|Plumage Evolution in Bearded Manakins 2002-2008|
Much of the data for this project was collected using specially-designed motion sensor cameras which recorded the activity of study males. These cameras were set up near an individual male's court and recorded all breeding activities of the male such as sexual diplays, courtships and matings.
| The evolution of bright, colorful and elaborate male secondary sexual characteristics is now widely accepted to be the product of sexual selection by female choice and/or male-male competition. More recently, sexual selection by female choice has also been argued to play an important role in the speciation process. In particular, it has been argued that when a female preference for a particular sexual trait diverges and there is a corresponding divergence in that male trait, it could inhibit different but essentially genetically similar, populations from interbreeding. Many studies have begun to elucidate the role of divergent sexual selection in reproductive isolation, but few have focused on the underlying mechanisms that drive the change in female preference.
For my PhD from the Uy lab, I studied an avian hybrid zone between Manacus candei and M. vitellinus, where the bright white secondary male plumage of M. candei is evolving into the bright yellow plumage through the introgression of plumage traits from M. vitellinus. This hybrid zone shows narrow, coincident clines in several measured genetic and morphological characteristics, typical of other hybrid zones, but the cline for male plumage color is shifted ~50 kilometers into M. candei's population where it forms a similarly narrow cline along the Changuinola River.
I wanted to investigate this unique hybrid zone in an attempt to discover what mechanisms may be responsible for causing sexual signals to diverge. To test whether male secondary sexual color was an important corollary to mating success, I monitored a group of male manakins throughout the breeding season and related the number of females they copulated with (mating success) to their respective plumage traits. I then focused on the population of males where the two color types came together within the hybrid zone. This population contained both yellow and white males that competed for the same females. I monitored selected pairs of males that consisted of one naturally white male and one naturally yellow male to see if there was any difference between the color types in mating success that may explain the observed introgression of yellow plumage traits. In an attempt to distingush between female choice and male-male competition for any observed difference in mating success between the two color types, I measured other physical and behavioral attributes considered important to male-male competition between naturally yellow and naturally white males. Further, I monitored both a population of male M. candei and a population of male M. vitellinus during the height of their breeding season to determine the mating success of each individual. I then modeled how females perceive their specific plumage in their particular environment to determine if females were simply choosing males with the most conspicuous plumage traits. Lastly, I examined if this pllumage color trait could serve another additional function outside of attracting females. To do so, I performed a plumage manipulation experiment in the population containing both yellow and white individuals.
I found that a certain aspect of color was indeed a strong predictor of mating success in this species complex (Stein and Uy 2006a) and that the introgression of yellow plumage traits into M. candei as a result of this hybridization was most likely the result of sexual selection via female choice (Stein and Uy 2006b). Although the spread and introgression of plumage traits is associated with changes in the signalling environment (Uy and Stein 2007), I was unable to find that females mated with the most conspicuous males. The results of the plumage manipulation experiment demonstrated that males were also using color, most likely to discriminate between familiar and unfamiliar males (Stein and Uy in prep.)
This project consisted of intensive fieldwork in various locations within Panama and Costa Rica, but was rooted in the rainforests along the Changuinola River on the Panamanian / Costa Rican border (Click here to read about the field site).