[Hibernal reproduction in Arvicola terrestris scherman Shaw (Mammalia, Rodentia)].
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[Allozyme variability of the European bean Castor fiber 1758 (Castoridae, Rodentia) from the Voronezh State Nature Reserve].
Electrophoretic methods were used to study protein products of 32 gene loci in the blood of European and Canadian beavers held in captivity at the Voronezh State Nature Reserve. In the studied samples, the levels of polymorphism and average heterozygosity exceeded the average values of corresponding indices determined for beavers that inhabit temperate zones. To what extent the studied samples represent the state of the gene pool of parental populations is discussed. A comparison between allozyme spectra of samples of European and Canadian beavers revealed many coinciding polymorphic loci, on the one hand, and pronounced genetic divergence of these species, on the other.
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[Genetic differentiation and phylogenetic relationships among Palearctic mice (Rodentia, Muridae)].
Genetic differentiation of 18 Palearctic mouse species (genera Sylvaemus, Mus, Apodemus, Micromys, and Rattus) with respect to 31 biochemical loci was estimated to define the taxonomic status of these genera. On the basis of genetic data, two independent centers of origin of species belonging to the family Muridae were identified. The first is the Indo-African center, from which the modern Sylvaemus species and Palearctic representatives of Mus originated in the Pleistocene (1.0-2.0 million years ago). Genera Micromys and Apodemus, which diverged in early Pliocene (about 7 million years ago), trace their origin to the same center. From the second center, located in Southeast Asia, Rattus species radiated. The genetic divergence of taxa issuing from these two centers attains the level characteristic of differentiation between families and dates back to the late Miocene (over 10 million years ago). Species were compared pairwise to determine the percent of fixed gene differences (Pfd) between them. Analysis of Pfd distribution confirmed distinct periodicity of speciation in mice and revealed two speciation peaks. The first, at the level of genera, occurred in the Pliocene, and the second, at the species level, in the Pleistocene.
Animals↗
Brain structure volumes in the mole rat, Spalax ehrenbergi (Spalacidae, Rodentia) in comparison to the rat and subterrestrial insectivores.
Natural blindness and a subterranean, digging mode of life demand peculiar adaptations of the central nervous system in the mole rat Spalax ehrenbergi, which are the focus of this quantitative investigation. Volumes of 25 brain structures in Spalax were evaluated allometrically, using the least encephalized mammalian species, the Madagassian hedgehog-like tenrecs (Tenrecinae) as a reference base, and their sizes compared with those of the rat (as a more generalized representative of rodents) and of some subterranean Insectivora. The allometric approach reveals that Spalax has a larger brain than tenrecs and the rat. Within the brain, the neocortex and diencephalon are well developed, an observation also made in other mammalian species with a relatively high encephalization. An unique feature in Spalax is the enlargement of motor structures of the brain, such as the cerebellum (and cerebellar nuclei), and the striatum. Most conspicuous is the large size of the nucleus motorius nervi trigemini, reflecting the importance of masticatory muscles for the special digging technique, which demand an intense use of the teeth for loosening the soil.
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[Aggressive behavior of the male volcano mouse Neotomodon alstoni (Rodentia: Cricetidae)].
A study was carried out on the agonistic behavior of the male volcano mouse, Neotomodon alstoni, with 50 pairs of males which were classified as possible dominants (D) and subordinates (S), utilizing Melzack-Thompson's Method. The aggressiveness levels exhibited by this mouse were recording in the combinations: D vs. D and S vs. S. Two groups were formed: Group I with 12 pairs of D males and 13 of S males, and Group II with 11 pairs of D males and 14 of S males. In Group I the aggressiveness level was quantified after one week of mating and after another week of isolation, and in Group II the sequence of observation was inverted. The aggressiveness level was measured by the number of attacks per hour, an attack being defined as the aggressive physical contac of an animal (aggressor) with another (attacked). The kinds of behavior registered, including offense, defense, and submission patterns, revealed hierarchic relationships. Dominance was correlated significatively (p < 0.05) with a higher level of aggressiveness.
