Proximate mechanisms of variation in the carotenoid-based plumage coloration of nestling great tits (Parus major L.)

Abstract

Many vertebrates use carotenoid-based signals in social or sexual interactions. Honest signalling via carotenoids implies some limitation of carotenoid-based colour expression among phenotypes in the wild, and at least five limiting proximate mechanisms have been hypothesized. Limitation may arise by carotenoid-availability, genetic constraints, body condition, parasites, or detrimental effects of carotenoids. An understanding of the relative importance of the five mechanisms is relevant in the context of natural and sexual selection acting on signal evolution. In an experimental field study with carotenoid supplementation, simultaneous cross-fostering, manipulation of brood size and ectoparasite load, we investigated the relative importance of these mechanisms for the variation in carotenoid-based coloration of nestling great tits (Parus major). Carotenoid-based plumage coloration was significantly related to genetic origin of nestlings, and was enhanced both in carotenoid-supplemented nestlings, and nestlings raised in reduced broods. We found a tendency for ectoparasite-induced limitation of colour expression and no evidence for detrimental effects of carotenoids on growth pattern, mortality and recruitment of nestlings to the local breeding population. Thus, three of the five proposed mechanisms can generate individual variation in the expression of carotenoid-based plumage coloration in the wild and thus could maintain honesty in a trait potentially used for signalling of individual quality.

Carotenoid availability in diet and phenotype of blue and great tit nestlings

“…This confirms the findings of previous studies showing that nestling great tits from carotenoid-poor habitats grew paler yellow plumage than nestlings from carotenoid-rich habitats (Slagsvold and Lifjeld, 1985). An enhancement of yellow plumage colour was also obtained in previous supplementary feeding experiments Tschirren et al, 2003). These studies did not investigate plasma carotenoid levels following supplementation.…”

“…All great tit nestlings in this study were fed when older than 5 days, suggesting that in great tit nestlings, feather colour may be determined after an age of 6 days (contrary to what was stated by Fitze et al, 2003). In great tit fledglings, plumage colour has been shown to reflect rearing conditions in terms of habitat quality, year effects, and experimental reduction in brood size (Hõrak et al, 2000;Tschirren et al, 2003). However, at present nothing is known about the possible function of juvenile plumage colour in parent-offspring and/or offspring/offspring communication after fledging.…”

“…However, very little is known in natural populations about the possible effects of carotenoid availability in the diet on growing nestlings. To our knowledge, the effect of dietary carotenoids has only been investigated in nestling great tits (Parus major) in a population breeding in deciduous woodland Tschirren et al, 2003). Nestlings in the study by Fitze et al were provided with extra carotenoids on two feeding occasions, either shortly after hatching or later during the nestling period.…”

Differential effects of vitamins E and C and carotenoids on growth, resistance to oxidative stress, fledging success and plumage colouration in wild great tits

“…The same result could be predicted if carotenoids were not limiting for nestling plumage colouration. However, some studies found a positive effect of carotenoids on nestling plumage colouration and thus suggest a limitation (Fitze et al, 2003b;Tschirren et al, 2003; but see Larcombe et al, 2010). It is also possible that the assimilation and transportation of carotenoids are the more limiting factors than their availability per se.…”

Colorful displays signal male quality in a tropical anole lizard

“…Ectoparasites have been found to limit color expression (Tschirren et al 2003) and behavioral display (Doucet and Montgomerie 2003); however, the degree to which ectoparasites affect fitness remains unclear (Proctor and Owens 2000). Among taxa as diverse as insects, fish, birds, and reptiles, individuals use coloration to communicate quality and status (Bradbury and Vehrencamp 2011), yet we lack a general understanding of whether ectoparasites alter the information signaled by colorful animal structures.…”