Starting with a handicap: effects of asynchronous hatching on growth rate, oxidative stress and telomere dynamics in free-living great tits

International audienceA trade-off between resource investment intogrowth rate and body self-maintenance is likely to occur,but the underlying molecular mediators of such a trade-offremain to be determined. In many altricial birds, hatchingasynchrony creates a sibling competitive hierarchy withinthe brood, with first-hatched nestlings enjoying substantialadvantages compared to last-hatched nestlings. We usedthis opportunity to test for a trade-off between growth andself-maintenance processes (oxidative stress, telomere erosion)in great tit nestlings, since resource availability andallocation are likely to differ between first-hatched andlast-hatched nestlings. We found that despite their startingcompetitive handicap (i.e. being smaller/lighter before day16), last-hatched nestlings exhibited growth rate and mass/size at fledging similar to first-hatched ones. However, lasthatchednestlings suffered more in terms of oxidative stress,and ended growth with shorter telomeres than first-hatchedones. Interestingly, growth rate was positively related toplasma antioxidant capacity and early life telomere length(i.e. at 7 days old), but among last-hatched nestlings, thoseexhibiting the faster body size growth were also thoseexhibiting the greatest telomere erosion. Last-hatched nestlingsexhibited 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 aspecific trade-off between growth rate and self-maintenanceprocesses, which is possibly driven by their need tocompete with their older siblings and potentially mediatedby elevated levels of T