The evolutionary success of rodents of the superfamily Muroidea makes this taxon the most interesting for evolution studies, including study at the chromosomal level. Chromosome-specific painting probes from the Chinese hamster and the Syrian (golden) hamster were used to delimit homologous chromosomal segments among 15 hamster species from eight genera: Allocricetulus, Calomyscus, Cricetulus, Cricetus, Mesocricetus, Peromyscus, Phodopus and Tscherskia (Cricetidae, Muroidea, Rodentia). Based on results of chromosome painting and G-banding, comparative maps between 20 rodent species have been established. The integrated maps demonstrate a high level of karyotype conservation among species in the Cricetus group (Cricetus, Cricetulus, Allocricetulus) with Tscherskia as its sister group. Species within the genera Mesocricetus and Phodopus also show a high degree of chromosomal conservation. Our results substantiate many of the conclusions suggested by other data and strengthen the topology of the Muroidea phylogenetic tree through the inclusion of genome-wide chromosome rearrangements. The derivation of the muroids karyotypes from the putative ancestral state involved centric fusions, fissions, addition of heterochromatic arms and a great number of inversions. Our results provide further insights into the karyotype relationships of all species investigated.

To examine phylogenetic relationships within the Asian lineage of voles (Microtus) belonging to subgenus Alexandromys, the mitochondrial cytochrome b gene (cytb) was sequenced for its representatives, and the results were compared with the cytogenetic, morphological, and paleontological data. In all the trees inferred from maximum likelihood, parsimony, and Bayesian phylogenetic analyses, the Asian clade is subdivided into highly supported Alexandromys s.s. and moderately supported Pallasiinus lineages. Four subclades are recovered within Alexandromys: (1) Microtus maximowiczii and Microtus sachalinensis; (2) Microtus miiddendorffii s.l., Microtus mongolicus and Microtus gromovi; (3) Microtus fortis; and (4) Microtus limnophilus. Thus, M. limnophilus demonstrates clear affinities to Alexandromys s.s. but not to Microtus oeconomus (subgenus Pallasiinus), which was always regarded as its sibling species. The results obtained indicate M. mongolicus as a member of Alexandromys but not of the Microtus arvalis group, thus being concordant with the cytogenetic data. The mitochondrial data support the species status of M. gromovi; moreover, its placement as a part of a trichotomy with M. miiddendorffii s.l. and M. mongolicus contradicts the traditional affiliation of M. gromovi with M. maximowiczii. The divergence rate of cytb third position transversions in Microtus is estimated at approximately 8% per Myr, which corresponds to approximately 30% per Myr for all substitution types at all codon positions. The maximum likelihood distance based on complete sequence showed a tendency for a progressive underestimation of divergence and time for older splits. According to our molecular clock analysis employing nonlinear estimation methods, the split between Alexandromys and Pallasiinus and basal radiation within Alexandromys date back to approximately 1.2 Mya and 800 Kya, respectively.

AimWe assessed the influence of past environmental changes, notably the importance of palaeogeographical and climatic drivers, in shaping the distribution patterns of Dipodoidea (Rodentia), the superfamily most closely related to the large species-rich superfamily Muroidea (c. 1300-1500 species). Dipodoids are suitable for testing several biogeographical hypotheses because of their disjunct distribution patterns in the Northern Hemisphere and the numerous species distributed in Asian deserts.Location Holarctic.Methods We inferred molecular phylogenetic relationships for Dipodoidea (34 out of 51 species and 15 out of 16 genera) based on five coding genes. A time-calibrated phylogeny was estimated using a Bayesian relaxed molecular clock with four fossil calibrations. A cross-validation procedure was adopted to examine the impact of each fossil on our estimates. The ancestral area of origin and biogeographical scenarios were reconstructed using time-stratified dispersal-extinction-cladogenesis models.Results Phylogenetic analyses recovered a well-resolved and supported topology. The divergence between Dipodoidea and Muroidea occurred in the late Palaeocene (c. 57.72 Ma) and modern Dipodoidea diversified during the middle Eocene (c. 40.62 Ma). Similar results were found with each calibration strategy used with the cross-validation procedure. The reconstruction of ancestral areas and biogeographical events indicated that modern Dipodoidea originated in the Himalaya-Tibetan and Central Asian region.Main conclusions At the time when Dipodoidea diversified (middle Eocene), the Central Asia and Himalaya-Tibetan Plateau region experienced major uplift episodes due to the collision of India with Asia, which also induced diversification events in many other groups. Other important diversification events (e.g. divergence between Zapodidae and Dipodidae in Central Asia) took placed during the Eocene-Oligocene transition when the global temperature decreased significantly and rodent/lagomorph-dominant faunas replaced Eocene perissodactyl-dominant faunas. All of these climatic and geological disruptions in the Central Asia and Himalaya-Tibetan Plateau region modified landscapes and offered new habitats that favoured diversification events, thus triggering the evolutionary history of Dipodoidea.

Despite some popularity of hamsters as pets and laboratory animals there is no reliable phylogeny of the subfamily Cricetinae available so far. Contradicting views exist not only about the actual number of species but also concerning the validity of several genera. We used partial DNA sequences of two mitochondrial (cytochrome b, 12S rRNA) and one partial nuclear gene (von Willebrand Factor exon 28) to provide a first gene tree of the Cricetinae based on 15 taxa comprising six genera. According to our data, Palaearctic hamsters fall into three distinct phylogenetic groups: Phodopus, Mesocricetus, and Cricetus-related species which evolved during the late Miocene about 7-12 MY ago. Surprisingly, the genus Phodopus, which was previously thought to have appeared during the Pleistocene, forms the oldest clade. The largest number of extant hamster genera is found in a group of Cricetus-related hamsters. The genus Cricetulus itself proved to be not truly monophyletic with Cricetulus migratorius appearing more closely related to Tscherskia, Cricetus, and Allocricetulus. We propose to place the species within a new monotypic genus. Molecular clock calculations are not always in line with the dating of fossil records. DNA based divergence time estimates as well as taxonomic relationships demand a reevaluation of morphological characters previously used to identify fossils and extant hamsters.

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