Mitogenomics of endemic Ethiopian shrews: looking for footprints of adaptive evolution along a remarkable altitudinal gradient

Abstract Mitochondria provide most of energy in animal cells through oxidative phosphorylation; therefore, the evaluation of selective pressures on the mitochondrial genome can yield valuable insights into evolution of adaptations to different energy requirements within unique environments. The distribution of East African shrews is directly related to an altitudinal gradient, implying their high level of adaptive divergence and making them a unique model for revealing molecular mechanisms of the adaptation. Here we analysed signs of adaptive evolution in 17 mitogenomes of endemic Ethiopian white-toothed shrews (three ecotypes of Crocidura glassi s.l.) that replace each other in adjacent altitudinal belts of the Bale Massif, possibly indicating large adaptive divergence. To test this hypothesis, we used a combination of different methods besides classic tests of selection; we also analysed physicochemical changes of amino acid properties in protein-coding genes. None of the analyses yielded significant results on positive selection. We can theorize that purifying selection might have been a common selection pattern for mitochondrial genes in C. glassi s.l. ecotypes. Finally, different environmental adaptations – reflecting organisms’ various strategies and possibly important in white-toothed shrews – are discussed.