A population genetic comparison of large- and small-bodied sage grouse in colorado using microsatellite and mitochondrial DNA markers

Sage grouse (Centrocercus urophasianus) from southwestern Colorado and southeastern Utah (United States) are 33% smaller than all other sage grouse and have obvious plumage and behavioural differences. Because of these differences, they have been tentatively recog-nized as a separate 'small-bodied' species. We collected genetic evidence to further test this proposal, using mitochondrial sequence data and microsatellite markers to determine whether there was gene flow between the two proposed species. Significant differences in the distribution of alleles between the large- and small-bodied birds were found in both data sets. Analysis of molecular variance (AMOVA) revealed that 65% of the variation in mitochondrial DNA (mtDNA) haplotypes could be explained by the large- vs. small-bodied distinction. Genetic distances and neighbour-joining trees based on allelic frequency data showed a distinct separation between the proposed species, although cladistic analysis of the phylogenetic history of the mitochondrial sequence haplotypes has shown a lack of reciprocal monophyly. These results further support the recognition of the small-bodied sage grouse as a distinct species based on the biological species concept, providing additional genetic evidence to augment the morphological and behavioural data. Furthermore, small-bodied sage grouse had much less genetic variation than large-bodied sage grouse, which may have implications for conservation issues.