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.     

Population structure and dynamics of sympatric Apodemus species (Rodentia: Muridae)

This paper describes the population biology of sympatric populations of Apodemus sylvaticus and A. flavicollis in western England. Annual changes in population siie closely resembled those seen in allopatric populations such that simultaneous peaks in number occurred only in autumn and early winter. Numbers of A. sylvaticus were low and stable in early summer increasing rapidly in late summer and autumn and remaining high throughout winter before a sharp decline in spring. Numbers of A. flavicollis increased after the start of reproduction and continued to rise throughout summer and autumn. The period of major decline of this species was during early winter. Densities of A. sylvaticus and A. flavicollis were comparable with those cited in allopatric studies. Spring populations of both species consisted of cohorts first appearing in the late summer and autumn of the previous year. Few individuals present in spring survived the summer. Reproduction of A. flavicollis commenced four to six weeks before that of A. sylvaticus . Seasonal variation in mean weight of adult males and females also indicates that those changes, due to the acquisition of secondary sex characteristics and reproductive maturity, occur earlier in A. flavicollis than in A. sylvaticus . Data presented contain no evidence of interspecific competition and it is concluded that interspecific differences, chiefly asynchrony in reproduction and annual population cycles, contribute to their stable coexistence.     

Chromosomal characterization of Arvicanthis species (Rodentia,Murinae) from western and central Africa: implications for taxonomy

A chromosome study of unstriped grass rats of the genus Arvicanthis (Rodentia, Murinae) in western and central Africa is presented. The observations extend the data available to 242 specimens from 59 localities. All individuals karyotyped belong to four karyotypic forms, or cytotypes, earlier described as ANI-1, ANI-2, ANI-3, and ANI-4 and are presumed to correspond to four distinct species. In order to provide diagnostic characters for these western and one central African Arvicanthis species, we standardized the chromosomal data available and developed a G- and C-banded chromosome nomenclature that allows easy species identification. Each form is characterized by a distinct geographical distribution, roughly following the biogeographical domains of western Africa, although their precise limits remain to be assessed. The sole area of sympatry detected is the region of the inner delta of the Niger River, where both ANI-1 and ANI-3 can be found. It is proposed that the three western African species ANI-1, ANI-3, and ANI-4 be renamed as A. niloticus, A. ansorgei, and A. rufinus, respectively.     

Molecular phylogeny and distribution of three Apodemus species (Muridae, Rodentia) in Serbia

Phylogenetic relationships among three species of the genus Apodemus ( A. flavicollis, A. sylvaticus and A. agrarius ) from seven different localities in Serbia were estimated using arbitrarily primed PCR (AP-PCR) profiling, which allowed clear distinction between the sibling species A. flavicollis and A. sylvaticus . Eight oligonucleotide primers out of the 22 screened, gained a total of 397 amplified bands. The average pairwise genetic distances within Apodemus species ranged from 0.51 between A. flavicollis and A. sylvaticus , to 0.74 between A. sylvaticus and A. agrarius. The large genetic distances obtained among populations of A. flavicollis (0.13) indicate that this part of the Balkan Peninsula was probably a refuge during the last glaciation. Furthermore, differences obtained between populations south and north from the river Danube suggest that this species survived the Last Glacial Maximum in at least two separate refuges. Although our data for molecular markers are from a limited number of localities, extended analyses of C-band distribution on chromosomes from previously studied localities south of the rivers Danube and Sava, indicate that distribution of A. sylvaticus is limited to northern Serbia. Therefore, it is possible that this part of the Balkan Peninsula was not a refuge for this species during the last glaciation.     

A new genus and species of long-clawed mouse (Rodentia: Muridae) from temperate rainforests of Chile

Morphological comparisons of long-clawed mice in southern South America reveal the existence of four genera, only three of which are named. The fourth genus is described and compared with Geoxus, Chelemys and Notiomys. External, cranial and dental characters indicate that the new mouse is most closely related to Geoxus , the raton topo or mole mouse. Geoxus and the new form may be distinguished using both qualitative and quantitative characters. The incipient specializations of the new mouse for fossorial life suggest that it represents an early offshoot along the line leading to the more highly specialized Geoxus. Discovery of a new mammalian genus in Chile, where naturalists have been active for more than two centuries, indicates the importance of continued biological surveys, even in ostensibly well-studied regions. The new mouse reinforces the strong differentiation of faunas inhabiting southern beech ( Nothofagus ) forests in South America, where generic endemism of rodents and marsupials reaches 67%.     

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.     

Activity responses of two species of Peromyscus (Rodentia,Muridae) to varying light cycles

Summary Activity of Peromyscus floridanus and P. gossypinus was studied through a sequence of light-dark regimes including 12-hr light, 12-hr dark; 18-hr light, 6-hr dark; continuous light; and 12-hr light, 12-hr dark. Two populations of each species and both wild caught (field) and first generation laboratory conceived and reared (lab) mice of each stock were tested. All mice were strongly nocturnal during the initial 12-hr and 18-hr photoperiods, although gossypinus was relatively more active during the light phase than floridanus. Both species tended to become aperiodic in constant light, but floridanus showed a greater tendency to adhere to the nocturnal cycle of the preceding 18-hr photoperiod. Although the two species were relatively more active in light during the second 12-hr photoperiod than during the first 12-hr light, 12-hr dark regime, floridanus reestablished a stronger nocturnal cycle than gossypinus. Lab groups exhibited essentially the same trends between species and populations as the field animals, thus indicating some genetic basis for the observed differences. P. gossypinus had a higher over-all absolute activity level than floridanus. There was also less difference between the performance of field and lab groups of gossypinus than of floridanus. Both species showed a decline in activity with increased photoperiod, the effect being more pronounced in floridanus.The difference in the activity responses of the two species appears to be correlated with the characteristics of their habitats and nest sites. The stricter nocturnality of floridanus is associated with relatively xeric, open habitat in which daytime activity would seem to involve higher risk of predation and greater heat strss and water loss than in the case of the more humid denser forest environments typical of gossypinus. P. floridanus also nests in burrows, whereas nests of gossypinus are typically located in more accessible places where a lower threshold for activity in light might increase a mouse's chances of escaping from a predator when surprised in the nest during the day. The floridanus populations tended to differ more in percentage of activity in light and level of absolute activity than the corresponding gossypinus stocks. The difference in the activity patterns of the two floridanus populations was correlated with the density of vegetation in their respective habitats. Relative eye size was not clearly associated with species and population differences in activity responses to light.     

