Balancing selection maintains polymorphisms at neurogenetic loci in field experiments

Area of Science:

• Behavioral genetics
• Evolutionary biology
• Neuroscience

Background:

• Behavioral variation often has a genetic basis, with genes like arginine vasopressin receptor 1a (Avpr1a) and oxytocin receptor (Oxtr) regulating social and reproductive behaviors.
• Extensive genetic diversity at these loci in natural populations suggests balancing selection is at play.

Purpose of the Study:

• To test the hypothesis that balancing selection maintains genetic diversity at behavioral loci.
• To investigate the role of regulatory region-associated microsatellites (RRAMs) in Avpr1a and Oxtr in regulating gene expression and reproductive success.

Main Methods:

• Released genetically diverse, artificially bred bank voles (Myodes glareolus) with varying RRAM allele lengths into field enclosures with differing population densities.
• Assessed the association between RRAM allele lengths of Avpr1a and Oxtr and reproductive success in males and females.

Main Results:

• RRAM allele length in Avpr1a and Oxtr was linked to reproductive success, with optimal genotypes varying based on population density and sex.
• Longer Avpr1a RRAMs benefited males, while shorter ones benefited females; the reverse was true for Oxtr RRAMs.
• Avpr1a RRAM length correlated with male offspring numbers and female weaned offspring numbers, indicating sex-specific selection pressures.

Conclusions:

• Density-dependence and sexual antagonism acting on the arginine vasopressin-oxytocin pathway explain the maintenance of genetic diversity at Avpr1a and Oxtr loci in natural populations.