Gene-Geographic Variation and Genetic Differentiation in Red-Backed Voles of the Genus Clethrionomys (Rodentia,Cricetidae) from the Region of the Sea of Okhotsk

Thirteen enzyme systems and three nonenzyme proteins were electrophoretically analyzed in red-backed voles of the genus Clethrionomys. In total, 25 loci were interpreted. Gene-geographic variation was studied and indices of genetic variability and differentiation were determined. By the distribution of electrophoretic variants of hemoglobin, C. rutilus was shown to be divided into two geographical groups (northern and southern). A low level of genetic differentiation was revealed in the island isolates of C. rutilus and C. rufocanus. Separation of C. rufocanus, C. rex, and C. sicotanensisinto a superspecies complex was confirmed. A study of differential G- and C-banding on C. rutilus andC. rufocanus chromosomes did not reveal intraspecific variation of autosomes. In these species, karyotypes of voles from Kamchatka Peninsula were studied for the first time. They appeared to be morphologically similar to the karyotypes continental voles by both autosomes and sex chromosomes.     

Chromosomal variation in social voles: a Robertsonian fusion in Günther’s vole

The study reports on chromosomes in several populations of social voles from south-eastern Europe and the Middle East. The standard karyotypes of individuals of Microtus hartingi and Microtus guentheri originating from both south-eastern Europe and Asia Minor comprised 54 mostly acrocentric chromosomes. However, variation between populations was found in the amount and distribution of C-heterochromatin in certain autosomes and the sex chromosomes. Furthermore, a specific pattern of argyrophilic nucleolar organizer region distribution was recorded in different geographic populations. In a population from Asia Minor, a heterozygous centric fusion of two autosomes was found. The G-banded karyotypes of M. guentheri and Microtus socialis were compared, and tandem fusions of autosomes were suggested as possible mechanism of the divergence. The karyotypes of the nine currently recognized species of social voles are reviewed, and implications of chromosomal data for systematics are evaluated.     

Multi-annual density fluctuations and habitat size enhance genetic variability in two northern voles

In order to gain a better understanding of the consequences of population density cycles and landscape structure for the genetic composition in time and space of vole populations, we analyzed the multiannual genetic structure of the two numerically dominant, sympatric small rodent species of northernmost Fennoscandia. Red voles Myodes rutilus and grey-sided voles M. rufocanus were trapped in the subarctic birch forest along three fjords over five years. Along each fjord, there were four or five altitudinal transects each with five trapping stations. Spring and fall population densities were estimated from mark–recapture data. Grey-sided voles exhibited higher amplitude density fluctuations than red voles. Polymorphism at eight or nine microsatellite loci, determined in 1228 voles, was used to estimate local genetic diversity and differentiation among samples. Genetic diversity was higher in grey-sided voles than in red voles. Spring densities had no effect on local genetic diversity or on differentiation. The amplitude of density fluctuations and the extent of favorable habitat (sub-arctic birch forest) surrounding each site had a positive effect on genetic diversity, and the amplitude of density fluctuations had a negative effect on differentiation in red voles, for which fluctuating populations were compared with more stable populations. The harmonic mean of densities, reflecting average population sizes, had a negative effect on genetic diversity in red voles, but a positive effect in grey-sided voles, for which only fluctuating populations were compared. No other effects were significant for grey-sided voles. A temporal assignment test showed that the spatial structure was more stable in time for populations with more stable population dynamics. Altogether our results suggest that high amplitude density fluctuations lead to more gene flow and higher genetic diversity in vole populations.     

The factors influencing the sound activity of forest voles]

The article is devoted to the effect of context on the acoustic activity of bank voles of 4 species (Clethrionomys glareolus, C. centralis, C. rutilus, and C. rufocanus) living in experimental groups. In addition to species differences and social state of a specimen in the group, the acoustic activities of vole is affected by such factors as locomotor activity of the vole itself and its partners (especially dominant ones) and aggression of surrounding voles.     

Genetic Distinctiveness of the Korean Red-Backed Vole (Myodes regulus) from Korea, Revealed by Mitochondrial Cytochrome b Gene Sequences

To examine the taxonomic status of the Korean red-backed vole (Myodes regulus), the full cytochrome b sequences of 21 red-backed voles from Korea and northeast China were compared with the corresponding haplotypes from 12 species of Myodes and Eothenomys from GenBank. We identified five red-backed voles from Mount Changbai and Harbin as Myodes rufocanus and three from Harbin as M. rutilus, and we confirmed that the red-backed voles from Korea are M. regulus and not Eothenomys regulus. We found that M. regulus from Korea differed from the other five species of Myodes and that the interspecific distances between M. regulus and each of the two species from northeast China were 4.55% (M. rufocanus) and 11.1% (M. rutilus). We concluded that M. regulus is also genetically distinct and is an endemic species of Korea.     

