“Maternal effects in a wild songbird are environmentally plastic but only marginally alter the rate of adaptation”
Jip J. C. Ramakers, Marleen M. P. Cobben, Piter Bijma, Thomas E. Reed, Marcel E. Visser, and Phillip Gienapp (May 2018)
Bridging the gap between theory and data: Plastic maternal effect in wild bird has limited potential to affect adaptation
Genes are not the only source of resemblance between you and your parents. Imagine, for example, how the amount of care that a mother provides influences the condition of her offspring or, more indirectly, how the number of offspring within the brood influences this condition through sibling competition. If the size of a brood negatively influences the condition of each individual offspring, this may create the odd situation where offspring that inherit genes for producing many offspring may actually produce few offspring; this is because they are in a poor condition, as a direct result from growing up with many siblings. We call this a negative maternal effect (NME). Ramakers and colleagues (2018) wondered: if the environment worsens, making raising many offspring difficult, can a population respond by producing fewer offspring, or is it inhibited in doing so because of NMEs? Looking at clutch size in a small woodland bird, the great tit (Parus major), in the Netherlands, they used long-term field observations, experiments, and predictive modelling to predict how populations would respond in case of an environmental change—for the better or the worse—and how NMEs may facilitate or hamper this response. They showed that NMEs indeed exist in the great tit but that in the long run, according to the predictive model, their effect is too small to make a difference in how rapidly a population can respond to new environments. Their work emphasizes that predictive models are important in understanding evolutionary processes, but they need to be backed up by data from actual populations to keep them realistic.
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 modelled 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.