Hybridization speeds adaptive evolution in an eight-year field experiment

Hybridizationis a common phenomenon, yet its evolutionary outcomes remain debated. Here, we ask whether hybridizationcan speed adaptive evolution using resynthesized hybridsbetween two species of Texas sunflowers ( Helianthus annuusand H. debilis) that form a natural hybridin the wild (H. annuus ssp. texanus). We established separate control and hybridpopulations and allowed them to evolvenaturally in a field evolutionary experiment. In a final common-garden, we measured fitness and a suite of key traits for these lineages. We show that hybridfitness evolvedin just seven generations, with fitness of the hybridlines exceeding that of the controls by 14% and 51% by the end of the experiment, though only the latter represents a significant increase. More traits evolvedsignificantly in hybridsrelative to controls, and hybridevolution was faster for most traits. Some traits in both hybridand control lineages evolvedin an adaptive manner consistent with the direction of phenotypic selection. These findings show a causal pathway from hybridizationto rapid adaptation and suggest an explanation for the frequently noted association between hybridizationand adaptive radiation, range expansion, and invasion.