Two mitochondrial genes under episodic positive selection in subterranean octodontoid rodents

- The genera Ctenomys and Spalacopus have invaded subterranean niche independently.
- The evolution of 2 mt genes was analyzed for these and related octodontoid rodents.
- Rates of synonymous (dS) and non-synonymous (dN) substitutions were estimated.
- dN/dS ratios were significantly higher in subterranean groups.
- Two codons in each gene were found to be under episodic selection.

Tuco-tucos (Ctenomys) and related coruros (Spalacopus) are South American subterranean rodents. An energetically demanding lifestyle within the hypoxic, underground atmosphere may change the selective regime on oxidative phosphorylation. We examined whether weak and/or episodic positive directional selection affected the evolution of two mitochondrial genes (COX2, CytB), in a background of purifying selection in these lineages. We estimated rates of synonymous (dS) and non-synonymous (dN) substitutions and found: 1) significantly higher dN/dS ratio in subterranean groups relative to non-subterranean related species, and 2) two codons in each gene under episodic selection: 94 and 277 of COX2 and 269 and 307 of CytB.