Accelerated evolution of morph-biased genes in pea aphids

Area of Science:

• Evolutionary Biology
• Genomics
• Developmental Biology

Background:

• Phenotypic plasticity allows a single genotype to produce different phenotypes (morphs) in response to environmental cues.
• Genes involved in producing these alternative morphs (morph-biased genes) are hypothesized to experience relaxed selection.
• Relaxed selection is predicted to lead to increased mutation accumulation and faster sequence divergence.

Purpose of the Study:

• To empirically investigate the evolutionary consequences of morph bias in genes associated with phenotypic plasticity.
• To test whether morph-biased genes in the pea aphid exhibit signatures of relaxed selection and accelerated evolution.
• To determine if the frequency of morph expression correlates with the rate of gene evolution.

Main Methods:

• Comparative analysis of gene evolution rates (dN/dS) between morph-biased and unbiased genes in the pea aphid.
• Quantification of morph bias and correlation with evolutionary rates.
• Assessment of purifying selection acting on genes expressed in different morphs.

Main Results:

• Morph-biased genes show significantly faster rates of evolution compared to unbiased genes.
• Gene evolutionary rates increase with the degree of morph bias.
• Genes expressed in rarer morphs (sexual females, males) evolve faster than those in common morphs (asexual females), indicating selection relaxation proportional to morph rarity.

Conclusions:

• Phenotypic plasticity, driven by polyphenism, influences gene evolution by relaxing purifying selection on morph-biased genes.
• The extent of morph bias and expression frequency in specific morphs are key determinants of gene evolutionary rates.
• This study provides empirical evidence for the theoretical link between phenotypic plasticity and accelerated molecular evolution.