Structure of colonies in the northern mole vole, Ellobius talpinus (Rodentia, Cricetidae)

The structure of two northern mole vole colonies from northern Chelyabinsk oblast (the Kunashak colony, 1981–1983) and southern Kurgan oblast (the Kurtamysh colony, 1985–1999) has been analyzed with respect to the number and composition of families, seasonal and annual population dynamics, age and sex composition and sex ratio, individual life span, migrations, breeding, and reproductive potential. The Kunashak colony is at the northwestern boundary of the species range, and its population is monomorphic (all animals are of the black color morph). The Kurtamysh colony is located in an optimal habitat, and its population is polymorphic, consisting of animals of three color morphs (black, brown, and transitional). Consideration is given to certain specific features of northern mole voles belonging to different color morphs.     

Exploring phylogeography and species limits in the Altai vole (Rodentia: Cricetidae)

Natural hybridization between species is not a rare event. In arvicoline rodents, hybridization is known to occur in the wild and/or in captivity. In the Microtus arvalis group, cytogenetic studies revealed that there were two distinct chromosomal forms (2n = 46 but a different fundamental number of autosomes). These forms have been attributed to two cryptic species: the common (arvalis) and Altai (obscurus) voles. Recently, individuals with intermediate karyotypes (F₁ and backcrosses) were discovered in central European Russia, and, for this reason, other studies have regarded obscurus and arvalis as conspecific. In the present study, to address the question of the species limits in the Altai vole and to infer its evolutionary history, a phylogeographical analysis combined with multivariate morphometric methods and original chromosome data was performed. Two obscurus lineages were identified: the Sino‐Russian and South Caucasian lineages. Both lineages are characterized by low genetic diversity, resulting, in the former, from a past bottleneck event caused by encroaching periglacial areas and, in the latter, from recent rapid population divergence. Introgressive hybridization between the Altai and common voles appears to be the result of a secondary contact following the Last Glacial Maximum in central European Russia. Despite the fact that speciation is an ongoing process in most arvicoline species, the common and Altai voles are genetically divergent, morphologically and karyologically distinct, and exhibit contrasting evolutionary histories. For all these reasons, they should be ranked as species: M. arvalis and M. obscurus. © 2013 The Linnean Society of London     

The role of chromosome rearrangements in evolution of mole voles of genus Ellobius (Rodentia, Mammalia)

Modern mole voles of the genus Ellobius are characterized by species-specific features of autosomes and sex chromosomes. Owing to the use of the Zoo-FISH method, the nomenclature of chromosomes was refined and nonhomologous Robertsonian translocations indistinguishable by G-staining were identified for Ellobius tancrei, which is a species with a wide chromosome variation of the Robertsonian type. The electron-microscopic analysis of synaptonemal complexes in F1 hybrids of forms with 2n = 50 and 2n = 48 revealed the formation of a closed SC-pentavalent composed of three metacentrics with monobrachial homology and two acrocentrics. Segregation of chromosomes of such complex systems is impeded by disturbances in the nucleus architecture leding to the formation of unbalanced gametes and to a dramatic reduction in fertility of hybrids. Our data support the hypothesis that the formation of monobrachial homologous metacentric chromosomes can be considered as a way of chromosomal speciation.     

Detection of two morphologically cryptic species from the cursor complex (Akodon spp; Rodentia, Cricetidae) through the use of RAPD markers

The cursor complex is a group within the Akodon genus of South American rodents, formed by Akodon cursor and A. montensis. Correct distinction between these two species is of great importance since they can harbor different Hantavirus strains. These species are only distinguishable by means of karyotypic or internal anatomic features, requiring dissection; recently, some other genetic methods have become available. We developed RAPD markers capable of distinguishing between A. cursor and A. montensis. Samples included 42 individuals of A. cursor from four localities and 16 individuals of A. montensis from two localities. Fifty-five bands, 41 of which were polymorphic, were analyzed. A principal component analysis showed that this set of markers could successfully distinguish between the two species, mainly based on three RAPD bands. The number of bands in each population was compared within a 95% confidence interval as a measure of intraspecific variability. The A. cursor populations were found to have marked genetic structure across the study area (AMOVA; F(ST?)= 0.21), which in part might be because of the relatively limited dispersal capabilities of this species. Species-specific bands, with potential for species identification, were identified.     

