Adaptive Alignment of Plasticity With Genetic Variation and Selection

Abstract

Theoretical research has outlined how selection may shape both genetic variation and the expression of phenotypic plasticity in multivariate trait space. Specifically, research regarding the evolution of patterns of additive genetic variances and covariances (summarized in matrix form as G) and complementary research into how selection may shape adaptive plasticity lead to the general prediction that G, plasticity, and selection surfaces are all expected to align with each other. However, less well discussed is how this prediction might be assessed and how the modeled theoretical processes are expected to manifest in actual populations. Here, we discuss the theoretical foundations of the overarching prediction of alignment, what alignment mathematically means, how researchers might test for alignment and important caveats to this testing. The most important caveat concerns the fact that, for plasticity, the prediction of alignment only applies to cases where plasticity is adaptive, whereas organisms express considerable plasticity that may be neutral or even maladaptive. We detail the ramifications of these alternative expressions of plasticity vis-à-vis predictions of alignment. Finally, we briefly highlight some important interpretations of deviations from the prediction of alignment and what alignment might mean for populations experiencing environmental and selective changes.

Criteria for acceptable studies of animal personality and behavioural syndromes

“…In such cases, it is important to report the variances, covariances and correlations at all levels (within and among individuals) either in the main text or supplementary materials. This enables meta‐analyses of the entire matrix structure (e.g., Dochtermann & Dingemanse, 2013; Royauté, Hedrick, & Dochtermann, 2020) and comparisons across biological levels (Berdal & Dochtermann, 2019; Niemelä & Dingemanse, 2018a). As above, it is the among‐individual correlation that best represents the behavioural syndrome in these instances, because it also takes into account additional (otherwise biasing) sources of variance and covariance within such data (e.g., Careau & Wilson, 2017; Downs & Dochtermann, 2014).…”

The structure of behavioral variation within a genotype

“…As such, these representations are a key part of predicting the future trajectories of evolution. Just as the phenotypic variance can be parsed into genetic variance, environmental variance, GxE interaction variance, etc., covariance can be similarly dissected ( Charmantier et al, 2014 ; Berdal and Dochtermann, 2019 ). For example, the classic model of phenotypic variance V P = V G + V E has a direct phenotypic covariance analogue: Cov P = Cov G + Cov E .…”

Phylogenetic conservation of behavioural variation and behavioural syndromes

“…Put another way, more closely related species will have more similar average behaviours. Do among‐individual variances differ among species?We did not have species‐level predictions but because selection and drift should both reduce among‐individual variance, we predicted that among‐individual variation would differ across species independent of phylogeny. Do within‐individual variances differ among species? Within‐individual variation, typically disregarded as residual variation, includes phenotypic plasticity—specifically reversible plasticity or ‘phenotypic flexibility’ not captured by factors and covariates of a statistical model (Berdal & Dochtermann, 2019; Piersma & Drent, 2003; Piersma & Van Gils, 2011; Westneat et al, 2015; Whitman & Agrawal, 2009). Differences across groups in the magnitude of within‐individual variation, therefore, are, in part, differences in the magnitude of plasticity.We did not have a priori expectations as to species differences or phylogenetic signals for within‐individual variances. Do behavioural syndromes differ among species?Because behavioural syndrome structure has been conserved at the genetic level across cricket populations of G. integer (Royauté et al, 2020), we predicted that syndromes would similarly be phylogenetically conserved and shared across species.…”