Hot Spots of Genetic Diversity Descended From Multiple Pleistocene Refugia in an Alpine Ungulate

Abstract

Species that inhabit naturally fragmented environments are expected to be spatially structured and exhibit reduced genetic diversity at the periphery of their range. Patterns of differentiation may also reflect historical processes such as recolonization from glacial refugia. We examined the relative importance of these factors in shaping the spatial patterns of genetic differentiation across the range of an alpine specialist, the North American mountain goat (Oreamnos americanus). Contrary to fossil evidence that suggests a single southern refugium, we detected evidence for additional refugia in northern British Columbia and the Alaskan coast using both mitochondrial and microsatellite DNA. A core area of elevated genetic diversity characterized both regions, and molecular dating suggested a recent Pleistocene split was followed by demographic expansion. Across their range, mountain goats were highly genetically structured and displayed the expected pattern of declining diversity toward the periphery. Gene flow was high within contiguous mountain ranges, but cross-assignments paradoxically suggest that long-distance contemporary dispersal movements are not uncommon. These results improve our understanding of how historical vicariance and contemporary fragmentation influence population differentiation, and have implications for conserving the adaptive potential of alpine populations and habitat.K E Y W O R D S : Biogeography, center-marginal hypothesis, isolation-by-distance, mountain goats, population structure, refugia.

When east meets west: population structure of a high-latitude resident species, the boreal chickadee (Poecile hudsonicus)

“…Both mtDNA and microsatellite data show significant isolation-by-distance, and short distance (o40 km) dispersal is supported by banding records. Reduced dispersal is consistent with other non-migratory, resident species, including both birds (Burg et al, 2005;Graham and Burg, 2012;Lait et al, 2012) and mammals (Chappell et al, 2004;Aubry et al, 2009;Shafer et al, 2010a).…”

Does reduced heterozygosity influence dispersal? A test using spatially structured populations in an alpine ungulate

“…Of these, 30 The four D I individuals averaged 5.7 per cent (+2.6%) less H O than the herd average (s ¼ 0, p ¼ 0.06) and were assigned by STRUCTURE to the S3 subpopulation in Shafer et al [7], which encompasses Caw Ridge.…”

“…All individuals were genotyped at the 19 microsatellite loci used in Shafer et al [7]. Although dispersal is male-biased, both sexes were included as they each disperse [7,9].…”

“…Using data from a range-wide population structure study [7] and a long-term study of individually marked goats at Caw Ridge, Alberta, Canada [9], we tested for an association between observed individual multi-locus heterozygosity (H O ) and dispersal at two hierarchical levels, subpopulation and herd, and discuss the implications for the evolution of dispersal.…”

“…The mountain goat is ideal for testing this hypothesis for two reasons: (i) higher individual heterozygosity is associated with increased survival [6] and (ii) mountain goat populations are spatially structured [7], which allows for dispersal to be detected through genetic assignment tests [8].…”