Increased plumage darkness of Shiny Cowbird females in the subtropics: an adaptation to bacterial degradation?

BETTINA MAHLER; NANCY I. LOPEZ; ALEJANDRO G. DI GIACOMO; JUAN C. REBOREDA

IBIS

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2010 vol. 52 p. 775 - 781

0019-1019

The Shiny Cowbird Molothrus bonariensis is a sexually dichromatic species, in which males are black blue iridescent and females are dull brown. However, in some subtropical areas of its distribution females show a plumage polymorphism that ranges from dull brown to dark brown and black. Plumage melanization has been shown to protect feathers from bacterial degradation, decreasing the effects of harmful bacterial activity and thus plumage damage. In this study, we tested whether bacterial feather degrading activity is acting as the selective force to increase darkness in the plumage of the female Shiny Cowbird. We compared the degradation of female feathers belonging to different colour morphs when exposed to bacterial strains isolated from subtropical and temperate zones of its distribution and to Bacillus licheniformis. We did not find differences in susceptibility to bacterial degradation between female’s brown feathers and female’s darker feathers. These results suggest that female plumage polymorphism in Shiny Cowbirds did not arise as a defense to bacterial feather-degrading activity.Molothrus bonariensis is a sexually dichromatic species, in which males are black blue iridescent and females are dull brown. However, in some subtropical areas of its distribution females show a plumage polymorphism that ranges from dull brown to dark brown and black. Plumage melanization has been shown to protect feathers from bacterial degradation, decreasing the effects of harmful bacterial activity and thus plumage damage. In this study, we tested whether bacterial feather degrading activity is acting as the selective force to increase darkness in the plumage of the female Shiny Cowbird. We compared the degradation of female feathers belonging to different colour morphs when exposed to bacterial strains isolated from subtropical and temperate zones of its distribution and to Bacillus licheniformis. We did not find differences in susceptibility to bacterial degradation between female’s brown feathers and female’s darker feathers. These results suggest that female plumage polymorphism in Shiny Cowbirds did not arise as a defense to bacterial feather-degrading activity.