Structural genomic variation and behavioral interactions underpin a balanced sexual mimicry polymorphism.

Area of Science:

• Evolutionary biology
• Genetics
• Animal behavior

Background:

• Phenotypic diversity and balanced polymorphisms are key evolutionary concepts.
• Understanding the genetic basis and selective pressures of such traits is crucial.
• The swordtail fish (Xiphophorus birchmanni) exhibits a sexual mimicry polymorphism.

Purpose of the Study:

• To investigate the genetic architecture of the "false gravid spot" polymorphism in X. birchmanni.
• To identify the behavioral mechanisms maintaining this balanced polymorphism.
• To explore the role of structural variants in gene regulation for evolutionary diversity.

Main Methods:

• Genome-wide association mapping to identify genetic loci.
• Long-read sequencing to analyze structural variations.
• Behavioral studies in laboratory and natural settings to assess social interactions.

Main Results:

• A single intergenic region upstream of the kitlga gene is associated with the false gravid spot.
• Complex structural rearrangements differentiate alleles at this locus.
• The false gravid spot haplotype increases kitlga expression, leading to melanophore abundance.
• Males with the false gravid spot experience reduced aggression but increased male attention and female disinterest.

Conclusions:

• Structural variants in regulatory regions can drive balanced polymorphisms.
• Behavioral interactions stemming from the false gravid spot phenotype contribute to its maintenance.
• This study provides a genetic and mechanistic explanation for a complex phenotypic polymorphism.