Agonistic Behavior↗
[Karyotypes and chromosomal differentiation of two species of the genus Tachyoryctes (Rodentia, Tachyoryctinae) from Ethiopia].
Karyotypes of two species of genus Tachyoryctes from four localities in the Bale Mountains National Park, Ethiopia, were analyzed. T. splendens has 2n = 48, NFa = 65-86. Variations of the autosome arm number are determined by different numbers of autosomes with additional heterochromatin arms (7-17). Karyological analysis indicated that the cytogenetic structures of T. splendens from the localities studied was unique, which might result from formation of the karyotypes optimal for the given habitats. T. macrocephalus has 2n = 50, NFa = 62. A high conservatism of the number and size of C-positive heterochromatin blocks reflects the extreme specialization of T. macrocephalus endemic for the Bale province and occupying a limited ecological niche. Homology of G-banding patterns of several chromosomes and chromosome arms demonstrated that karyotypes of T. splendens and T. macrocephalus were formed from the common ancestral karyotype through different rearrangements in some chromosomes.
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[Population cytogenetics in Myospalax myospalax Laxm. (Rodentia, Myospalacinae)].
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[Auditory sensitivity of the lerot (Eliomys quercinus L.) (Rodentia Gliridae). Study of evoked potentials at the level of the cochlea].
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Animals↗
[Novel data on porcupine quill structure (Hystricomorpha, Rodentia)].
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Animals↗
Further ultrastructural observations on the sperm head of the plains mouse, Pseudomys australis (Rodentia: Muridae).
Ultrastructural and histochemical techniques have been utilized to study selected aspects of the fine structure of the three-hooked sperm head of the plains mouse, Pseudomys australis. The peripheral layer of the two ventral hooks was found to consist of a continuation of the postacrosomal dense lamina. Parallel ridges connected the dense lamina and plasma membrane in the postacrosomal region and ventral hooks. Both these regions stained intensely with silver nitrate. The distribution of actin filaments in the hooks was investigated using NBD-phallacidin. Fluorescence was more intense in the apical regions of the ventral hooks, and two bands of fluorescence extended caudally from their base. It was also shown that the equatorial segment of the acrosome extended onto the dorsal hook. The structural features of the three hooks are discussed in relation to their possible functional significance.
Actins↗
Genetic similarity between species of Akodon (Rodentia, Cricetidae).
Genetic similarity between species of rodents of the Akodon genus (A. dolores, A. molinae, and A. azarae) has been estimated by analysis of electrophoretic zymograms corresponding to 23 loci. Nei's coefficient between A. dolores and A. molinae was within the range usually found in conspecific populations. This evidence plus the successful production of "hybrids" (Merani et al., J. Exp. Zool., 206:343-346, '78) suggests that A. dolores and A. molinae may represent geographic races of the same species.
Animal Population Groups↗
Sexual dimorphism and seasonal variation in submandibular gland histology of Bolomys lasiurus (Rodentia, Muridae).
Wild rodents (Bolomys lasiurus) of both sexes were caught in a cerrado grassland area during the dry (July-September) and rainy (January-March) seasons of Brazil. Fasted animals were perfused with Karnovsky fixative through the left ventricle, under ether anesthesia, and the submandibular gland was processed for embedding in historesin. Histological and histometric data show sexual dimorphism at both seasons. In the volume percentage of the granular convoluted tubules (GCT) and their secretory granules, the males exhibited higher values. The absolute volume occupied by these structures, however, was dimorphic only in the rainy season. The diameter of the GCT, the height of its epithelium, and its total length were also greater in males during the rainy season. The absolute volumes of the acini and of the ductal tree were identical in both sexes in the dry and rainy seasons but the acinar diameter increased in the males and females during the rainy season. The sexual dimorphism and the seasonal variations now described in the B. lasiurus submandibular glands could be explained by the augmented reproductive activity of the males in the rainy period.
Animals↗
Relationship between vestibular lamina, dental lamina, and the developing oral vestibule in the upper jaw of the field vole (Microtus agrestis, Rodentia).