Chromosomal and ontogenetic instability in sibling species of common vole (Microtus arvalis group): comparative aspects

Populations of chromosomal sibling species Microtus arvalis and Microtus rossiaemeridionalis were studied in Ural region in habitats affected by high radiation and the control ones. Frequency of chromosome disturbances in the marrow cells and fluctuating asymmetry (FA) of 8 craniometric characters were investigated. In impact populations the frequency of chromosome aberration was very high. Such frequency was also maintained in the offspring of the first laboratory generation of M. arvalis. In natural and control populations of both species frequently occurred individuals with anomalies in sex chromosome. Individuals of M. rossiaemeridionalis from Totsky radioactive region (forest-steppe zone) were characterized by very high integrative FA in comparison with control populations (southern taiga). At the same time neighboring impact and control populations of M. arvalis from southern taiga did not differ in this character. Despite the high level of caryotype divergence M. arvalis and M. rossiaemeridionalis showed similarity in mutation process that causes chromosome disturbances in somatic and germinative cells. Probably the level of FA of measured characters in both species is connected rather with geographical location than with man influence.     

Geometric morphometrics, neural networks and diagnosis of sibling Taterillus species (Rodentia, Gerbillinae)

The lack of diagnostic traits in sibling species means that great quantities of biogeographical and ecological data held in museum collections cannot be utilized effectively, leading to underestimates of biodiversity. In this study we applied neural networks (NN) and canonical variates analyses (CVA) to landmark measurements on the skulls of the West African species Taterillus arenarius , T. petteri , T. gracilis and T. pygargus in an attempt to discriminate species previously identified unambiguously from their karyotypes. Among suggested differences, the relationship between inflation of the tympanic bullae and lower population density is discussed. Cross-validated classification rates did not exceed 73%. Two hypotheses are proposed to explain such high phenotypic similarity: morphological plasticity limited by environmental constraints and the possibility that speciation has been too recent to allow significant morphological divergence.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 319−327.     

X-Y chromosome synapsis and recombination in 3 vole species of Asian lineage of the genus Microtus (Rodentia: Arvicolinae)

The pattern of X-Y chromosome pairing in male meiosis is an important taxonomic feature of grey voles of the genus Microtus. Asynaptic sex chromosomes have been found in the majority of species of the Palearctic phylogenetic lineage of this genus, while normal X-Y synapsis has been observed in the species of subgenus Pallasiinus belonging to the Asian phylogenetic lineage. We analyzed sex chromosome pairing and recombination in M. maximowiczii, M. mujanensis and M. fortis which also belong to the Asian phylogenetic lineage (subgenus Alexandromys). Using immunostaining for the proteins of the synaptonemal complex (SCP3) and recombination nodules (MLH1) we demonstrated that X and Y chromosomes of these species paired and recombined in a short subtelomeric region. This indicates that the sex chromosomes of these species retain an ancestral fully functional pseudoautosomal region, which has been lost or rearranged in the asynaptic species of the genus Microtus.     

Cross fertilization in vivo and in vitro between three species of vesper mice, Calomys (Rodentia, Cricetidae)

Cross fertilization was tested between oocytes of Calomys callidus and spermatozoa from C. callidus, C. musculinus and C. laucha by both in vivo and in vitro insemination. After in vivo and in vitro insemination, respectively, percentages of oocytes fertilized were 68.8 and 46.6 (C. callidus X C. callidus), 20.3 and 12.7 (C. callidus X C. musculinus), 26.7 and 4.3 (C. callidus X C. laucha). Thus, the percentages obtained after in vitro insemination were always lower than those obtained with in vivo insemination. It was found that 23.9% and 44.4% of two-cell hybrid embryos were present in oviducts 30 hr after in vivo insemination of C. callidus females with C. musculinus or C. laucha spermatozoa, respectively. At a later stage (56 hr postinsemination), development did not progress further, and abnormal embryos were found both at 30 and 56 hr postinsemination, suggesting some kind of cleavage arrest or degeneration of the embryos. We suggest that fertilization is not strictly species-specific, at least among the species we studied, but that there are some factors that reduce the efficiency of interspecific fertilization.     

