Myopus Research Articles

Express method for determining the sex of fingerlings of mouse-like rodents (Rodentia: Cricetidae) without anatomization

A new effective method for sex determination of immature mouse-like rodents of the hamster family has been used (Cricetidae Fischer, 1817) based on physical impact on the urinary perineal area. The 212 immature specimens of five rodent species was tested: Myodes rutilus Pallas, 1779, M. glareolus (Schreber, 1780), Alexandromys oeconomus Pallas, 1776, Agricola agrestis (Linnaeus, 1761), Myopus schisticolor (Lilljeborg, 1844). Verification of the new method was provided using a control dissection of the studied samples of rodent. The effectiveness of express method of sex determination for under yearling rodent was 88.5–100% among samples of studied species. The effectiveness of morphological characteristics (body weight and length, anogenital distance) was 76.2–93.5% in the sex identification and only for four studied species. The new method was more successful than morphometric methods in sex determination for studied samples of immature M. schisticolor and M. glareolus by 19% and 6.8%, respectively. The close results had been detected for both methods in sex determination of M. rutilus. For sex determination of immature specimens of A. agrestis the morphometric characteristics effectiveness was 4.6% higher compared to the new method. For studied samples of A. oeconomus only the new method of sex determination of an under yearling specimens was effective. The preference in choose of non-anatomical method of sex determination of immature specimens of Cricetidae family is directly depends on the species of study rodent. The new method can be used in studies with vital animals.

The wood lemming and the development of taiga in Late Pleistocene Central Europe

Taxonomic identification remains a challenge for fossil small mammals, in particular in the case of morphologically close species. These identifications are especially essential in the case of species with different ecological tolerances for paleoenvironmental and paleoclimatic inferences. Among rodents which depend on peculiar environments, the wood lemming (Myopus schisticolor) only inhabits boreal forests and is a bryophage specialist burrowing under specific moss covers. In the fossil record, its identification has long been problematic and Myopus has often been mixed up with the tundra lemming (Lemmus sp.), a rodent inhabiting the arctic open landscape. By applying geometric morphometrics on fossil Lemmini specimens from Late Pleistocene Central Europe, this paper demonstrates the occurrence of Myopus at least during Marine Isotopic Stage 3 and Last Glacial Maximum in the region. Its presence has a strong impact on paleoclimatic and paleoenvironmental reconstructions as demonstrated by the application of the Bioclimatic analysis method suggesting a colder climate as well as the identification of a taiga biozone that remained undetected if this species is not included. This work definitively attests the essential contribution of geometric morphometric analyses to a better understanding of small mammal communities.

Биофаунистические заметки по млекопитающим южных отрогов хребта Черского (Магаданская область)

Data on the species composition of theriofauna in the mountain-lake district of the Cherskiу Range southern spurs are given. New data on habitats, relative abundance, and some population characteristics of mass species of small mammals are also reported. The basins of Lake Momontay and Lake Urultun, located at 1048 and 944 m above the sea level and belonging to the basin of the Omulyovka River upper reaches, were inspected in August 2021. Small mammals were caught using the standard trap-line and cone methods. A total of 650 trap-days and 80 cone-days were worked out; 260 animals were caught. The species composition of large and medium-size mammals was identified by traces of their life activity and by visual contacts during route surveys of the total area about 350 km2. The routes made 50 km of length. 18 species of mammals referring to 16 genera, 9 families, and 5 orders were found to inhabit the area; they prevalently belong to the most numerous and elements of the theriofauna, widespread in the North-East of Siberia boreal Holarctic (Clethrionomys rutilus, Alexandromys oeconomus, Ursus arctos, Rangifer tarandus, Alces alces) and ancient taiga Palearctic (Sorex caecutiens, S. isodon, Myopus schisticolor, Craseomys rufocanus, Martes zibellina). A new habitat (the northwestern coast of Lake Momontai) was identified for the North Siberian vole (Alexandromys hyperboreus). Besides, the findings of the equal-toothed shrew (Sorex isodon) in the study area expand its distribution borders 160-180 km to the north of the Upper Kolyma basin.

