Linz, Brandon , Willyard, Ann , Liston, Aaron , Cronn, RC .
Nesting microsatellite genotype data within low-copy nuclear gene trees to interpret the complex evolutionary relationships of Pinus washoensis (Ponderosae; Pinaceae).
The classification of Pinus washoensis Mason & Stockwell (Ponderosae; Pinaceae) is ambiguous. Some treat these high altitude pine populations at the specific level, while others include them within the widespread and highly variable P. ponderosa Douglas ex. P.&C. Lawson. Inter-specific hybridization is thought to occur where P. washoensis and P. jeffreyi Balf. are sympatric, although its frequency may be rare. Evolutionary relationships within Pinus are especially challenging due to their plastic and homoplasious morphological character states. Recent species-level phylogenetic trees for the Ponderosae using low-copy nuclear genes display rampant incomplete lineage sorting. Thus, the challenge includes species delimitation as well as clade relationships. We chose to attack this inter-specific question from a population genetic viewpoint, placing our results in a phylogenetic framework by simultaneously analyzing low copy nuclear sequences of an exemplar from each population. Our experiment genotyped ca. 250 individuals representing P. washoensis (4 populations), P. scopulorum Lemmon (2 populations), P. jeffreyi (3 populations), and the geographic range of P. ponderosa (6 populations). We created multi-locus nuclear genotypes from seven microsatellite loci (SSRs) and scored a plastid haplotype using PCR-RFLP. Genetic distances based on allele frequencies were calculated using the stepwise mutation model and a geometric chord distance. Individual-based admixture models and the plastid haplotype were used to assess the frequency of inter-specific hybridization, and we compared the inferred frequency of introgressed individuals in sympatric and allopatric population pairs. We visualized the clustering of individuals within their putative species and discuss evidence for three competing hypotheses: 1) the high-altitude Ponderosae from California, Nevada, and Oregon share a common origin and fit the P. washoensis concept; 2) these individuals are contained within the variability of P. ponderosa; or 3) P. washoensis has been influenced by introgressive hybridization with P. jeffreyi. Importantly, we show the benefits of A) using both plastid and nuclear genomes and B) nesting population-level inferences from hypervariable SSRs in a phylogenetic framework from low-copy nuclear gene trees.
Understanding the evolutionary history of Washoe pines will support research into expected physiological response to climate change and will contribute to their conservation.
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1 - Hendrix College, Biology, 1600 Washington Ave, Conway, AR, 72032, USA
2 - Hendrix College, Biology, 1600 Washington Ave, Conway, AR, 70032, USA
3 - Oregon State University, Department of Botany & Plant Pathology, 2082 Cordley Hall, Corvallis, Oregon, 97331-2902, USA
4 - USDA Forest Service, Forest Genetics, Pacific Nothwest Research Station, 3200 SW Jefferson Way, Corvallis, Oregon, 97331, USA
Low-copy Nuclear Markers.
Presentation Type: Oral Paper:Papers for Sections
Location: 555A/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 3:00 PM