Demographically-Based Evaluation of Genomic Regions under Selection in Domestic Dogs

Abstract

Controlling for background demographic effects is important for accurately identifying loci that have recently undergone positive selection. To date, the effects of demography have not yet been explicitly considered when identifying loci under selection during dog domestication. To investigate positive selection on the dog lineage early in the domestication, we examined patterns of polymorphism in six canid genomes that were previously used to infer a demographic model of dog domestication. Using an inferred demographic model, we computed false discovery rates (FDR) and identified 349 outlier regions consistent with positive selection at a low FDR. The signals in the top 100 regions were frequently centered on candidate genes related to brain function and behavior, including LHFPL3, CADM2, GRIK3, SH3GL2, MBP, PDE7B, NTAN1, and GLRA1. These regions contained significant enrichments in behavioral ontology categories. The 3 ^rd top hit, CCRN4L, plays a major role in lipid metabolism, that is supported by additional metabolism related candidates revealed in our scan, including SCP2D1 and PDXC1. Comparing our method to an empirical outlier approach that does not directly account for demography, we found only modest overlaps between the two methods, with 60% of empirical outliers having no overlap with our demography-based outlier detection approach. Demography-aware approaches have lower-rates of false discovery. Our top candidates for selection, in addition to expanding the set of neurobehavioral candidate genes, include genes related to lipid metabolism, suggesting a dietary target of selection that was important during the period when proto-dogs hunted and fed alongside hunter-gatherers.

Author Summary

Identification of the genomic regions under selection during dog domestication is extremely challenging because the demographic fluctuations associated with domestication can produce signals in polymorphism data that mimic those imposed by selective sweeps. We perform the first analysis of selection on the dog lineage that explicitly incorporates a demographic model, that by controlling for the rate of false discovery, more robustly identifies targets of selection. To do so, we conduct a selection scan using three wolf genomes representing the putative centers of dog domestication, two basal dog breeds (Basenji and Dingo), and a golden jackal as outgroup, for which we previously inferred a demographic model. We find that our demographically informed analyses filters out many signals that would be otherwise classified as putative selection signals under an empirical outlier approach. We identify 68 regions of the genome that have likely experienced positive selection. Besides identifying a number of new neurobehavioral candidate genes, our candidate regions contain genes related to lipid metabolism, including CCRN4L, which is centered in the 3 ^rd ranked region. This suggests a previously unreported locus of dietary adaptation, potentially due to the change in diet composition as hunting efficiency increased when proto dogs began hunting alongside hunter-gatherers.