Revision of Chaetodipus arenarius (Rodentia: Heteromyidae)

Chaetodipus arenarius is an endemic species of the Baja California Peninsula. It has undergone taxonomic changes in the last few years. Today, two species, C. arenarius and Chaetodipus dalquesti, are formally recognized with an unknown range for each. However, genetic analysis showed the possible presence of a third species. The objectives of this study were to use molecular data (cytochrome b and cytochrome c oxidase subunit III genes) to determine how many genetic groups are present in C. arenarius in the Baja California Peninsula; if these groups have morphological characteristics that could be used to distinguish them; if the genetic groups have limited distributions; identify taxonomic implications; and establish if there are any associations amongst genetic groups and different habitats. Bayesian inference, maximum parsimony, maximum likelihood, distance optimality criteria, and minimum spanning network indicated three monophyletic groups with high genetic differences (5.54–13.59%). These groups are morphologically diagnosable based on pelage and morphometric characters and geographical range. The three genetic groups correspond to three taxa previously described as subspecies or species. Based on our results, these should be considered to be different species: C. arenarius occupies the most extreme habitats with hot summers; C. dalquesti occupies the moistest coastal areas in the southern part of the peninsula, and Chaetodipus siccus is restricted by mountain ranges to the isolated Los Planes Basin and Cerralvo Island. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010.     

Development of a toxic bait for control of eastern lubber grasshopper (Orthoptera: Acrididae)

This study assessed baits for eastern lubber grasshopper, Romalea guttata (Houttuyn). When offered a choice among several grain-based baits (rolled oats, wheat bran, oat bran, yeast, corn meal, cornflakes) and vegetable oils (canola, corn, peanut, soybean), eastern lubber grasshopper adults preferred bait consisting of wheat bran carrier with corn oil as an added phagostimulant. Other carriers were accepted but consumed less frequently. Discrimination by eastern lubber grasshoppers among oils was poor. Similarly, addition of flavorings (peppermint, anise, lemon, banana) resulted in few significant effects. The carbaryl, wheat bran, and oil bait developed in this study was effective at causing eastern lubber grasshopper mortality in field-cage studies. Significant mortality occurred even though grasshoppers had to locate dishes of bait in a large cage, and could feed on daylilies, or grass growing through the bottom of the cage, rather than on the bran flakes. Consumption of as little as a single carbaryl-treated bran flake could induce mortality, although individuals varied greatly in their susceptibility. The bait matrix developed in this study was readily consumed when in the presence of some plant species. We expect that wheat bran and corn oil bait would be most effective as protection for less preferred plants (tomato, pepper, eggplant, leek, parsley, fennel, daylily, lily of the Nile, and canna lily) because baits were readily consumed in the presence of these plants. Plants that are readily consumed in the presence of bait (preferred plants) included butter crunch lettuce, carrot, yellow squash, cauliflower, collards, green onion, chive, cucumber, cabbage, cantalope, endive, red leaf lettuce, society garlic, caladium, and amaryllis. Baits are likely to be less effective in the presence of such plants. On average, vegetables in Solanaceae (i.e., tomato, pepper, and eggplant) and Apiaceae (i.e., fennel and parsley) elicited high levels of bait-feeding activity, indicating that these vegetables were not highly preferred. The plants tested from Liliaceae, Cucurbitaceae, Asteraceae, and Brassicaceae elicited an intermediate-to-low level of bait feeding.     

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.     

Hindlimb muscle activity during locomotion in the rat (Rattus norvegicus) (Rodentia: Muridae)

Electromyographic studies of mammalian locomotion have concentrated on cursorial species. Since these may not be typical of mammals in general, the present study has been made on the relatively non-cursorial rat.
Electromyography has been performed on 20 muscles or muscle groups of the hind-limb in decerebrate rats, moving at from one to eight steps per second. All muscles were active in discrete bursts, with fixed phase relations in the step cycle. They can be categorized as flexors–active just before and during swing, extensors/adductors–active just before and during stance, muscles controlling the foot, and some double joint muscles. The latter, represented by semitendinosus and rectus femoris, tend to be active twice in each step cycle. There is a distinct reciprocity in the activities of these two muscles. The duration of the extensor/adductor activity decreases with increase of stepping speed.
The pattern of muscle activity during the step cycle is very similar in both cursorial species and the rat. This suggests that central nervous mechanisms controlling the timing of single limb motor output in mammals may be very conservative.     

Population dynamics of the rat Microryzomys minutus (Rodentia: Muridae) in the Venezuelan Andes

The population dynamics of the small forest rice rat Microryzomys minutus, a murid rodent that occurs in the high altitudes of the northern and central Andes, was studied in disturbed and primary environments in a cloud forest of the Venezuelan Andes (Juan Pablo Pe?aloza National Park, 8 degrees 11'N, 71 degrees 49'W). We collected 121 animals (66 female female and 55 male male) between 1995 and 1998, using pitfall traps with formalin. Adult males were heavier than adult females. Relative abundance was much greater in the disturbed environments (over 10 individuals in some periods) than in the primary cloud forest: 4-8 individuals. In the disturbed environments, the rats were extremely abundant in the first sampling period, and less frequent afterwards. In the cropland, abundance showed some fluctuations during the study and displayed two small abundance peaks in March-June 1997 and 1998. In the mined area, the rats had irregular fluctuations until March-June 1997 and were not recorded in July-October 1997. The occurrence of this rat in both disturbed and natural habitats confirms the wide ecological tolerance of this species.     

