Abstract
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, questions remain about how maternal effect senescence impacts evolutionary fitness. To understand the influence of maternal effect senescence on population dynamics, fitness, and selection, we developed matrix population models in which individuals are jointly classified by age and maternal age. We fit these models to data from individual-based culture experiments on the aquatic invertebrate, Brachionus manjavacas (Rotifera). By comparing models with and without maternal effects, we found that maternal effect senescence significantly reduces fitness for B. manjavacas and that this decrease arises primarily through reduced fertility, particularly at maternal ages corresponding to peak reproductive output. We also used the models to estimate selection gradients, which measure the strength of selection, in both high growth rate (laboratory) and two simulated low growth rate environments. In all environments, selection gradients on survival and fertility decrease with increasing age. They also decrease with increasing 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 age-related senescence. The models we developed are widely applicable to evaluate the fitness consequences of maternal effect senescence across species with diverse aging and fertility schedule phenotypes.
Highlights
Maternal effect senescence—a decline in offspring survival or fertility with maternal age—has been demonstrated in many taxa, including humans
To understand the influence of maternal effect senescence on population dynamics, fitness, and selection, we developed matrix population models in which individuals are jointly classified by age and maternal age
By comparing models with and without maternal effects, we found that maternal effect senescence significantly reduces fitness for B. manjavacas and that this decrease arises primarily through reduced fertility, at maternal ages corresponding to peak reproductive output
Summary
Our demographic model uses the general age-by-stage structured approach thoroughly described by Caswell et al [37]. An individual with maternal age i and age j produces fij daughters in 1 d and survives to age j + 1 with probability pij. These vital rates are incorporated into a fertility matrix Fand a survival matrix U. A population described by model [2] will converge to a stable structure wand grow exponentially at the rate log λ, where λ is the largest eigenvalue of the projection matrix A, and wis the corresponding right eigenvector. The selection gradient on a trait that affects For U (e.g., pij or fij ) is the partial derivative of λ with respect to that trait [39] Formulas for these selection gradients are given in SI Appendix
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