effects of divergent plumage and song on subspecies interactions
In this video, a territorial male red-backed fairy-wren responds aggressively to the combined stimulus of song playback and presence of an ARTIFICIAL mount. some males are so aggressive that they will even attack a mount of the wrong species if it is paired with the correct song type.
The two Red-backed Fairy-wren subspecies have diverged predominantly in two social signals: plumage color and song type. Once they came into secondary contact, song appears to have not introgressed across the hybrid zone, whereas red plumage color has introgressed eastward into populations of the orange subspecies. I conducted a mount presentation/song playback experiment with the help of a lab mate, Dr. Emma Greig, to test the hypothesis that the increased reproductive success of red males in an otherwise orange population – and the resulting introgression of red plumage – is due a competitive advantage of red over orange males.
For this experiment, I presented territorial males with various combinations of local, foreign, and heterospecific male mounts paired with local, foreign, and heterospecific songs. This experimental protocol was replicated in allopatric populations on both sides of the hybrid zone. Results were similar in both populations: territorial males consistently responded most aggressively to the local song regardless of mount plumage color, and there was no asymmetry between populations in response strength or behaviors.
These results suggest that song is used as an intrasexual signal between males during social competition, and may be used as a species recognition signal in the hybrid zone. In contrast, male plumage color does not appear to be used by males as a signal during competition, corroborating the conclusion of the plumage manipulation experiment that it is an intersexual signal used by females to evaluate potential extra-pair mates. Thus, female preference for red, and not a competitive advantage to red males, likely drives the asymmetrical introgression of red plumage.
For this experiment, I presented territorial males with various combinations of local, foreign, and heterospecific male mounts paired with local, foreign, and heterospecific songs. This experimental protocol was replicated in allopatric populations on both sides of the hybrid zone. Results were similar in both populations: territorial males consistently responded most aggressively to the local song regardless of mount plumage color, and there was no asymmetry between populations in response strength or behaviors.
These results suggest that song is used as an intrasexual signal between males during social competition, and may be used as a species recognition signal in the hybrid zone. In contrast, male plumage color does not appear to be used by males as a signal during competition, corroborating the conclusion of the plumage manipulation experiment that it is an intersexual signal used by females to evaluate potential extra-pair mates. Thus, female preference for red, and not a competitive advantage to red males, likely drives the asymmetrical introgression of red plumage.
