Speciation occurs when populations evolve barriers to reproduction. Understanding how these barriers form is a longstanding challenge in evolutionary biology because recurrent migration between populations tends to erase any emerging differences. Speciation might be completed through a process called reinforcement, where natural selection favors the avoidance of hybridization when hybrid offspring are less fit. Dr. Brian Hollis was awarded a three year grant for $383,432 from the National Science Foundation to conduct a project titled "Experimental speciation: reinforcement in Drosophila melanogaster”. This work will use experimental evolution—studying evolutionary change as it occurs—to track reproductive barriers between genetically-differentiated populations of the fruit fly Drosophila melanogaster. By varying the amount of migration between populations and the strength of selection against hybridization over many generations, this project will provide a direct test of the hypothesis that reinforcing selection can sharpen reproductive isolation. Congrats Brian!