Evolution of individual variation in a competitive trait: a theoretical analysis

Abstract

When competitive traits are costly, negative frequency-dependence can maintain genetic variance. Most theoretical studies examining this question assume binary polymorphisms, yet most trait variation in wild populations is continuous. We propose that continuous trait variation can result from continuous variation in resource quality and that the shape of the resource distribution determines trait maintenance. We used an individual-based model to test which conditions favour the stable maintenance of variation and which cause temporal fluctuations in trait values. This approach, inspired by contrasting outcomes of previous studies, clearly showed the decisive role played by the shape of resource distributions. Under extreme conditions, like the absence of resource variation or with very scarce resources for weak competitors, traits evolved to a single non-competitive or highly competitive strategy, respectively. Some distributions led to strong temporal fluctuations on trait values, whereas others led to the maintenance of large standing variation in competitive traits together with stable mean trait values. Our results thus explain the contradicting outcomes of previous theoretical studies and at the same time provide hypotheses to explain the maintenance of genetic variation and individual differences. We also suggest how the proposed effects of resource variation on trait maintenance can be tested empirically.

Maintenance and evolution of individual differences in a prey defence trait examined with a dynamic predator-prey model

“…Similar freedom (in terms of the evolution of trait distributions) is afforded by individual based models (e.g. Baldauf et al 2014; Colombo et al 2019; Kikuchi and Reinhold 2021; Netz et al 2022; Reinhold et al 2023), and an extension of the quantitative genetics framework, termed “oligomorphic dynamics”, that constructs trait distributions as the sum of an arbitrarily large number of normal distributions (Lion et al 2022; Lion et al 2023; Sasaki and Dieckmann 2011).…”

“…In this paper, we fill this underexplored topic by developing a “trait-diffusion” PDE framework that enables the evolution of individual variation as part of the eco-evolutionary dynamics. Our approach is inspired by recently developed individual based models that have been applied in the contexts of intraspecific competition dynamics among a single population only (Baldauf et al 2014; Kikuchi and Reinhold 2021; Reinhold et al 2023), the coevolution of movement strategies in predator-prey systems (Netz et al 2022), and the evolution of predator perception ranges (Colombo et al 2019). The idea of “trait diffusion”, in which a trait of interest is considered as an independent variable and individuals can “move” in the “trait space” according to a random walk, has also been applied in continuum models (in which the random walk becomes a diffusion process).…”