A Three-Sample Test for Introgression

Many methods exist for detecting introgression between nonsister species, but the most commonly used require either a single sequence from four or more taxa or multiple sequences from each of three taxa. Here, we present a test for introgression that uses only a single sequence from three taxa. This test, denoted D-3, uses similar logic as the standard D-test for introgression, but by using pairwise distances instead of site patterns it is able to detect the same signal of introgression with fewer species. We use simulations to show that D-3 has statistical power almost equal to D, demonstrating its use on a data set of wild bananas (Musa). The new test is easy to apply and easy to interpret, and should find wide use among currently available data sets.