The fester locus in Botryllus schlosseri experiences selection.

Area of Science:

• Evolutionary biology
• Genetics
• Immunology

Background:

• Allorecognition, the self/non-self recognition crucial for life, is genetically understood mainly in vertebrates (MHC) and plants (SI).
• The evolutionary history of allorecognition loci remains largely unexplored.
• In Botryllus schlosseri, the fester locus is implicated in histocompatibility reactions, acting as receptors.

Purpose of the Study:

• To investigate the evolutionary pressures acting on the fester locus in Botryllus schlosseri.
• To determine if fester proteins evolve neutrally or under balancing, directional, or purifying selection.

Main Methods:

• Analysis of genetic variation within the fester locus across different populations.
• Comparison of polymorphism statistics (Tajima's D, Fu and Li's D*, F*) between fester and housekeeping genes.
• Calculation of dN/dS ratios (ω) for codons within fester proteins.

Main Results:

• The majority of genetic variation in the fester locus is found within populations.
• Polymorphism statistics indicate significant negative values for East and West Coast A-type alleles, suggesting selection.
• A proportion of codons in fester proteins exhibit ω > 1, indicating potential balancing or directional selection, while most show purifying selection (ω < 1).

Conclusions:

• Fester proteins are under non-neutral evolutionary forces.
• Purifying selection acts on most of the protein, while specific codons experience balancing or directional selection.
• The distribution of variation suggests balancing selection is a significant factor in the evolution of allorecognition in B. schlosseri.