Reply to Nozawa et al.: Complementary statistical methods support positive selection of a duplicated UV opsin gene in Heliconius

Abstract

Statistical methods used to test for positive selection have a long history and continue to evolve (1–4). In their letter, Nozawa et al. (5) question our use of the branch-site method in our recent paper in PNAS (6). As experimental biologists, we welcome all methods that facilitate the detection of interesting parts of the genome for functional exploration. In this case, a statistically significant result using the branch-site method combined with structural modeling and the identification of a few biochemically relevant substitutions provided us with an incentive for the in vivo physiological characterization of the UV-sensitive rhodopsins in Heliconius. Had we not had that first hint from sequence data alone, it is unlikely that we would have made that functional discovery, which makes the eyes of Heliconius unique compared with all other studied butterflies.