Meeting Abstract
Plasticity can enhance an individual’s fitness in dynamic environments. For instance, conspecific territorial aggression may be adaptive during pre-breeding competition for territories or nesting sites, but high levels of conspecific aggression may be more costly to maintain during parental stages, particularly for animals with substantial parental duties. Selection may therefore favor individuals that modulate aggression across breeding stages; however, plasticity is not necessarily infinite. To understand how selection may shape plasticity of aggression across breeding stages, we need to assess the degree of individual plasticity in aggression and how it varies with other life history and fitness correlates. We are exploring these questions using the tree swallow (Tachycineta bicolor), a single-brooded species in which females compete for and defend limited nesting sites throughout the breeding season. We performed over 200 simulated territorial intrusions to repeatedly assay aggression across multiple breeding stages. At the population level, we found that average aggression levels decreased over the breeding season, consistent with previous work. However, at the individual level, we found substantial variation in plasticity: some females dramatically reduce aggression as the breeding season progresses while others maintain more moderate levels of aggression. Results will further explore how variation in behavioral plasticity relates to proxies of reproductive success and other life history traits, including age. In doing so, this study will provide a critical first step in understanding the causes and consequences of plasticity in territorial aggression.
