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Independent sources of condition dependency and multiple pathways determine a composite trait: lessons from carotenoid-based plumage colouration


Romero-Diaz, Cristina; Richner, Heinz; Granado-Lorencio, Fernando; Tschirren, Barbara; Fitze, Patrick (2013). Independent sources of condition dependency and multiple pathways determine a composite trait: lessons from carotenoid-based plumage colouration. Journal of Evolutionary Biology, 26(3):635-646.

Abstract

Many colour ornaments are composite traits consisting of at least four components, which themselves may be more complex, determined by inde- pendent evolutionary pathways, and potentially being under different environmental control. To date, little evidence exists that several different components of colour elaboration are condition dependent and no direct evidence exists that different ornamental components are affected by differ- ent sources of variation. For example, in carotenoid-based plumage colour- ation, one of the best-known condition-dependent ornaments, colour elaboration stems from both condition-dependent pigment concentration and structural components. Some environmental flexibility of these compo- nents has been suggested, but specifically which and how they are affected remains unknown. Here, we tested whether multiple colour components may be condition dependent, by using a comprehensive 3 9 2 experimental design, in which we carotenoid supplemented and immune challenged great tit nestlings (Parus major) and quantified effects on different components of colouration. Plumage colouration was affected by an interaction between carotenoid availability and immune challenge. Path analyses showed that carotenoid supplementation increased plumage saturation via feather carot- enoid concentration and via mechanisms unrelated to carotenoid deposition, while immune challenge affected feather length, but not carotenoid concen- tration. Thus, independent condition-dependent pathways, affected by dif- ferent sources of variation, determine colour elaboration. This provides opportunities for the evolution of multiple signals within components of ornamental traits. This finding indicates that the selective forces shaping the evolution of different components of a composite trait and the trait’s signal content may be more complex than believed so far, and that holistic approaches are required for drawing comprehensive evolutionary conclu- sions.

Abstract

Many colour ornaments are composite traits consisting of at least four components, which themselves may be more complex, determined by inde- pendent evolutionary pathways, and potentially being under different environmental control. To date, little evidence exists that several different components of colour elaboration are condition dependent and no direct evidence exists that different ornamental components are affected by differ- ent sources of variation. For example, in carotenoid-based plumage colour- ation, one of the best-known condition-dependent ornaments, colour elaboration stems from both condition-dependent pigment concentration and structural components. Some environmental flexibility of these compo- nents has been suggested, but specifically which and how they are affected remains unknown. Here, we tested whether multiple colour components may be condition dependent, by using a comprehensive 3 9 2 experimental design, in which we carotenoid supplemented and immune challenged great tit nestlings (Parus major) and quantified effects on different components of colouration. Plumage colouration was affected by an interaction between carotenoid availability and immune challenge. Path analyses showed that carotenoid supplementation increased plumage saturation via feather carot- enoid concentration and via mechanisms unrelated to carotenoid deposition, while immune challenge affected feather length, but not carotenoid concen- tration. Thus, independent condition-dependent pathways, affected by dif- ferent sources of variation, determine colour elaboration. This provides opportunities for the evolution of multiple signals within components of ornamental traits. This finding indicates that the selective forces shaping the evolution of different components of a composite trait and the trait’s signal content may be more complex than believed so far, and that holistic approaches are required for drawing comprehensive evolutionary conclu- sions.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Evolutionary Biology and Environmental Studies
Dewey Decimal Classification:570 Life sciences; biology
590 Animals (Zoology)
Language:English
Date:2013
Deposited On:15 Mar 2013 12:24
Last Modified:10 Dec 2017 11:46
Publisher:Wiley-Blackwell
ISSN:1010-061X
Funders:Swiss National Science Foundation
Additional Information:The definitive version is available at www.blackwell-synergy.com
Publisher DOI:https://doi.org/10.1111/jeb.12082

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