The missing Myopus: plugging the gaps in Late Pleistocene small mammal identification in western Europe with geometric morphometrics

AbstractLemmus and Myopus are two lemming species with distinct habitat requirements but which show very similar dental morphologies. They are thus extremely difficult to distinguish from one another in the fossil record on the basis of their dental remains, leading to poor understanding of the palaeobiogeographical evolution of Myopus as well as inaccurate palaeoenvrionmental reconstructions. Currently, the presence of Myopus in the fossil register from the Pleistocene is still debated and no firm occurrence of this lemming in western Europe has yet been confirmed for the Late Pleistocene. In this paper, we used geometric morphometrics on modern material to establish morphological differences between Lemmus and Myopus teeth (first lower and third upper molars). Morphological data were then used to build a robust linear discriminant model able to confidently classify isolated teeth of these two genera, and finally, linear discriminant models were used on fossil remains of Lemmus/Myopus from two Late Pleistocene archaeological/palaeontological sites (Grotte des Gorges and Gully Cave). This study demonstrates, for the first time, the presence of Myopus schisticolor in west European Late Pleistocene sites between the end of Marine Isotope Stage 3 and the beginning of the Holocene, during climatic events that favoured the development of taiga forest of birch and pine in these regions.

Small mammal assemblage in beaver-modified habitats

One of the less studied positive interactions among organisms is facilitation. Facilitation may have significant impact on diversity of species especially in low productive environments. We studied the effects of well-known facilitator and ecosystem engineer, the North American beaver (Castor canadensis), on small mammal assemblages in the boreal zone. The small mammals, namely voles, mice, and shrews, were trapped over 2 years in ten beaver-modified habitats and in ten control sites. Contrary to our expectations, we did not observe any differences between species or individual numbers between beaver-modified and control sites. However, there were differences in species composition between sites; grass-eating field voles (Microtus agrestis) and invertebrate-eating shrews (Sorex araneus, Neomys fodiens) tended to be more common in beaver sites while forest-dwelling wood lemmings (Myopus schisticolor) and yellow-necked mice (Apodemus flavicollis) were only captured in control sites. The most common species in both habitats was the bank vole (Myodes glareolus), which is a generalist in its habitat requirements. The bank vole’s population structures were similar between the two habitat types. The actions of beavers in water bodies within boreal forests seem to have no effect on the small mammal diversity and their numbers at the regional scale but may have positive effect on them at the larger landscape level as beavers are increasing the overall habitat diversity in the landscape.

Makhnevskaya Ledyanaya Cave (Middle Urals, Russia): Biostratigraphical reconstruction

Pollen and fossil mammals of the terrigenous deposits in the Makhnevskaya Ledyanaya Cave (59°26′ N 57°41’ E), located in the northern part of the Middle Urals and on the border with the Northern Urals, were studied. The spore-and-pollen spectra are divided into four pollen zones. In all the spectra, pollen concentrations of tree species amount to 50–70%. The presence of pollen in thermophilic (Quercus robur-type, Tilia cordata-type, Ulmus sp., Carpinus betulus, Corylus avellana-type) and moderate boreal (Abies, Picea, Pinus, Betula, Alnus) species and a lack of any tundra flora elements indicate their interglacial nature. The following have been identified as small mammal fauna: 8 taxa of insectivorous mammals, 4 taxa of bats, 2 taxa of lagomorphs, 4 species of carnivores, 16 species of rodents, 1 species of odd-toed ungulates and 4 species of even-toed ungulates. The remains of cryoxerophilous (Dicrostonyx sp., Lasiopodomys gregalis) and steppe (Ochotona sp.) species are scarce in the studied fauna. Species typical of forests (genus Sorex, genus Craseomys, genus Myodes, Myopus schisticolor, Microtus agrestis) are dominant. Remains of Erinaceus sp., Talpa sp., Crocidura leucodon, Sciurus vulgaris, Hystrix brachyura, Dryomys nitedula, Apodemus flavicollis, Stephanorhinus kirchbergensis have been found. The morphology and dimensions of the teeth of Panthera spelaea fossilis, Hystrix brachyura, Dryomys nitedula, Arvicola amphibius, mice of genus Apodemus are described. The compositions of the palynocomplexes and mammal fauna as well as the SDQ values for m1 of Arvicola amphibius allow us to date the deposits from the Makhnevskaya Ledyanaya Cave to the Eemian interglacial period (MIS 5e).

