Can mothers help to cope with climate change?
​Daily temperatures fluctuate during the laying season and a mother hence produces eggs at different ambient temperatures during the egg laying period. How does this effect her offspring?

Temperature and maternal investment

​We studied whether maternal investment of hormones in the eggs is temperature- related: egg hormones, just like hormones during pregnancy in e.g. humans, are known to be important in modifying offspring phenotypic traits and even offspring survival and reproduction. Our study organism is the great tit, which suffers from environmental changes caused by global warming: In this species, as in many others, it is important to match the time of chick rearing to the maximum supply of its main prey, the caterpillars. If timing is wrong, reproductive success is lower. Global warming has led to earlier the timing of its main prey, caterpillars, in the spring but birds have not advanced their breeding time as fast.
We collected data on the association between temperature and egg hormone levels from wild birds, and from experiments where birds were exposed to different temperatures before and during egg-laying. We found that variation in egg hormone levels is associated with temperatures both before egg laying (which may be used as cues to predict whether birds are early or late), and during egg  formation. This was true both for steroid hormones and thyroid hormones. The consequences of this variation on offspring should be now tested in different environments to understand if it can benefit (or not) the offspring.
Suvi Ruuskanen