High molecular variability in three pine vole species of the subgenus <i>Terricola</i> ( <i>Microtus</i> , Arvicolinae) and plausible source of polymorphism

Abstract

We studied molecular variability to clarify intraspecific differentiation and phylogenetic relationships in three pine vole species (genus Microtus, subgenus Terricola): Microtus subterraneus, Microtus daghestanicus, and Microtus majori. Multilocus analysis was performed using the entire mitochondrial cytb gene and fragments of nuclear BRCA1, IRBP, and XIST genes. Results confirmed separation of the species, especially M. majori compared with M. daghestanicus and M. subterraneus. These species showed different molecular polymorphism in the genetic markers. We identified two close forms of M. majori, differing in cytb gene and the nuclear gene XIST; one form inhabits the northern slopes of the Greater Caucasus, another the Transcaucasia. Separation of M. daghestanicus populations from North Ossetia and the others was clear. Microtus subterraneus populations from southern Europe and Asia Minor were characterized by maximal genetic heterogeneity; the specimen from Samsun (northern Asia Minor) appeared to be most distant from the others. Despite polymorphism in the chromosome number in M. subterraneus populations from the East European Plain, they possess a depleted gene pool. Results indicated that M. subterraneus colonized the East European Plain in the Holocene, and chromosome variability originated in this part of the species' range as a result of chromosomal fission and quick fixation of the arrangement in northern populations. We argue that differences in the genetic differentiation patterns of Terricola species are mainly due to their ecological peculiarities. Nous avons étudié la variabilité moléculaire pour clarifier la différenciation intraspécifique et les relations phylogénétiques chez trois espèces de campagnols des pins (genre Microtus, sous-genre Terricola): Microtus subterraneus, Microtus daghestanicus et Microtus majori. L'analyse multilocus a été réalisée en utilisant l'intégralité du gène cytb mitochondrial et des fragments des gènes nucléaires BRCA1, IRBP et XIST. Les résultats ont confirmé la séparation des espèces, en particulier M. majori par rapport à M. daghestanicus et M. subterraneus. Ces espèces ont montré un polymorphisme moléculaire différent dans les marqueurs génétiques. Nous avons identifié deux formes proches de M. majori, différant par le gène cytb et le gène nucléaire XIST; une forme habite les pentes nord du Grand Caucase, une autre la Transcaucasie. La séparation des populations de M. daghestanicus d'Ossétie du Nord et des autres était claire. Les populations de Microtus subterraneus du sud de l'Europe et de l'Asie Mineure étaient caractérisées par une hétérogénéité génétique maximale; le spécimen de Samsun (nord de l'Asie Mineure) semblait le plus éloigné des autres. Malgré le polymorphisme du nombre de chromosomes dans les populations de M. subterraneus de la plaine d'Europe de l'Est, elles possèdent un pool génétique appauvri. Les résultats ont indiqué que M. subterraneus a colonisé la plaine d'Europe de l'Est à l'Holocène et que la variabilité chromosomique est née dans cette partie de l'aire de répartition de l'espèce en raison de la fission chromosomique et de la fixation rapide de l'arrangement dans les populations du nord. Nous soutenons que les différences dans les modèles de différenciation génétique des espèces Terricola sont principalement dues à leurs particularités écologiques. Figure S1. Bayesian inference dendrogram constructed from a comparison of the entire mitochondrial cytb gene sequences (1143 bp) of the subgenus Terricola pine voles, as well as other vole species of the genus Microtus. Figure S2. Bayesian inference dendrogram constructed from a comparison of the nuclear IRBP gene fragments (807 bp) of the subgenus Terricola pine voles, as well as Microtus obscurus and Microtus rossiaemeridionalis representatives. Figure S3. Bayesian inference dendrogram constructed from a comparison of the nuclear BRCA1 gene fragments (1698 bp) of the subgenus Terricola pine voles, as well as Microtus obscurus and Microtus rossiaemeridionalis representatives. Figure S4. Bayesian inference dendrogram constructed from a comparison of two joined non-overlapping fragments (998 bp in total) of the nuclear XIST gene of the subgenus Terricola pine voles, as well as Microtus obscurus and Microtus rossiaemeridionalis representatives. Figure S5. Bayesian inference dendrogram constructed from a comparison of joined fragments of all studied nuclear genes (3503 bp in total) of the subgenus Terricola pine voles, as well as Microtus obscurus and Microtus rossiaemeridionalis representatives. Figure S6. The ML dendrogram constructed from a comparison of joined fragments of all studied mitochondrial and nuclear genes (4646 bp in total) of the subgenus Terricola pine voles, as well as Microtus obscurus and Microtus rossiaemeridionalis representatives. Figure S7. Bayesian inference dendrogram constructed from a comparison of joined fragments of all studied mitochondrial and nuclear genes (4646 bp in total) of the subgenus Terricola pine voles, as well as Microtus obscurus and Microtus rossiaemeridionalis representatives. Table S1. Average genetic distances (p-distances) calculated by comparing sequences of the cytb gene (1143 bp) of different vole species. Table S2. Average values of pairwise genetic distances, calculated by comparing sequences of the cytb gene (1143 bp) within a sample, an intraspecific group, or an entire species of pine voles. Table S3. Genetic variability parameters calculated for united samples of the subgenus Terricola species, based on total sequences of the cytb gene. Table S4. Average p-distance values and the number of fixed substitutions (in brackets) calculated by comparing fragments of three nuclear genes of the vole species. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.