Asymmetric song recognition does not influence gene flow in an emergent songbird hybrid zone

Hybrid zones can be used to examine the mechanisms affecting reproductive isolation and speciation, like song. Song has equivocal support as a driver of speciation; we did not find song to cause reproductive isolation. We examined an emerging secondary contact zone between White-crowned Sparrow subspecies pugetensis and gambelii by measuring song variation, song recognition, plumage, morphology and mtDNA. Plumage and morphological characters provided evidence of hybridization in the contact zone, with some birds possessing plumage and song characteristics intermediate between the subspecies. Playback experiments revealed asymmetric song recognition: male pugetensis displayed greater response to their own song than gambelii song, whereas gambelii did not discriminate significantly. If female choice operates similarly to male song discrimination, we predicted asymmetric gene flow, resulting in a greater number of hybrids with gambelii mitochondrial DNA (mtDNA). Contrary to our prediction,...