Evolution under a model of functionally buffered deleterious mutations can lead to positive selection in...

Area of Science:

• Evolutionary biology
• Population genetics
• Molecular evolution

Background:

• Selective pressures on DNA sequences can deviate from neutral evolution, detectable via the McDonald-Kreitman (MK) test.
• Amino acid substitutions driven by natural selection are often linked to genetic arms races or evolving protein functions.
• A buffering mechanism, potentially influenced by Wolbachia endosymbionts, may drive selective amino acid fixation, as suggested by studies on bag of marbles (bam) and Sex lethal (Sxl) in Drosophila melanogaster.

Purpose of the Study:

• To evaluate population genetic patterns under a buffering mechanism for selective amino acid fixation.
• To compare the evolutionary dynamics of a Wolbachia buffering model with an arms race/change-in-function model.
• To assess the impact of these models on the statistical power of the MK test.

Main Methods:

• Simulations were used to model the evolutionary dynamics of a Wolbachia buffering mechanism.
• Population genetic patterns were analyzed under both buffering and arms race models.
• The statistical power of the MK test was evaluated for detecting departures from neutral evolution.

Main Results:

• The buffering model predicts selective amino acid replacements but with a lower proportion of adaptive fixations compared to the arms race model.
• The MK test shows significantly lower statistical power to detect departures from neutral evolution under the buffering model.
• Observed selection patterns in Drosophila melanogaster's bam gene are more consistent with an arms race model than a buffering model.

Conclusions:

• A buffering mechanism leads to fewer detectable adaptive amino acid substitutions than an arms race model.
• The MK test's power to detect selection is reduced under a buffering scenario.
• Empirical data for the bam gene in D. melanogaster supports an arms race model over the proposed buffering mechanism.