Journal Article

Female plumage spottiness signals parasite resistance in the barn owl (<i>Tyto alba</i>)

Alexandre Roulin, Christian Riols, Cor Dijkstra and Anne-Lyse Ducrest

in Behavioral Ecology

Published on behalf of International Society for Behavioral Ecology

Volume 12, issue 1, pages 103-110
Published in print January 2001 | ISSN: 1045-2249
Published online January 2001 | e-ISSN: 1465-7279 | DOI: http://dx.doi.org/10.1093/oxfordjournals.beheco.a000371
Female plumage spottiness signals parasite resistance in the barn owl
 (Tyto alba)

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  • Evolutionary Biology
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The hypothesis that extravagant ornaments signal parasite resistance has received support in several species for ornamented males but more rarely for ornamented females. However, recent theories have proposed that females should often be under sexual selection, and therefore females may signal the heritable capacity to resist parasites. We investigated this hypothesis in the socially monogamous barn owl, Tyto alba, in which females exhibit on average more and larger black spots on the plumage than males, and in which males were suggested to choose a mate with respect to female plumage spottiness. We hypothesized that the proportion of the plumage surface covered by black spots signals parasite resistance. In line with this hypothesis, we found that the ectoparasitic fly, Carnus hemapterus, was less abundant on young raised by more heavily spotted females and those flies were less fecund. In an experiment, where entire clutches were cross-fostered between nests, we found that the fecundity of the flies collected on nestlings was negatively correlated with the genetic mother's plumage spottiness. These results suggest that the ability to resist parasites covaries with the extent of female plumage spottiness. Among females collected dead along roads, those with a lot of black spots had a small bursa of Fabricius. Given that parasites trigger the development of this immune organ, this observation further suggests that more spotted females are usually less parasitized. The same analyses performed on male plumage spottiness all provided non-significant results. To our knowledge, this study is the first one showing that a heritable secondary sexual characteristics displayed by females reflects parasite resistance.

Keywords: bursa of Fabricius; Carnus hemapterus; fecundity; female plumage ornamentation; good gene; parasite resistance; Tyto alba

Journal Article.  6725 words.  Illustrated.

Subjects: Evolutionary Biology ; Ecology and Conservation ; Zoology and Animal Sciences

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