Rapid evolution of body size in response to consistent natural selection in a wild lizard

Although directional selection and additive genetic variance are frequently detected in wild populations, evolutionary responses are often weak or absent, giving rise to a "paradox of stasis." To explore the relationship between selection and evolution, we used a pedigreed wild population of lizards (Anolis sagrei) to quantify natural selection, estimate additive genetic (co)variances, and track phenotypic and genetic change in adult body size while addressing several factors that could lead to evolutionary stasis. Selection via adult reproductive success consistently favored larger body size in both sexes and was stronger in males. Body size was heritable and genetically correlated with adult reproductive success in both sexes, indicating that selection acted on underlying additive genetic variance. Across five annual cohorts, mean phenotypic values and breeding values for body size increased in both sexes, exceeding expectations under genetic drift. This rapid evolutionary response was not obscured by several processes commonly invoked to explain stasis. For example, accounting for phenotypic skew strengthened expected responses, and prior viability selection on juveniles did not phenotypically or genetically oppose selection on adult body size. Our results show that rapid evolutionary change is detectable in the wild when directional selection is consistent, acts on additive genetic variance, and is not genetically opposed by early-life viability selection.