Evaluating the diversity of maternal age effects upon neonatal survival across animal species

Maternal effect senescence is the detrimental effect of increased maternal age on offspring performance. Despite much recent interest given to describing this phenomenon, its origins and distribution across the tree-of-life are poorly understood. We find that age affects neonatal survival in 83 of 90 studies across 51 species, but we observed a puzzling difference between groups of animal species. Amongst wild bird populations, the average effect of age was only −0.7% per standardized unit of increasing age, but maternal effects clearly senesced in laboratory invertebrates (−67.1%) and wild mammals (−57.8%). Comparisons amongst demographic predictions derived from evolutionary theory and conventional demographic models suggest that natural selection has shaped maternal effect senescence in the natural world. These results emphasize both the general importance of maternal age effects and the potential for evolutionary genetics to provide a valuable framework for understanding the diversity of this manifestation of ageing in animal species.