Thyroid hormones from the mom: a novel mechanism for mothers to affect offspring in birds
​Our new study made it to the cover of Hormones and Behavior

​Thyroid hormones and eggs

We studied how thyroid hormones from the mother may influence offspring in birds: we experimentally manipulated hormone levels in eggs with hormone injections into eggs in a wild bird, the great tit (Parus major). We then compared offspring traits from eggs with elevated hormone levels and eggs with control injections. We found that high egg thyroid hormone level increased the growth of male chicks but decreased the growth of female chicks. These are the first results to show that egg thyroid hormones are important for offspring development in (wild) birds. These results suggest that in birds, just like in mammals, variation in maternal levels of thyroid hormone may be a mechanism via which mothers can influence offspring traits, e.i. a novel mechanism for so-called maternal effects in birds. We did not yet test any effects of thyroid hormones on neurodevelopment, found in mammals, but our findings suggest that the egg model may be useful for experimentally studying the potential neurodevelopmental effects of thyroid hormones, and thus may contribute important information concerning the role of thyroid hormone also in humans.
Suvi Ruuskanen