Paradoxical Evolution of Apis mellifera Mitogenomes: Deviation From the Mutation-Selection-Drift Balance

Area of Science:

• Evolutionary Biology
• Genomics
• Mitochondrial DNA (mtDNA) Evolution

Background:

• Mitochondrial genomes are crucial for understanding evolutionary biology due to influences from niche adaptation, energy demands, and phenotypic plasticity.
• Generalizing mitogenome evolution is challenging, often yielding inconsistent results, as they must balance mutation, selection, and genetic drift to avoid mutational meltdown.
• Apis mellifera (honey bees) offer a unique model for studying mitogenome evolution due to adaptations in lifestyle and energy metabolism.

Purpose of the Study:

• To investigate the evolutionary drivers shaping mitochondrial genome evolution in Apis mellifera.
• To evaluate mutation/variation processes, genome-wide mutational patterns, and selection forces acting on protein-coding genes.
• To predict the direction of selection and examine potential effects on protein 3D structures.

Main Methods:

• Analysis of 66 mitogenome data from 21 Apis mellifera subspecies.
• Assessment of nucleotide content, rearrangements, and open reading frame (ORF) remnants to estimate mutational processes.
• Phylogenetic tree-based inferences to predict selection direction on protein-coding genes and analyze structural impacts.

Main Results:

• The mutation-selection-drift balance in Apis mellifera mitogenomes deviates from equilibrium, maintained by relaxed selection acting indirectly.
• Relaxed selection impacts the mitogenome via gene copies/remnants, particularly through repetitive sequences in the d-loop and gene remnants in rRNA genes, influencing the genome via selective sweeps.
• The nd3 gene exhibited positive selection in Apis mellifera mitogenomes.

Conclusions:

• Mitochondrial genome evolution in Apis mellifera is characterized by a complex interplay of evolutionary forces, with relaxed selection playing an indirect but significant role.
• Indirect effects of relaxed selection, including insertions and selective sweeps, appear to be key mechanisms shaping the mitogenome.
• Specific genes like nd3 are subject to positive selection, highlighting varied evolutionary pressures across the mitochondrial genome.