Widespread Adaptive Introgression of Major Histocompatibility Complex Genes across Vertebrate Hybrid Zones

Area of Science:

• Evolutionary Biology
• Genetics
• Immunology

Background:

• Interspecific introgression introduces novel genetic variation, potentially driving adaptation.
• While adaptive introgression cases are known, general patterns of targets and mechanisms remain unclear.
• Multiallelic balancing selection, especially with rare allele advantage, is predicted to favor adaptive introgression.

Purpose of the Study:

• To investigate whether adaptive introgression is widespread for vertebrate Major Histocompatibility Complex (MHC) genes.
• To test the hypothesis that MHC introgression exceeds genome-wide introgression levels.
• To link adaptive introgression to the underlying mechanism of multiallelic balancing selection.

Main Methods:

• Analysis of data from 29 vertebrate hybrid zones across fish, amphibians, reptiles, birds, and mammals.
• Utilized three complementary statistical approaches to compare MHC introgression with genome-wide introgression.
• Focused on species at advanced stages of speciation to capture significant introgression events.

Main Results:

• Evidence found for widespread adaptive introgression of Major Histocompatibility Complex (MHC) genes across diverse vertebrate taxa.
• MHC introgression was significantly more extensive than genome-wide introgression in the studied hybrid zones.
• This supports the role of balancing selection in facilitating the establishment of introgressed adaptive alleles.

Conclusions:

• Major Histocompatibility Complex (MHC) introgression is a general mechanism for acquiring novel adaptive variation.
• This process enhances species' ability to defend against pathogens and increases their adaptive potential.
• The study provides a mechanistic link between adaptive introgression and balancing selection.