The interplay between habitat availability and population differentiation: a case study on genetic and morphological structure in an inland wader (Charadriiformes)

Long-distance migrant waders breeding in the Arctic often have globally structured populations, largely because they were isolated in glacial or interstadial refugia or were restricted to fragmented coastal wetlands in winter. Conversely, inland species using continentally distributed wetlands appear to be less structured (more often panmictic), presumably because they are less likely to have been isolated by multiple refugia or by current events. We analyzed genetic variation in a widely distributed inland species, the ruff (Philomachus pugnax), sampled from seven Eurasian breeding localities, and from migration routes and wintering areas in Europe and Africa. One mitochondrial marker (N = 118) and eight nuclear microsatellites (N = 170) showed: (1) high genetic variation; (2) large genetic distances among mitochondrial (private) haplotypes within breeding populations; (3) the absence of a signature of isolation-by-distance; and (4) a distribution of private microsatellite alleles indicating dispersal between Scandinavia and Siberia but not between western and eastern Siberia. These results were consistent with a large refugial population during the Last Glacial Maximum, and postglacial long range expansions spreading ancestral polymorphisms, and not with a stepping-stone model of gene flow. The divergence between breeding populations in Europe and Siberia was dated to approximately 12 000 years ago. Although genetic population structure is presently statistically non-existent, support for evolving population structure came from analyses of geographical variation in two relevant phenotypic traits: wing length and the timing of migration. Analysis of 6077 individuals sampled on migration in 2002-08 revealed that, in each year, shorter-winged birds migrated through significantly later than longer-winged birds. The late-passing birds were associated with more westerly breeding localities. In conclusion, the lack of genetic structuring in ruffs (and other inland species we examined) contrasts with strong structuring in many coastal species. This suggests that the ability to use more widely available inland habitat influences the evolution of genetic structure and the maintenance of genetic variation in waders. (C) 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 641656.