Much of the research of understanding cooperative behaviors has focused on why helpers assist. There has been less attention to why the recipient of the apparent help participates; the benefit is often assumed. It is equally important to understand the costs and benefits of cooperation for the recipient. Separately, variation in the behavioral strategies of individuals within the same population is intriguing as it means that individuals may achieve similar ends through different behaviors.
In Corapipo altera, a lek-breeding neotropical manakin (Aves: Pipridae), we've found natural variation within a single population where some males engage in cooperative display coalitions in their courtship for females while others display solo. Males of this species can be long-lived (>14 years) and have delayed plumage maturation, reaching definitive plumage in their third year after hatching. Our previous work has found that males in cooperative display coalitions are not close relatives.
Using six years of observation data, I tested the hypotheses that dominant males in coalitions have 1) higher annual reproductive success by displaying for and mating with more females than do solo males and 2) longer lifespan but have 3) shorter tenure at a lek display site due to competition from the cooperating subordinate.
Surprisingly, we find that dominant males in cooperative display coalitions do not increase their annual reproductive success as measured by female visitation and copulation rates. Instead, dominant males gain lifetime fitness benefits through an increased duration of tenure at the display site and increased lifespan. As males are rarely seen in the breeding season after loosing display-site tenure, we are unable to tease apart the relative impacts of tenure length and lifespan. This result highlights the importance of studying lifetime fitness, important for an evolutionary explanation of cooperation in this and other species, and not using annual reproductive success as a proxy. This result emphasizes the need to study organisms entire lifespan, or in the case of very long-lived species at least multiple breeding seasons.