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 sout heastern Utah (United States) are 33% smaller than all other sage grouse an d have obvious plumage and behavioural differences. Because of these differ ences, they have been tentatively recognized as a separate 'small-bodied' s pecies. 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 differen ces in the distribution of alleles between the large- and small-bodied bird s were found in both data sets. Analysis of molecular variance (AMOVA) reve aled that 65% of the variation in mitochondrial DNA (mtDNA) haplotypes coul d be explained by the large- vs, small-bodied distinction. Genetic distance s and neighbour-joining trees based on allelic frequency data showed a dist inct separation between the proposed species, although cladistic analysis o f the phylogenetic history of the mitochondrial sequence haplotypes has sho wn a lack of reciprocal monophyly. These results further support the recogn ition of the small-bodied sage grouse as a distinct species based on the bi ological species concept, providing additional genetic evidence to augment the morphological and behavioural data. Furthermore, small-bodied sage grou se had much less genetic variation than large-bodied sage grouse, which may have implications for conservation issues.