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animals receive to carotenoids affects their carotenoid accumulation abilities and skin coloration
later in life. Leg color is sexually dichromatic in this species, though it is thought to be a product
of artii cial selection more than adaptive trait expression favored originally by natural or sexual
selection (McGraw and Klasing 2006). Koutsos and colleagues have conducted several excel-
lent nutritional, immunological, and ontogenetic studies of carotenoids and uncovered several
important relationships that factor into adult coloration. Because carotenoids at a very early
age can come either from mother (via egg yolk) or from the neonate diet, Koutsos et al. (2003)
manipulated levels of carotenoids from both sources and examined carotenoid accumulation into
body tissues four weeks later (admittedly still months before full sexual maturity). They found
that yolk carotenoids were especially key for carotenoid accumulation later in life; when birds
hatched from carotenoid-free eggs, even when they were fed high supplies of dietary carote-
noids post-hatch, they were never able to accumulate as much carotenoids as those who received
maternal yolk carotenoids. We can posit then that, if this constraint continued into adulthood, the
ability of a bird to become sexually colorful can be permanently impaired by the diet it received
from its mother even prior to hatching. Blount et al. (2003) similarly demonstrated in altricial
zebra i nches (see Section 23.3) that brief exposure to a low-quality nestling diet reduces anti-
oxidant (including carotenoid) circulation in adults, although an irreversible effect on adult male
coloration or attractiveness was not apparent in this study.
Carotenoid intake/exposure during development may have long-term effects on avian immuno-
competence also. In the above-mentioned study, deposition of carotenoids (e.g., lutein) into immune
tissues (e.g., thymus, bursa) was sensitive to the same embryonic carotenoid mechanism (Koutsos
et al. 2003), as was lutein accumulation in monocytes from one month-old chickens (Selvaraj et al.
2006). Koutsos et al. (2006) went on to directly measure immune system performance, by assessing
the systemic inl ammatory response to lipopolysaccharide injection (which simulates an infection),
and showed important
in ovo
carotenoid effects on immunity. Saino et al. (2003) found a similar
result in free-ranging barn swallows (
Hirundo rustica
), using injections with carotenoids directly
into egg yolk as opposed to manipulating the maternal diet (and thus perhaps affecting many other
maternal processes and products, not just carotenoids, that change the composition of the egg and
yolk). These studies bring into question the actual mechanism for carotenoid “organization” of
health (and perhaps coloration); as antioxidants, carotenoids may protect maturing immune cells
from damage, hence permitting optimal formation of the immune system and thus optimal perfor-
mance later in life; this would leave fewer carotenoids required to maintain good health and thus
more for color development. Alternatively, early carotenoid exposure may affect carotenoid accumu-
lation mechanisms (e.g., gut lining, lipoproteins) and permanently increase assimilation efi ciency,
allowing optimal antioxidant, immunoenhancing, and coloring actions of carotenoid supplies later
in life. Careful physiological and immunological manipulations and measurements will be required
to disentangle these alternative hypotheses.
Even more relevant to sexual signal developments have been the developmental nutrition studies
conducted on ring-necked pheasants (
Phasianus colchicus
) in Europe. Male pheasants are elabo-
rately adorned with many colorful plumage features, as well as rich red facial wattles that contain
carotenoid pigments like astaxanthin (Brockmann and Volker 1934). Wattles are enlarged during
sexual encounters, and females prefer to mate with males that have redder wattles (Hillgarth and
Wingi eld 1997); wattle size is also correlated with dominance in juvenile males (Papeschi et al.
2003). Pheasants are also ideal study subjects for this line of work because, as a precocial species,
nutrition can be manipulated independent of any parental involvement. Ohlsson and colleagues have
conducted intricate experiments to investigate the role of early nutritional conditions on wattle col-
oration and size as well as on adult immune system performance. In their i rst study (Ohlsson et al.
2002), dietary protein was manipulated (either 27% as a high dose or 20.5% as a normal growth
amount) in a factorial design at two developmental stages (0-3 weeks = very early; 4-8 weeks =
early), wattles were scored at weeks 20 and 40, and immunocompetence (measured as antibody
response to the human diphtheria-tetanus vaccine and as wing-web swelling in response to local
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