Résumé
In migratory animals, high mobility may reduce population structure
through increased dispersal and enable adaptive responses to environmental
change, whereas rigid migratory routines predict low dispersal, increased
structure, and limited flexibility to respond to change. We explore the
global population structure and phylogeographic history of the bar-tailed
godwit, Limosa lapponica, a migratory shorebird known for making the
longest non-stop flights of any landbird. Using nextRAD sequencing of
14,318 single-nucleotide polymorphisms and scenario-testing in an
Approximate Bayesian Computation framework, we infer that bar-tailed
godwits existed in two main lineages at the Last Glacial Maximum, when
much of their present-day breeding range persisted in a vast, unglaciated
Siberian-Beringian refugium, followed by admixture of these lineages in
the eastern Palearctic. Subsequently, population structure developed at
both longitudinal extremes: in the east, a genetic cline exists across
latitude in the Alaska breeding range of subspecies L. l. baueri; in the
west, one lineage diversified into three extant subspecies L. l.
lapponica, taymyrensis, and yamalensis, the former two of which migrate
through previously glaciated western Europe. In the global range of this
long-distance migrant, we found evidence of both (1) fidelity to rigid
behavioral routines promoting fine-scale geographic population structure
(in the east), and (2) flexibility to colonize recently available
migratory flyways and non-breeding areas (in the west). Our results
suggest that cultural traditions in highly mobile vertebrates can override
the expected effects of high dispersal ability on population structure,
and provide insights for the evolution and flexibility of some of the
world’s longest migrations.