Diet quality affects an attractive white plumage pattern in dark-eyed juncos (Junco hyemalis) |
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Authors: | Joel W McGlothlin Deborah L Duffy Jessica L Henry-Freeman Ellen D Ketterson |
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Institution: | (1) Department of Biology, Indiana University, Bloomington, IN 47405, USA;(2) Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington, IN 47405, USA;(3) Present address: Department of Clinical Studies, Center for the Interaction of Animals and Society, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA |
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Abstract: | Sexually selected traits that act as signals of quality often display some degree of condition dependence. In birds, condition
dependence of ornamental plumage is often mediated by production costs related to acquisition or allocation of dietary resources.
White plumage ornaments, however, have often been assumed to be inexpensive because their production requires neither pigment
nor specialized feather structure. In male dark-eyed juncos (Junco hyemalis), the size of a white patch on the tail contributes to attractiveness and mating success. Using captive males, we examined
the effects of diet quality on the size and brightness of the tail-white patch. After removing four tail feathers to induce
replacement, we maintained subjects on a subsistence (low-protein) or enriched (high-protein) diet while induced feathers
grew. Birds that received an enriched diet grew their feathers more quickly and grew larger, brighter white patches. Feather
growth rate was positively correlated with the increase in the size of the tail-white patch, a relationship that was stronger
in the subsistence diet group. However, within diet treatments, faster-grown feathers were slightly duller. Taken together,
these results suggest that variation in diet quality may lead to condition-dependent expression of tail white and that condition
dependence may be stronger in more stressful environments. We suggest a mechanism by which increased feather growth rate may
lead to an increase in the size of the tail-white patch and discuss potential trade-offs between signal size and brightness. |
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Keywords: | Honest signals Condition dependence Sexual selection Plumage development Junco hyemalis |
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