Yeh, S.-D. | Search bioRxiv

bioRxiv2018

Tempo, mode, and fitness effects of mutation in Caenorhabditis elegans over 400 generations of minimal selection

The mutational process varies at many levels, from within genomes to among taxa. Many mechanisms have been linked to variation in mutation, but understanding of the evolution of the mutational process is rudimentary. Physiological condition is often implicated as a source of variation in microbial mutation rate and may contribute to mutation rate variation in multicellular organisms.\n\nDeleterious mutations are a ubiquitous source of variation in condition. We test the hypothesis that the mutational process depends on the underlying mutation load in two groups of Caenorhabditis elegans mutation accumulation (MA) lines that differ in their starting mutation loads. \"First-Order MA\" (O1MA) lines maintained under minimal selection for [~]250 generations were divided into high-fitness and low-fitness groups and sets of \"second-order MA\" (O2MA) lines derived from each O1MA line were maintained for [~]150 additional generations. Genomes of 48 O2MA lines and their progenitors were sequenced. There is significant variation among O2MA lines in base-substitution rate ({micro}bs), but no effect of initial fitness, whereas the indel rate is greater in high-fitness O2MA lines. Overall, {micro}bs is positively correlated with recombination and proximity to short tandem repeats and negatively correlated with 10 bp and 1 Kb GC content. However, probability of mutation is well-predicted by the three-nucleotide motif. [~]90% of the variance in standing nucleotide variation is explained by mutability. Total mutation rate increased in the O2MA lines, as predicted by the \"drift barrier\" model of mutation rate evolution. These data, combined with experimental estimates of fitness, suggest that epistasis is synergistic.

evolutionary biology↗

bioRxiv2017

The mutational decay of male and hermaphrodite competitive fitness in the androdioecious nematode C. elegans, in which males are naturally rare

Androdioecious Caenorhabditis have a high frequency of self-compatible hermaphrodites and a low frequency of males. The effects of mutations on male fitness are of interest for two reasons. First, when males are rare, selection on male-specific mutations is less efficient than in hermaphrodites. Second, males may present a larger mutational target than hermaphrodites because of the different ways in which fitness accrues in the two sexes.\n\nWe report the first estimates of male-specific mutational effects in an androdioecious organism. The rate of male-specific inviable or sterile mutations is [≤] 5 x 10-4/generation, below the rate at which males would be lost solely due to those kinds of mutations. The rate of mutational decay of male competitive fitness is ~0.17%/generation; that of hermaphrodite competitive fitness is ~0.11%/generation. The point estimate of ~1.5X faster rate of mutational decay of male fitness is nearly identical to the same ratio in Drosophila. Estimates of mutational variance (VM) for male mating success and competitive fitness are not significantly different from zero, whereas VM for hermaphrodite competitive fitness is similar to that of non-competitive fitness. The discrepancy between the two sexes is probably due to the greater inherent variability of mating relative to internal self-fertilization.

evolutionary biology↗