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0.080
0.048
0.016
-0.016
-0.048
Control injected
Immunized
-0.080
Control
CarotF
CarotN
FIGURE 23.4
Effects of dietary supplementation with carotenoids on cell-mediated immune responses to
intradermal injection with phytohaemagglutinin in the wing-web in nestling great tits (
P. major
). Values are
the residuals (means ± SE) from an analysis of variance including nest as a random factor, therefore statistically
controlling for the nonindependence of related individuals within nests. Means that are signii cantly different
are denoted by asterisks (
**
P
< 0.01). CarotF = feather carotenoids; CarotN = nonfeather carotenoids.
is not correlated with coloration as a breeding adult the following year, suggesting that these color
traits have different signal functions (Fitze et al. 2003a). One possibility is that nestling coloration
functions as a signal in parent-offspring communication, where parents decide how to allocate care
among their chicks based on their coloration. However, no effect of experimentally manipulated
offspring color on parental preference has been found (Tschirren et al. 2005). Moreover, chick col-
oration is unrelated to survival post-l edging, suggesting that this plumage trait is not under natural
selection (Fitze and Tschirren 2006). Clearly, more work is needed in this area.
23.6 DEVELOPMENTAL PREDICTORS OF ADULT COLORATION IN
PRECOCIAL CAPTIVE BIRD MODELS
While numerous investigations have been performed on the ontogenetic conditions that inl uence
carotenoid accumulation and coloration, even in wild birds, they still have made limited contribu-
tions to our understanding of carotenoid sexual signaling because the color is developed in sexually
immature animals and has no known visual communication function (see Section 23.5). In con-
trast, there are several insightful studies on domesticated birds, especially gamebirds (e.g., pheasant,
chicken), where the effects of developmental stressors were examined in relation to later-life color
expression, including some adult sexual ornaments. This mechanistic approach to “organizational
control” of sexual traits provides an excellent supplement to the dominant lines of research on “acti-
vational control” of ornamental coloration in adults (see Sections 23.2 and 23.4). Until very recently,
studies of organizational effects on animal signals were largely limited to the neurobiological, endo-
crinological, and nutritional investigations of bird song learning and development (e.g., Nowicki
et al. (1998)). From this framework emerge several key principles in nutrition, immunology, and
development that make carotenoid color systems excellent models for studying the ontogeny of
signal production.
Domestic chicken (
Gallus gallus domesticus
) has long been an ideal species for studying
carotenoids, given the industrial production needs for high carotenoid accumulation in legs and
yolk and the various problems that can prevent this from happening (e.g., pale bird syndrome,
due to parasites and poor diets; Bauernfeind 1981). Within the last i ve years, however, a new
line of work has emerged in chickens, with the goal of understanding how early-life access that
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