1
Discussion S1. Yolk carotenoid variation.
2
We report a yolk total carotenoid concentration in 2007 similar to the one found in the same
3
population in 2008 (Midamegbe et al., submitted). The concentration in our study population is on
4
average 1.5 times higher than in another population of blue tits breeding in eastern France, but is
5
similar to the concentration found in this population after the females got carotenoid
6
supplementation in diet [1]. Because environmental variability and/or differences in foraging
7
ability, absorption, or metabolizing efficiency (reviewed in [2,3]) may make carotenoids a limited
8
resource, this result suggests that carotenoids might be quite abundant in our study population or
9
that females face a lower level of exposure to parasites (that likely limit maternal transfer to the
10
egg yolk [4]) or stress. Carotenoids can only be acquired from specific food items [5] and play
11
crucial roles in immune defense mechanisms and embryonic development [6,7]. Thus if they are
12
highly available, female quality should have a limited influence (in terms of foraging and/or
13
immunity capacity) on their allocation to the eggs. In accordance with this idea, none of the
14
several proxies of female quality used in this study predicted egg yolk concentrations. In addition,
15
if females in our population are indeed not limited in carotenoids, the association between yolk
16
carotenoid content and male plumage coloration may be best explained by variation in territory
17
quality rather than differential allocation.
18
As previously found in several passerines (e.g. [8,9,10,11,12]), our results showed a decrease
19
in maternal deposition of yolk carotenoids over the laying sequence (note that the yolk antibody
20
level did not vary with laying order, which is consistent with the absence of systematic variation
21
within clutches [13]). Carotenoid supplementation in the diets of several bird species did not
22
prevent its decrease over the laying sequence (e.g. [10,14], but see [1]). Moreover, carotenoids
23
might not be limited in our study population. It suggests that there might be a trade-off with
24
mother’s own somatic maintenance to fight oxidative stress accumulated over the egg laying [15]
1
25
or an active regulation of antioxidant concentration in eggs by females (control over sibling
26
competition, offspring sex or brood reduction, e.g. [16,17,18]; differential allocation in favor of
27
extra-pair young [19]).
28
29
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31
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