Abstract

Avian plumage coloration deriving from carotenoid-based pigments is among the most honest signals of individual quality. It has been argued that females may differentially allocate resources based on mate attractiveness or quality, paying the costs of investing more in a current breeding attempt. We tested predictions of the differential allocation hypothesis on the natural variation of carotenoid-based plumage using the brightly red-colored head plumage of the Red-crested Cardinal (Paroaria coronata). It is to our knowledge the first time this hypothesis is tested on the natural variation of this pigment on a wild bird. We found that the brightness of the males’ red plumage patch is positively associated with their reproductive success and the nest defence they provide. We also found that brighter males invest less in their offspring (by delivering less food to their nestlings and poorly cleaning the nest) than duller males and, by contrast, females mated with brighter males invest more in parental care. Our results are consistent with the differential allocation hypothesis: differential allocation allowed breeding pairs with brighter males to produce more offspring, suggesting that it can be considered adaptive and should be included in studies of eco-evolutionary dynamics.

Highlights

  • The expression of morphological characters that function as indicators of individual quality is well documented among animals[1]

  • This hypothesis especially applies to socially monogamous species with biparental care and carotenoid-based plumage[21], and predicts that females should be willing to pay the costs of investing more in the current breeding attempt when mated to attractive males[19]

  • There are no studies that focus on the natural variation of carotenoid-based plumages as traits that can function as indicators of quality to shed light on this mechanism in the context of sexual selection

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Summary

Introduction

The expression of morphological characters that function as indicators of individual quality is well documented among animals[1]. Whenever offspring reproductive value is directly related to the attractiveness of the mate, the ‘differential allocation hypothesis’ receives special interest[19,20,21] This hypothesis especially applies to socially monogamous species with biparental care and carotenoid-based plumage[21], and predicts that females should be willing to pay the costs of investing more in the current breeding attempt when mated to attractive males[19]. If high-quality Red-crested Cardinal males can afford to extract, metabolize and deposit more carotenoids in their plumage, these individuals will be the most intensely coloured ones[7]. We studied Red-crested Cardinal breeding pairs in a natural nesting habitat and obtained data of the main reproductive parameters and of the males’ plumage coloration. We tested the following predictions derived from the differential allocation hypothesis: 1) breeding pairs with more attractive males (i.e., with a more intense red plumage) will have higher breeding success (i.e., higher proportion of successful nests and higher egg and nestling survival) than breeding pairs with less attractive males; 2) more attractive males will invest less in parental care (i.e., lower intensity of nest defence and lower feeding and faecal extraction rates) than less attractive males; and 3) females mated with more attractive males will invest more in parental care (i.e., higher intensity of nest defence and higher feeding and faecal extraction rates) than females mated with less attractive males

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