Genomic insights into hybridization in a localized region of sympatr y between pewee sister species (Contopus sordidulus × C. virens) and their chromosomal patterns of differentiation

摘要

Background: The Great Plains of the United States includes a large number of hybrid and contact zones between bird species. The amount of gene lfow between sister species in these zones ranges from very rare hybridization events to widespread and prevalent introgression. Some of these avian systems have been studied extensively, while others have been indeterminate of whether hybridization exists in areas of sympatry. Using genomic-level approaches allows investigation of genomic patterns of hybridization and gene lfow between species—or lack thereof. Methods: We investigated a narrow zone of sympatry in Nebraska, USA between pewee species (Contopus sordidu-lus and C. virens), for which no hybridization has been conifrmed. We used thousands of single nucleotide polymor-phisms to identify potential hybridization and investigate genomic patterns of differentiation between these two species. Results: We found evidence of multiple hybrid individuals in the contact zone. Little genomic variation was ifxed between species, but a large proportion had differentiated allele frequencies between species. There was a positive relationship between genetic differentiation and chromosome size. Conclusions: We provided the ifrst conclusive evidence of hybridization between C. sordidulus and C. virens, in a region where secondary contact likely occurred due to human disturbance and habitat modiifcation. The genomic patterns of differentiation affrm that these species split in the relatively recent past. Finally, the relationship of chro-mosome size and genetic differentiation may have resulted from differential rates of chromosomal recombination in songbirds and genetic differentiation between species largely due to genetic drift (possibly in concert with selection).