Title

Plumage evolution in bearded manakins (Manacus spps.)

Date of Award

2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

J. Albert C. Uy

Keywords

Plumage, Bearded manakins, Manacus

Subject Categories

Animal Sciences | Ecology and Evolutionary Biology | Evolution | Life Sciences | Zoology

Abstract

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 now 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. We studied a unique avian hybrid zone between Manacus candei and M. vitellinus, where the bright white secondary male plumage of Manacus candei is evolving into bright yellow plumage through the introgression of plumage traits from Manacus vitellinus. We 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, we monitored a group of male Manacus vitellinus throughout the breeding season and related the number of females they copulated with (mating success) to their respective plumage traits. We then focused on a population of males where the two color forms came together at the hybrid zone. This population contained both yellow and white males that competed for the same females. We 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 color types in mating success that may explain the observed introgression of yellow plumage traits. In attempt to distinguish between female choice and male male-competition for any observed difference in mating success between the two color forms, we measured other physical and behavioral attributes considered important to male-male competition between naturally yellow and naturally white males. Further, we monitored both a population of male Manacus candei and a population of male Manacus vitellinus during the height of their breeding season to determine the mating success of each individual. We then modeled how females perceive their specific plumage traits in their particular environment to determine if females were simply choosing the males with the most conspicuous plumage traits. Lastly, we examined if this sexually-selected color trait could serve another additional function outside of attracting females by performing a plumage manipulation experiment in the population containing both yellow and white individuals.

We found that aspects of color were indeed strong predictors of mating success in this species complex and that the introgression of novel yellow plumage traits into Manacus candei as a result of this hybridization was most likely the result of sexual selection via female choice. Females, however, did not choose the most conspicuous males in leks outside of the hybrid zone, leading us to conclude that female preference for particular colors may be more complex than just favoring the most effective signal. Results of the plumage manipulation experiment demonstrated that males were also using color, most likely to discriminate between familiar and unfamiliar males.

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