Phenotypic Selection in Natural Populations: What Limits Directional Selection?

Abstract

Studies of phenotypic selection document directional selection in many natural populations. What factors reduce total directional selection and the cumulative evolutionary responses to selection? We combine two data sets for phenotypic selection, representing more than 4,600 distinct estimates of selection from 143 studies, to evaluate the potential roles of fitness trade-offs, indirect (correlated) selection, temporally varying selection, and stabilizing selection for reducing net directional selection and cumulative responses to selection. We detected little evidence that trade-offs among different fitness components reduced total directional selection in most study systems. Comparisons of selection gradients and selection differentials suggest that correlated selection frequently reduced total selection on size but not on other types of traits. The direction of selection on a trait often changes over time in many temporally replicated studies, but these fluctuations have limited impact in reducing cumulative directional selection in most study systems. Analyses of quadratic selection gradients indicated stabilizing selection on body size in at least some studies but provided little evidence that stabilizing selection is more common than disruptive selection for most traits or study systems. Our analyses provide little evidence that fitness trade-offs, correlated selection, or stabilizing selection strongly constrains the directional selection reported for most quantitative traits.

Evolutionary optimum for male sexual traits characterized using the multivariate Robertson–Price Identity

“…Characterizing evolutionary optima and hence, determining what limits directional evolutionary change have proven to be remarkably difficult empirical challenges (5,11,37). We have shown that a set of traits known to be under strong directional selection measured through one fitness component (male mating success) is, in fact, under net stabilizing selection when fitness is considered in a more complete fashion.…”

“…The genetic analysis of trait deviations provides a way of detecting the missing stabilizing selection inferred by recent metaanalyses. cuticular hydrocarbons | evolutionary stasis D irectional selection on quantitative traits is both common in nature and frequently strong (1)(2)(3)(4), but sustained evolutionary responses are rare (5,6). Instead, phenotypes in natural populations tend to remain relatively stationary in value over various timescales (7), suggesting a limit to trait evolution.…”

How does epistasis influence the response to selection?

“…Direct estimates of directional and stabilising selection, made by correlating trait values with fitness components, typically give strong values. The survey of Kingsolver and Diamond (2011) of 143 studies found an average directional selection gradient of 0.08 on survival, 0.19 on fecundity and 0.17 on mating success, standardised relative to phenotypic s.d. Stabilising selection is also typically strong but, surprisingly, is as often negative (that is, disruptive) as positive.…”

Determining Selection across Heterogeneous Landscapes: A Perturbation-Based Method and Its Application to Modeling Evolution in Space

“…It is far from obvious under which circumstances this interplay of local selection, resulting from local ecological dynamics, and homogenizing dispersal results in directional selection, evolutionary stasis, or evolutionary diversification. It has, for example, been conjectured that mild geographical population structure may-paradoxically-be critical to the maintenance of evolutionary stasis at the species level over longer periods of time (Eldredge et al 2005), in spite of widespread directional local selection (Kingsolver and Diamond 2011). Clearly, there is a need for a theory of evolution in space that can describe how spatially integrated selection in heterogeneous environments is driven by the interplay of local ecological dynamics and dispersal.…”