Biology subjects

Ness, R.

Publications and source records attributed to Ness, R..

2 recordsLinked to original sources

bioRxiv2019

The effects of losing sex on the molecular evolution of plant defense

It is hypothesized that the loss of sexual reproduction and reduced recombination rates decrease the ability for hosts to evolve in response to selection by parasites. Using transcriptomes from 32 species, we test whether repeated losses of sex in the plant genus Oenothera has resulted in changes to the evolution of defense genes against herbivores and pathogens. To achieve this, the function of 2,431 Oenothera orthologous genes was determined based on GO annotations from Arabidopsis thaliana. Phylogenetic Analysis by Maximum Likelihood (PAML) was then used to examine how the patterns of molecular evolution in 721 defense and 1,710 non-defense genes differ between sexual (16 spp.) and asexual (16 spp.) taxa. We test whether the relative rates of nonsynonymous to synonymous substitutions ({omega} = dN/dS) in proteins with defensive function were higher in lineages with sexual reproduction ({omega}sexual> {omega}a-sexual), and we asked if such patterns were exclusive for defense genes or not. We detected variability in the rate of amino acid replacements of proteins in >50% of genes and positive selection on 3% of the genes examined. Nevertheless, our results clearly show that on average, signatures of positive and purifying selection on defense and non-defense genes are similar and only a small number of specific genes related to plant immune function may be affected by a loss of sex.

evolutionary biology↗

bioRxiv2019

Direct inference of the distribution of fitness effects of spontaneous mutations in Chlamydomonas reinhardtii

Spontaneous mutations are the source of new genetic variation and are thus central to the evolutionary process. In molecular evolution and quantitative genetics, the nature of genetic variation depends critically on the distribution of fitness effects (DFE) of mutations. Spontaneous mutation accumulation (MA) experiments have been the principal approach for investigating the overall rate of occurrence and cumulative effect of mutations, but have not allowed the effects of individual mutations to be studied directly. Here, we crossed MA lines of the green alga Chlamydomonas reinhardtii with its unmutated ancestral strain to create haploid recombinant lines, each carrying an average of 50% of the accumulated mutations in a variety of combinations. With the aid of the genome sequences of the MA lines, we inferred the genotypes of the mutations, assayed their growth rate as a measure of fitness, and inferred the DFE using a novel Bayesian mixture model that allows the effects of individual mutations to be estimated. We infer that the DFE is highly leptokurtic (L-shaped), and that a high proportion of mutations increase fitness in the laboratory environment. The inferred distribution of effects for deleterious mutations is consistent with a strong role for nearly neutral evolution. Specifically, such a distribution predicts that nucleotide variation and genetic variation for quantitative traits will be insensitive to change in the effective population size.

evolutionary biology↗