Population genetic structure of two ecologically distinct multimammate rats: the commensal Mastomys natalensis and the wild Mastomys erythroleucus in southeastern Senegal

Using the same set of microsatellite markers, we compared the population genetic structure of two Mastomys species, one being exclusively commensal in southeastern Senegal, and the other being continuously distributed outside villages in this region. Both species were sampled in the same landscape context and at the same spatial scale. According to the expectations based on the degree of habitat patchiness (which is higher for commensal populations in this rural area), genetic diversity was lower and genetic differentiation was higher in commensal populations of Mastomys natalensis than in wild populations of Mastomys erythroleucus. Contrasting estimates of effective dispersal and current migration rates corroborates previous data on differences in social structure between the two species. Isolation-by-distance analyses showed that human-mediated dispersal is not a major factor explaining the pattern of genetic differentiation for M. natalensis, and that gene flow is high and random between M. erythroleucus populations at the spatial scale considered.     

Effects of predation and dispersal on Mastomys natalensis population dynamics in Tanzanian maize fields

1. We investigate the effects of different levels of predation pressure and rodent dispersal on the population dynamics of the African pest rodent Mastomys natalensis in maize fields in Tanzania. 2. Three levels of predation risk were used in an experimental set-up: natural level (control), excluding predators by nets and attracting avian predators by nest boxes and perch poles. Because dispersal of the rodents could mask the predation pressure treatment effects, control and predator exclusion treatments were repeated with enclosed rodent populations. 3. Population growth during the annual population rise period was faster in the absence of predators and peak population size was higher, but otherwise dynamics patterns were similar for populations where predators had access or were attracted, indicating that compensatory mechanisms operate when rodents are exposed to high levels of predation risk. Reducing dispersal of rodents removed the effect of predation on population growth and peak size, suggesting that local predators may play a role in driving rodent dispersal, but have otherwise little direct effect on population dynamics.     

Experimentally induced infection with autonomous parvoviruses, minute virus of mice and H-1, in the African multimammate mouse (Mastomys coucha)

To determine whether the multimammate mouse (Mastomys coucha) could be used to evaluate rodent parvovirus-based vectors, neonates were subcutaneously inoculated with minute virus of mice (prototype strain, MVMp) or rat parvovirus H-1. The course of infection with both viruses was similar. Seroconversion occurred within two weeks after virus inoculation, as detected by use of hemagglutination-inhibition assays, and antibody titers remained high for the entire observation period of 12 months. Viral DNA and infective virions were detected in several organs of inoculated animals prior to seroconversion, as measured by use of Southern blotting and plaque assays, respectively. Infective particles subsequently became undetectable, whereas viral DNA imprints persisted in distinct organs for at least nine months. Clinical signs of parvovirus infection appeared around six weeks after virus inoculation, and consisted of hemorrhages, stunted growth, and transient hair color changes. Sudden death occurred in a significant fraction of animals infected with MVMp, but not H-1 virus, at the time of weaning. Altogether, MVMp, which is innocuous to its natural host, the mouse, and H-1 virus, which is poorly pathogenic to the rat, appear to be pathogenic for Mastomys coucha.     

Life-history decisions under predation risk: Importance of a game perspective

We model ontogenetic shifts (e.g. in food or habitat use) during development under predation risk. We ask whether inclusion of state and frequency dependence will provide new insights when compared with game-free life-history theory. We model a simple biological scenario in which a prey animal must switch from a low-predation, low-growth habitat to a high-predation, high-growth habitat. To assess the importance of frequency dependence, we compare the results of four scenarios of increasing complexity: (1) no predation; (2) constant predation; (3) frequency-dependent predation (predation risk diluted at high prey density); and (4) frequency-dependent predation as in (3) but with predators allowed to respond adaptively to prey behaviour. State dependence is included in all scenarios through initial size, assumed to be environmental. A genetic algorithm is used to search for optimal solutions to the scenarios. We find substantially different results in the four different scenarios and suggest a decision tree by which biological systems could be tested to ascertain which scenario is most applicable.     

