Adaptive phenotypic plasticity for life-history and less fitness-related traits

Abstract

Organisms are faced with variable environments and one of the most common solutions to cope with such variability is phenotypic plasticity, a modification of the phenotype to the environment. These modifications are commonly modelled in evolutionary theories as adaptive, influencing ecological and evolutionary processes. If plasticity is adaptive, we would predict that the closer to fitness a trait is, the less plastic it would be. To test this hypothesis, we conducted a meta-analysis of 213 studies and measured the plasticity of each reported trait as a coefficient of variation. Traits were categorized as closer to fitness-life-history traits including reproduction and survival related traits, and farther from fitness-non-life-history traits including traits related to development, metabolism and physiology, morphology and behaviour. Our results showed, unexpectedly, that although traits differed in their amounts of plasticity, trait plasticity was not related to its proximity to fitness. These findings were independent of taxonomic groups or environmental types assessed. We caution against general expectations that plasticity is adaptive, as assumed by many models of its evolution. More studies are needed that test the adaptive nature of plasticity, and additional theoretical explorations on adaptive and non-adaptive plasticity are encouraged.

Keywords: (non-) adaptive plasticity; demographic buffering; environmental variation; evolution; fitness; life-history.

Figure 1.

Plasticity (coefficients of variation; CV) among different trait types, environment types and taxa. Trait types are ordered roughly in accordance with the relative distance to fitness. We categorized life-history traits (LHt) into survivorship and reproductive; and non-life-history traits (N-LHt) into behavioural, morphological, metabolism and physiology, and developmental. The top left panel shows the trait means across all environments on an expanded scale. Directly to its right are these means shown at the same scale as the boxplot. Top, far right, CVs for each environment and trait type (colour coded). The widths of the boxes are relative to the amount of data; whiskers represent the standard deviations. The grand mean (μ) is denoted by the black line across all graphs. °T, temperature; env. q., environmental quality; light, photoperiods and light; intra, intraspecific interactions; inter, interspecific interactions; resource, intrinsic resources. (b) CVs among taxa and trait types. The widths of the boxes are relative to sample size; whiskers represent the standard deviations. The dotted lines denote the means per taxa. For green algae and plants, no behavioural or developmental data are available.

Figure 2.

Distribution of differences in CV between life-history traits (LHt) and non-life-history traits (N-LHt), large panel. Small panels illustrate distributions of differences in CV between survivorship and N-LHt (behavioural, developmental, metabolism and physiology, and morphological) left column of panels, and reproductive and N-LHt (right column of panels). Red solid line depicts no difference in CV (0), white dashed line depicts the mean and dotted line depicts the median. The grey dashed line depicts a normal distribution based on the observed mean and variance. (Online version in colour.)

Figure 3.

Variance in CV among genotypes within the same study and trait, plotted for the different trait types: beh., behaviour; morph., morphology; phys., metabolism and physiology; devel., development; surv., survival; repr., reproduction. Note y-axis is limited to values less than 0.1 for better visibility, i.e. not all outliers are shown. Model selection for generalized linear models with a gamma error structure and variance of CV as response variable: AIC for model with trait types (−1426.6), null model (intercept only model) AIC (−1422.0). (Online version in colour.)

Figure 4.

The correlation between plasticity and genetic variance (a reciprocal measure for genetic canalization) is significant (r_s = 0.77, Spearman). However, the order of the traits did not correspond to their proximity to fitness. The black dashed line illustrates the linear relationship between the trait types if ordered as follows: developmental, morphological, survivorship, metabolism and physiology, reproduction, and behaviour. The red (solid) lines link the traits in order as defined previously in relation to their distance to fitness: beh.-morph.-phys.-devel.-surv.-rep. If the distance to fitness was a main determining factor to the relationship between plasticity and genetic canalization, the lines should coincide. (Online version in colour.)