Formation of the oral vestibule is ignored in most studies on tooth development, although dental and vestibular lamina are closely related to each other. Knowledge about morphogenetic processes shaping the oral vestibule is missing almost completely. The aim of this study was to assess the developmental relationship between dental and vestibular lamina as well as formation of the oral vestibule in the upper jaw of the field vole (Microtus agrestis), a small rodent representing an attractive model species for comparative dental studies. Three-dimensional reconstruction revealed that the upper vestibular lamina of the vole joins the antemolar part of the diastemal dental lamina, similar to mouse. Later, this lamina complex regresses and the vestibular lamina is separated from the molar epithelium. Participation of the vestibular lamina in dental lamina formation, as hypothesized for mouse, therefore remains unclear. Except for increased apoptosis in the regressing diastemal dental lamina, spatial segregation of mitoses or apoptoses could be detected neither in the jaw arch epithelium nor in the adjacent mesenchyme. Therefore, in contrast to tooth primordia, apoptosis and mitosis seem to play a minor role in shaping of the upper oral vestibule. The buccal vestibule develops secondarily, probably in consequence of general growth of the head and localized differentiation of cells.
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Experimental infection of Akodon molinae (Rodentia, Cricetidae) with Junín virus.
Experimental infection with the XJ-Clone 3 strain of Junín virus in laboratory bred Akodon molinae, a cricetid rodent inhabiting the borders of endemic Argentine hemorrhagic fever areas, was studied. Suckling animals inoculated intracerebrally proved sensitive and became chronically infected. Sixty percent of the rodents showed neurologic involvement, with mortality reaching 60%. Virus was recovered from the brain at 7, 15, 21, 37, and 57 days postinfection (pi). By immunofluorescence (IF), viral antigens were observed up to 182 days pi in cells of the central nervous system (CNS). Concurrently, immunoglobulin deposits were detected in infected CNS cells from 21 up to 182 days pi. These deposits increased with the progression of the immune response as measured by IF antibodies. The detection of immune complexes in brain cells of apparently healthy animals suggests that neither viral replication nor the development of a humoral immune response are necessary requisites for neurovirulence in this host. Infection of adult rodents by different routes failed to induce disease or mortality and virus could not be recovered from oral swabs, blood, or organs. Our data suggest that Akodon molinae could play a role in nature as an alternative reservoir of Junín virus in addition to the main reservoir, Calomys musculinus.
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A molecular perspective on the systematics and evolution of the genus Arvicanthis (Rodentia, Muridae): inferences from complete cytochrome b gene sequences.
Systematics of the genus Arvicanthis, the African unstriped grass rat, are somewhat controversial. Most recent taxonomic revisions list five to six species but the definition of some of these (Arvicanthis dembeensis, Arvicanthis nairobae, and Arvicanthis niloticus) is uncertain. The complete mitochondrial cytochrome b gene (1140 bp) was sequenced for 20 specimens from throughout the range of the genus to determine the intrageneric genetic structure, construct a molecular phylogeny, and evaluate classical taxonomies. Neighbor-joining and maximum parsimony analyses yielded identical phylogenetic trees that identify two major lineages: the first one (1) is composed of specimens usually referred to A. niloticus but representing several distinct species, and the other (2) is a complex including "true" A. niloticus from Egypt and northern West Africa as well as Arvicanthis abyssinicus, Arvicanthis dembeensis, and Arvicanthis somalicus. An analysis on a 357-bp fragment of the cytochrome b including published data on A. nairobae indicates that this taxon is part of clade (1). Calibration of the number of 3rd position transversion changes with the murid fossil record suggests that clades (1) and (2) diverged approximately 5 Myr ago. Arvicanthis niloticus as currently recognized is a paraphyletic association and this name should be restricted to the Egyptian and northern West African sample. We also suggest referring to A. dembeensis as A. niloticus, as our cytochrome b data do not support its recognition as a distinct species. Clade (1) is subdivided in three lineages, geographically corresponding to southern West, Central, and East Africa. The high genetic divergence detected between the Central African lineage and the other two lineages suggests that they probably represent separate species. Clade (2) experienced rapid cladogenetic events during the late Pliocene, with the A. somalicus lineage being the first to emerge, followed by the ancestor of A. abyssinicus and A. blicki. This period was characterized by significant climatic and environmental changes, such as the extension of open habitats, which might have provided a stimulus for speciation in this savanna-dwelling genus. Confrontation of our molecular results with chromosomal data shows a high degree of congruence between the two datasets.
