title: Behavioural response to song and genetic divergence in two subspecies of white-crowned sparrows (Zonotrichia leucophrys).
abstract: Divergence in sexual signals may drive reproductive isolation between lineages, but behavioural barriers can weaken in contact zones. Here, we investigate the role of song as a behavioural and genetic barrier in a contact zone between two subspecies of white-crowned sparrows (Zonotrichia leucophrys). We employed a reduced genomic data set to assess population structure and infer the history underlying divergence, gene flow and hybridization. We also measured divergence in song and tested behavioural responses to song using playback experiments within and outside the contact zone. We found that the subspecies form distinct genetic clusters, and demographic inference supported a model of secondary contact. Song phenotype, particularly length of the first note (a whistle), was a significant predictor of genetic subspecies identity and genetic distance along the hybrid zone, suggesting a close link between song and genetic divergence in this system. Individuals from both parental and admixed localities responded significantly more strongly to their own song than to the other subspecies song, supporting song as a behavioural barrier. Putative parental and admixed individuals were not significantly different in their strength of discrimination between own and other songs; however, individuals from admixed localities tended to discriminate less strongly, and this difference in discrimination strength was explained by song dissimilarity as well as genetic distance. Therefore, we find that song acts as a reproductive isolating mechanism that is potentially weakening in a contact zone between the subspecies. Our findings also support the hypothesis that intraspecific song variation can reduce gene flow between populations.
authors.affiliation: Department of Ecology and Evolutionary Biology, Tulane University, 400 Lindy Boggs, New Orleans, LA, 70118, USA.
authors.forename: Sara E
authors.identifier: http://orcid.org/0000-0002-9816-2977
authors.initials: SE
authors.lastname: Lipshutz
authors.affiliation: Subprogram in Ecology, Evolution and Behavior, The Graduate Center, City University of New York, New York, NY, 10016, USA.
authors.forename: Isaac A
authors.initials: IA
authors.lastname: Overcast
authors.affiliation: Subprogram in Ecology, Evolution and Behavior, The Graduate Center, City University of New York, New York, NY, 10016, USA.|Department of Biology, Marshak Science Building, City College of New York, Room 526, 160 Convent Avenue, New York, NY, 10031, USA.|Division of Invertebrate Zoology, The American Museum of Natural History, Central Park West and 79th Street, New York, NY, 10024, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Hickerson
authors.affiliation: Museum of Natural Science and Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, 70803, USA.
authors.forename: Robb T
authors.initials: RT
authors.lastname: Brumfield
authors.affiliation: Department of Ecology and Evolutionary Biology, Tulane University, 400 Lindy Boggs, New Orleans, LA, 70118, USA.|Museum of Natural Science and Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, 70803, USA.
authors.forename: Elizabeth P
authors.initials: EP
authors.lastname: Derryberry
mesh_terms: D000818:Animals; D051456:Gene Flow; D040961:Genetic Drift; D006824:Hybridization, Genetic; D060047:Reproductive Isolation; D046370:Sparrows / Q000235:genetics* / Q000502:physiology; D014828:Vocalization, Animal
keywords: 
  Zonotrichia leucophrys
  ; birdsong; genotyping-by-sequencing; hybrid zone; reproductive isolation; subspecies