Why Birds of a Feather Stick Together

Manakins associate with close relatives to enhance mating success.

Coral Gables (March 05, 2012) — Certain kinds of male birds gather into small clusters of land called leks to perform their courtship dances, and with whom they associate matters. A new study by University of Miami evolutionary biologist J. Albert Uy and collaborators has found that some male birds are better at attracting females if they gather with close male kin than distant relatives.

The study, “Kin selection may contribute to lek evolution and trait introgression across an avian hybrid zone,” is available online and appears in the March (Volume 21, No. 6) issue of Molecular Ecology.

In relatively recent times in the evolution of life, some manakin birds of Central America split into two groups. White-collared manakins occupy the area from Mexico to Panama, while yellow-collared manakins live between Panama and Colombia. Males are colorful, while females are brown. The two species meet in northwest Panama and form leks, giving scientists the opportunity to see what happens when new species reunite.

Researchers found that in the area where the two manakin species come together, females are more attracted to yellow-collared males than to white-collared males, but only when there are several yellow males within leks. Biologists call this effect “positive frequency dependent selection.”

“Where females can compare white and yellow males simultaneously, the yellow males do a lot better than white males, but only with high numbers of other yellow males independent of lek size,” says Uy, associate professor of biology in UM’s College of Arts and Sciences and principal investigator of the study. “White males do not experience a mating advantage, regardless of lek composition.”

However, only a few of the yellow males in each lek get all the girls. So why do other yellow males help? The new study found that yellow males within leks are more closely related than males between leks. This suggests the possibility that even less successful relatives may profit from lekking with their Don Juan-like cousins.

“We think that these yellow males that help out their relatives are benefiting by passing on their family genes indirectly,” says Uy, who is also the Aresty Chair in Tropical Ecology at UM. “It’s a bit controversial, but it adds evidence of what is called kin selection—selection driven by kinship—pushing some of the dynamics of lekking, as well affecting the interactions between two species when they re-establish contact.”

Moira R. Concannon, a graduate student at the University of Massachusetts and a former undergraduate researcher in Uy’s lab, is co-author of the study. Adam C. Stein, instructor in the Monteverde Institute, also collaborated on the study.

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Manakins of Central America. Photo credit: Kyle Elliot.

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