ESCUDERO , A. MARCIAL , Hipp, Andrew , BROWN, BETHANY , MARLENE, HAHN .
Chromosome evolution and its effects on the most diverse angiosperm genus of the temperate zone (Carex, Cyperaceae).
Carex (ca. 43 mya) is one of the most diversified angiosperm genera (ca. 2100 spp.) and displays one of the largest non-polyploid chromosome number radiations (2n = 12 - 124). Cyperaceae species have holocentric chromosomes (meaning that kinetic activity is distributed along the whole chromosome rather than localized in a centromere), which may promote high chromosome number variation through fusion and fission. Chromosome number evolution is potentially a driver of diversification in genus Carex; its relation with diversification patterns has been tested at different evolutionary scales: genus, section, species and population level. In genus Carex, a shift in diversification rates is detected at the origin ca. 31 mya of the "non-Siderostictae" clade¯, which includes ca. 99% of species in the genus. This transition coincides with a sudden decrease in Earth's mean temperature and also with an abrupt transition to higher chromosome numbers due to a shift in the mode of chromosome evolution. Fine-scale study within section Spirostachye (ca. 13my) suggests that chromosome number variation within species accrues gradually as a function of species age. There is nonetheless evidence that chromosome number may not be entirely neutral: chromosome number distributions across the non-Siderostictae clade are compatible with the theory that low chromosome numbers (and thus recombination rates) are selected for where immediate fitness is required, while high recombination rates are favored in environments in which evolutionary innovation is less risky. Chromosome evolution is also shown to play an important role in sedge biodiversity. At macroevolutionary scales, an abrupt transition in the rate of chromosome number evolution and mean chromosome number in section Ovales (ca. 5 mya) suggests a link between chromosome evolution and species diversification. At microevolutionary scales, chromosome rearrangements within the North American Carex scoparia explain genetic variance both within and among populations. All of this evidence strongly suggests that holocentric chromosome rearrangements comprise an important driver of genetic diversification, and potentially speciation, in one of the largest angiosperm genera.
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1 - The Morton Arboretum, 4100 Illinois Route 53, Lisle, IL, 60532-1293, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Franklin B/Hyatt
Date: Tuesday, July 10th, 2012
Time: 8:45 AM