Seasonal variation in growth of Mastomys natalensis (Rodentia: Muridae) in Morogoro, Tanzania

The paper describes seasonal growth variation in a free living population of Mastomys natalensis (Smith, 1834) from Morogoro, Tanzania. Growth patterns are associated with rainfall patterns. Young animals enter a growth stop at the end of the dry season (October-November) and growth is only resumed after the first heavy rains. Reproduction is more related to size than to age. If the heavy rains come early in the rainy season, animals start reproducing in the beginning of the year. The resulting young reach their maximal size without growth stop and start reproducing immediately. Possible causes for the growth stop are discussed. Growth phenomena are thought to explain at least partially the relation between rainfall and reproduction in Mastomys .

Résumé

Cet article décrit la variation de croissance saisonnière d'une population de Mastomys natalensis (Smith, 1834) vivant en libertéà Morogoro, en Tanzanie. Les graphiques de croissance sont associés à ceux des chutes de pluie. Les jeunes animaux connaissent un arrêt de la croissance à la fin de la saison sèche (octobre-novembre) et la croissance ne reprend qu'après les premières fortes pluies. La reproduction est plus liée à la taille qu'à l'âge. Si les fortes pluies surviennent tôt en saison des pluies, les animaux commencent à se reproduire au début de l'année. Les jeunes atteignent alors leur taille maximale sans avoir connu d'arrêt de croissance et commencent à se reproduire immédiatement. On pense que les phénomènes de croissance expliquent au moins partiellement la relation entre les chutes de pluie et la reproduction chez Mastomys .     

Xanthine oxidase, superoxide dismutase, catalase and lipid peroxidation in Mastomys natalensis: effect of Dipetalonema viteae infection

Status of xanthine oxidase, superoxide dismutase, catalase and lipid peroxidation, the enzymes metabolizing reactive oxygen intermediates in liver, lungs and spleen of M. natalensis during D. viteae infection was investigated. Xanthine oxidase and lipid peroxidation exhibited stimulation, while superoxide dismutase and catalase showed depression in liver and spleen of the infected animals. The filarial infection therefore appears to create O2 toxicity in these tissues. Lungs, on the other hand was found safe as it possessed elevated xanthine oxidase, superoxide dismutase and catalase. Lipid peroxidation in lungs operated below the control level. The impact of these changes in the establishment and development of the infection has been discussed.     

Sparrows and a brushpile: Foraging responses to different combinations of predation risk and energy cost

Our observations of wintering house sparrows (Passer domesticus) feeding on cracked corn at feeders placed at different distances from a brushpile and in positions differentially exposed to the wind supported the hypothesis that where food patches are equal in net energy return, foragers use the one furnishing the most protection from predation. Results reinforced the hypothesis that when food sources furnish equal protection from predators, homeotherms below their lower critical temperature use the one providing the largest net energy return. When the sparrows had available both a colder, safer feeding site and a warmer, riskier one, they frequented both over the course of the winter and, as predicted, their use of the colder, safer site was negatively correlated with wind velocity and positively related to temperature and solar radiation. In this last case, it appeared the birds decided where to feed on the basis of some threshold difference between metabolic rates at the colder, safer site and the warmer, riskier location.     

Increased incidence of squamous cell carcinomas in Mastomys natalensis papillomavirus E6 transgenic mice during two-stage skin carcinogenesis

Papillomaviruses cause certain forms of human cancers, most notably carcinomas of the uterine cervix. In contrast to the well-established involvement of papillomavirus infection in the etiology of cervical carcinomas and in carcinomas of a rare hereditary condition, epidermodysplasia verruciformis, a causative role for cutaneous human papillomavirus types in the development of nonmelanoma skin cancer has not been proven. In order to better understand the functions of individual genes of cutaneous papillomavirus types, we generated transgenic mice carrying oncogene E6 of the Mastomys natalensis papillomavirus (MnPV), which causes keratoacanthomas of the skin in its natural host. In the present study, we demonstrate that under conditions of experimental two-stage skin carcinogenesis, fast-paced squamous cell carcinomas develop in nearly 100% of MnPV E6 transgenic mice in comparison to 10% in their nontransgenic littermates (log rank test; P < 0.0001). Therefore, we conclude that the MnPV E6 transgene favors the malignant progression of chemically induced tumors. Whereas an activating H-ras mutation is a consistent feature in benign and malignant tumors in wild-type mice, the majority of papillomas and keratoacanthomas and all squamous cell carcinomas obtained in MnPV E6 transgenic mice contain nonmutated ras alleles. These results indicate that the development of squamous cell carcinomas in MnPV E6 transgenic mice does not depend on an activated H-ras oncogene.     

