Mitochondrial DNA sequences should not be used to test for isolation by geographic distance

What is it about?

Tests for isolation by distance (IBD) are the most commonly used method for studying spatial genetic structure. The genetic marker that is most frequently used to test for IBD is mitochondrial DNA (mtDNA), but it is often in conflict with nuclear markers. We show that comprehensive microsatellite and SNP data sets may identify IBD when mtDNA does not, and conclude that mtDNA should not be used to test for IBD. SNP data, on the other hand, represent the "gold standard" about whether or not IBD is present. This study illustrates an important implication of the fact that the neutral theory of evolution does not apply to mtDNA because this marker tends to be under strong selection. In this case, the failure to reliably identify IBD is likely a result of a selection-driven reduction in genetic diversity obscuring spatial genetic variation.

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Why is it important?

A Google search using the search terms "mitochondrial DNA isolation by distance" returns >4 million matches, indicating that the results of a huge number of population genetic studies are questionable. The present study shows that a negative result does not mean that a species is panmictic throughout its range. In species of conservation concern or exploited species, where the presence of IBD has important implications for management, past results need to be re-assessed using more sophisticated methods.

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