Fisher's exact test is based on raw numbers of nonsynonomous substitutions (NSS) and synonomous substitutions (SS); McDonald-Kreitman test is based on comparisons dN/dS for fixed differences between populations and polymorphism within a population. n/a indicates the test was not applicable because there were no substitutions observed for OWNorth at ATPase8. Dog sequence Catp04 was excluded from analysis because it clustered independently and may have been influenced by breeding selection. OWNorth includes haplotypes Catp03 and Catp18 from the NWT, Canada, Catp08 from Sweden, and Catp09 from Russia. Clades are those identified in Figure 2b. Higher dN/dS values in samples from more northern climates suggest a selective advantage at colder temperatures.