Starting with a handicap: effects of asynchronous hatching on growth rate, oxidative stress and telomere dynamics in free-living great tits
Résumé
A trade-off between resource investment into
growth rate and body self-maintenance is likely to occur,
but the underlying molecular mediators of such a trade-off
remain to be determined. In many altricial birds, hatching
asynchrony creates a sibling competitive hierarchy within
the brood, with first-hatched nestlings enjoying substantial
advantages compared to last-hatched nestlings. We used
this opportunity to test for a trade-off between growth and
self-maintenance processes (oxidative stress, telomere erosion)
in great tit nestlings, since resource availability and
allocation are likely to differ between first-hatched and
last-hatched nestlings. We found that despite their starting
competitive handicap (i.e. being smaller/lighter before day
16), last-hatched nestlings exhibited growth rate and mass/
size at fledging similar to first-hatched ones. However, lasthatched
nestlings suffered more in terms of oxidative stress,
and ended growth with shorter telomeres than first-hatched
ones. Interestingly, growth rate was positively related to
plasma antioxidant capacity and early life telomere length
(i.e. at 7 days old), but among last-hatched nestlings, those
exhibiting the faster body size growth were also those
exhibiting the greatest telomere erosion. Last-hatched nestlings
exhibited elevated levels of plasma testosterone (T),
but only at day 7. T levels were positively associated with oxidative damage levels and plasma antioxidant capacity,
the latter being only significant for first-hatched nestlings.
Our results suggest that last-hatched nestlings present a
specific trade-off between growth rate and self-maintenance
processes, which is possibly driven by their need to
compete with their older siblings and potentially mediated
by elevated levels of T.