Brood size, telomere length and parent-offspring color signaling in barn swallows

Telomeres are nucleoproteins that confer stability to eukaryotic genome, but shorten at each cell
division, impairing bodily functions. The rate of telomere shortening can vary according to extrinsic
factors. We found that nestling barn swallows in experimentally enlarged broods had shorter
telomeres, implying social effects on telomere dynamics. However, nestlings displaying darker
plumage retained longer telomeres. Because barn swallows preferentially feed darker nestlings, our
study shows that parents privilege offspring with larger phenotypic quality.