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Arvicanthis Niloticus (Arvicanthi + niloticu)
Selected AbstractsDaily rhythms and sex differences in vasoactive intestinal polypeptide, VIPR2 receptor and arginine vasopressin mRNA in the suprachiasmatic nucleus of a diurnal rodent, Arvicanthis niloticusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2009M. M. Mahoney Abstract Diurnal and nocturnal animals differ with respect to the time of day at which the ovulatory surge in luteinizing hormone occurs. In some species this is regulated by the suprachiasmatic nucleus (SCN), the primary circadian clock, via cells that contain vasoactive intestinal polypeptide (VIP) and vasopressin (AVP). Here, we evaluated the hypothesis that chronotype differences in the timing of the luteinizing hormone surge are associated with rhythms in expression of the genes that encode these neuropeptides. Diurnal grass rats (Arvicanthis niloticus) were housed in a 12/12-h light,dark cycle and killed at one of six times of day (Zeitgeber time 1, 5, 9, 13, 17, 21; ZT 0 = lights-on). In-situ hybridization was used to compare levels of vip, avp and VIP receptor mRNA (vipr2) in the SCN of intact females, ovariectomized females, ovariectomized females given estradiol and intact males. We found a sex difference in vip rhythms with a peak occurring at ZT 13 in males and ZT 5 in intact females. In all groups avp mRNA rhythms peaked during the day, from ZT 5 to ZT 9, and had a trough in the dark at ZT 21. There was a modest rhythm and sex difference in the pattern of vipr2. Most importantly, the patterns of each of these SCN rhythms relative to the light,dark cycle resembled those seen in nocturnal rodents. Chronotype differences in timing of neuroendocrine events associated with ovulation are thus likely to be generated downstream of the SCN. [source] Effects of climate and local aridity on the latitudinal and habitat distribution of Arvicanthis niloticus and Arvicanthis ansorgei (Rodentia, Murinae) in MaliJOURNAL OF BIOGEOGRAPHY, Issue 1 2004B. Sicard Abstract Introduction, The genus Arvicanthis (Lesson 1842) (Rodentia: Murinae), usually referred to as the unstriped grass rat, is mainly distributed in savanna and grassland habitats of Sub-Saharan Africa. Among the four chromosomal forms of Arvicanthis recently differentiated in Western and Central Africa, the one with a diploid chromosomal number (2n) of 62 and an autosomal fundamental number (NFa) of 62 or 64 is ascribed to Arvicanthis niloticus (Demarest 1822), while the one with 2n = 62 and a NFa between 74 and 76 is referred to A. ansorgei (Thomas 1910). Despite the broad area of sympatry recently uncovered along the inner delta of the Niger river in Mali [details in Volobouev et al. (2002) Cytogenetics and Genome Research, 96, 250,260], the distribution of the two species is largely parapatric and follows the latitudinal patterns of the West-African biogeographical domains, which are related to the latitudinal patterns of annual rainfall in this region. Here, we analyse the suggestion that the two species show specific adaptations to differences in climate aridity. Methods, Karyologically screened animals were sampled in 19 localities in seasonally flooded regions located along the ,Niger' river in Mali and extending from 1100 to 200 mm of mean annual rainfall. The analysis of trapping success (TS) data allowed us to investigate the respective effects of climate (i.e. annual rainfall) and local (i.e. duration of the green herbaceous vegetation) aridity on the latitudinal and habitat distribution of the two species. Conclusions, The broad zone of sympatry was found to correspond to a northward expansion of the recognized distribution area of A. ansorgei. TS values indicated that the two species responded very differently to climatic and local conditions of aridity. Arvicanthis ansorgei decreased in TS as regional conditions became more arid; a similar trend was also observed within regions where habitat occupancy decreased with local aridity. The higher TS observed in the most humid habitat relative to the others persisted throughout the latitudinal rainfall gradient. In contrast, TS of A. niloticus increased with latitudinal aridity. This species was present in more arid habitats than A. ansorgei from 1000 mm down to 400 mm of mean annual rainfall where a shift to the most humid habitat occurred. These opposite trends in TS distribution between species suggest that A. ansorgei is less adapted than A. niloticus to arid environments at both a regional and habitat level; thus, A. ansorgei would be able to invade dry regions only along the extensive floodplains bordering the inner delta of the ,Niger' river. Several biological traits that may be involved in limiting the southward distribution of A. niloticus are discussed. [source] Effects of photoperiod on the reproductive condition of Nile grass rats (Arvicanthis niloticus) from an equatorial populationAFRICAN JOURNAL OF ECOLOGY, Issue 3 2002Scott Nunes Abstract We evaluated the effects of photoperiod on the reproductive condition of male and female