Unification of Criteria for Distinguishing Morphotypes of Cheek Teeth in Lemmings (Lemmini, Arvicolinae, Rodentia)

This paper summarizes the data on morphotype dental patterns in recent lemmings (Lemmini) and their earliest presumed ancestors based on analysis of both the existing literature and zoological collections. The criteria for distinguishing the morphotypes are unified, and four metrics are proposed for assessment: (1) the occlusal surface complexity, (2) the regularity of enamel cutting edges, (3) the asymmetry of the lingual and buccal prisms, and (4) the degree of cement deposition in reentrant angles. A catalogue of basic, reserve, and rare morphotypes has been created for Lemmus sibiricus and Myopus schisticolor. The approach developed here is recommended for further research into the spatial, temporal, and ontogenetic variation in Lemmini, based on their dental characters.

Cyclic small rodents in boreal forests and the effects of even-aged forest management: Patterns and predictions from a long-term study in southeastern Norway

Small mammals, especially microtine rodents, play an important role in the dynamics of boreal forest ecosystems. Even-aged forest management, in which old, semi-natural forests are converted to clear-cuts and culturally regenerated stands, is expected to have pronounced impact on the abundance and composition of this group of animals due to changes in the understory vegetation. During a 39 year-period we sampled autumn numbers of small mammals in uncut, semi-natural old forest and in recent clearcuts, supplemented by a 7-year sample from middle-aged plantations. Field voles Microtus agrestis were almost exclusively trapped in clearcuts. Bank voles Myodes glareolus dominated in the old forest, but reached equal or higher densities than field voles in clearcuts. Here, their combined abundance exceeded that of bank voles in old forest. Some years, wood lemmings Myopus schisticolor contributed significantly to vole abundance in old forest. Other rodents Apodemus spp. were rarely captured, mainly in clearcuts, and shrews Sorex spp. numbered <15 percent of the total number of captured animals. Throughout the whole period we discerned 11 vole cycles, with highest peaks in bank voles in old forest. After high numbers during the 1980s, abundances of all species fell markedly during the 1990s, most distinctively in clearcuts, where the field vole almost totally disappeared. From the late 2000s, abundances of all species returned to pre-1990 levels and beyond. In the early and late periods, combined vole numbers were 26% higher in clearcuts compared to old forest, whereas the opposite was true in the middle period. In middle-aged plantations, bank voles numbered only one third of what it was in clearcuts and old forest, and other voles were rarely trapped. The results support the general notion that bank voles thrive in bilberry-rich, older forest and field voles in grass-dominated habitat. Contrary to general assertions, bank vole was abundant also in clearcuts, possibly due to invasion from surrounding old forest, but peak densities were lower than in old forest, possibly due to suppression by field voles. The variation of small mammals in forest age classes concurred closely with recent results reported from Finland. On a landscape scale, the results from these two and other studies predict that the total biomass of small rodents will be reduced by even-aged forest management, not because of conversion of older, semi-natural forest to clearcuts, but because of a decline in numbers in middle-aged and older, secondary forests.

