Phenotypic selection in natural populations: what limits directional selection?

Area of Science:

• Evolutionary Biology
• Quantitative Genetics
• Ecology

Background:

• Phenotypic selection studies reveal directional selection in natural populations.
• Understanding factors that reduce selection and evolutionary response is crucial.

Purpose of the Study:

• To evaluate the roles of fitness trade-offs, correlated selection, temporally varying selection, and stabilizing selection in reducing net directional selection.
• To assess their impact on cumulative evolutionary responses to selection.

Main Methods:

• Combined two datasets on phenotypic selection (over 4,600 estimates from 143 studies).
• Analyzed selection gradients, selection differentials, and quadratic selection gradients.
• Investigated trait-specific and system-wide patterns.

Main Results:

• Little evidence that fitness trade-offs reduce total directional selection.
• Correlated selection frequently reduced selection on size, but not other traits.
• Temporal fluctuations in selection had limited impact on cumulative directional selection.
• Stabilizing selection was detected for body size but not consistently across traits.

Conclusions:

• Fitness trade-offs, correlated selection, and stabilizing selection show limited constraints on directional selection for most quantitative traits.
• Net directional selection and cumulative evolutionary responses are not strongly limited by these factors in most studied systems.