Eimeria ladronensis n. sp. and E. albigulae (Apicomplexa: Eimeriidae) from the Woodrat,Neotoma albigula (Rodentia: Cricetidae)1

Of 50 white-throated woodrats (Neotoma albigula) collected from Socorro Co., New Mexico, 21 (42%) had eimerian oocysts in their feces when examined. Of the 21 Neotoma found positive for Eimeria, 19 (90%) harbored a single eimerian species at time of examination. Eimeria albigulae Levine, Ivens & Kruidenier, 1957, was found in 18 (86%), and E. ladronensis n. sp. was found in five (24%) infected woodrats. Sporulated oocysts of E. ladronensis are ellipsoidal, 19–25 × 13–15 (21.4 ± 1.3 × 14.1 ± 1.1) μm, have a smooth wall and one or two polar granules, but lack a micropyle and an oocyst residuum. Sporocysts are tapered at one end, 7–10 × 6–7 (8.5 ± 0.7 × 6.5 ± 0.3) μm, and have a Stieda body and sporocyst residuum, but no substieda body. Prepatent periods for E. albigulae and E. ladronensis n. sp. are 5–6 and 8–9 days, respectively; patent periods are 7–18 and approximately 11 days, respectively.     

Hidden heterochromatin: Characterization in the Rodentia species Cricetus cricetus, Peromyscus eremicus (Cricetidae) and Praomys tullbergi (Muridae)

The use of in situ restriction endonuclease (RE) (which cleaves DNA at specific sequences) digestion has proven to be a useful technique in improving the dissection of constitutive heterochromatin (CH), and in the understanding of the CH evolution in different genomes. In the present work we describe in detail the CH of the three Rodentia species, Cricetus cricetus, Peromyscus eremicus (family Cricetidae) and Praomys tullbergi (family Muridae) using a panel of seven REs followed by C-banding. Comparison of the amount, distribution and molecular nature of C-positive heterochromatin revealed molecular heterogeneity in the heterochromatin of the three species. The large number of subclasses of CH identified in Praomys tullbergi chromosomes indicated that the karyotype of this species is the more derived when compared with the other two genomes analyzed, probably originated by a great number of complex chromosomal rearrangements. The high level of sequence heterogeneity identified in the CH of the three genomes suggests the coexistence of different satellite DNA families, or variants of these families in these genomes.     

A new genus and species of lungworm (Nemata: Metastrongyloidea) from Akodon mollis Thomas, 1894 (Rodentia: Cricetidae) in Peru

Akodonema luzsarmientae n.g., n.sp. (Nemata: Metastrongyloidea) is described from the pulmonary arteries and heart from several individuals of "soft grass mouse," Akodon mollis (Rodentia: Cricetidae), collected in the region of Ancash, Peru. The new genus and species is distinguished by a reduction of the dorsal ray to 2 small widely separated papillae.     

Geographic distribution and phenetic skull variation in two close species of Graomys (Rodentia, Cricetidae, Sigmodontinae)

The interspecific differentiation of South American rodents of the genus Graomys was assayed at ecological and morphometric levels in two species. At the ecological level, niche modelling was used. At the morphometric level, the hypothesis that the size and shape of the skull vary with the geographic location was tested using geometric morphometrics by assessing the extent and spatial distribution of phenotypic skull variation within and among two species, Graomys griseoflavus and Graomys chacoensis. Our results of niche modelling indicate the spatial differentiation between the two species, with G. chacoensis inhabiting preferably the Chaco ecoregion and G. griseoflavus inhabiting mainly the Monte ecoregion. In multiple linear regressions, approximately 20% of the skull size variation is explained by latitude, altitude, and temperature seasonality. The partial least square analysis reveals strong correlation between shape and environmental variables, mainly with latitude, annual mean temperature, and annual precipitation. Discrimination between G. griseoflavus and G. chacoensis was highly reliable when using geometric morphometric tools. These results permit us to elucidate some evolutionary processes that have occurred in these species.     

