures such as reproduction. Collectively, this system demonstrates that a reproductively flexible organism may breed when conditions allow simultaneous investment in survival-related processes rather than at the expense of them.