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Selection at linked sites in the partial selfer Caenorhabditis elegans
Asher D Cutter1, Bret A Payseur
1Department of Ecology and Evolutionary Biology, University of Arizona, USA. acutter@email.arizona.edu
Molecular Biology and Evolution
|April 8, 2003
Summary
Natural selection influences neutral DNA polymorphism in Caenorhabditis elegans, a partially selfing nematode. Higher recombination rates correlate with increased neutral polymorphism, demonstrating selection
Area of Science:
- Evolutionary genetics
- Population genetics
- Genomics
Background:
- Natural selection can create correlations between recombination rates and neutral DNA polymorphism through genetic hitchhiking and background selection.
- Theoretical models predict stronger effects of selection at linked sites in partially selfing populations compared to outcrossing ones.
- Empirical studies on selection at linked sites have predominantly focused on outcrossing species, leaving a gap in understanding selfing organisms.
Purpose of the Study:
- To investigate the role of natural selection in determining neutral polymorphism within a partially selfing organism.
- To analyze genome-wide single-nucleotide polymorphism (SNP) density in relation to recombination rates and gene density in Caenorhabditis elegans.
Main Methods:
- Utilized a published single-nucleotide polymorphism (SNP) dataset for Caenorhabditis elegans.
- Partitioned the genome into windows to calculate SNP densities, recombination rates, and gene densities across all chromosomes.
- Performed multivariate analyses incorporating local divergence estimates between C. elegans and C. briggsae.
Main Results:
- Identified a significant positive correlation between recombination rate and neutral polymorphism (estimated by noncoding SNP density) across the C. elegans genome.
- Observed lower levels of neutral polymorphism in gene-dense regions compared to gene-poor regions in some analyses.
- Found that mutational explanations alone are insufficient to account for the observed patterns, suggesting a role for selection.
Conclusions:
- Provided the first empirical evidence that natural selection shapes genome-wide neutral polymorphism patterns in a partially selfing animal.
- Concluded that genetic hitchhiking and background selection models can explain the observed relationship between recombination rate and SNP density, but require incorporation of selfing rates.
- Highlighted the need for theoretical models accounting for partial self-fertilization and biased sex ratios to clarify the relative roles of genetic hitchhiking and background selection.