Inter- and intra-individual chromosome variability in Thamnomys (Grammomys) gazellae (Rodentia,Muridae) B-chromosomes and structural heteromorphisms

The present paper reports intra- and inter-individual variability related to the occurrence of numerous B-chromosomes in Thamnomys (Grammomys) gazellae, a species of African Climber rat belonging to the dolichurus group. The frequency of B-chromosomes in somatic and spermatogonial metaphases is investigated, together with their behaviour during meiosis. Moreover, G-banding makes it possible to identify a structural polymorphism resulting from a pericentric inversion in a large chromosome (no. 6). The distribution of the constitutive heterochromatin has been assessed by C-banding. The nucleolus organizer regions (NOR's) were located by means of silver staining in four chromosomal pairs (nos. 1, 2, 4, and 6). The karyotype of T. (G.) gazellae is compared with that of other taxa of the dolichurus group, particularly the Somaliland population which also exhibits the occurrence of B-chromosomes. The origin and significance of B-chromosomes is discussed.     

Chromosomal variability of the field mouse Apodemus agarius (Rodentia, Muridae)

Chromosome sets of 114 Apodemus agrarius mice from 29 localities in Moldova, Ukraine, Siberia, and Far East were studied by means of G-, C-, and NOR-banding. In all populations studied, the Y chromosome was shown to be a medium-size acrocentric chromosome consisting of heterochromatin. Chromosome polymorphism observed in populations from Primorskii krai concerned (1) the morphology of the first two autosome pairs (variants A/A, A/ST, and ST/ST), (2) the number of metacentric chromosomes (from 6 to 8), and (3) heterochromatin localization in the pericentromeric regions of two metacentric chromosome pairs. A karyotype with an additional heterochromatic microchromosome found in all the metaphases studied was described in one mouse from a locality of western Primorye that has not been studied previously. In the karyotype of 15 mice from four populations of Primorye, the pool of nucleolus organizer regions is distributed over three autosome pairs rather than over four, as is the case A. agrarius from Europe. Based on the analysis of literature sources and our own data, the problem of chromosome polymorphism in the field mouse is discussed.     

Reproductive characteristics of free-livingCalomys venustus (Rodentia, Muridae)

Calomys venustus showed a cyclic seasonal pattern of reproductive activity characterized by a period of repose and a variable length of the period of sexual activity between August—September to May—June. The study was done from 1983 to 1999. During this time the population density increased from October—November to the end of autumn and sharply decreased in winter. Three peaks in rate of pregnancy were recognized in the breeding period: spring, summer and late summer. The average litter size was different among the three peaks in rate of pregnancy. The reproductive pattern had a peak at the beginning of the spring produced by overwintering animals, and another peak in summer-autumn caused by the reproductive activity of young born in the same period in which they breed. The spring cohort exhibited the greatest breeding contribution suggesting that this cohort is principally responsible for the yearly peak in abundance.     

Bibliography of the genus Apodemus (Rodentia, Muridae)

A complete bibliography of the genus Apodemus for the period 1970–1980 is presented, with a selection of the more important papers from earlier years, and a few references for 1981. A coded index to species and subjects is provided. All titles have been translated into English.     

The mitochondrial genome of Apodemus peninsulae (Rodentia, Muridae)

The complete mitochondrial (mt) genome of the Korean field mouse Apodemus peninsulae was sequenced and found to be 16,266 bp in length. The mt protein-coding genes of A. peninsulae had ATG, GTG, ATC, and ATA as initiation codons and TAA, TAG, TA, and T as termination codons. Two forms each of trnL and trnS and the three tRNA clusters, IQM, WANCY, and HSL were identified, as in the typical Rodentia mt genome. Among tRNAs, abnormal cloverleaf structure of trnS((AGY)) was identified in DHU arm. The l-strand replication origin has the potential to form a stable stem-loop structure and control region has several conserved sequence elements.     

