Determinants of mutation load in birds

Area of Science:

• Evolutionary biology
• Population genetics
• Genomics

Background:

• Deleterious mutations accumulate due to ineffective purifying selection.
• Understanding mutation load is crucial for evolutionary and conservation biology.
• Bird genomes offer a unique model due to conserved karyotypes and variable recombination rates.

Purpose of the Study:

• To estimate the proportion of deleterious mutations in bird populations.
• To investigate the influence of effective population size (Ne), recombination (r), and GC-biased gene conversion (gBGC) on mutation load.
• To explore how these factors interact to shape genetic variation.

Main Methods:

• Analysis of 24 population samples from 19 bird species.
• Quantification of mutation load in relation to Ne, r, and gBGC.
• Leveraging variations in recombination rate and GC content across the avian genome.

Main Results:

• Mutation load is significantly higher in populations with smaller effective population sizes (Ne).
• Purging efficacy increases with recombination rate, causing a two-fold difference in genetic load between large and small chromosomes.
• GC-biased mutations constitute about one-third of deleterious mutations, with their accumulation influenced by population size and recombination.

Conclusions:

• The interplay of Ne, recombination, and gBGC critically shapes mutation load.
• Small populations exhibit higher genetic risk factors, driven by gBGC and concentrated in low-recombination regions.
• Findings align with the nearly-neutral theory of molecular evolution, highlighting complex evolutionary dynamics.