DNA barcoding of Murinae (Rodentia: Muridae) and Arvicolinae (Rodentia: Cricetidae) distributed in China

Identification of rodents is very difficult mainly due to high similarities in morphology and controversial taxonomy. In this study, mitochondrial cytochrome oxidase subunit I (COI) was used as DNA barcode to identify the Murinae and Arvicolinae species distributed in China and to facilitate the systematics studies of Rodentia. In total, 242 sequences (31 species, 11 genera) from Murinae and 130 sequences (23 species, 6 genera) from Arvicolinae were investigated, of which 90 individuals were novel. Genetic distance, threshold method, tree‐based method, online BLAST and BLOG were employed to analyse the data sets. There was no obvious barcode gap. The average K2P distance within species and genera was 2.10% and 12.61% in Murinae, and 2.86% and 11.80% in Arvicolinae, respectively. The optimal threshold was 5.62% for Murinae and 3.34% for Arvicolinae. All phylogenetic trees exhibited similar topology and could distinguish 90.32% of surveyed species in Murinae and 82.60% in Arvicolinae with high support values. BLAST analyses yielded similar results with identification success rates of 92.15% and 93.85% for Murinae and Arvicolinae, respectively. BLOG successfully authenticated 100% of detected species except Leopoldamys edwardsi based on the latest taxonomic revision. Our results support the species status of recently recognized Micromys erythrotis, Eothenomys tarquinius and E. hintoni and confirm the important roles of comprehensive taxonomy and accurate morphological identification in DNA barcoding studies. We believe that, when proper analytic methods are applied or combined, DNA barcoding could serve as an accurate and effective species identification approach for Murinae and Arvicolinae based on a proper taxonomic framework.     

Patterns of morphological evolution in the mandible of the house mouse Mus musculus (Rodentia: Muridae)

The worldwide distributed house mouse, Mus musculus, is subdivided into at least three lineages, Mus musculus musculus, Mus musculus domesticus, and Mus musculus castaneus. The subspecies occur parapatrically in a region considered to be the cradle of the species in Southern Asia (‘central region’), as well as in the rest of the world (‘peripheral region’). The morphological evolution of this species in a phylogeographical context is studied using a landmark‐based approach on mandible morphology of different populations of the three lineages. The morphological variation increases from central to peripheral regions at the population and subspecific levels, confirming a centrifugal sub‐speciation within this species. Furthermore, the outgroup comparison with sister species suggests that M. musculus musculus and populations of all subspecies inhabiting the Iranian plateau have retained a more ancestral mandible morphology, suggesting that this region may represent one of the relevant places of the origin of the species. Mus musculus castaneus, both from central and peripheral regions, is morphologically the most variable and divergent subspecies. Finally, the results obtained in the present study suggest that the independent evolution to commensalism in the three lineages is not accompanied by a convergence detectable on jaw morphology. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 635–647.     

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.     

Breeding season, litter size and nestling mortality of the Harvest mouse, Micromys minutus (Rodentia: Muridae), in Britain

Data are presented on the breeding biology of Micromys minutus in Britain. It is shown that although litters are produced over a protracted period (May-December), 74% of the litters are born in August and September. Mean litter size is 5·40±0·16( n = 62), which is a significant reduction on the mean litter size of 6·75±0·40( n = 16) calculated from pre-1917 literature. Litter size was found to be constant throughout the breeding season, and there was no difference in mean litter size between two samples collected close to the northern and southern limits of the known British range. By comparing the mean litter size of samples 1–5, 6–10 and 11+ days old, no significant loss of individual mice within litters could be detected, although 12·3% of all litters died prior to weaning. This loss was predominantly of autumnal litters, cold and wet being important climatic factors that terminate the breeding season. Comparisons are made with data from other parts of the animal's range.     

