Sexual Selection and Adaptations for Performance of an Elaborate Courtship Display by the Golden-collared manakin (Manacus vitellinus)
Animal courtship displays can be spectacular behaviors employing extraordinary and specialized movements. How and why males perform these displays is still a matter of some debate. The male golden-collared manakin (Manacus vitellinus) is a neotropical passerine that spends up to seven months each year on a lek, performing courtship displays to attract females. The display involves the production of mechanical sounds while rapidly jumping around in a cleared court on the forest floor. I hypothesize that females prefer males with optimal neuromuscular control enabling them to excel in the performance of their displays. I propose that courtship displays pose high energetic demands with accompanying behavioral and/or cardiovascular adaptations. Lastly, as testosterone has been shown to activate courtship in male manakins, and the heart is known for being an androgen target in mammals, I propose that testosterone regulates manakin cardiovascular function. I used high-speed videography to film courting male manakins and heart rate transmitters to estimate their energy expenditure. With molecular and histological techniques I investigated the male manakin myocardium. Knowing that female manakins are able to distinguish males by tens of milliseconds, choosing faster males for copulations, I show here that females ultimately challenge males by joining them in their display before finalizing their decision to mate. Heart rates rise up to 1300 beats per minute during some of the behaviors preferred by females, but average daily heart rates are comparatively low, comparable to those of other tropical birds. From a metabolic perspective, male manakin courtship resembles many sprints as opposed to a marathon, as successful males display up to 140 times a day, but each display lasts only ~10 seconds. Compared to a passerine bird of similar size that does not perform elaborate courtship, I found that the muscular walls of the manakin left ventricle are enlarged. The manakin heart expresses androgen receptors at a high level and androgens appear to be involved in calcium handling in the manakin myocardium. A functional approach to animal behavior or sexual selection suggests that physiological costs are associated with mate choice and provides a unique window into anatomical and physiological potential.