Meeting Abstract
In social species, groups of individuals that live, forage, or interact with each other often form a linear dominance hierarchy. Dominant individuals are thought to have greater access to resources and the ability to obtain higher-quality territories or mates, but maintaining status comes with an energetic cost. This cost could produce a trade-off between investment into behaviors that maintain dominance and other systems, such as innate immunity. A strong innate immune system enables individuals to resist infections and survive to reproduce but may be costly to maintain. The links between dominance rank, health and fitness have been studied extensively in systems where dominance is displayed year-round and across generations, but rarely in species that live in temporary or seasonal social groups. Many songbirds, such as the black-capped chickadee (Poecile atricapillus) form flocks during the winter then divide into pairs for breeding during the spring. Our study used chickadees to determine whether dominance status in the winter flock is related to innate immune function across seasons, and whether a challenge to the immune system affects social status. In captive flocks, top-ranked individuals were given an immune challenge in the form of a lipopolysaccharide (LPS) injection, and dominance behavior was observed to determine if status was altered. LPS injected individuals lost a significant amount of weight and increased feeding rate when compared to control injected birds, indicating an energetic cost, but did not exhibit a change in behavior or loss of rank. In addition, a negative trend was observed between dominance behavior and innate immune function in captive and wild populations.
