Gape coloration reliably reflects immunocompetence of barn swallow (Hirundo rustica) nestlings |
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Authors: | Saino Nicola; Ambrosini Roberto; Martinelli Roberta; Ninni Paola; Moller Anders Pape |
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Institution: | aDipartimento di Biologia, Sez. Zoologia Scienze Naturali, Università degli Studi di Milano, via Celoria 26, I-20133 Milano, Italy
bLaboratoire d'Ecologie, CNRS UMR 7625, Université Pierre et Marie Curie, 7 quai St. Bernard, Case 237, F-75252 Paris Cedex 05, France |
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Abstract: | In some passerines, parents allocate more food to offspringwith the brightest red gapes, but the function of parental decisionsbased on offspring gape coloration is unknown. We hypothesizethat gape coloration is part of a communication system wherenestlings reveal their condition to attending parents, whichmay thus base their decisions on reliable signals of offspringreproductive value. We analyze the effects of brood size manipulation,injection with an immunogen and food deprivation, on gape coloration,morphology, and T-cellmediated immunocompetence of nestlingbarn swallows (Hirundo rustica). For each gape we measured threecomponents of coloration (hue, saturation, and brightness) andobtained an overall color score by principal component analysis.Enlargement of brood size and injection with an antigen resultedin less red and less saturated and brighter gape color. Nestlingsin enlarged broods had smaller body mass and T-cellmediatedimmunocompetence compared to those in reduced broods. A positivecovariation existed between redness and saturation of gape colorand T-cellmediated immunocompetence. Gape color siblingsraised in different nests did not depend on parentage. Thus,condition-dependent gape coloration can reveal different componentsof nestling state on which parents may base their adaptive decisionsabout allocation of care to the offspring. |
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Keywords: | begging food provisioning parental food allocation parent offspring conflict reproductive value |
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