Results
There were no significant effects of the ages of the natal or foster
parents on offspring telomeres at hatching or the change in offspring
telomere length from hatching to the end of post-natal development
(Figure 1, see Tables 2 and S2 for results with age groups, young vs
old, and Tables 3 and S1 for results with parental age as a continuous
factor). When we entered the parental age squared in the models, it did
not change this result (Tables S7-S9). Telomere length was individually
repeatable between the first and second sampling, separated by on
average 11 days (repeatability r = 0.55, CI= 0.368 to 0.69, p
< 0.0001, Figure 2). Chick telomere length between the first
and second telomere measurements increased rather than decreased (the
estimated change in relative telomere length was 0.08 ± 0.05, p=0.003,
Table 2; when one outlier chick with highest increase in telomere length
was removed, the results stayed similar, estimated change 0.06 ± 0.04, p
= 0.005). The rate of growth during post-natal development was not
significantly related to the change in telomere length (measured as
change of head size, r < 0.0001; p = 0.97, Figure 3). Chick
growth rate was not related to the age of the parents and foster parents
(all parental effect p-values > 0.31, Tables S4-S5). The
power for detecting potential effects of parental age on telomere length
and telomere shortening in our sample is reported in Table S3. The study
set up also allowed us to assess wide-sense heritability of telomere
length, although these results must be taken with caution, since we did
not use a split nest cross-fostering design. Chick telomere length at
both first (h2=0.27 CI=0.05 to 0.50) and second
(h2=0.30 CI=0.08 to 0.54) measurement as well as the
change of telomere length (calculated as telomere length 2 - telomere
length 1, h2=0.14 CI=0.03 to 0.29) were heritable.