Population dynamics of wood lemming (Myopus schisticolor) in different landscapes of the Northern Pre-Urals

Population dynamics of wood lemming (Myopus schisticolor) in different landscapes of the Northern Pre-Urals

Population fluctuations of moths and small rodents in relation to plant reproduction indices in southern Norway

Trophic interaction hypotheses for multiannual population fluctuations of herbivores include the predation hypothesis, the induction hypothesis and the plant stress hypothesis. Spatial synchrony is best explained by plant stress, such as high reproduction, because weather may synchronize resource allocation in plants over large areas. We used a 29‐yr time series on moth light trapping (6 selected species) and small rodent snap trapping (2 selected species) from southern Norway to test whether herbivore population fluctuations can be related to sexual reproduction of their host plants. The fluctuation pattern of the moths Parashwammerdamia lutarea and Yponomeuta padella, feeding on leaves of rowan (Sorbus aucuparia), could be explained by fluctuations in an annual index of rowanberry production, whereas the fluctuation pattern of Yponomeuta evonymella, feeding on leaves of bird cherry (Prunus padus), could not. The moth Eulithis populata, feeding on bilberry (Vaccinium myrtillus) leaves, fluctuated in synchrony with the bank vole (Myodes clethrionomys), which feeds on bilberry twigs in winter. E. populata and the bank vole also fluctuated in synchrony with a shorter index on bilberry seed crops. Finally, two moths feeding on mosses, Eudonia truncicolella and Catoptria falsella, fluctuated in synchrony with the moss‐feeding wood lemming (Myopus schisticolor). The observed patterns could be caused by a positive effect of the supply of highly nutritious reproductive plant tissue, but the one‐year delayed response by the rodents, which to a large extent feed on the plant species in question during winter, suggests that feeding deterrents are involved.

A redescription of Arostrilepis beringiensis (Kontrimavichus et Smirnova, 1991) and descriptions of two new species from Palaearctic microtine rodents, Arostrilepis intermedia sp. n. and A. janickii sp. n. (Cestoda: Hymenolepididae)

Arostrilepis beringiensis (Kontrimavichus et Smirnova, 1991) is redescribed on the basis of its type specimens from Lemmus trimucronatus (Richardson) and material from the collections of the Institute of Systematics and Ecology of Animals, Novosibirsk from the lemmings Myopus schisticolor (Lilljeborg) and Lemmus sibiricus (Kerr) from the Asian part of Russia. Specimens previously identified as Arostrilepis horrida (Linstow, 1901) from voles are revised and newly collected materials are addressed. Two new species of the genus Arostrilepis Mas-Coma et Tenora, 1997, A. intermedia sp. n. from red-backed voles (Myodes Pallas) from the Asian part of Russia and A. janickii sp. n. from Europe, are described. These species are clearly distinguished from congeners by form and size of the cirrus and its armature as well as the type of arrangement for the testes, position of the cirrus-sac with regard to poral ventral osmoregulatory canals, and host specificity.

An early (1834) illustration of the wood lemming, Myopus schisticolor (Lilljeborg, 1844), from Finland

The wood lemming, Myopus schisticolor, was described as a new species by the Swedish zoologist Wilhelm Lilljeborg in 1844 from a specimen captured in Norway the year before. With the original description was a fine hand-coloured lithograph by the artist Magnus Körner. A Latin translation of the description published later that year also used an illustration by Körner, but it was of lesser quality. However, the species had been observed, described and depicted earlier, but these renderings never reached the scientific community. In 2008 and 2009 respectively, one illustration of the wood lemming made by the Finnish-born artist Wilhelm von Wright was sold twice at auctions in Stockholm. The illustration is dated 1834 and shows a specimen that was found dead at the artist's native home, Haminalaks, in Kuopio parish, Central Finland, that year. However, an accurate description of the species had already been made in 1765, by a group of young naturalists on a tour in the Swedish province Dalecarlia.

