A Mouse Model of Mitochondrial Disease Reveals Germline Selection Against Severe mtDNA Mutations

The interesting recent Report, “A mouse model of mitochondrial disease reveals germline selection against severe mtDNA mutations” by W. Fan et al. (15 February 2008, p. 958) provides convincing evidence that mitochondrial mutations with severe effects are eliminated from the female germ line by selection within the ovary. We agree that such a “germline filter for severely deleterious mtDNA mutations makes evolutionary sense,” (p. 962), but not for the reason suggested by the authors, who argue that without such a filter, the high mitochondrial mutation rate would lower species fitness. The implication of this argument is that the germline mutational filter evolved because it was advantageous at the species level. A more parsimonious explanation, which is also more consistent with modern evolutionary theory (1), is that the adaptive significance of a germline filter for deleterious mitochondrial mutations lies in the greater reproductive success enjoyed by individual females that possess such a filter. As a result, the ability to selectively eliminate deleterious mitochondrial mutations during oogenesis is a trait that would have spread through the species relatively rapidly via individual selection. While species that possess a germline filter might very well have greater reproductive potential than those in which the filter is lacking, it is unlikely that the filter evolved as a consequence of this difference.

Alexander Berlin, Jacqueline Betsch, Tanya Corman, Ryan Ely, John Emhardt, Dennis Fisher, Kyle Foster, Andrew Hadley, Wade Hazel, Lauren Huff, Brock Sishc, and Brian Smith

Population Genetics and Evolution class (Bio 444), DePauw University, Greencastle, IN 46135, USA.

Reference

1. D. J. Futuyma, Evolution (Sinauer Associates, Inc., Sunderland, MA, 2005), p. 258.