Shared evolutionary origin of major histocompatibility complex polymorphism in sympatric lemurs

Area of Science:

• Evolutionary immunology
• Molecular evolution
• Primate genetics

Background:

• Major Histocompatibility Complex (MHC) genes are crucial for vertebrate adaptive immunity and exhibit high polymorphism.
• Shared MHC alleles across species suggest either trans-species polymorphism maintained by balancing selection or convergent evolution.
• Understanding MHC evolution is key to comprehending host-parasite co-evolutionary dynamics.

Purpose of the Study:

• To investigate the origins of MHC similarity in dwarf and mouse lemurs (Cheirogaleidae).
• To determine if shared parasite communities drive selection for similar MHC alleles across lemur species.
• To differentiate between convergent evolution and trans-species polymorphism in explaining shared MHC sequences.

Main Methods:

• Examined Major Histocompatibility Complex (MHC) class II variation (DRB, DQB loci) in multiple lemur species.
• Assessed overlap of gut-parasite communities in sympatric lemur populations.
• Integrated new MHC data with existing Cheirogaleidae data, analyzing codon usage at functional vs. neutral sites.

Main Results:

• Identified shared gut parasites across lemur species, suggesting parallel selective pressures.
• Demonstrated that shared parasites can select for functionally similar MHC alleles in distinct species.
• Concluded that balancing selection maintaining trans-species polymorphism is the primary driver of shared MHC motifs, not convergent evolution.

Conclusions:

• MHC-parasite co-evolutionary dynamics operate at the community level, influenced by shared parasite communities.
• Trans-species polymorphism, not convergent evolution, explains the long-term maintenance of shared MHC alleles across divergent lemur lineages.
• This study highlights the significant role of historical selective pressures in shaping immune gene diversity.