Many studies have identified the reproductive benefits of cooperative behaviors, yet few have identified the mechanisms that underlie these behaviors. Mechanistic studies can inform our understanding of why some individuals are more or less cooperative as well as identify the physiological constraints imposed upon the evolution of reproductive traits. Male wire-tailed manakins (Pipra filicauda) exhibit cooperative courtship behaviors and more cooperative territory-holders have been shown to exhibit higher reproductive success. To begin to understand the proximate basis of cooperative display behaviors, we conducted both an observational study and an experimental study. Because coordinated courtship displays underlie this form of cooperation, our study also examined both the hormonal and social drivers of individual variation in courtship behavior more broadly (e.g., display rates). Our observational study revealed that males with higher testosterone levels performed fewer cooperative display bouts. In addition, our experimental implant study, males that received a testosterone-implant significantly decreased the proportion of their displays that were cooperative. We found no relationship between an individual’s courtship display effort (i.e., display rate and time spent performing courtship displays) and circulating testosterone in either study. However, more cooperative males spent a greater proportion of time performing courtship displays than did less cooperative males, suggesting that testosterone may indirectly mediate courtship display behaviors by influencing a territory holder’s cooperative behavior. Overall, both our observational and experimental results suggest that reduced cooperative behavior is a cost of maintaining high levels of testosterone for territory-holding males.

Male courtship behavior was measured using video recordings and data were manually transcribed. Circulating testosterone was measured from blood samples collected males on the lek. Testosterone levels were manipulated using silastic implants sealed with silicon. 

See the data ReadMe file for more information, including column descriptions, about the each dataset.