Demographic determinants of the phenotypic mother–offspring correlation

Abstract

Phenotypic traits partly determine expected survival and reproduction, and so have been used as the basis for demographic models of population dynamics. Within a population, the distribution of phenotypic traits depends upon their transmission from parents to offspring, yet we still have a limited understanding of the factors shaping phenotypic transmission in wild populations. Phenotypic transmission can be measured using the phenotypic parent-offspring correlation (C), defined as the slope of the regression of offspring phenotypic trait on parental phenotypic trait, both traits measured at the same age, often at birth. This correlation reflects phenotypic variation due to both additive genetic effects and parental effects. Researchers seldom account for the possible influence of selection on estimates of the phenotypic parent-offspring correlation. However, because individuals must grow, survive, and reproduce before giving birth to offspring, these ,aphic processes might influence the phenotypic parent-offspring correlation in addition to the inheritance process, the latter being the direct relationship between parental and offspring phenotypic traits when the parental trait is measured at age of reproduction and the offspring trait is measured at birth. Here we used a female-based population model to study the relative effects of fertility and viability selections, trait ontogeny and inheritance on C. The relative influence of each demographic process is estimated by deriving the exact formulas for the proportional changes in C to changes in the parameters of integral projection models structured by age and phenotypic traits. We illustrate our method for two long-lived species. We find that C can be strongly affected by both viability and fertility selections, mediated by growth and inheritance. Generally, demographic processes that result in mothers reproducing at similar phenotypic traits regardless of their birth traits, such as high fertility selection or converging developmental trajectories, lead to a decreased C. More generally, our models show how the age and phenotypic dependence of fertility and viability selections can influence phenotypic mother-offspring correlation to a much larger extent than ontogeny and inheritance. Our results suggest that accounting for such dependence is needed to model the distribution of offspring phenotypic traits and the ecoevolutionary dynamics of phenotypic traits reliably.

Density dependent environments can select for extremes of body size

“…We keep the models simple by assuming that each reproducing parent produces the same distribution of offspring body sizes regardless of their size or life history strategy (Fig 1(A)). Body size is consequently not heritable within each life history strategy (Plard et al, 2021), but each life history strategy is passed from generation to generation with perfect fidelity (Childs et al, 2004). We also assume that all offspring initially develop at the same pace regardless of life history strategy.…”

Density-dependent environments can select for extremes of body size

“…Thus how one dies, or how one is negatively affected by a density-dependent factor, impacts body size and life history evolution. Minimization of the impact of a limiting factor on the demographic rates it affects generates selection on phenotypic traits associated with surviving and reproducing in the factor's presence (Coulson, 2021). If predation is the limiting factor, then camouflage or the ability to out-run a predator might be selected, while in a food-limited environment, traits subject to selection might be the ability to efficiently use energy, to migrate to greener pastures, or to defend a food source against conspecifics (Travis et al, 2014).…”

“…When resources are limiting, being either hard to detect or acquire, this will generate trade-offs in their allocation (B Kooijman and S Kooijman, 2009). The fittest combination of traits will be the one that improves resource detection and acquisition while optimizing the allocation of resources to traits in a way that maximally reduces the likelihood of death or failure to reproduce from the limiting factors (Coulson, 2021).…”

“…To understand why a particular body size and life history evolves, it is consequently insightful to explore why the survival, development, reproduction, and inheritance functions take the shapes they do, and how they covary. What are the genetic, physiological, or environmental factors that determine the size-survival function, for example (Coulson, 2021)? As a population adapts to a new environment, the strength and form of feedbacks may change, and this will be reflected in the way the functions that constitute models change as adaptation occurs.…”