Alexey V. Surov

Karyotype Reorganisation in the subtilis Group of Birch Mice (Rodentia, Dipodidae, Sicista): Unexpected Taxonomic Diversity within a Limited Distribution

Conventional cytogenetic studies of Sicista subtilis and S. severtzovi (Dipodidae, Sicistinae), both attributable to the subtilis group of birch mice, revealed extensive karyotype diversity with 2n = 16–26 and NFa values of 26–46 indicating the overwhelming non-Robertsonian nature of chromosomal reorganization in these species. The numerical and structural chromosome variability was principally found in specimens located within a confined region of the East European (Russian) Plain. The approximately 135,000-km2 area occurs in the vicinity of the Don River bend between 49°13’N/43°46’E and 51°32’N/36°16’E. The detection of cytotypes sharing similar 2n and NF values, but having morphologically distinct chromosomes, suggests that these may result from polymorphisms present both within recognized species and in cryptic taxa not hitherto described. We conducted a comprehensive, comparative chromosome banding analysis of 52 birch mice (21 localities) referable to the subtilis group and report the presence of 5 distinct karyotypes, each characterized by a combination of stable, variable, and partly overlapping 2n/NFa values. These karyotypes differed from each other by 10–29 structural chromosomal rearrangements (18.1 ± 6.3) that comprised Rb fusions/fissions (42.2%), pericentric inversions (31.1%), and tandem translocations (22.2%). The composition, and the high numbers of these chromosomal changes, is likely to provide an effective means of post-mating isolation, suggesting that taxonomic diversity within the subtilis group is larger than currently accepted. Additionally, we report the frequent fixation of tandem translocations in sample populations, one of which was found in a polymorphic state representing, as far as we are aware, the first case of an in statu nascendi tandem fusion in wild populations. Moreover, our data revealed that bi-armed chromosomes were involved in fusions detected in some of the subtilis taxa. In each instance, however, fusions were preceded by pericentric inversions that transform one or both bi-armed chromosomes into acrocentrics resulting in either centromere-telomere or Robertsonian translocations. Finally, a phylogenetic scenario inferred from a cladistic analysis of the chromosomal data suggests that the extensive karyotypic diversification within the subtilis group in the south-east region of the Russian Plain most likely results from fragmentation of a continuously distributed, ancestral population. It is thought that this occurred at the last glacial maximum (18,000–14,000 years B.P.), and that the process of isolation has been exacerbated by increasing human activity in the region in modern times.

Analysis of Spatial Organization of a Desert Rodent Community in Bolson de Mapimi, Mexico

We studied the distribution of niches in resource space and niche patterns of a 12-species community of desert rodents by use of canonical-variate and principal-component analyses. Fourteen characters of the environment, measured at 475 sample plots within 19 1-ha grid areas (474 captures of rodents on plots), and eight morphological indicators of niches were used. The first three canonical axes of resource space accounted for 81% of the variance; each of the axes is identified by one of the characteristics of the substrate and one to two characteristics of the vegetation. There was a high level of continuity in distribution of species in the resource space. The lowest values of coefficients of variation of niche overlap and of distances between niche centers characterize a group of the nearest-neighbor species. There was a marked negative correlation of morphological distances to the nearest neighbor with the distances between the same species in the resource space. This evidence indicates certain limitations of ecological similarity of cohabitating species. Negative correlations between niche breadth and the position of the niche in resource space, and between the maximal density of population and niche breadth, are demonstrated.

ADRENOCORTICAL AND BIOENERGETIC RESPONSES TO COLD IN FIVE SPECIES OF MURINE RODENT

Abstract Oxygen consumption, rectal temperature, and plasma concentrations of glucocorticoids, free fatty acids, and glucose were studied in 5 species of rodents after cold exposure that exceeded their homeostatic capability (7°C for 15 min). Adrenocortical responses and metabolic responses (oxygen consumption) to cold were large in 3 solitary, terrestrial species, dwarf hamsters (Phodopus sungorus, P. campbelli, and P. roborovskii) and were minimal in a colonial fossorial species, mole voles (Ellobius talpinus). Bank voles (Clethrionomys glareolus) showed intermediate responses. There were no interspecific differences in mobilization of main bioenergetic substrates (glucose and free fatty acids). Results are interpreted in terms of evolutionary changes of stress: reactivity was positively correlated with the rate of social stimuli and negatively correlated with physically stressful stimuli in the natural environment of the species.