Nile grass rats (Arvicanthis niloticus) descended from members of an equatorial population trapped 2°S of the equator. Study animals housed in 12:12 light:dark (LD) cycles were transferred either to short photoperiod (9:15) or long photoperiod (15:9) for 9 weeks (males) or 11 weeks (females), and various reproductive parameters were assessed. We observed no differences between short- and long-day males with respect to plasma concentration of testosterone, testicular mass, seminal vesicle mass, or spermatogenesis. Similarly, we observed no differences between short- and long-day females with respect to oestrous cycles, uterine mass, follicle size, or presence of corpora lutea. Reproductive parameters of male and female A. niloticus housed in short- and long photoperiods were similar to those typically observed among animals descended from the same equatorial population and housed in LD 12:12. Thus, photoperiod appears not to elicit changes in reproductive condition among A. niloticus from populations whose native habitat lies within 2° of the equator. These data contrast with the results of other studies indicating that photoperiod alters reproductive condition in A. niloticus populations living >10° from the equator. Résumé Nous avons étudié les effets de la photopériode sur la condition reproductive des mâles et des femelles des rats Arvicanthis niloticus, issus de membres d'une population équatoriale attrapée à 2° au sud de l'Equateur. Les animaux de l'étude soumis à des cycles 12 : 12 lumière : obscurité (LD) ont été transférés dans des conditions de photopériodes courtes (9 : 15) ou longues (15 : 9) pendant 9 semaines (mâles) ou 11 semaines (femelles), et on a étudié les différents paramètres de la reproduction. Nous n'avons constaté aucune différence entre les mâles soumis aux jours longs ou courts, en ce qui concerne la concentration de testostérone dans le plasma, le poids des testicules, celui de la vésicule séminale ou la spermatogenèse. De même, nous n'avons observé aucune différence entre les femelles soumises aux jours longs ou courts en ce qui concerne le cycle oestral, le poids de l'utérus, la taille des follicules ou la présence de corps jaune. Les paramètres reproducteurs des A. niloticus mâles et femelles soumis à des photopériodes longues ou courtes étaient semblables à ceux que l'on observe classiquement chez les animaux issus de cette même population équatoriale et logés dans des conditions LD 12 : 12. Il semble donc que la photopériode ne suscite aucun changement de l'état reproductif chez les A. niloticus issus de populations dont l'habitat original se situe à 2° sous l'Equateur. Ces données sont en contradiction avec les résultats d'autres études qui montraient que la photopériode altère l'état reproductif des populations de A. niloticus vivant à plus de 10° de l'Equateur. [source] The small mammal community of a coastal site of south-west MauritaniaAFRICAN JOURNAL OF ECOLOGY, Issue 1 2002L. Granjon Abstract The small mammal community of a coastal site of south-western Mauritania was monitored using live trapping, owl pellet analysis and nocturnal visual censuses. Ten species of rodents and two shrews were recorded. Gerbillid rodents (Gerbillus nanus, G. gerbillus, G. tarabuli, G. nigeriae and Taterillus arenarius) were the most prevalent in traps, whereas a relatively large proportion of owl pellets were made up of a murid rodent, Mastomys huberti. The presence of two species of murids (M. huberti and Arvicanthis niloticus) in this presaharian environment is made possible by the presence of small patches of green vegetation associated with localized fresh water inputs. The contradiction of results from the sampling methods indicate potential biases in the determination of community composition and relative species abundance. Results are also discussed in estimating the potential role of predation and competition in this small mammal community. Résumé On a surveillé de façon continue la communauté de petits mammifères d'un site côtier du sud-ouest de la Mauritanie en servant de pièges, de l'analyse des pelotes de réjection des chouettes et de recensements visuels nocturnes. On a rapporté la présence de 10 espèces de rongeurs et de deux musaraignes. Les Gerbillidés (Gerbillus nanus, G. gerbillus, G. tarabuli, G. nigeriae et Taterillus arenarius) étaient ceux qu'on trouvait le plus dans les pièges, alors qu'une assez forte proportion de pelotes étaient constituées des restes d'un rongeur muridé, Mastomys huberti. La présence de deux espèces de muridés (M. huberti et Arvicanthis niloticus) dans cet environnement pré-saharien est rendue possible par de petits îlots de végétation verdoyante associés à des arrivées locales d'eau douce. La contradiction entre les résultats obtenus par les différentes méthodes d'échantillonnage indique la possibilité de biais dans la détermination de la composition de la communauté et l'abondance relative des espèces. On discute aussi les résultats en estimant le rôle potentiel de la prédation et de la compétition dans cette communauté de petits mammifères. [source] | ||||||||||