Fig. 3. Odorant receptor (OR) gene Or41 evolved through a species-specific selective sweep.

a The only E. dilemma-specific selective sweep identified was located within an F_ST outlier window (dashed lines) overlapping with a high interspecific difference in π within a tandem array containing 39 OR genes on scaffold_61 (green: E. viridissima; intermediate blue: E. dilemma). High composite likelihood ratios (CLR, bottom) in Ed_north (light blue) and Ed_south (dark blue) but not in Ev (green) indicate a selective sweep shared by both E. dilemma lineages that overlap with Or41 in the center (shaded regions). Horizontal dashed lines in the CLR panel indicate significance threshold for each lineage as indicated in the respective colors. b A maximum likelihood phylogeny of Or41 (n = 47 individuals) demonstrates that genotypes are species-specific. π was five times lower in E. dilemma in comparison with E. viridissima. A d_N/d_S analysis of species-specific genotypes with five outgroup species (gray dot) indicates positive selection on the E. dilemma branch (d_N/d_S = 3.6), but purifying selection of the ancestral genotype in E. viridissima (d_N/d_S = 0.3). Bootstrap support for tested branches is indicated. Color code as in a. c Seventeen of 19 substitutions mapped on the predicted membrane topology of the Or41 protein were non-synonymous (red), whereas 2 were synonymous (blue).