Phylogeographic patterns inPackera subnudareveal an east–west divergence along the Continental Divide and reduced haplotype diversity in northern populations

Abstract

Packera subnuda (DC.) D.K. Trock & T.M. Barkley is a cordilleran species that is unusual within Packera in possessing diverse cpDNA haplotypes but no intrapopulational cpDNA diversity in the populations so far examined. In an effort to determine what factors are shaping this lack of diversity and whether it persists throughout the species, we sampled extensively throughout the range of the species. Unlike previous results, new population samples were not all monomorphic for cpDNA and some contained diverse haplotypes. Overall, the haplotype diversity pattern revealed, with one exception, a split into two groups separated by the Continental Divide. The exception (Beartooth Mountains, Wyo., USA) suggests the key factor in shaping the groups’ distributions may be the proximity to prairie populations of Packera species that increases the likelihood of hybridization. The pattern of diversity in ITS repeat type revealed in previous studies was also examined in more detail, with diversity found at both the intraindividual and intrapopulational level. ITS revealed a similar east–west separation into two groups on either side of the Continental Divide. Overall, the pattern suggests ancient hybridization injected haplotype and repeat type diversity into the species and that this diversity has since been reduced by the effects of drift in small populations, most significantly in populations at the northern and eastern edge of the range.