Small mammals as potential reservoir hosts of Babesia microti in the Middle Urals

Using PCR and nested PCR methods, 382 blood samples from adult small mammals of 14 species were examined for Babesia microti. The mammals were trapped in the southern taiga of the Middle Urals (Chusovskoi district, Perm Region). The DNA of human babesiosis agent was detected in the blood of 172 small mammals (45.0% of the samples examined) of 11 rodent and insectivore species (Chlethrionomys glareolus, C. rutilus, C. rufocanus, Microtus oeconomus, M. agrestis, Myopus schisticolor, Apodemus uralensis, Sorex araneus, S. caecutiens, S. isodon, S. tundrensis). Especially high infection rates were characteristic of C. glareolus and S. araneus (47.1 and 38.2 %, respectively), the most abundant small mammal species in the study area. The results confirm the high frequency of contact of small mammals with B. microti in forest ecosystems of the Middle Urals and indicate that they probably maintain circulation of this pathogen.

A hypothesis explaining the exceptional sex ratio in the wood lemming (Myopus schisticolor)

The wood lemming is unique in the following respects: (1) the sex ratio is unequal, the frequency of males is 0.20–0.30; (2) two types of females occur, type MF producing progeny of both sexes, type F producing daughters only; and (3) two sex chromosome types of females exist, XX and XY. The hypothesis presented accounts for these and other known facts concerning sex ratio, reproduction biology and chromosome constitution. It is suggested that an X-linked mutant gene affects the male-determining action of the Y, thus converting some XY animals into females. These females normally produce one kind of eggs only; by a mechanism of selective non-disjunction in the foetal ovary only X-carrying eggs are formed. Thus, XY females are of type F, XX of type MF.

Comparative phylogeography and demographic history of the wood lemming (Myopus schisticolor): implications for late Quaternary history of the taiga species in Eurasia

The association between demographic history, genealogy and geographical distribution of mitochondrial DNA cytochrome b haplotypes was studied in the wood lemming (Myopus schisticolor), a species that is closely associated with the boreal forest of the Eurasian taiga zone from Scandinavia to the Pacific coast. Except for a major phylogeographic discontinuity (0.9% nucleotide divergence) in southeastern Siberia, only shallow regional genetic structure was detected across northern Eurasia. Genetic signs of demographic expansions imply that successive range contractions and expansions on different spatial scales represented the primary historical events that shaped geographical patterns of genetic variation. Comparison of phylogeographic structure across a taxonomically diverse array of other species that are ecologically associated with the taiga forest revealed similar patterns and identified two general aspects. First, the major south-north phylogeographic discontinuity observed in five out of six species studied in southeastern Siberia and the Far East implies vicariant separation in two different refugial areas. The limited distribution range of the southeastern lineages provides no evidence of the importance of the putative southeastern refugial area for postglacial colonization of northern Eurasia by boreal forest species. Second, the lack of phylogeographic structure associated with significant reciprocal monophyly and genetic signatures of demographic expansion in all nine boreal forest animal species studied to date across most of northern Eurasia imply contraction of each species to a single refugial area during the late Pleistocene followed by range expansion on a continental scale. Similar phylogeographic patterns observed in this taxonomically diverse set of organisms with different life histories and dispersal potentials reflect the historical dynamics of their shared environment, the taiga forest in northern Eurasia.

Genes in conflict: the biology of selfish genetic elements

Genes in conflict: the biology of selfish genetic elements

Long-term stability of allozyme frequencies in a wood lemming, Myopus schisticolor, population with a biased sex ratio and density fluctuations

Wood lemming (Myopus schisticolor) populations are characterized by female biased sex ratios and cyclic variations in population size. Both of these characteristics are assumed to reduce genetic variation and thus affect the evolutionary adaptation of the species. We addressed these questions by studying the genetic structure of a wood lemming population from eastern Finland by isozyme markers during a 21-year period, which corresponds to 40-50 generations. Contingency tests showed that genotypic proportions conformed to Hardy-Weinberg equilibrium in each of the four sampling years. Among the temporal replicates, allele frequencies differed most by 0.14 and were not significant. Genetic variation was also stable and fairly high with a mean observed heterozygosity of H = 0.057. Variability in the Heinavesi population was higher than previously reported in wood lemming. The difference was mainly caused by variation at a phosphoglucomutase locus that was monomorphic in earlier studies. Significant linkage disequilibrium was observed in three of the comparisons but the disequilibrium did not appear consistently in all years. This pattern was also evidenced by the variance components, which indicated that selection favoured for specific allele pairs only in few subsamples.

