The theory predicts that natural selection is effective in removing deleterious mutations from large outbred populations whereas small population isolates may accumulate them due to increased genetic drift and/or inbreeding. We assessed the frequency and genomic distribution of deleterious mutations in 17 wild nine-spined stickleback (Pungitius pungitius) populations differing in their effective population sizes. Using whole-genome resequencing data (10-20X) for 363 individuals and the program SnpEff we annotated SNP variants and predicted their effects on protein-coding sequences, categorizing mutations as putative high, moderate, or low-level deleterious mutations. We compared the frequency of putative deleterious alleles between populations and invested the influence of demographic history and population isolation on the accumulation of putative deleterious mutations. Preliminary results indicate a significantly lower frequency of putative deleterious mutations in populations with high contemporary effective population sizes both for homozygous and heterozygous mutations, suggesting that deleterious mutations have been efficiently removed by purifying selection from larger populations. As expected, drift load (fixed homozygous mutations) was higher in pond (smaller Ne) than marine populations. The majority of putative deleterious mutations were unique to given pond population, indicating that the accumulation of deleterious mutations has occurred independently in each population rather than in their common ancestor.
Variation in deleterious mutation load in nine-spined stickleback (Pungitius pungitius) populations