From middens to molecules: phylogeography of the piñon pine,Pinus edulis

Aim Data from packrat middens have established a hypothesized historical biogeography of piñon pine, Pinus edulis, including locations of glacial refugia in the south‐western USA and subsequent migration out of the refugia. In this study, we used molecular techniques to test the glacial refugial hypotheses inferred from packrat (Neotoma) midden data for P. edulis. Location South‐western USA. Methods Two fragments of chloroplast DNA (a portion of the matK gene and a portion of the rbcL gene) for a total of 1045 base pairs were amplified and sequenced for 100 individuals. Thirty‐one populations were sampled throughout the range of P. edulis. Phylogenetic analyses included maximum parsimony and maximum likelihood. Results Very little variation existed among the individuals sampled. Four haplotypes were identified. The inferred ancestral haplotype was the most widespread; it was most common in Texas and New Mexico where, with the exception of one individual, it was the only haplotype found. Arizona and Utah populations were more diverse, with almost half of the populations containing two or more haplotypes. The most derived haplotype was most abundant in Arizona. Main conclusions The distribution of haplotypes is geographically informative. Only one haplotype exists in the south‐eastern portion of the range of P. edulis whereas up to four haplotypes are found in other populations, suggesting one of two hypotheses: either all modern populations are descended from a refugial population in central Arizona, or modern populations are descended from two refugial populations, one in central Arizona and another in Texas–southern New Mexico. Interpreting these data in the light of packrat midden data gives more support for the latter hypothesis.