Mechanisms and behavioural consequences of egg-mediated maternal effects

One of the major transitions in evolution is the origin of animal societies. Animal societies have different group sizes. Group size determines the formation of social structures in a group, which are maintain by social interactions among group members. This work focus on the proximate mechanism underpinning the influences of group size on social behaviours of the cooperative breeder Neolamprologus pulcher. The ability to flexibly adjust behaviour to social and non-social challenges is important for successfully navigating variable environments. However, it is unknown if social and non-social behavioural flexibility share common underlying cognitive mechanisms. Support for such shared mechanism would be provided if the same neural mechanisms in the brain affected social and non-social behavioural flexibility similarly. Evidence was found that early-life hypothalamic-pituitary-interrenal axis programming with cortisol reduces both social and non-social behavioural flexibility, suggesting a shared cognitive basis of behavioural flexibility. In cooperative breeders, group size could influence dominant female’s reproductive strategies because the number of carers in the group can contribute with alloparental care and have a load lightening effect. Therefore, maternal social environment could be a key factor that offers mothers the opportunity to implement maternal effects to adjust offspring phenotype. There is no evidence that N. pulcher used egg-mediated maternal effects in the form of bigger eggs or endowment with corticosteroid hormones. In a wild population the size of the social group may offers the opportunity to large subordinate individuals to specialize in two behavioural phenotypes, namely philopatric with high propensity to show submissive behaviour or early dispersal with high frequency of helping in the natal territory. Evidence was found that in small social groups, large subordinate individuals show a lower frequency of submissive behaviour and tend to show a higher frequency of sand digging. This suggest that group size may influence two energetically costly behaviours known to enhance the probability to be accepted in a social group. To conclude, this work provides important insight on the mechanisms that regulate behavioural flexibility and the importance of the social environment to further shape individuals’ behaviour