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Systematics Section / ASPT

Willyard, Ann [1], Syring, John V. [1], Gernandt, David S. [2], Cronn, RC [3], Liston, Aaron [1].

Molecular evolutionary rates and the age of pine lineages: Are Pinus (Pinaceae) rates comparable to angiosperms?

Substitution rates for 12 nuclear and four chloroplast loci (ca. 11 000 nucleotides) from four Pinus species representing each of the major lineages and an outgroup are characterized. Two putatively non-orthologous nuclear loci and the nrITS were excluded from subsequent analyses. A robust sample of noncoding regions demonstrates that both nuclear and chloroplast Pinus silent rates (third codons plus noncoding) are consistently slower than synonymous rates between the two subgenera. Even though there was substantial rate heterogeneity between loci, eight nuclear and four chloroplast loci showed internal rate constancy and nonconflicting topologies. This supported creation of clock-enforced phylogenies using 5962 nucleotides of nuclear silent sites and 1838 nucleotides of chloroplast silent sites. We calibrated with thefive earliest subg. Strobus fossils to bracket the divergence of subg. Pinus and subg. Strobus between 60 and 46 mya, yielding mean absolute rate estimates of 1.11 x 10-9 substitutions per site per year at nuclear and 3.58 x 10-10 at chloroplast silent sites. These rates are comparable to those reported for long-lived angiosperm taxa. Projections using proportional branch lengths on the nuclear chronogram place the divergence of sect. Trifoliae from sect. Pinus at 22 to 17 mya, sect. Quinquefoliae from sect. Parrya at 34 to 26 mya, and the origin of the genus at 175 to 135 mya. Chloroplast rates were ca. three fold slower, and placed the origin of the genus at 116 to 89 mya. The nuclear estimate is more congruent with the 130 mya age for the oldest pine fossil, the early Cretaceous P. belgica. We confirm lower levels of variation in subg. Pinus and suggest that the paradoxical lack of Cretaceous subg. Strobus fossils may be explained by the earliest pines being "subg. Pinus-like", while most extant species of subg. Pinus arose from a relatively recent, rapid radiation.


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1 - Oregon State University, Department of Botany & Plant Pathology, 2082 Cordley Hall, Corvallis, Oregon, 97331-2902, USA
2 - Universidad Autonoma del Estado de Hidalgo, Centro de Investigaciones Biologicas, AP 1-69, Plaza Juarez, Pachuca, Hidalgo, 42001, Mexico
3 - USDA Forest Service, Forest Genetics, Pacific Nothwest Research Station, 3200 SW Jefferson Way, Corvallis, Oregon, 97331, USA

Keywords:
nuclear gene phylogeny
molecular clock.

Presentation Type: Oral Paper
Session: 38-9
Location: 400/Hilton
Date: Tuesday, August 16th, 2005
Time: 4:15 PM
Abstract ID:376


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