The common hamster as a synurbist: a history of settlement in european cities

Abstract Following the expansion of agriculture in the Neolithic period, the common hamster has spread throughout Europe, and occurred abundantly until the recent past. However, in the last 45 years, populations declined markedly, partly attributable to urbanization and to major changes in agricultural practices. As a result, the species has been considered endangered at international levels as well as in most European countries. At the same time, the species has established populations in large Central and Eastern-European cities such as Vienna (Austria), Simferopol (Ukraine) and Nalchik (Russia), where it inhabits green spaces such as parks, gardens, embankments and buffer strips. In an attempt to reveal factors enabling hamsters to cope with urban environments, we reviewed historical data and habitat conditions of several urban hamster populations. We suggest that supplemental food resources and reduced predation pressure were the main factors promoting urban occurrence of common hamsters in the last 30 years. Its notable adaptability may be associated with higher stress resilience, ecological opportunism, polyphagy and higher fertility compared to species relying on non-urban habitats. The phenomenon of synurbization implies coexistence of wildlife and our urban civilization, but at the same time conflicting interests in conservation and urban development. Thus, the common hamster might serve as a model species for efficient mitigation and compensation concepts in urbanism and spatial planning. STRESZCZENIE Chomik europejski rozprzestrzenił się w Europie w następstwie rozwoju rolnictwa w Neolicie i do niedawna występował bardzo licznie. Jednak w ciągu ostatnich 45 lat. liczebność populacji wyraźnie spadła częściowo ze względu na urba- nizację i znaczące zmiany w rolnictwie. W efekcie gatunek jest obecnie uważany za zagrożony zarówno na poziomic międzynarodowym, jak i w poszczególnych państwach europejskich. Jednocześnie jednak powstały populacje w dużych miastach Europy Centralnej i Wschodniej, na przykład w Wiedniu (Austria), Symferopolu (Ukraina) i Nalchiku (Rosja), gdzie chomik zamieszkuje tereny zielone takie jak parki, ogrody na nabrzeżach rzek i pasy buforowe. W celu ustalenia czyn- ników umożliwiających chomikom dostosowanie do warunków zurbanizowanych, stworzyliśmy przegląd danych historycznych i warunków siedliskowych w kilku miejskich populacjach chomika. Sugerujemy, że dodatkowe źródła pokarmu i zmniejszony nacisk drapieżników były głównymi czynnikami sprzyjającymi występowaniu chomika europejskiego w miastach w ciągu ostatnich 30 lat. Szczególna adaptacyjność chomika może być związana z wyższą odpornością na stres, ekologicznym oportunizmem, wszystkożcmością i wyższą płodnością w porównaniu do gatunków polegających na niczurbanizowanych siedliskach. Fenomen synurbizacji zakłada współistnienie przyrody i naszej miejskiej cywilizacji, ale w tym samym czasie przeciwstawne interesy ochrony i rozwoju urbanistycznego. Tak więc chomik europejski może posłużyć za gatunek modelowy dla idei skutecznego łagodzenia konfliktów i wyrównywania strat w urbanistyce i plano- waniu przestrzennym.

Sporadic disorders in the meiotic prophase I in Cricetulus barabensis hybrids (Cricetidae, Rodentia) do not lead to reproductive isolation between karyomorphs

Electron microscopy analysis of the synaptonemal complex was carried out for the first time in Cricetulus barabensis pseudogriseus, fertile F1 hybrids of C. b. pseudogriseus × C. b. griseus, C. b. griseus × C. b. barabensis, and back-cross hybrids C. b. pseudogriseus × (F1 C. b. pseudogriseus × C. b. griseus). Meiotic disturbances were identified in the nuclei of single hybrid spermatocytes, including atypical synapsis, associations of autosomes with a sex bivalent, and sex body formation errors. Our study confirms the results of the molecular genetic and craniometric analysis of these forms. Despite the geographical segregation, three chromosomal forms of Cricetulus barabensis complex do not establish reliable cytogenetic barriers.

