Benefits of assisted gene flow diminish with latitudinal distance between populations in Chamaecrista fasciculata

Abstract

In ecological restoration, seed sourcing is often among the first and most critical steps in achieving restored populations that establish and reproduce successfully, while also having the genetic capacity to adapt to future change. Many approaches have been proposed to guide seed sourcing for restoration, including a strong focus on local seed sources, the use of assisted gene flow or assisted migration, and regional admixture provenancing. The goal of this research was to evaluate these issues in the context of grassland restoration. We collected seed of Chamaecrista fasciculata, an annual native to the prairies of North America, from four locations along a latitudinal gradient. We generated inter‐ and intrapopulation crosses and grew them in two common gardens located in restored prairies in southeast Minnesota. We found that northern populations tended to flower and fruit earlier than southern populations, while hybrids generally had intermediate phenologies. There were strong fitness benefits of hybridization, particularly among the local crosses. However, the plants grown from our southernmost seed source produced few mature seed pods in the common gardens before the advent of fall frost, suggesting that translocating populations across significant latitudinal distances may be problematic. Taken together, our findings support a regional admixture provenancing approach while indicating that assisted migration and assisted gene flow across latitudinal distances of three degrees or more compromises fitness in this species.