MBE Advance Access first published online on December 23, 2008
This version published online on December 26, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn287
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Research Article |
Spontaneous Mutational and Standing Genetic (Co)Variation at Dinucleotide Microsatellites in Caenorhabditis briggsae and C. elegans
University of Florida
Address for correspondence: Charles F. Baer, Department of Botany and Zoology, University of Florida, Gainesville, FL 32611-8525 USA. Phone: 352-392-3550, Fax: 352-392-3704, email: cbaer{at}ufl.edu
Received for publication October 8, 2008. Revision received December 9, 2008. Accepted for publication December 10, 2008.
Understanding the evolutionary processes responsible for shaping genetic variation within and between species requires separating the effects of mutation and selection. Differences between the patterns of genetic variation observed in nature and when mutations are allowed to accumulate in the relative absence of selection can reveal biases imposed by selection. We characterize the genetic variation at dinucleotide microsatellite repeats in four sets of 250-generation mutation accumulation (MA) lines, two in the species Caenorhabditis briggsae and two in C. elegans, and compare the mutational variation to the standing variation in those species. We also compare the mutational properties of microsatellites to the cumulative effects of mutations on fitness in the same lines. Integrated over the whole genome, we infer that the mutation rate of C. briggsae is about twice that of C. elegans, consistent with the cumulative mutational effects on fitness. The mutational spectrum (ratio of insertions to deletions) differs between repeat types and, in some cases, between species. The per-locus mutation rate is significantly positively correlated with the standing genetic variation at the same locus in both species, providing justification for the common practice of using the standing genetic variance as a surrogate for the mutation rate.
Key Words: heterozygosity microsatellite mutation accumulation mutational variance spontaneous mutation tandem repeat
1 These authors contributed equally
2 Present address: Department of Biology, Arcadia University, 450 S. Easton Rd., Glenside, PA 19038, USA
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