Meeting Abstract
Life history theory predicts that, when resources are limited, energy allocation will be split between somatic and reproductive effort. In order to maximize fitness, organisms should invest these limited resources optimally into either of these efforts via a wide range of traits. This split allocation creates trade-offs when investing in some traits over others such as predator evasion over parental effort, or egg production over immunity. Here, we evaluate the evidence supporting a trade-off between the strength of immunity and life history traits in female Tree Swallows, Tachycineta bicolor, from a breeding population in Ithaca, NY. We hypothesize that there should be a trade-off between immunity, the ability to respond to stressors and reproductive effort during demanding life history events such as breeding. Individuals with investment closest to the optimal should have higher lifetime fitness. Bacteria killing assays run using blood plasma, which provide an index of the strength of the innate immune response, revealed wide variation in the response to an E. coli challenge. Killing capacity varied from 0 to 100%, with a mean of 47%. Here, we report the relationship between killing capacity and a suite of behavioral (e.g., provisioning rate), physiological (e.g., baseline and stress-induced corticosterone, plasma glucose), and fitness (e.g., clutch size and number of chicks fledged) metrics. We anticipate that this study will provide a better understanding of resource allocation in a migratory bird with a fast pace of life.