紫貂冬季食性的分析

１９９１至１９９８年的三个冬季,在大兴安岭地区共收集紫貂粪样２２３个．食性分析结果表明,紫貂冬季食物主要为小型哺乳类（５４．１％）、植物浆果和种子（３２．４％）、鸟类（１２．５％）和昆虫（１．０％）．在紫貂选择的７种小型哺乳类中,主要以棕背（２７．３％）和红背（１９．２％）为食,其次为雪兔和冬眠的花鼠。对于鸟类,紫貂主要捕食花尾榛鸡（８．１％）,松鸦（０．７％）,大山雀（０．５％）和黑啄本鸟等。有２．２％的粪样中含有小型鸟的卵壳、紫貂的植物性食物主要为越桔浆果（２０．８％）和偃松种籽（８．８％）。昆虫中只有蚂蚁在紫貂食性中出现（１．０％）．紫貂冬季食物构成没有年度间差异（Ｐ＞０．０５）。通过捕食迹,我们还发现紫貂捕食黑嘴松鸡。虽然红背的捕获率（７９．４％）高于棕背（２．９％）,但食性分析结果却相反,说明紫貂更喜欢捕捉身体较大的鼠类。有较强气味的中虽有一定的数量,但在紫貂冬季食物中未出现过。     

棕背的核型分析

本文利用骨髓染色体制片法,对棕背Ｃｌｅｔｈｒｉｏｎｅｍｙｓｒｕｆｏｃａｎｕｓ的核型进行了研究。结果表明,其二倍体数目为５６,常染色体由２个中着丝粒染色体和５２个端着丝粒染色体组成,Ｘ染色体为端着丝粒染色体。核型公式为：２Ｍ＋５２Ａ＋ＸＸ（Ａ,Ａ）。结合前人的报道,属动物的核型在进化中显示出其保守性。     

Historical biogeography at the crossroads of the northern continents: molecular phylogenetics of red-backed voles (Rodentia: Arvicolinae)

Evolutionary relationships of red-backed voles and their relatives were examined and used to test biogeographic hypotheses. Sequences of the mitochondrial cytochrome b gene were obtained for 25 individuals representing Alticola macrotis, Clethrionomys californicus, C. gapperi, C. glareolus, C. rutilus, and C. rufocanus. These were combined with 21 partial sequences from GenBank for C. regulus, C. rex, C. rufocanus, C. rutilus, Eothenomys imaizumii, E. melanogaster, Phaulomys andersoni, and P. smithii. Complete sequences of three species of Microtus (M. montanus, M. oeconomus, and M. pennsylvanicus), representative species of other arvicoline genera (Myopus, Synaptomys, Arvicola, Ellobius, Ondatra, Lemmus, Dicrostonyx, and Phenacomys), and a sigmodontine representative (Peromyscus) were included as outgroups. We used maximum parsimony, maximum likelihood, distance, and Bayesian based methods and conducted statistical tests on proposed hypotheses of phylogenetic relationships and biogeographic histories. A close relationship of species representing the genera Alticola, Clethrionomys, and Eothenomys was supported (Clethrionomyini); however, the genus Clethrionomys was paraphyletic with respect to both Alticola and Eothenomys. Three major clades were identified as Asian (Eothenomys andersoni, E. smithii, C. rex, C. regulus, and C. rufocanus), Trans-beringian (Alticola macrotis, C. californicus, C. gapperi, C. glarelolus, and C. rutilus), and Taiwanese (E. melanogaster). These results are consistent with the fossil record which indicates an initial diversification in Asia followed by colonization of the Nearctic on at least two occasions. The holarctic species, C. rutilus, appears to have either reinvaded Asia from North America or colonized North America more recently (late Pleistocene) than the two species of Clethrionomys (C. gapperi and C. californicus) that are endemic to North America (early to mid-Pleistocene). Finally, C. gapperi, appears to be comprised of an eastern and a western species, the former with affinities to the Asian C. glareolus and the latter more closely related to C. californicus.     