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Intrageneric phylogeny of Acomys (rodentia, muridae) using mitochondrial gene cytochrome b.
This paper investigates interspecies relationships within the genus Acomys (spiny mice) by analyzing entire mitochondrial cytochrome b gene (1141 bp). This gene provides strong phylogenetic signal, as shown by high support of the topology obtained (bootstrap value and RNA support number). The phylogeny is congruent with inferences from allozymes for the species considered. Controversial taxonomy of Acomys cahirinus, dimidiatus, airensis, and ignitus is clarified, with their specific ranks confirmed on the basis of tree topology and nucleotide distances. Phylogenetic relationship between the undescribed species Acomys sp. from west Africa and A. airensis argue in favor of two distinct colonization events in this zone.
Africa↗
The phylogenetic position of "Acomyinae" (Rodentia, Mammalia) as sister group of a Murinae + Gerbillinae clade: evidence from the nuclear ribonuclease gene.
The phylogenetic relationships of Acomys and Uranomys within Muridae were investigated using nuclear pancreatic ribonuclease A gene sequences. The various kinds of substitutions in the data matrix (15 taxa x 375 nucleotides) were examined for saturation, in order to apply a weighted parsimony approach. Phylogenies were derived by maximum parsimony (weighted and unweighted) and maximum likelihood procedures, using a dormouse (Gliridae) as outgroup. Maximum likelihood gave the most robust results. All analyses cluster some traditional taxa with a strong robustness, such as three species of the genus Mus, two South-East Asian rats, and two genera in each of the gerbil and vole families. When analyzed with those of other murid rodents representing Murinae, Gerbillinae, Arvicolinae, Cricetinae, and Sigmodontinae, sequences of the ribonuclease gene suggest that Acomys and Uranomys constitute a monophyletic clade at the subfamily level, denoted "Acomyinae." The relationships between the six subfamilies of Muridae appear poorly resolved, except for a clade uniting Murinae, Acomyinae, and Gerbillinae. Within this clade, the sister group of Acomyinae could not be identified, as the branch length defining a Gerbillinae + Murinae cluster is extremely short. The poor resolution of our phylogenetic inferences is probably the result of two confounding factors, namely the limited size of the pancreatic ribonuclease sequence and the probable short time intervals during the radiation of the six murid subfamilies involved in this study.
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Molecular phylogenetics of the Peromyscus boylii species group (Rodentia: muridae) based on mitochondrial cytochrome b sequences.
Variation in the mitochondrial cytochrome b gene (1143 bp) was examined to estimate the phylogenetic relationships of taxa within the Peromyscus boylii species group. In addition, phylogenetic relationships among the aztecus, boylii, and truei species groups were addressed. Maximum-likelihood, neighbor-joining, and maximum-parsimony (weighted and equally weighted) analyses produced similar topologies with P. boylii, P. beatae, P. simulus, P. stephani, P. madrensis, P. levipes, and three undescribed taxa from western Mexico forming a monophyletic unit. At least two of the undescribed taxa from western Mexico potentially represent species. Members of the P. aztecus species group formed a clade separate from the P. boylii group and should be recognized as a distinct species group. P. sagax, P. polius, and P. pectoralis, formerly placed in the P. boylii species group, generally formed an unresolved polytomy with the P. truei, P. aztecus, and P. boylii species groups. P. attwateri formed a sister taxon relationship with members of the P. truei species group (P. difficilis and P. nasutus) and should be considered a member of this group. Members of the P. truei species group did not form a monophyletic unit, indicating that this species group is not monophyletic and may be composed of two assemblages.
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