Carotenoid coloration is related to fat digestion efficiency in a wild bird
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Some of the most spectacular visual signals found in the animal kingdom are based on dietarily derived carotenoid pigments (which cannot be produced de novo), with a general assumption that carotenoids are limited resources for wild organisms, causing trade-offs in allocation of carotenoids to different physiological functions and ornamentation. This resource trade-off view has been recently questioned, since the efficiency of carotenoid processing may relax the trade-off between allocation toward condition or ornamentation. This hypothesis has so far received little exploratory support, since studies of digestive efficiency of wild animals are limited due to methodological difficulties. Recently, a method for quantifying the percentage of fat in fecal samples to measure digestive efficiency has been developed in birds. Here, we use this method to test if the intensity of the carotenoid-based coloration predicts digestive efficiency in a wild bird, the house finch (Haemorhous mexicanus). The redness of carotenoid feather coloration (hue) positively predicted digestion efficiency, with redder birds being more efficient at absorbing fats from seeds. We show for the first time in a wild species that digestive efficiency predicts ornamental coloration. Though not conclusive due to the correlative nature of our study, these results strongly suggest that fat extraction might be a crucial but overlooked process behind many ornamental traits.
KeywordsSexual selection Steatocrit Ornamentation Metabolism Coccidia
We thank Devon Allred, Aaron Craig, Brittany Switzer, Randi Bromm, Kevin McGraw, Peeter Hõrak, and Richard Meitern for help and advice. The publication reflects only the authors’ views; the Research Executive Agency is not responsible for any use that may be made of the information it contains.
This study was supported by the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 701747 to T.S.
Compliance with ethical standards
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. This research was approved by ASU Institutional Animal Care and Use Committee by animal protocol number 15-1401RRFC43.
Conflict of interest
The authors declare that they have no competing interests.
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