Chromosomal evidence for a polytypic structure of Arvicanthis niloticus (Rodentia, Muridae)

The analysis of R- and C-banding patterns of chromosomes of Arvicanthis niloticus from five localities of Africa (Egypt, Senegal, Burkina-Faso, Mali and Central African Republic) revealed the existence of three karyotypic forms labelled in the study as ANI-1, ANI-2 and ANI-3. These forms differ from each other by 6 to 8 chromosomal rearrangements such as reciprocal and Robertsonian translocations and pericentric inversions. Moreover, they possess different quantities of C-heterochromatin. The data indicate that these three forms are distinct species, cytogenetically isolated, and that a further taxonomic analysis of the genus Arvicanthis is needed.     

Systematics and geographic variation of Ethiopian Arvicanthis (Rodentia, Muridae)

Arvicanthis , the unstriped grass-rat, is a widespread genus occurring in many regions of Africa and is major pest in agricultural farmland. Despite its economic importance for developing countries, the taxonomy of the genus is stillin a chaotic state. We used univariate and multivariate morphometrics to investigate two species, A. abyssinicus and A. dembeensis , occurring in Ethiopia. Results show that these taxa are well separated, this contradicting authors who lump all Arvicanthis as A. niloticus . There is a longitudinal cline in the morphology of A. dembeensis from eastern regions along the Rift Valley. Differences between the species in morphlogy seem to reflect adaptation to different ecological niches at high ( A. abyssinicus ) and low ( A. dembeensis ) altitudes.     

Gene Flow Among Calomys Musculinus (Rodentia, Muridae) Populations in Argentina

Calomys musculinus is a Sigmodontinae rodent inhabiting periodically disturbed habitats in the central eastern plains of Argentina. It is the natural reservoir host of Junin virus, the etiological agent of Argentine Hemorrhagic Fever (AHF). In order to analyze the levels of gene flow among populations of this species, allozymic variability at 26 loci was studied in 291 individuals from the endemic zone of AHF and localities outside it. All populations showed high levels of polymorphism (H _e between 0.107 and 0.144; P_95% between 38 and 54%). Individual loci f values were in most cases negative, although not significantly different from zero. Mean genetic differentiation among populations was low, but statistically significant (=0.020; P<0.01). There was no correlation between genetic and geographic distances between pairs of populations, and scatter of the pairwise points suggests that, at the regional scale, genetic drift is more influential than gene flow. This result can be interpreted as indicative of a relatively recent expansion of C. musculinus habitat and restricted on-going gene flow, which would be compatible with a relatively slow expansion rate of AHF.     

Cranial morphometric and fine scale genetic variability of two adjacentMastomys natalensis (Rodentia: Muridae) populations

The objective of this multidisciplinary project was to study the intra-specific morphometric and genetic variability between two adjacent populations ofMastomys natalensis Smith, 1834 living in different environments. The study of micro-evolutionary processes at work by using geometrical morphometrics allowed us to define two groups, characterized by different features of the skull shape. Using molecular microsatellites analysis, we showed that the two populations exchanged high gene flow and could be considered as a single panmictic unit. These results suggest that this widely-distributed species exhibits a local population-level differentiation in shape variation of skulls, probably due to different ecological situations. We speculate that the variability in the cranial characteristics (connected with the feeding ability) could reveal a local adaptation preferentially based on the food availability. We propose an explanation linking the shape differences to the fitness gain in the exploitation of resources available in the two environments. Since we suggest a potential differentiation process between populations, we believe that the two groups constitute even better models to understand the factors involved in the early stages of local adaptations.     