Isozyme and allozyme markers distinguishing two morphologically similar, medically important Mastomys species (Rodentia: Muridae)

Background  

Two common southern African mice species, Mastomys coucha and M. natalensis, are widely distributed throughout the subregion and overlap in many areas. They also share a high degree of morphological similarity, making them impossible to distinguish in the field at present. These multimammate mice are documented carriers of serious disease vectors causing Lassa fever, plague and encephalomyocarditis, which coupled to their cohabitation with humans in many areas, could pose a significant health risk. A preliminary study reported the presence of isozyme markers at three loci (GPI-2, PT-2, -3) in one population each of M. coucha and M. natalensis. Two additional populations (from the Vaal Dam and Richards Bay) were sampled to determine the reliability of these markers, and to seek additional genetic markers.     

Phylogeographic study of Apodemus ilex (Rodentia: Muridae) in Southwest China

Background

The Mountains of southwest China have complex river systems and a profoundly complex topography and are among the most important biodiversity hotspots in the world. However, only a few studies have shed light on how the mountains and river valleys promote genetic diversity. Apodemus ilex is a fine model for investigating this subject.

Methodology/Principal Findings

To assess the genetic diversity and biogeographic patterns of Apodemus ilex, the complete cytochrome b gene sequences (1,140 bp) were determined from 203 samples of A. draco/ilex that were collected from southwest China. The results obtained suggested that A. ilex and A. draco are sistergroups and diverged from each other approximately 2.25 million years ago. A. ilex could be divided into Eastern and Western phylogroups, each containing two sub-groups and being widespread in different geographical regions of the southern Hengduan Mountains and the western Yunnan - Guizhou Plateau. The population expansions of A. ilex were roughly from 0.089 Mya to 0.023 Mya.

Conclusions

Our result suggested that A. ilex is a valid species rather than synonym of A. draco. As a middle-high elevation inhabitant, the phylogenetic pattern of A. ilex was strongly related to the complex geographical structures in southwest China, particularly the existence of deep river valley systems, such as the Mekong and Salween rivers. Also, it appears that the evolutionary history of A. ilex, such as lineage divergences and population expansions were strongly affected by climate fluctuation in the Late Pleistocene.     

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.     

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 and protein evolution in morphologically similar species of Praomys sensu lato (Rodentia, Muridae)

Evidence of extensive chromosomal evolution in a biologically and economically important group of African murids of the Praomys/Mastomys complex was provided by examination of G- and C-band chromosomal data on P. coucha (2n = 32), P. fumatus (2n = 38), P. hildebrandti (2n = 32), P. jacksoni (2n = 28), P. misonnei (2n = 36), and P. cf. tullbergi (2n = 35). A coding system was developed for the chromosomal characters, and analyses were performed by a computer program to find the shortest tree with a minimum of 35 autosomal rearrangements (pericentric inversions, complex translocations, centric fusions, centric fissions, tandem fusions, euchromatic additions, and heterochromatic additions). The resulting phylogenetic hypothesis differs from traditionally accepted hypotheses regarding this complex group of rodents. The cytogenetic data show that 1) there is no support for the dichotomy of Mastomys/Praomys previously based on morphology, 2) the 2n = 32 species from eastern Africa (P. hildebrandti) is distinct from the 2n = 32 species from southern Africa (P. natalensis), and 3) there is a close association between P. jacksoni and P. cf. tullbergi. Polyacrylamide gel electrophoresis of liver membrane proteins demonstrated few differences in protein mobilities between species and even fewer between individuals of the same species taken from different habitats and localities in Kenya. Monoclonal antibodies produced against liver proteins of one species and tested for reactivity to other species confirmed the evolutionary similarity of species of this complex. This immunologic approach may provide a robust data set for future phylogenetic studies of muroid rodents.(ABSTRACT TRUNCATED AT 250 WORDS)     

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 comparison of the locomotion of two desert-living Australian mammals, Antechinomys spenceri (Marsupialia: Dasyuridae) and Notomys cervinus (Rodentia: Muridae)

The locomotion of the marsupial, Antechinomys spenceri and the rodent, Notomys cervinus was studied by recording their tracks on long strips of smoked kymograph paper and by means of slow-motion cinematography. Although both animals occupy the same habitat and are similar in their general appearance, their methods of locomotion differ greatly, since Antechinomys leaps quadrupedally, while Notomys leaps bipedally at fast speeds and runs quadrupedally at slower speeds. The mean speed of both genera was 2.7 m/sec but the mean length of stride of Notomys was 51.2 cm compared with 44.3 cm in Antechinomys. The locomotion of the two Australian genera is compared with that of the North American rodents, Dipodomys and Microdipodops.
The significance of the different types of locomotion is discussed.