MHC-mediated spatial distribution in brown trout (Salmo trutta) fry

Area of Science:

• Population genetics
• Behavioral ecology
• Immunogenetics

Background:

• The Major Histocompatibility Complex (MHC) plays a crucial role in immune response and is known to influence social recognition in various species.
• Previous laboratory studies suggested that individuals prefer to associate with others sharing similar MHC alleles, but evidence in natural settings was lacking.

Purpose of the Study:

• To investigate whether wild brown trout fry exhibit kin association based on shared MHC class I alleles under natural conditions.
• To determine if MHC similarity influences the spatial aggregation patterns of young fish after emergence from nests (redds).

Main Methods:

• Microsatellite data and parental assignment were used to analyze MHC class I alleles in wild brown trout fry.
• Spatial distances between pairs of fry (full-siblings and unrelated individuals) were measured and correlated with the number of shared MHC class I alleles.

Main Results:

• A significant trend showed reduced distances between full-sibling fry as the number of shared MHC class I alleles increased.
• Even unrelated fry displayed closer aggregation with a higher number of shared MHC class I alleles, indicating a non-familial association pattern.
• These aggregation patterns were statistically significant (P<0.0001) for both sibling and unrelated pairs.

Conclusions:

• Sharing MHC class I alleles appears to play a role in maintaining kin association among brown trout fry after emergence.
• This study provides the first evidence of MHC-mediated kin association in a wild fish population, supporting previous laboratory findings.
• The results suggest that MHC-based recognition influences social structure and aggregation behavior in natural environments.