Gradual transitions in genetics and songs between coastal and inland populations of Setophaga townsendi

Setophaga townsendi is a species of wood-warbler (family Parulidae) in
northwestern North America that has a geographic structure in the
mitochondrial and nuclear genomes: while interior populations have
differentiated mitonuclear ancestry from the sister species S.
occidentalis, coastal populations have a mix of inland and S. occidentalis
mitonuclear ancestries. This coastal-to-inland transition in genomic
ancestry raises the possibility of similar geographic structure in
phenotypic traits, especially those involved in mate choice. Using
qualitative and multivariate approaches, we investigated whether there is
a sharp transition between coastal and inland populations in both songs
and nuclear DNA. We find there is a shallow geographic cline in the Type I
song but not in the Type II song. Nuclear DNA shows a gradient between the
coast and inland. There is little correlation between variation in song
and the isolation-by-distance pattern in the nuclear DNA. The learned
songbird song is shaped by both genetic and cultural processes. There has
been a debate on whether song learning promotes or slows down population
differentiation. By comparing the within-species variation in song and
genetic structures, we can expand our understanding of the dynamic
interplay between mating signals and population differentiation.