Seasonal changes in the energy metabolism of subarctic rodents

In widespread species, northern taiga voles, most significant differences in the intensity of energy metabolism (M), maximum (Mmax) and reserve (Mres) metabolism were observed at winter temperatures (-5-20 degrees C): Clethrionomys rutilus greater than C. rufocanus greater than Microtus oeconomus; differences in seasonal increase of Mmax and Mres exhibit an inverse proportion. Seasonal changes in M and Mmax in autochthonous tundra rodents indicate that Lemmus sibiricus belongs to a more eurybiont species as compared to Dicrostonyx torquatus. The main characteristic feature of seasonal adaptation of M in lemmings, as compared to voles, is the evident decrease of M value in winter which is accompanied by a more significant increase of Mmax and Mres. Operative pattern and high seasonal mobility of chemical thermoregulation in lemmings are suggested which account for adaptation of these animals mainly to short-term extreme effects of low temperatures.     

Karyotypes and systematics of Asian high-mountain voles, genus Alticola (Rodentia, Arvicolidae). Results of Mongolian-German biological expeditions since 1962, No. 211.

Six species/subspecies of Asian high-mountain voles, genus Alticola, were studied cytogenetically via conventional staining and C- and G-banding. The karyotypes are very similar. The standard karyotype, as in A. strelzovi strelzovi, consists of 56 chromosomes. These are split into 25 acrocentric pairs, one large subtelocentric pair, one small metacentric pair, a large acrocentric X chromosome, and a small Y chromosome, which varies in shape. Constitutive heterochromatin is almost entirely restricted to small centromeric regions. A small submetacentric pair of autosomes in both subspecies of A. semicanus and a medium-sized Y chromosome in A. argentatus severtzovi are of importance in systematics. The data suggest that A. barakshin, A. semicanus, and A. argentatus are separate species.     

Genetic variation in the African rodent subfamily Otomyinae (Muridae). II. Chromosomal changes in some populations of Otomys irroratus.

Chromosome-banding studies have been carried out on 31 specimens of Otomys irroratus from six localities. Light-microscope preparations of chromosomes were obtained from cultures of fibroblasts, spleen lymphocytes, peripheral blood lymphocytes, and directly from bone marrow. Karyotypic variability, both numerical and morphological, was detected in three populations. Diploid numbers ranged from 2n = 23 to 2n = 32. Intrapopulation differences were chiefly caused by variation in the number of copies in two pairs of small, biarmed, partly heterochromatic autosomes suggestive of B chromosomes. A major morphological variation in the karyotypes involved the presence of seven pairs of biarmed autosomes with totally heterochromatic short arms in the populations distributed to the west of 26 degrees 57' E. To the east of this longitude, populations of this species exhibited mostly acrocentric autosomes. G-banding patterns of these karyotypes and those of a karyotype from a previous study (Robinson and Elder, 1987) were compared. A chromosome originating from a tandem fusion, possibly leading to partial reproductive isolation, was found in one population. Possible implications of these results for mechanisms of speciation are discussed.     

High chromosomal polymorphism and heterozygosity in Cyclocephala tridentata from Guadeloupe: chromosome comparison with some other species of Dynastinae (Coleoptera: Scarabaeidae)

Very distinct karyotypes have been observed in two Cyclocephala species from Guadeloupe, considered as very close and possibly vicariant: C. insulicola with only metacentric and C. tridentata tridentata with many acrocentric autosomes. This prompted us to study the karyotype of a few other neotropical Dynastinae belonging to four of the eight existing tribes, to find out which one of these two species had the most divergent chromosomes from their ancestral condition. In the four additional species studied, i.e., Cyclocephalamaffafa, Strategus syphax, Ligyrus cuniculus and Megasoma actaeon, a karyotype composed of 20 chromosomes, including 18 meta- or submetacentric autosomes was found, as it was in C. insulicola. Thus, the karyotype of C. t. tridentata, in which most of the 18 autosomes were acrocentric, is apomorphic. In addition, it was highly polymorphic, with six different karyotypes observed among the ten specimens studied. All had one to four heterozygous chromosome pairs formed by one acrocentric and one submetacentric carrying a large juxta-centromeric heterochromatic component. This heterozygosity did not seem to impair either meiotic synapsis or chiasma formation and chromosome segregation. Such high rates of chromosome heterozygosity and polymorphism are infrequent and never described in beetles. This suggests that C. t. tridentata undergoes an active process of chromosome evolution. A possible relationship with insularity and/or pesticide exposure is briefly discussed.     

