Abstract 

1. Animal personality traits emerge developmentally from the interaction of genetic and

early environmental factors. Maternal hormones, such as androgens (testosterone, T and

androstenedione, A4), transferred to embryos and egg yolks may simultaneously organize

multiple behavioural and physiological traits. Whereas previous studies demonstrated an

association between the mother’s personality and yolk androgen levels, the independent

effects of the male partner’s personality and pair combination are unknown.

2. We test this association using an ecological model species for personality research, the

great tit (Parus major) using multiple approaches: 1) a wild population, 2) a randomly

mated captive population, and 3) an experimental study with (dis)assortatively mated

pairs from lines selected for fast exploration/boldness or slow exploration/shyness.

3. Egg androgen concentrations were associated with variation in female personality traits,

and the experimental data suggested that this is independent of male personality:

experimental females from slow-shy line tended to have higher egg T concentrations than

females from the fast-bold line, with no effect of male personality. Shy females from the

wild population had higher egg A4 concentration than bold females. However, in the

correlative data yolk hormones were linked with male personality, as well as the

interaction between female and male traits and yolk androgen levels: Male handling

responsiveness correlated negatively with egg A4 concentration in wild birds. In

randomly-mated birds, pairs that were mated assortatively for personality had lower egg

T concentrations than disassortatively mated pairs.

4. Given that egg androgens are known developmental mediators of avian personality, our

results suggest that maternal hormones might contribute to the heritability of personality,

may be sensitive to the social context of mating, and act as key environmental drivers of

individual differences.