Data for: Population structure of a grassland songbird (Dolichonyx oryzivorus) to inform conservation units

Understanding the patterns and processes driving population structure is
crucial for conservation planning. Spatial conservation units
(CUs) for one or more species have been defined using similarities in
communities, habitats, and resource management concerns. Additionally, CU
boundaries can be informed by population genetic structure. Here, we
determined the population structure of the Bobolink (Dolichonyx
oryzivorus), a migratory grassland bird. Its breeding range spans
longitudinally across most of North America in the northern U.S. and
southern Canada, and its population has declined by 59% from 1971 to 2014.
We sampled blood from Bobolinks at seven breeding sites and used a ddRAD
sequencing approach to identify 3236 SNPs for population genetic analyses.
Using the Bayesian clustering approach, STRUCTURE, we found low levels of
genetic differentiation across the breeding range. F st values ranged from
0.002 to 0.036 among all population pairs, and genetic structure followed
an isolation-by-distance model. Despite low levels of genetic
differentiation, we found evidence for four genetic groupings— breeding
populations in Oregon and British Columbia were distinct from each other
as well as from Central and eastern North American breeding populations.
Investigating the demographic history of the populations using approximate
Bayesian computation, we found evidence that western Bobolink populations
are not relict populations but instead were founded during a recent
westward range expansion, possibly enabled by agricultural expansion. We
identify four genetics-based CUs that may serve as a complementary spatial
framework, broader in scale compared to the commonly-used Bird
Conservation Regions, for defining and achieving population objectives.