A review of habitat selection by the swamp rat,Rattus lutreolus (Rodentia: Muridae)

Abstract This review clarifies important points on habitat selection by the Swamp Rat Rattus lutreolus (Rodentia: Muridae), a species that has been the subject of much research in Australia and has provided a useful model for understanding ecological and biological processes. It also provides an opportunity to cite important earlier research, not readily available through electronic search engines, thus bringing it into current literature to avoid its disappearance into Internet obscurity. We comment on some papers in the literature to correct errors detected and to emphasize the importance of due care in all aspects of a research project, including its reporting. We show that both floristic and structural components have been reported as important to an understanding of habitat and microhabitat selection by R. lutreolus and conclude that it is vegetation density that is of paramount importance. Female R. lutreolus are clearly dominant in driving microhabitat selection, occupying the ‘best’ or densest habitats with male R. lutreolus occupying the next best and Pseudomys or other species, where present occupying the remainder. This demonstrates the important role that intraspecific and interspecific competition play in determining habitat selection. Direct predation and the perception of predation risk may also play a role in habitat selection, again perceived to be pushing individuals towards denser vegetation, representing ‘better cover’. Whether these effects operate as bottom‐up or top‐down needs careful consideration. Climatic variables, such as ENSO‐affecting productivity, and related variables such as temperature and humidity may also play important roles in habitat selection, as can disturbance effects such as wildfire. The relative importance of all of these potential determining factors may vary from place to place, particularly when climatic clines are involved.     

Comparative water balance in two species of Liomys (Rodentia: Heteromyidae)

• 1.1. Water metabolism in Liomys irroratus and L. pictus was studied by measuring water loss and gain by several routes.
• 2.2. Urine concentrations and fecal water contents were similar in the two species; L. pictus experiences significantly higher evaporative water loss than does L. irroratus.
• 3.3. Observed differences in water loss between the two species are largely a function of parameters related to weight-specific metabolic rate; the differential water losses are offset by differences in metabolic water production and ease of obtaining free water, so that the two species appear equally capable of attaining water balance.
• 4.4. The physiological characteristics of these two species are discussed relative to their respective ecological distributions and to a current hypothesis about the evolution of Liomys.

     

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%.     

Genetic variation and evolution in the genus Apodemus (Muridae: Rodentia)

Genetic variation was studied using protein electrophoresis of 28–38 gene loci in 1347 specimens of Apodemus agrar-ius, A. peninsulae, A. flavicollis, A. sylvaticus, A. alpicola, A. uralensis, A . cf. hyrcanicus, A. hermonensis, A. m. mystacinus and A. m. epimelas , representing 121 populations from Europe, the Middle East, and North Africa. Mean values of heterozygosity per locus for each species ranged from 0.02 to 0.04. Mean values of Nel's genetic distance ( D ) between the taxa ranged from 0.06 (between A. flavicollis and A. alpicola) to 1.34 (between A. uralensis and A. agrarius ). The highest values of D were found between A. agrarius and other Apodemus species (0.62-1.34). These values correspond to those generally observed between genera in small mammals. Our data show that A. agrarius and A. peninsulae are sister species, well-differentiated from other taxa. High genetic distance between A. m. mystacinus and A. m. epimelas leads us to consider them distinct species and sister taxa to other Western Palaearctic species of the subgenus Sylvaemus . The data also suggest a recent separation of members of the latter group from a common ancestor, and subsequent rapid radiation, making it difficult to infer phylogenetic relationships. Some taxonomic implications of the results are discussed further.© 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 395–419.     

Population dynamics of the wood mouse Apodemus sylvaticus (Rodentia: Muridae) in a Sitka spruce successional mosaic

A population of wood mice, Apodemus sylvaticus (L.), was studied by capture-mark-recapture, in five 0.81 ha grids within a habitat mosaic produced by the felling of a plantation of mature Sitka spruce ( Picea sitchensis Carriere). From May 1990 to June 1992, we estimated population sizes, survival (total and by weight classes), recruitment, and home-range sizes, usually at monthly intervals, for the study area taken as a whole. Inter-grid movements were frequent for both sexes, supporting the assumption that the population could be analysed in this way. Wood mice were more abundant in 1991 than in 1990, associated with increased seed supply. In both years, numbers were low in spring and increased gradually towards an autumn peak, which was of similar size in both years. Male home-range areas varied seasonally, and were negatively correlated with population sizes, while female home ranges showed little seasonal variation. Survival and recruitment both declined sharply in late autumn, apparently in a densitydependent way. Except for this latter result, the population dynamics in a heterogeneous coniferous woodland were consistent with those described previously for this species in more homogeneous deciduous woodlands, suggesting that the same regulatory processes are operating in both habitats.     

Chromosomal banding pattern and idiogram of the cotton rat,Sigmodon arizonae (Rodentia,Muridae)

A procedure for obtaining G-bands on chromosomes of mammals is outlined. The procedure was utilized in an investigation of the idiogram and banding pattern of the mitotic chromosomes of the cotton rat, Sigmodon arizonae. The diploid number of this species is 22, and each pair of homologues is easily separated on the basis of size, centromeric position, and banding pattern. The autosomes are represented by four pairs of large submetacentric chromosomes, three pairs of medium to small submetacentric chromosomes, two pairs of large subtelocentric chromosomes and one pair of small acrocentric chromosomes. The X chromosome is acrocentric and averages from 5.42% to 5.46% of the haploid female complement. The Y chromosome is a minute acrocentric and easily separated from the smallest acrocentric autosome. The usefulnes of Sigmodon arizonae as a laboratory animal for cytogenetic studies is substantiated.