Genomic and acoustic differences separate Lilian’s Meadowlark (Sturnella magna lilianae) from Eastern (S. magna) and Western (S. neglecta) Meadowlarks

Examining differences among recently diverged populations can provide
insight into the traits and evolutionary mechanisms that drive or maintain
divergence. The genus Sturnella includes two recently diverged species,
Sturnella magna (Eastern Meadowlark) and S. neglecta (Western Meadowlark),
the former of which has a complex of subspecies distributed across the
Americas. Of the S. magna subspecies that occur in the United States, S.
m. lilianae is the only one with a disjunct range, occurring in the
southwestern U.S. and central Mexico. It also has markedly different song
patterns than all other S. magna subspecies. In order to assess population
differentiation, we performed whole-genome sequencing of 35 birds, and
analyzed song characteristics from 85 birds. Songs from each species and
S. m. lilianae were diagnosable using linear discriminant function
analysis and support divergence in song between all taxa. Phylogenetic
analysis and admixture proportions support three distinct clades within
North American meadowlarks, and tests of introgression failed to detect a
significant signal. Overall, our results indicate that S. m. lilianae
exhibits high levels of genetic and vocal differentiation from both S.
magna and S. neglecta, with no evidence of introgression between any
group, and forms a distinct evolutionary lineage. We thus recommend the
elevation of S. m. lilianae to species status.