This study evaluates signatures of selection in the evolution of the mitochondrial DNA of voles, subfamily Arvicolinae, during the colonization of subterranean environments. The comparative sequence analysis of mitochondrial protein-coding genes of eight subterranean vole species (Prometheomys schaposchnikowi, three species of the genus Ellobius: Ellobius talpinus, Ellobius fuscocapillus and Ellobius lutescens, two species of the genus Terricola: Terricola subterraneus and Terricola daghestanicus, Lasiopodomys mandarinus, and Hyperacrius fertilis) and their closest aboveground relatives was applied using codon-substitution models. The highest number of selection signatures was detected in genes ATP8 and CYTB. The relaxation of selection was observed in most mitochondrial DNA protein-coding genes for subterranean species. The largest amount of relaxed genes is discovered in mole voles (genus Ellobius). The number of selection signatures was found to be independent of the evolutionary age of the lineage but fits the degree of specialization to the subterranean niche. The common trends of selective pressures were observed among the evolutionary ancient and highly specialized subterranean rodent families and phylogenetically young lineages of voles. It suggests that the signatures of adaptation in individual mitochondrial protein-coding genes associated with the colonization of the subterranean niche may appear within a rather short evolutionary timespan.

Background: Mitochondrial genes encode proteins involved in oxidative phosphorylation. Variations in lifestyle and ecological niche can be directly reflected in metabolic performance. Subterranean rodents represent a good model for testing hypotheses on adaptive evolution driven by important ecological shifts. Voles and lemmings of the subfamily Arvicolinae (Rodentia: Cricetidae) provide a good example for studies of adaptive radiation. This is the youngest group within the order Rodentia showing the fastest rates of diversification, including the transition to the subterranean lifestyle in several phylogenetically independent lineages.Results: We evaluated the signatures of selection in the mitochondrial cytochromeb(cytB) gene in 62 Arvicolinae species characterized by either subterranean or surface-dwelling lifestyle by assessing amino acid sequence variation, exploring the functional consequences of the observed variation in the tertiary protein structure, and estimating selection pressure. Our analysis revealed that: (1) three of the convergent amino acid substitutions were found among phylogenetically distant subterranean species and (2) these substitutions may have an influence on the protein complex structure, (3)cytBshowed an increased ω and evidence of relaxed selection in subterranean lineages, relative to non-subterranean, and (4) eight protein domains possess increased nonsynonymous substitutions ratio in subterranean species.Conclusions: Our study provides insights into the adaptive evolution of the cytochromebgene in the Arvicolinae subfamily and its potential implications in the molecular mechanism of adaptation. We present a framework for future characterizations of the impact of specific mutations on the function, physiology, and interactions of the mtDNA-encoded proteins involved in oxidative phosphorylation.

In this article, we present the nearly complete mitochondrial genome of the Subalpine Kashmir voleHyperacrius fertilis(Arvicolinae, Cricetidae, Rodentia), assembled using data from Illumina next-generation sequencing (NGS) of the DNA from a century-old museum specimen. De novo assembly consisted of 16,341 bp and included all mitogenome protein-coding genes as well as 12S and 16S RNAs, tRNAs and D-loop. Using the alignment of protein-coding genes of 14 previously published Arvicolini tribe mitogenomes, seven Clethrionomyini mitogenomes, and alsoOndatraandDicrostonyxoutgroups, we conducted phylogenetic reconstructions based on a dataset of 13 protein-coding genes (PCGs) under maximum likelihood and Bayesian inference. Phylogenetic analyses robustly supported the phylogenetic position of this species within the tribe Arvicolini. Among the Arvicolini,Hyperacriusrepresents one of the early-diverged lineages. This result of phylogenetic analysis altered the conventional view on phylogenetic relatedness betweenHyperacriusandAlticolaand prompted the revision of morphological characters underlying the former assumption. Morphological analysis performed here confirmed molecular data and provided additional evidence for taxonomic replacement of the genusHyperacriusfrom the tribe Clethrionomyini to the tribe Arvicolini.

Life under the earth surface is highly challenging and associated with a number of morphological, physiological and behavioral modifications. Subterranean niche protects animals from predators, fluctuations in environmental parameters, but is characterized by high levels of carbon dioxide and low levels of oxygen and implies high energy requirements associated with burrowing. Moreover, it lacks most of the sensory inputs available above ground. The current study describes results from RNA-seq analysis of four subterranean voles from subfamily Arvicolinae:Prometheomys schaposchnikowi,Ellobius lutescens,Terricola subterraneus, andLasiopodomys mandarinus. Original RNA-seq data were obtained for eight species, for nine species, SRA data were downloaded from the NCBI SRA database. Additionally assembled transcriptomes of Mynomes ochrogaster and Cricetulus griseus were included in the analysis. We searched for the selection signatures and parallel amino acid substitutions in a total of 19 species. Even within this limited data set, we found significant changes ofdN/dSratio by free-ratio model analysis for subterranean Arvicolinae. Parallel substitutions were detected in genesRAD23BandPYCR2. These genes are associated with DNA repair processes and response to oxidative stress. Similar substitutions were discovered in theRAD23genes for highly specialized subterraneanHeterocephalus glaberandFukomys damarensis. The most pronounced signatures of adaptive evolution related to subterranean niche within species of Arvicolinae subfamily were detected forEllobius lutescens. Our results suggest that genomic adaptations can occur very quickly so far as the amount of selection signatures was found to be compliant with the degree of specialization to the subterranean niche and independent from the evolutionary age of the taxon. We found that the number of genomic signatures of selection does not depend on the age of the taxon, but is positively correlated with the degree of specialization to the subterranean niche.

Voles and lemmings (subfamily Arvicolinae) remain some of the most difficult groups for disentangling phylogenetic relations owing to recent and very fast explosive radiation. The rapid radiation events are challenging for phylogenetic analysis and produce bushes of various shapes that are impossible to resolve with a straightforward approach using individual loci. Here using the quaddRAD-seq technique and transcriptomes, we tested whether data from the nuclear genome are consistent with trees inferred earlier from individual loci and from mitogenomes in topology and divergence dating. Both the transcriptome and quaddRAD-seq data convincingly place Arvicola as the earliest derivative within Arvicolini. This result is in agreement with the fossil record and conventional taxonomy. For the first time, whole-genome sequencing data resolved relations within the third radiation wave of the subfamily’s taxa, namely the tribes Arvicolini, Lagurini, and Ellobiusini, which have formed polytomy in mitochondrial trees in earlier articles. This study indicates that divergence dating is highly dependent on the number and position of calibration points in a tree and on taxa sampling. In terms of phylogenetic inference, the position of nodes with insufficient taxa representation is the most susceptible to errors.