Investigation of marmoset hybrids (Cebuella pygmaea x Callithrix jacchus) and related Callitrichinae (Platyrrhini) by cross-species chromosome painting and comparative genomic hybridization

We report on the cytogenetics of twin offspring from an interspecies cross in marmosets (Callitrichinae, Platyrrhini), resulting from a pairing between a female Common marmoset (Callithrix jacchus, 2n = 46) and a male Pygmy marmoset (Cebuella pygmaea, 2n = 44). We analyzed their karyotypes by multi-directional chromosome painting employing human, Saguinus oedipus and Lagothrix lagothricha chromosome-specific probes. Both hybrid individuals had a karyotype with a diploid chromosome number of 2n = 45. As a complementary tool, interspecies comparative genomic hybridization (iCGH) was performed in order to screen for genomic imbalances between the hybrids and their parental species, and between Callithrix argentata and S. oedipus, respectively. These genomic imbalances were confined to centromeric and telomeric heterochromatin, while euchromatic chromosome regions appeared balanced in all species investigated. When comparing marmosets and tamarins, sequence divergence of centromeric heterochromatin was already clearly noticeable. In the C. argentata and C. pygmaea genomes numerous subtelomeric regions were affected by amplification of different repetitive sequences. Cross-species FISH with a microdissection-derived C. pygmaea repetitive probe revealed species specificity of this repetitive sequence at the molecular cytogenetic level of resolution.     

Eimeria ladronensis n. sp. and E. albigulae (Apicomplexa: Eimeriidae) from the woodrat, Neotoma albigula (Rodentia: Cricetidae)

Of 50 white-throated woodrats (Neotoma albigula) collected from Socorro Co., New Mexico, 21 (42%) had eimerian oocysts in their feces when examined. Of the 21 Neotoma found positive for Eimeria, 19 (90%) harbored a single eimerian species at time of examination. Eimeria albigulae Levine, Ivens & Kruidenier, 1957, was found in 18 (86%), and E. ladronensis n. sp. was found in five (24%) infected woodrats. Sporulated oocysts of E. ladronensis are ellipsoidal, 19-25 X 13-15 (21.4 +/- 1.3 X 14.1 +/- 1.1) micron, have a smooth wall and one or two polar granules, but lack a micropyle and an oocyst residuum. Sporocysts are tapered at one end, 7-10 X 6-7 (8.5 +/- 0.7 X 6.5 +/- 0.3) micron, and have a Stieda body and sporocyst residuum, but no substieda body. Prepatent periods for E. albigulae and E. ladronensis n. sp. are 5-6 and 8-9 days, respectively; patent periods are 7-18 and approximately 11 days, respectively.     

Comparative chromosome analysis (R- and C-bands) of two South African murid species, Lemniscomys rosalia and Rhabdomys pumilio (Rodentia, murinae)

We carried out a comparative chromosome analysis (R- and C-bands) on two South African murid rodent species, Lemniscomys rosalia and Rhabdomys pumilio, whose banded karyotypes are reported here for the first time. The study revealed that, in spite of minor differences in diploid number and the number of autosomal arms (48 vs. 46 and 58 vs. 60, respectively), these species differ by at least 10 structural rearrangements, comprising seven Robertsonian translocations (two of which share monobrachial homology), two tandem translocations, and one pericentric inversion. Despite the high level of chromosomal differentiation observed, almost complete homologous banding patterns were detected between the two species. The present study therefore strengthens the hypothesis about the close phylogenetic affinities between L. rosalia and R. pumilio and their belonging to a set of genera referred to as "arvicanthine" rodents.     

Discrimination of the sibling species Apodemus flavicollis and A. sylvaticus (Rodentia,Muridae)

Karyotyping and several molecular methods have allowed successful identification of two morphologically similar wide-ranging Western Palearctic species, the yellow-necked field mouse Apodemus flavicollis (Melchior, 1934) and the long-tailed wood mouse A. sylvaticus (Linnaeus, 1758), but reliable species diagnosis on the basis of morphometric characters is particularly problematic. Although they are easily morphologically distinguishable in Central and Northern Europe, this is not the case in southern parts of their distribution areas. Despite that, we have successfully discriminated A. flavicollis and A. sylvaticus from Serbia (Southern Europe) using geometric and traditional morphometric methods on a data set for ventral crania of specimens previously genotyped by the Inter Simple Sequence Repeat-PCR (ISSR-PCR). Discrimination power of applied approaches was more or less similar. The majority of our results were consistent with those obtained for specimens collected across the Czech Republic (Central Europe). Morphological differences observed herein, as well as those already reported between A. flavicollis and A. sylvaticus from the central and northern parts of their distribution areas, could be the outcome of their biology, i.e. ecological discrepancies, different assumed evolutionary scenarios considering biogeography, phylogeny, history and ontogeny.