Maternal Effects in a Wild Songbird Are Environmentally Plastic but Only Marginally Alter the Rate of Adaptation.

Despite ample evidence for the presence of maternal effects (MEs) in a variety of traits and strong theoretical indications for their evolutionary consequences, empirical evidence to what extent MEs can influence evolutionary responses to selection remains ambiguous. We tested the degree to which MEs can alter the rate of adaptation of a key life-history trait, clutch size, using an individual-based model approach parameterized with experimental data from a long-term study of great tits (Parus major). We modeled two types of MEs: (i) an environmentally plastic ME, in which the relationship between maternal and offspring clutch size depended on the maternal environment via offspring condition, and (ii) a fixed ME, in which this relationship was constant. Although both types of ME affected the rate of adaptation following an abrupt environmental shift, the overall effects were small. We conclude that evolutionary consequences of MEs are modest at best in our study system, at least for the trait and the particular type of ME we considered here. A closer link between theoretical and empirical work on MEs would hence be useful to obtain accurate predictions about the evolutionary consequences of MEs more generally.