Western Flycatcher Populations

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The bird formally known as Western flycatcher was divided into two species in 1989 by the American Ornithologists’ Union Committee on Classification and Nomenclature: Pacific-slope Flycatcher which occupies the coastal region of Western North America and Cordilleran Flycatcher which resides the inland regions. However, Rush, Cannings and Irwin (2009) revealed a contact zone with hybridization between these two species in Southwestern Canada, which might indicate that they are actually one species instead of two. The two western flycatcher populations remain as distinct species because of genetic variation, possible reproductive isolation and the community integrity of each species except for the hybrid zone.
In terms of evolutionary genetics, the two Western Flycatcher populations are two species. If the genetic aspects of the two populations show significant differences, then it is reasonable to make inference about their divergence. Johnson and Marten (1988) illustrated the differentiation of allopatric populations by examining 41 genetic loci in 11 breeding populations through electrophoresis. By examining the allelic frequency in coastal and interior populations, some alleles appearing in one population with high frequencies do not exist or have low
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Despite of communication, the songs of flycatchers play an important role in mate attraction (Eriksson and Wallin 1986). If two populations have different songs, they are likely to attract different females that can recognize their songs and then mate. Indeed, Howell and Cannings (1992) have analyzed the songs of two Mexican populations of the Western Flycatcher. The frequency and pattern of their songs are distinct after recording and plotting, which is the evidence of pre-mating isolating barriers. Therefore, vocal divergence can function as a possible mechanism of reproductive isolation between these two species and prevent them interbreeding in a large

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