Maternal effect senescence—a decline in offspring survival or fertility with maternal age—has been demonstrated in many taxa, including humans. Despite decades of phenotypic studies, it remains unclear how maternal effect senescence impacts evolutionary fitness. To understand the influence of maternal effect senescence on population dynamics, fitness, and selection, we used data from individual-based culture experiments on the aquatic invertebrate, Brachionus manjavacas (Rotifera), to develop matrix population models in which individuals are classified jointly by age and maternal age.
Results/Conclusions
By comparing the results derived from models with and without maternal effects, we found that the fitness difference due to maternal effect senescence arises primarily through decreased fertility, particularly at maternal ages corresponding to peak reproductive output. In all models, and in both high (laboratory) and low (natural) population growth rate environments, selection gradients, a measure of the strength of selection, decrease with increasing age. Selection gradients also decrease with maternal age for late maternal ages, implying that maternal effect senescence can evolve through the same process as in Hamilton’s theory of the evolution of demographic senescence. We find that maternal effect senescence significantly decreases fitness for B. manjavacas, a species with high maternal investment and maximum reproduction in early- to mid-life. This study provides the first calculations of selection gradients for maternal age effects. The models we developed were built with data from an emerging model organism and are widely applicable to evaluate the fitness consequences of maternal effect senescence across species with diverse aging and fertility schedule phenotypes.