High site fidelity does not equate to population structure for common goldeneye and Barrow’s goldeneye in North America.

Delineation of population structure provides valuable information for
conservation and management of species, as levels of demographic and
genetic connectivity not only affect population dynamics but also have
important implications for adaptability and resiliency of populations and
species. Here, we measure population genetic structure and connectivity
across the respective ranges of two sister species of Goldeneye, Barrow’s
Goldeneye (Bucephala islandica) and Common Goldeneye (B. clangula). We use
two different marker types: 7 nuclear microsatellite loci assayed across
229 samples and 3,678 double digest Restriction-site Associated DNA
Sequencing (ddRAD-seq) loci assayed across 61 samples. First, both
datasets failed to uncover genetic structure within Common or Barrow’s
Goldeneye, including between North American and European samples of Common
Goldeneye. These results are in contrast with previous mitochondrial DNA,
band recovery, and telemetry data which suggests that goldeneyes are
structured across their range. We posit that the discordance between
autosomal genetic markers and other data types suggests that males,
possibly subadult males, may be maintaining genetic connectivity across
each species’ respective ranges. Next, although inter-specific brood
parasitism was expected to cause some level of gene flow, we only
identified a single F1 hybrid with no further evidence of contemporary or
historical gene flow. Despite ddRAD-seq demographic analyses which
recovered an optimum evolutionary model of split with migration (i.e.,
secondary contact), estimates of gene flow were <<1 migrant
per generation in both directions. Together, we conclude that either
strong ecological barriers or assortative mating are likely playing a role
in preventing further backcrossing. Finally, demographic analyses
estimated a relatively deep divergence time between Barrow’s Goldeneye and
Common Goldeneye of ~1.6 million years before present and that the genomes
of both species have been under similar evolutionary constraints.