Dynamics of Deleterious Mutations and Purifying Selection in Small Population Isolates

Area of Science:

• Evolutionary genetics
• Population genetics
• Genomics

Background:

• Prolonged population decline and isolation can lead to significant genomic consequences.
• Quantitative assessments of mutation loads and the impact of inbreeding and selection are limited.
• Understanding how genetic variation is shaped by these factors is crucial for conservation.

Purpose of the Study:

• To evaluate the abundance and frequency of deleterious mutations in wild stickleback populations.
• To characterize the genomic landscape of deleterious variation across varying inbreeding levels.
• To measure the efficacy of purifying selection in isolated and inbred populations.

Main Methods:

• Analysis of 17 wild nine-spined stickleback (Pungitius pungitius) populations.
• Assessment of inbreeding levels (FROH) and histories of isolation.
• Quantification of deleterious mutations and runs of homozygosity.

Main Results:

• Small, isolated, and inbred populations exhibited higher loads of deleterious homozygous mutations and more frequent mildly deleterious variants.
• Deleterious homozygotes were enriched in runs of homozygosity, with greater enrichment in outbred populations.
• Historical effective population size predicted purifying selection efficacy for mildly deleterious alleles.

Conclusions:

• Deleterious variant accumulation and purging can occur concurrently.
• A significant fraction of segregating strongly deleterious variants are recessive lethals.
• Inbreeding level is a strong predictor of realized deleterious mutation loads in isolated populations.