Population fluctuations of the wood lemmingMyopus schisticolor in eastern and western Finland

Olavi Eskelinen, Pertti Sulkava and Risto Sulkava From 1982 to 2003 we studied fluctuations in populations of the wood lemmingMyopus schisticolor (Liljeborg, 1844) in the Heinavesi (eastern Finland) and Keuruu regions (western Finland) by counting field signs and dead animals in standardized field surveys. We compared the population fluctuations of lemmings to those of other voles, owls and small mustelids in these regions. The lemming population in Heinavesi fluctuated regularly in 3-year cycles and in synchrony with the field vole population. Populations of owls also fluctuated in synchrony with wood lemming and field vole populations. In the Keuruu region, oscillations in the wood lemming population were irregular, and neither lemming and vole populations nor lemming and owl populations were correlated. Although direct mechanistic evidence is lacking, specialist predators such as weasels and owls probably cause the cyclicity in the field vole and wood lemming populations in the Heinavesi area. On the other hand, scarcity of high-quality habitats, unfavourable winter weather conditions and generalist predators may prevent the development of cyclicity in the wood lemming population of Keuruu.

Characterization of the Xp21-23 region in the wood lemming, a region involved in XY sex reversal.

The wood lemming (Myopus schisticolor) harbors two types of X chromosome, a normal X and a variant X, designated X*. The X* chromosome contains a mutation that causes XY sex reversal. We have previously demonstrated that the Xp21-23 region is deleted from X* and is associated with XY sex reversal. To further analyze the deleted region, we have constructed and characterized seven X chromosome- and region-specific recombinant DNA libraries. Further, we have screened mouse fetal gonad cDNA libraries with the microdissected Xp21-23 DNA as a probe in an attempt to identify homologous and expressed sequences from the deletion. Fourteen positive clones were isolated, and sequence analyses showed that ten of these contained identical sequences homologous to mouse gamma-satellite sequences. One of the remaining four was perfectly homologous to the mouse gene Ccth (chaperonin containing t-complex polypeptide 1, eta subunit). Southern blot indicated that the Ccth cDNA was located on the X chromosome, not deleted from the X* but closely linked to the deletion region. Although the role of the Ccth containing region in sex determination of the wood lemming requires additional studies, the isolation of the mouse Ccth gene by the deletion Xp21-23 probe could be important since this gene is mainly expressed in testis.

EM studies of female meiosis in wood lemmings with different sex chromosome constitutions.

The chromosomes were studied throughout meiotic prophase by electron microscopy of surface-spread oocytes from one XX, four X*X, and three X*Y female wood lemmings, Myopus schisticolor. The X* chromosome had originated from X by a deletion and an inversion in the short arm. The deletion was confirmed in pachytene cells from X*X females; a D-loop was present in the sex bivalent in 16.8% of the cells, and asynapsis of unequal ends was seen in 9.1% of other cells. At late pachytene the D-loop underwent synaptic adjustment. The breakpoints of the deletion are in G-light bands. No inversion loop was seen, which also is in agreement with Ashley's ('88) hypothesis; at least one of the presumed breakpoints of the inversion is in G-dark chromatin. Various types of synaptic abnormalities, such as nonhomologous pairing (triple pairing, interchange, self-synapsis), univalents, foldbacks, and broken lateral elements, were encountered in all types of female. X*Y females showed a high frequency of abnormal oocytes (70.7%), which significantly exceeded that of X*X (23.1%) and XX (8.1%). Univalents were particularly common in the X*Y females. J. Exp. Zool. 290:504-516, 2001.