Evolutionary relationships among eight species of South American phyllotine rodents (Rodentia: Muridae) based on allozymic data

Rodents of the tribe Phyllotini represents one of the main radiations of South American Sigmodontini. Phylogenetic relationships among species of this highly diversified group are poorly known. In this paper we analyse evolutionary relationships among eight phyllotine species belonging to the genera Calomys , Graomys , Phyllotis and Eligmodontia , on the basis of allozymic polymorphisms. Most of the differences among species were in allele frequencies and not of allele class. Neighbour-joining and maximum likelihood methods place P. xanthopygus in the same group as E. typus and G. griseoflavus , in agreement with results obtained by several authors on the basis of morphological characters. Parsimony analysis of 0–9 coded data suggest that the genus Calomys is paraphyletic, but with a low bootstrap support. In the tree based on genetic distance data, the genus also appears as paraphyletic. The maximum likelihood method yields a tree where Calomys is monophyletic, but this phylogeny is supported by only two out of 78 alleles analysed. Calomys hummelincki and C. venustus occupy a basal position among Calomys species. Calomys musculinus and C. lepidus are the most closely related species of the genus, with C. laucha as sister to them. These relationships are strongly supported by bootstrap percentages.     

Cytogenetic differentiation of Apodemus peninsulae populations (Rodentia, Muridae) in eastern Siberia

Population and cytogenetics studies of geographical karyotype changes in East Asiatic mice in East Siberia showed that each population has unique cytogenetic structure, owing to different variants of B-chromosomes system, including 1 to 18 B-chromosomes differing in morphology and size. For each population, we observed the prevalence of mice with a definite number and morphology of B-chromosomes, which is probably the result of homeostatic processes in the population. Local changes were revealed, due to increase in the number of dot-like B-chromosomes in the direction from the West to the East.     

Systematics and evolution of the subfamily Gerbillinae (Mammalia, Rodentia, Muridae)

Although they represent a quarter of the mammalian species, the evolutionary relationships among as well as within, the main murid lineages are still controversial. The subfamily Gerbillinae is no exception as previous studies based on morphological, karyotypical, and allozyme characters are highly incongruent. Here, we present the first molecular phylogeny for gerbils based on cytochrome b and 12S rRNA mitochondrial genes. Results are largely congruent between the two genes as well as with the concatenated data set with most of the nodes being well-supported. Based on the topologies retrieved here, we (1) propose the identification of three main clades, (2) support the split of Tatera genus into an Asian and an African group, the latter including Gerbillurus species, and (3) provide some evidence towards the inaccuracy of subgeneric divisions within both Gerbillus and Meriones. In addition, the sharp contrast between the genetic characters and morphological data sets suggest high levels of convergence, probably as a result of strong environmental constraints imposed on these rodents adapted to arid and semi-arid regions. Finally, molecular datings for the various cladogenetic events are in good agreement with the known gerbilline fossil record and support an African origin with subsequent migrations to Asia.     

Karyotypie diversity and taxonomic problems in the genus Arvicanthis (Rodentia,Muridae)

The analyses of R- and C-banding patterns of chromosomes of Arvicanthis niloticus originating from two different localities (Egypt and Central African Republic) revealed karyotypic differences caused by one pericentric inversion and three translocations, one being reciprocal and the others Robertsonian. There were also some differences in centromeric heterochromatin patterns.The data indicate that these two forms are distinct species, cytogenetically isolated, and that a revision of the taxonomic status of the genus Arvicanthis is needed.     

Dietary Ecology of Murinae (Muridae,Rodentia): A Geometric Morphometric Approach

Murine rodents represent a highly diverse group, which displays great ecological versatility. In the present paper we analyse the relationship between dental morphology, on one hand, using geometric morphometrics based upon the outline of first upper molar and the dietary preference of extant murine genera, on the other. This ecomorphological study of extant murine rodents demonstrates that dietary groups can be distinguished with the use of a quantitative geometric morphometric approach based on first upper molar outline. A discriminant analysis of the geometric morphometric variables of the first upper molars enables us to infer the dietary preferences of extinct murine genera from the Iberian Peninsula. Most of the extinct genera were omnivore; only Stephanomys showed a pattern of dental morphology alike that of the herbivore genera.