Hepatic superoxide dismutase, catalase and lipid peroxidation products in Mastomys natalensis infected with Plasmodium berghei

P. berghei infection in M. natalensis caused a significant reduction in the hepatic SOD and catalase activities. Cu-Zn SOD was more susceptible to infection than Mn SOD. The inhibition of enzyme activities was associated with marked increase in the levels of lipid peroxides, lipid hydroperoxides and conjugated dienes in infected M. natalensis. The alterations in the hepatic SOD, catalase and lipid peroxides are related with the severity of infection.     

The distribution, identification, and naming of the Mastomys natalensis species complex in southern Africa (Rodentia: Muridae)

Three hundred and forty seven rats belonging to the Mastomys natalensis complex (Smith, 1834) were live trapped from 60 localities in southern Africa. They were identified as species A, or B using either or both diploid chromosome number and haemoglobin electromorphs. These, and previously published data are presented to give a distribution of the species in southern Africa. It is suggested that workers may safely use the haemoglobin marker for identification purposes in this region as opposed to the more difficult chromosome marker. We suggest that species A can be referred to M. natalensis (Smith, 1834), and species B to M. coucha (Smith, 1836). We consider the two other oldest synonyms, M. caffer (Smith, 1834), and M. marikquensis (Smith, 1836).     

Morphological and histochemical study of the submandibular gland in Praomys (Mastomys) natalensis

The submandibular gland in female and male Praomys (Mastomys) natalensis (a South African multimammate rodent) was studied using light microscopy and techniques for the demonstration of carbohydrates. Hematoxylin and eosin stain revealed the presence of a single secreting component that gave a strongly positive PAS reaction. Limiting elements of the granular tubules gave a weakly positive PAS reaction. Acidic glycoproteins were evidenced only in granules of the acinar component.     

Capillaria hepatica infection of Mastomys natalensis: on the development, egg production and host reaction (author's transl)]

Studies on the development and egg production of Capillaria hepatica and on the macroscopically visible alterations of the liver and spleen of the host were carried out in experimentally infected Mastomys natalensis. Following the oral administration of infective eggs the first stage larvae hatched in the caecum of fasting and fed animals after about 8 and 15 hours respectively. The prepatency could be found with 20 days. The dynamics and duration of egg production of the parasite proved to be dependent on the infective dose. After the first week of patency increasing numbers of eggs/liver were found with increasing doses of infection up to 800 eggs per animal. This relation could not be observed 76 days post infection. After infections with 50, 300 und 800 eggs per animal maximum egg production was found between 60 and 72, 36 and 48 and about 30 days p.i., respectively. The egg production of the parasites correspondently continued for more than 85 days after infection or had ceased 72 or 48 days p.i. Intraperitoneal administration of infective eggs revealed a lower infection rate, evaluated by the number of eggs per liver, than oral infection.     

Morphological and histochemical studies on the parotid gland of Praomys (Mastomys) natalensis

The parotid gland of Praomys (Mastomys) natalensis follows the same anatomical pattern of Rodentia since no peculiar morphological and histochemical features were found in the present study that differentiate it from homologous glands in other rodents. It consists of serous secreting components and intralobular ducts that demonstrate no sexual dimorphism. Histochemical studies reveal that the glandular cells of the Praomys' parotid gland contain no acid mucosubstance, but that material of a neutral glycoprotein nature can be found in the secreting cells of acini, epithelium of the ducts, and the ductal lumina.