Data from: Complex selection on a regulator of social cognition: evidence of balancing selection, regulatory interactions and population differentiation in the prairie vole Avpr1a locus

Adaptive variation in social behavior depends upon standing genetic
variation, but we know little about how evolutionary forces shape genetic
diversity relevant to brain and behavior. In prairie voles (Microtus
ochrogaster), variants at the Avpr1a locus predict expression of the
vasopressin 1a receptor in the retrosplenial cortex (RSC), a brain region
that mediates spatial and contextual memory; cortical V1aR abundance in
turn predicts diversity in space-use and sexual fidelity in the field. To
examine the potential contributions of adaptive and neutral forces to
variation at the Avpr1a locus, we explore sequence diversity at the Avpr1a
locus and throughout the genome in two populations of wild prairie voles.
First, we refine results demonstrating balancing selection at the locus by
comparing the frequency spectrum of variants at the locus to a random
sample of the genome. Next, we find that the four SNPs that predict high
V1aR expression in the RSC are in stronger linkage disequilibrium than
expected by chance despite high recombination among intervening variants,
suggesting that epistatic selection maintains their association despite
recombination. Analysis of population structure and a haplotype network
for two populations revealed that this excessive LD was unlikely to be due
to admixture alone. Furthermore, the two populations differed considerably
in the region shown to be a regulator of V1aR expression despite the
extremely low levels of genome-wide genetic differentiation. Together, our
data suggest that complex selection on Avpr1a locus favors specific
combinations of regulatory polymorphisms, maintains the resulting alleles
at populations-specific frequencies, and may contribute to unique patterns
of spatial cognition and sexual fidelity among populations.