Data from: 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 of the
glutathione-s-transferase, a major antioxidant enzyme, than control
nestlings at day 12, a few days before fledging, but they did not differ
in oxidative damage and overall intracellular oxidative state. These
results suggest that the early growth-enhancing effects incurred no
observable oxidative stress. We hypothesize that such a transient
growth-enhancing effect might be adaptive in advancing the development and
maturation of the offspring so they are well-prepared in time for the
upcoming migration. Further studies investigating whether such advancing
effects can influence long-term fitness, will be more than valuable.