Karyology and karyotype analysis of diploid freshwater planarian populations of the Dugesia gonocephala group (Platyhelminthes,Tricladida) found in Sardinia

Karyology and karyotype analysis were carried out on freshwater planarian populations of the Dugesia gonocephala group. The strains studied were all diploid with chromosomic number 2n = 16; n = 8. They came from 12 sites mainly localized on the west of the island of Sardinia. Three karyotypes indicated with the letters A, B and C were found in which eight homomorphic pairs of chromosomes were easily identified. In karyotype A all chromosomes are metacentric. Ten populations of the twelve examined showed this karyotype which appears to be the most common. In karyotype B the seventh pair of chromosomes is submetacentric. This karyotype is quite common having been previously found in another eight Sardinian localities. Karyotype C differs from the others in having submetacentric third and seventh pairs of the chromosome complement. It was found in only one locality. The differences observed between these three karyotypes could be interpreted either as sign of differentiation at species level, or as an intraspecific variation due to chromosome mutations (pericentric inversions). This revised version was published online in July 2006 with corrections to the Cover Date.     

Karyotypes of 5 species of Soricidae-Crocidura in the fauna of the USSR

The chromosomes of five Crocidura species have been studied by means of routine, G-, C- and Ag NOR-banding techniques. The karyotypes of the species with 2n = 40, i.e. C. gueldenstaedtii, C. suaveolens and C. sibirica, are identical. Short arms of the Y-chromosome of C. sibirica are larger. The karyotypes of C. leucodon (2n = 28) and C. zarudnyi (2n = 22) could be obtained as a result of tandem and centric fusion and pericentric inversions. Small amounts of heterochromatin were detected in autosomes of the species investigated. The Y-chromosomes are completely heterochromatic. Four NOR-bearing pairs are detected in the species investigated.     

Chromosome banding in Amphibia. XXII. Atypical y chromosomes in Gastrotheca walkeri and Gastrotheca ovifera (Anura,Hylidae)

The chromosomes of the rare South American marsupial frogs Gastrotheca walkeri and G. ovifera were extensively reexamined with various banding techniques. The karyotypes of both species are distinguished by a new category of XY female symbol /XX male symbol female sex chromosomes. The unusual Y chromosomes are characterized by containing the least amount of constitutive heterochromatin in the karyotypes. This is in contrast to all previously known amphibian Y chromosomes and does not fit the evolutionary model of early XY differentiation in vertebrates. In male meiosis, the heteromorphic XY chromosomes of both species still exhibit the same pairing configurations as the autosomes. DNA flow cytometric measurements show the nuclear DNA amount of G. walkeri to be 10.90 pg. The significance of the XY/XX sex chromosomes of these marsupial frogs, the various classes of constitutive heterochromatin detected, and the data obtained from meiotic analyses are discussed in detail.     

Mating within the meiotic tetrad and the maintenance of genomic heterozygosity

Mating among the products of a single meiosis (automixis or meiotic parthenogenesis) is found in diverse groups of plant, animal, and fungal taxa. Restoration of the diploid stage is often strictly controlled and brings together products separated at the first meiotic division. Despite apparent similarities to diploid selfing, the theoretical prediction is that heterozygosity should be maintained on all chromosomes when it is linked to the centromeres and thus also segregates at the first meiotic division. Using the fungus Microbotryum, we directly test this prediction by linear tetrad analysis. The patterns of meiotic segregation for chromosome size variation (electrophoretic karyotypes) and PCR products (AFLP procedures) were determined for Microbotryum lineages native to North America and Europe. Our data reveal a surprisingly dynamic genome that is rich in heterozygosity and where size-dimorphic autosomes are common. The genetic variation agrees with the prediction of centromere-linked heterozygosity. This was observed to the greatest extent in the lineage of Microbotryum native to North America where there was consistent first-division segregation and independent assortment of multiple linkage groups. The data also show properties that distinguish the fungal sex chromosomes from the autosomes in both lineages of Microbotryum. We describe a scenario where the mating system of automixis with first-division restitution is the result of feedback mechanisms to control exposure of genetic load.     

A chromosomal analysis of some water beetle species recently transferred from Agabus Leach to Ilybius Erichson, with particular reference to the variation in chromosome number shown by I. montanus Stephens (Coleoptera: Dytiscidae)

