Transient growth-enhancing effects of elevated maternal thyroid hormones at no apparent oxidative cost during early postnatal period

Maternal thyroid hormones (THs) have been proven crucial for embryonic development in humans, but their influence within the natural variation on wild animals remains unknown. So far the only two studies that experimentally investigated the potential fitness consequences of maternal THs in birds found inconsistent results. More studies are thus required to assess the general effects of maternal THs and their influences on more behavioral and physiological parameters. In this study, we experimentally elevated yolk TH content in a wild migratory passerine species, the collared flycatcher (Ficedula albicollis), to investigate the effects on hatching success, nestling growth and oxidative stress. We found that TH-injected eggs had a higher hatching success, and the nestlings hatched from TH-injected eggs were heavier and larger than control nestlings, but only during the early postnatal period. These differences vanished by fledging. Nestlings from TH-injected eggs exhibited lower activity ...