Effect of yolk corticosterone on begging in the yellow-legged gull.

Behavioral lateralization is widespread across vertebrates. The development of lateralization is affected by both genetic and environmental factors. In birds, maternal substances in the egg can affect offspring lateralization via activational and/or organizational effects. Corticosterone affects the development of brain asymmetry, suggesting that variation in yolk corticosterone concentration may also influence post-natal behavioral lateralization, a hypothesis that has never been tested so far. In the yellow-legged gull (Larus michahellis), we increased yolk corticosterone concentration within physiological limits and analyzed the direction of lateralization of hatchlings in reverting from supine to prone position ('RTP' response) and in pecking at dummy parental bills to solicit food provisioning ('begging' response). We found that corticosterone treatment negatively affected the frequency of begging and it may cause a slight leftward lateralization. However, the direction of lateralization of the RTP response was not affected by corticosterone administration. Thus, our study shows a maternal effect mediated by corticosterone on a behavioral trait involved in parent-offspring communication during food provisioning events. The findings on lateralization are not conclusive due to the weak effect size but provide information for further ecological and evolutionary studies, investigating mechanisms underlying the development of lateralization.