Gene conversion and purifying selection shape nucleotide variation in gibbon L/M opsin genes

Area of Science:

• Genetics
• Evolutionary Biology
• Primate Vision

Background:

• Routine trichromatic color vision in catarrhines relies on X-linked L/M opsin genes and an autosomal S opsin gene.
• Genetic variation in L and M opsin genes is considered rare in non-human catarrhines, despite potential homogenization by gene conversion.
• Previous studies on nucleotide variation were limited, particularly in gibbons.

Purpose of the Study:

• To investigate nucleotide variation in gibbon L and M opsin genes, focusing on exons 3-5.
• To understand the role of gene conversion and selection in shaping opsin gene evolution in gibbons.

Main Methods:

• DNA sequencing of L and M opsin genes from 94 gibbon individuals across three genera.
• Analysis of nucleotide divergence between L and M opsin genes in both exons and introns.
• Phylogenetic reconstruction using exon and intron sequences.
• Detection of gene conversion events using the GENECONV program.

Main Results:

• All studied gibbons possessed both L and M opsin genes without hybrid forms.
• Exonic nucleotide divergence between L and M opsin genes was significantly higher than intronic divergence.
• Phylogenetic analysis indicated multiple gene duplication events when using intron sequences, contrasting with a single ancestral duplication event when using exon sequences.
• Gene conversion events were predominantly identified within intron regions.

Conclusions:

• Gibbon L and M opsin genes have undergone historical gene conversion, primarily in introns.
• Gene conversion plays a homogenizing role between L and M opsin genes.
• Purifying selection acts on central exons to preserve spectral differences, crucial for non-human catarrhine color vision.