SEMINAR: Sexual Signals, Divergence, & Speciation in Australian Fairy-wrens.

Sexual selection is generally thought to promote divergence between populations and potentially also lead to reproductive isolation (i.e., speciation), but the behavioral mechanisms underlying this generally are not well understood. We are exploring these mechanisms in populations of the red-backed fairy-wren, an Australian passerine bird. Broad geographic sampling shows strong divergence across populations in male sexual signals, including both plumage coloration and song. Genomic approaches reveal a strong cline of genetic divergence separating eastern from western populations. This genetic cline is concordant with variation in songs, but differs significantly from the cline in plumage signals, indicating that plumage traits, but not song traits, are introgressing across populations. Field experiments that manipulated both signal types reveal that female mating preferences promote introgression of plumage traits, and also that male-male competition limits introgression of song but allows introgression of plumage. Together these results call for increased attention to the behavioral responses of conspecifics to divergent sexual signals, as these responses will determine the patterns of reproductive isolation that result.