The karyotypes of seven Ilybius species are described and illustrated. All except I. wasastjernae have a basic karyotype of 34 autosomes plus sex chromosomes which are X0 ( male symbol ), XX ( female symbol ), with the X chromosome among the largest in the nucleus. This karyotype appears to be the norm for Ilybius and supports the transfer of the species concerned from Agabus to Ilybius. I. wasastjernae has 36 autosomes and the X chromosome is the smallest in the nucleus and its karyotype is unlike any other known karyotype in either Ilybius or Agabus. In most of the species studied no intraspecific variation has been detected. Exceptions are I. chalconatus, where there is one inversion polymorphism in one of the autosomes, and I. montanus whose autosome number has been found to vary from 29 to 34. Such variation is highly unusual among Coleoptera. The variation results from fusion-fission polymorphisms involving three different pairs of autosomes. In each case the fusions may be homozygous, heterozygous or absent. All populations investigated were polymorphic for some of the fusions, but only one (La Salceda, Spain) included individuals lacking all fusions. The frequencies of fused and unfused chromosomes were analysed in three English populations. In only one case was there a departure from the values expected from the Hardy-Weinberg equilibrium, and this population also showed a significant difference from the other two. Meiosis in males heterozygous for fusions involves the production of trivalents in first division, but results in the production of abundant sperm, with no evidence of chromosomal abnormalities in second metaphase, or of degenerating cells as a result of failed meiosis. The three fusions sites are consistent in all the populations studied, and it is concluded that these fusions represent unique historical events rather than current chromosomal instability.     

The genomic signature of sexual selection in the genetic diversity of the sex chromosomes and autosomes

Genomic levels of variation can help reveal the selective and demographic forces that have affected a species during its history. The relative amount of genetic diversity observed on the sex chromosomes as compared to the autosomes is predicted to differ among monogamous and polygynous species. Many species show departures from the expectation for monogamy, but it can be difficult to conclude that this pattern results from variation in mating system because forces other than sexual selection can act upon sex chromosome genetic diversity. As a critical test of the role of mating system, we compared levels of genetic diversity on the Z chromosome and autosomes of phylogenetically independent pairs of shorebirds that differed in their mating systems. We found general support for sexual selection shaping sex chromosome diversity because most polygynous species showed relatively reduced genetic variation on their Z chromosomes as compared to monogamous species. Differences in levels of genetic diversity between the sex chromosomes and autosomes may therefore contribute to understanding the long-term history of sexual selection experienced by a species.     

Cytological evidence for a complex of species within the taxon Bactrocera tau (Diptera: Tephritidae) in Thailand

Analysis of mitotic karyotypes of wild specimens of larvae of the Bactrocera tea-like fruit flies (Diptera: Tephritidae) in Thailand has revealed seven distinct chromosome forms, based on the amount and distribution of heterochromatin in sex chromosomes and autosomes. Such cytological differences are perfecdy correlated with morphological observations and molecular genetics data. These findings clearly suggest that B. tau is a cluster of at least seven closely related species temporarily designated as species A (= B. tau) , B, C, D, E, F and G. On die basis of the gross quantity of heterochromatin accumulation in the genome, three groups of mitotic karyotypes can be recognized. Group 1 comprises species A and E. Species E specifically occurs only in fruits of Strychnos thorelii while species A attacks many kinds of host plants. Group 2 contains species B, F and G. Species B has been found only in Siphonodon celastrineus fruit, whereas species F and G attack die same host species, the medically important plant, Hydnocarpus anthelminthicus , albeit in different localities. Group 3 includes species C and D, each of which comprises larger amounts of pericentric heterochromatin in all chromosomes than die other two groups. Hence, diese two species are cytologically remote from those of groups 1 and 2. Species C and D occur allopatrically but they attack the same host plant species, Momordica cochinchinensis. Thus, genetic differentiation at the chromosomal level to specific host plant species and geographic isolation seem to play an important role in speciation of members of the B. tau complex.     

Increased differentiation and reduced gene flow in sex chromosomes relative to autosomes between lineages of the brown creeper Certhia americana

The properties of sex chromosomes, including patterns of inheritance, reduced levels of recombination, and hemizygosity in one of the sexes may result in the faster fixation of new mutations via drift and natural selection. Due to these patterns and processes, the two rules of speciation to describe the genetics of postzygotic isolation, Haldane's rule and the large‐X effect, both explicitly include quicker evolution on sex chromosomes relative to autosomes. Because sex‐linked mutations may be the first to become fixed in the speciation process, and appear to be due to stronger genetic drift (in birds), we may identify pronounced genetic differentiation in sex chromosomes in taxa experiencing recent speciation and diverging mainly via genetic drift. Here, we use nine sex‐linked and 21 autosomal genetic markers to investigate differential divergence and introgression between marker types in Certhia americana. We identified increased levels of genetic differentiation and reduced levels of gene flow on sex chromosomes relative to autosomes. This pattern is similar to those observed in other recently‐divergent avian species, providing another case study of the earlier role of sex chromosomes in divergence, relative to autosomes. Additionally, we identify three markers that may be under selection between Certhia americana lineages.