Experimental speciation: reinforcement in Drosophila melanogaster

University Of South Carolina At Columbia, Columbia SC

Investigators

Abstract

Speciation occurs when populations evolve barriers to reproduction. Understanding how these barriers form is a longstanding challenge in evolutionary biology. This is because recurrent migration is expected to erase any emerging differences between populations. One way to complete speciation is through a process called reinforcement. Reinforcement occurs where natural selection favors the avoidance of hybridization when hybrid offsprings are less fit. This project uses experimental evolution—studying evolutionary change as it occurs—to track reproductive barriers between populations over time. The work will examine whether relatively weak barriers to reproduction between populations are strengthened or decay over time. Using these data, the researchers will determine the scenarios under which reinforcement can occur. As part of this project, high school, undergraduate, and graduate-level students will receive science education and training. An outreach program operating at a local middle school and scout troop will increase exposure to genetics and promote interest in science amongst underrepresented groups. Evidence for and against the evolution of reproductive isolation by reinforcement comes largely from comparative approaches and snapshot studies in natural populations. However, these methods often encounter difficulties when trying to ascribe patterns of reproductive isolation to specific evolutionary forces. This project will directly test the hypothesis that reinforcing selection can overwhelm the homogenizing force of gene flow. To test this hypothesis, the work will follow the evolution of reproductive isolation in populations of Drosophila melanogaster that show some degree of initial reproductive isolation. Some experimental populations will remain allopatric, while others will experience gene flow. In these populations, the strength of selection against hybridization will be manipulated. A time series of measures of both competitive and non-competitive reproductive isolation from these populations will reveal the answers to three questions. First, how often and how consistently is reinforcement able to strengthen reproductive isolation? Second, how strong must selection against hybrids be for this to occur? Third, is pre-mating (sexual) or postmating-prezygotic (gametic) isolation more evolutionarily labile? This project is jointly funded by Evolutionary Processes and the Established Program to Stimulate Competitive Research (EPSCoR). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.