Phylogeographic structure of the Common hamster (Cricetus cricetus L.): Late Pleistocene connections between Caucasus and Western European populations

The Common hamster (Cricetus cricetus) is one of the most endangered mammals in Western and Central Europe. Its genetic diversity in Russia and Kazakhstan was investigated for the first time. The analysis of sequences of an mtDNA control region and cytochrome b gene revealed at least three phylogenetic lineages. Most of the species range (approximately 3 million km2), including central Russia, Crimea, the Ural region, and northern Kazakhstan), is inhabited by a single, well-supported phylogroup, E0. Phylogroup E1, previously reported from southeastern Poland and western Ukraine, was first described from Russia (Bryansk Province). E0 and E1 are sister lineages but both are monophyletic and separated by considerable genetic distance. Hamsters inhabiting Ciscaucasia represent a separate, distant phylogenetic lineage, named “Caucasus”. It is sister to the North phylogroup from Western Europe and the contemporary phylogeography for this species is discussed considering new data. These data enabled us to develop a new hypothesis to propose that in the Late Pleistocene, the continuous range of the Common hamster in the northern Mediterranean extended from the central and southern parts of modern France to the Caucasus; however, its distribution was subsequently interrupted, likely because of climate change.

Karyotype Evolution and Phylogenetic Relationships of Cricetulus sokolovi Orlov et Malygin 1988 (Cricetidae, Rodentia) Inferred from Chromosomal Painting and Molecular Data

Sokolovs dwarf hamster (Cricetulus sokolovi) is the least studied representative of the striped hamsters (Cricetulus barabensis species group), the taxonomy of which remains controversial. The species was described based on chromosome morphology, but neither the details of the karyotype nor the phylogenetic relationships with other Cricetulus are known. In the present study, the karyotype of C. sokolovi was examined using cross-species chromosome painting. Molecular and cytogenetic data were employed to determine the phylogenetic position of Sokolovs hamster and to analyze the potential pathways of chromosome evolution in Cricetulus. Both the chromosome and molecular data support the species status of Sokolovs hamster. Phylogenetic analysis of the CYTB data placed C. sokolovi as sister to all other striped hamsters (sequence divergence of 8.1%). FISH data revealed that the karyotype of C. sokolovi is highly rearranged, with the most parsimonious scenario of its origin implying at least 4 robertsonian events and a centromere shift. Comparative cytogenetic data on Cricetinae suggest that their evolutionary history includes both periods of chromosomal conservatism and episodes of rapid chromosomal change.

Comparative Cytogenetics of Hamsters of the Genus Allocricetulus Argyropulo 1932 (Cricetidae, Rodentia)

Chromosome painting and G-banding analyses were used to delimit homologous chromosomal segments among 4 taxa of the hamsters genus Allocricetulus Argyropulo 1932 (Cricetidae, Murоidea, Rodentia) - A. curtatus (2n = 20), A. eversmanni eversmanni, A. eversmanni pseudocurtatus, and the hybrid A. eversmanni beljaevi × A. eversmanni pseudocurtatus (all 2n = 26). Comparative maps between the 4 karyotypes were established based on chromosome painting of chromosome-specific probes from the Syrian hamster (Mesocricetus auratus, 2n = 44). A putative ancestral karyotype for the genus Allocricetulus (AAK) was proposed and contains 12-13 ancestral autosomal elements. Integrated maps demonstrate extended conservation of syntenies within this rodent genus and show the predominant role of Robertsonian rearrangements in the karyotype evolution of the genus Allocricetulus. At the cytogenetic level, we clearly demonstrate karyological differences between karyotypes of species (A. curtatus vs. A. eversmanni) and subspecies A. e. eversmanni and A. e. beljaevi versus A. e. pseudocurtatus, but the karyotypes of A. e. eversmanni and A. e. beljaevi are identical at this level of resolution.