Comparative chromosome mapping of the rRNA genes and telomeric repeats in three Italian pine voles of the Microtus savii s.l. complex (Rodentia, Cricetidae)

Abstract

The Microtus (Terricola) savii s. l. complex is a group of five species/subspecies of the Italian pine voles, which diverged at different times either with or without chromosomal differentiation. The evidence of chromosomal diversification has so far concerned the shape of the sex chromosomes, especially the X chromosome. Three taxa of the group, Microtus savii savii, Microtus savii nebrodensis, and Microtus savii tolfetanus have identical karyotypes with metacentric X chromosomes. The X chromosomes of Microtus brachycercus and Microtus brachycercus niethammericus are, respectively, subtelocentric and acrocentric in shape. The Microtus savii complex has been long an object of conventional karyological studies, but comparative molecular cytogenetic data were completely missing. Therefore, we conducted a comparative chromosomal mapping of rRNA genes (rDNA) and telomeric repeats in three of the five taxa of the group: Microtus savii savii, Microtus savii nebrodensis, and Microtus brachycercus niethammericus, each of which belongs to a distinct mitochondrial clade.The survey revealed that differentiation of the clades was accompanied by remarkable changes with regard to the number and locations of the rDNA sites. Thus, Microtus savii savii and Microtus savii nebrodensis have especially high numbers of rDNA sites, which are located in the centromeric regions of, correspondingly, 18 and 13 chromosome pairs, whereas Microtus brachycercus niethammericus shows variable (8–10) and heteromorphic rDNA sites on both centromeric and telomeric regions. Interstitial telomeric sites (ITS), which are believed to indicate possible breakpoints of recurring chromosomal rearrangements, are present on the largest biarmed chromosomes and on the metacentric X chromosomes in Microtus savii savii and Microtus savii nebrodensis. These preliminary results are discussed in the context of recent advances in phylogeny of the group, as well as the rDNA genomic organization and X chromosome rearrangements in the genus Microtus.

From biology to management of Savi's pine vole (Microtus savii)

“…brachycercus . These data would be in agreement with the genetic divergence of the clade brachycercus , which departed from M. s. savii only in the Middle Pleistocene (0.3–0.5 million years ago) …”

“…Two other subspecies, M. s. tolfetanus (Contoli, 2003) and M. s. niethammericus (Contoli, 2008), have recently been described in a small area of central Italy (Tolfa Hills, near Rome) and in Gargano (Apulia) respectively . Genetic studies recently addressed the phylogenetic relationships between M. savii subspecies . There is evidence of a separation between Calabrian populations and the other Italian populations, but whether M. s. brachycercus should be elevated to the rank of a species is not yet clear.…”

“…12 These data would be in agreement with the genetic divergence of the clade brachycercus, which departed from M. s. savii only in the Middle Pleistocene (0.3-0.5 million years ago). 12,15 Regarding Savi's pine vole morphology, some authors argued that the pattern of teeth morphology among the populations of north-central and southern Italy reflects the interaction between morphological and environmental variability. 19 The variability of tooth morphology indeed shows two geographical scales: at a regional level, morphological variability seems to be related to the pressure of climatic conditions, while at a more local scale it may be linked to the fragmentation of areas where small populations undergo ecological isolation, thus developing different morphotypes.…”

Karyotype and Chromosome Variability in the Armadillo <b><i>Chaetophractus villosus</i></b> in Argentina

“…It is well known that clusters of different repetitive DNA sequences, including subtelomeric and interstitial telomeric repeats, characterize the breakpoints of recurrent chromosomal rearrangements [Azzalin et al, 2001;Nergadze et al, 2004]. However, the telomeric probes Telo1 and Telo2 used in the present work and by other authors [Gornung et al, 2011] detected interstitial telomeric sequences in chromosomes 4, 12, 16, and 26; these were interpreted as remnants of acrocentric fusions.…”

Mammal endemism In Italy: A review

“…It seems to be missing from the slopes of Etna. Castiglia et al (2008) suggested a possible specific status of the Sicilian Microtus, then they confirmed this in further papers based on molecular genetics, karyotypic and morphological studies (Gornung et al 2011, Bezerra et al 2016. The split of this species with the other species of the complex, M. savii and M. brachycercus, dated about 1.81 million years ago (MYA) (Tougard 2017).…”