DOI: 10.5061/dryad.2v6wwpzr6
title: Asymmetric song recognition does not influence gene flow in an emergent songbird hybrid zone

description: 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, more gambelii and putative hybrids in the
 contact zone possessed pugetensis mtDNA haplotypes,
 possibly due to greater pugetensis abundance and
 female-biased dispersal.
description: White-crowned sparrow census We
 performed song censuses to provide inference into where the hybrid zone is
 and how large populations are of <em>pugetensis </em>and
 <em>gambelii</em>. Censuses were carried
 out in the breeding season (May-July) in sites spanning the secondary
 contact zone and zones of allopatry across the North Cascade Mountains in
 Washington state. Counts of males singing each
 subspecie song type were tallied for each site. 
 Playback experiments We carried
 out song playback experiments to characterize male song recogntion between
 the two subpecies Recordings
 of <em>pugetensis,</em> <em>gambelii, </em>and
 Harris's sparrow (hetero-specific control) were broadcast to
 territorial males inside and outside the secondary contact zone. The three
 playback trials were carried out on consecutive days for each
 male. Counts of six different territorial variables
 were collected across the six minute playback trial.
 Capturing sparrows for plumage and genetic
 analysis We drew male sparrows into mist
 nets using song playback for photographs for plumage analysis and blood
 for genetic analysis.  Capture success was counted by
 subspecies. Photographs were taken from 1.1 m with a
 Nikon d7100 and a 70-300mm lens at 70mm in manual mode with a shutter
 speed of 1/250, ISO 100, and the built-in flash on.
 Photographs were processed with Fiji to determine RGB luminance
 of the nape, back, and bill of each bird using the color histogram
 function. We used mean RGB luminance to calculate a red dominance value
 for each region (red dominance value = mean red luminance / [mean green
 luminance + mean blue luminance]) The control region
 of the mtDNA was sequenced and uploaded to Genbank.
description: White-crowned sparrow census Not
 all site were surveyed every year Males were only
 identified to subspecies by song. Thus the subspecies counts do not
 reflect genetic lineage. Censuses are still
 ongoing.