Mutation Rate and Spectrum of the Silkworm in Normal and Temperature Stress Conditions

Mutation rate is a crucial parameter in evolutionary genetics. However, the mutation rate of most species as well as the extent to which the environment can alter the genome of multicellular organisms remain poorly understood. Here, we used parents-progeny sequencing to investigate the mutation rate and spectrum of the domestic silkworm (Bombyx mori) among normal and two temperature stress conditions (32 degrees C and 0 degrees C). The rate of single-nucleotide mutations in the normal temperature rearing condition was 0.41 x 10(-8) (95% confidence interval, 0.33 x 10(-8)-0.49 x 10(-8)) per site per generation, which was up to 1.5-fold higher than in four previously studied insects. Moreover, the mutation rates of the silkworm under the stresses are significantly higher than in normal conditions. Furthermore, the mutation rate varies less in gene regions under normal and temperature stresses. Together, these findings expand the known diversity of the mutation rate among eukaryotes but also have implications for evolutionary analysis that assumes a constant mutation rate among species and environments.