title: Spontaneous Mutation Accumulation in Daphnia pulex in Selection-Free vs. Competitive Environments.
abstract: Understanding the rates, spectra, and fitness effects of spontaneous mutations is fundamental to answering key questions in evolution, molecular biology, disease genetics, and conservation biology. To estimate mutation rates and evaluate the effect of selection on new mutations, we propagated mutation accumulation (MA) lines of Daphnia pulex for more than 82 generations and maintained a non-MA population under conditions where selection could act. Both experiments were started with the same obligate asexual progenitor clone. By sequencing 30 genomes and implementing a series of validation steps that informed the bioinformatic analyses, we identified a total of 477 single nucleotide mutations (SNMs) in the MA lines, corresponding to a mutation rate of 2.30 × 10-9(95% CI 1.90-2.70 × 10-9) per nucleotide per generation. The high overall rate of loss of heterozygosity (LOH) of 4.82 × 10-5per site per generation was due to a large ameiotic recombination event spanning an entire arm of a chromosome (∼6 Mb) and several hemizygous deletion events spanning ∼2 kb each. In the non-MA population, we found significantly fewer mutations than expected based on the rate derived from the MA experiment, indicating purifying selection was likely acting to remove new deleterious mutations. We observed a surprisingly high level of genetic variability in the non-MA population, which we propose to be driven by balancing selection. Our findings suggest that both positive and negative selection on new mutations is powerful and effective in a strictly clonal population.
authors: Department of Biology, McGill University Montreal, Quebec, Canada jmf422@cornell.edu.
authors: Jullien M
authors: JM
authors: Flynn
authors: Department of Biology, McGill University Montreal, Quebec, Canada.
authors: Frédéric J J
authors: FJ
authors: Chain
authors: Department of Biology, McGill University Montreal, Quebec, Canada.
authors: Daniel J
authors: DJ
authors: Schoen
authors: Department of Biology, McGill University Montreal, Quebec, Canada.
authors: Melania E
authors: ME
authors: Cristescu
mesh_terms: D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D019295:Computational Biology / Q000379:methods; D003621:Daphnia / Q000235:genetics* / Q000378:metabolism; D004777:Environment; D019143:Evolution, Molecular; D005260:Female; D056084:Genetic Fitness; D008297:Male; D009154:Mutation; D000067552:Mutation Accumulation; D059645:Mutation Rate; D012641:Selection, Genetic
keywords: ameiotic recombination; loss of heterozygosity; mutation rates; selection