Naomi Phillips et al. (2008) Development & Evolution Meeting "Direct Estimate of the Rate and Spectrum of Microsatellite Mutation in Rhabditid Nematodes"

Andy Custer, Matthew Salomon, Gigi Ostrow, Naomi Phillips, Charles Baer

[Development & Evolution Meeting, 2008]

Simple sequence repeats (SSR, or microsatellites) are one of the most widely used classes of genetic markers, from genetic mapping and association studies to investigations of population structure and conservation. Despite their utilization, many unresolved questions concerning the mutational processes shaping SSR evolution remain. Here we describe a study aimed to provide unbiased estimates of the rate and spectrum of new SSR mutations in a novel mutation accumulation (MA) model system. The mutational properties of dinucleotide SSRs were characterized in two strains (= genotypes) of two species in the genus Caenorhabditis, C. briggsae and C.elegans after 250 generations of MA. Mutations have been allowed to accumulate in the (relative) absence of natural selection, thus allowing us to genotype paired control and generation 250 MA lines at approximately 40 dinucleotide loci of perfect, imperfect, and compound SSRs. Furthermore, we investigate how the mutational properties of SSRs are correlated with the genomic mutation rate for fitness in these two species.

Charles F Baer et al. (2005) International Worm Meeting "Comparative mutational biology of Rhabditid nematodes: Rate of decline in fitness and mutational covariance in two thermal environments"

Naomi Phillips, Edward Mezerhane, Thomas Keller, Dustin Blanton, Gigi Ostrow, Charles F Baer, Catherine Steding, Frank Shaw, Laura Levy, Ashley Boggs

[International Worm Meeting, 2005]

Deleterious mutations are of fundamental importance to all aspects of organismal biology. Evolutionary geneticists have expended tremendous effort to estimate the genome-wide rate of mutation and the effects of new mutations on fitness, but the degree to which genomic mutational properties vary within and between taxa is largely unknown, particularly in multicellular organisms. Beginning with two highly inbred strains from each of three species in the nematode family Rhabditidae (Caenorhabditis briggsae, Caenorhabditis elegans, and Oscheius myriophila) we allowed mutations to accumulate in the relative absence of natural selection for over 200 generations. We document significant variation in the rate of decay of fitness due to new mutations between strains and between species: C. briggsae declines in fitness approximately twice as fast as C. elegans or O. myriophila. Estimates of the per-generation mutational decay of fitness were very consistent within strains between assays 100 generations apart. The results were very similar when fitness was assayed at 20C and 25C, although the relative fitness of the unmutated controls differed among species at the two temperatures. We report the mutational correlation between fitness in the different thermal environments. Rate of mutational decay in fitness was positively associated with genomic mutation rate and negatively associated with average mutational effect. These results provide unambiguous experimental evidence for substantial variation in genome-wide properties of mutation both within and between species and reinforce conclusions from previous experiments that the cumulative effects on fitness of new mutations can differ markedly among related taxa.