Patterns of genetic, phenotypic, and acoustic variation across a chiffchaff (Phylloscopus collybita abietinus/tristis) hybrid zoneстатья
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Аннотация:Abstract
Characterizing patterns of evolution of genetic and phenotypic divergence between
incipient species is essential to understand how evolution of reproductive isolation
proceeds. Hybrid zones are excellent for studying such processes, as they provide opportunities
to assess trait variation in individuals with mixed genetic background and
to quantify gene flow across different genomic regions. Here, we combine plumage,
song, mtDNA and whole-genome
sequence data and analyze variation across a sympatric
zone between the European and the Siberian chiffchaff (Phylloscopus collybita
abietinus/tristis) to study how gene exchange between the lineages affects trait variation.
Our results show that chiffchaff within the sympatric region show more extensive
trait variation than allopatric birds, with a large proportion of individuals exhibiting
intermediate phenotypic characters. The genomic differentiation between the subspecies
is lower in sympatry than in allopatry and sympatric birds have a mix of genetic
ancestry indicating extensive ongoing and past gene flow. Patterns of phenotypic and
genetic variation also vary between regions within the hybrid zone, potentially reflecting
differences in population densities, age of secondary contact, or differences in
mate recognition or mate preference. The genomic data support the presence of two
distinct genetic clades corresponding to allopatric abietinus and tristis and that genetic
admixture is the force underlying trait variation in the sympatric region—the previously
described subspecies (“fulvescens”) from the region is therefore not likely a distinct
taxon. In addition, we conclude that subspecies identification based on
appearance is uncertain as an individual with an apparently distinct phenotype can
have a considerable proportion of the genome composed of mixed alleles, or even a
major part of the genome introgressed from the other subspecies. Our results provide
insights into the dynamics of admixture across subspecies boundaries and have implications
for understanding speciation processes and for the identification of specific
chiffchaff individuals based on phenotypic characters.