Letteratura scientifica selezionata sul tema "Muridae africa southern"

We combined evidence from biogeography, craniodental traits, linear and geometric morphometrics (233 skulls), cytogenetics (karyotypes of 18 individuals) and mitochondrial DNA sequences (44 cytochrome b and 21 12S rRNA sequences) to test species limits within Otomys typus s.l. (Muridae: Murinae: Otomyini), a complex that is patchily distributed across alpine zones of Ethiopia and East Africa. Our results confirm the specific validity of O. dartmouthi, O. jacksoni, O. orestes, and O. uzungwensis, forms recently removed from synonymy under typus s.l.; support elevation of four other alpine forms to species (O. fortior, O. helleri, O. thomasi, and O. zinki); identify three additional new species (O. cheesmani sp. nov., O. simiensis sp. nov., O. yaldeni sp. nov.); and enable redefinition of O. typus s.s. as a species restricted to certain mountains west of the Great Rift Valley in Ethiopia (Simien and Guna Mountains in the north, extending to the highlands of the western rim of the Rift Valley). Phylogenetic interpretation of the cytochrome b data clearly demonstrates that the alpine morphotype once united under O. typus s.l. has originated independently at high elevations on several mountain ranges in eastern and northeastern Africa; although generally adapted to high-elevation vegetation, such alpine species are ecologically segregated from one another. Patterns of morphometric, genetic, and ecological differentiation among populations once misassigned to nominal O. tropicalis and O. typus more parsimoniously reflect regional cladogenesis along elevational gradients, rather than multiple, successive colonization by different ancestral forms from southern Africa as earlier supposed. Although incomplete and preliminary, information gathered for O. tropicalis indicates that it too is a species composite; several lines of research are discussed to redress its polyphyletic content. Our results, together with other recent taxonomic studies of Otomys, appreciably elevate the level of endemism within eastern Africa and underscore the significance of Africa's eastern highlands to the continental diversification of Otomyini.

The systematics of the African rodent genus Gerbilliscus is still a matter of debate. At the genus level it has been said toinclude the related genus Gerbillurus, and at the species level some species still need to be definitely recognized as dis-tinct. To tackle these questions, we gathered and analyzed mitochondrial (cytochrome b) and nuclear (BRCA1) gene se-quences in a number of specimens representing ten species of Gerbilliscus and three species of Gerbillurus. Phylogeneticreconstructions confirm that Gerbillurus should be considered a synonym of Gerbilliscus. They also clearly show that spe-cies diversity in this group is spatially organized, with geographically well-defined species groups covering major areasof sub-Saharan Africa, namely Southern, Eastern and Western Africa. In the latter area, a well-supported genetic lineageappears to correspond to a hitherto overlooked species, also characterized by a distinctive karyotype. This species is char-acterized by an overall large size, a relatively long tail, a distinct karyotype, and represents a well-differentiated geneticcluster. It ranges from Benin to Guinea in Sudano-Guinean forest-savanna mosaic habitats, where it can be sympatric withthe congeneric species G. kempi and G. guineae. Detailed body and skull morphological and biometrical analyses per-formed on samples of the West African species, including type specimens described in this region, suggest that this speciesmay correspond to G. kempi. If confirmed, this would imply that what is currently named G. kempi would deserve another species name, the most likely of which would be G. giffardi.

African rock rats of the genera Aethomys Thomas, 1915 and Micaelamys Ellerman, 1941, are endemic to East, Central and southern Africa but extend marginally into West Africa. In the past 16 subspecies have been described in the Namaqua rock mouse M. namaquensis Smith, 1834. Recent morphometric and morphological patterns of intraspecific variation suggested the recognition of only four subspecies: M. n. namaquensis, M. n. alborarius, M. n. monticularis and M. n. lehocla, of which the distributions appeared to coincide with the major phytogeographical zones of southern Africa. In the present study earlier analyses of mitochondrial DNA (mtDNA) cytochrome b (cyt b) gene variation were extended. Taken together these results show that M. namaquensis represents a polytypic species complex but with much more diversity than detected using morphology. Phylogenetic and phylogeographic analyses revealed 14 genetically distinct lineages of which several show strong geographic association with particular vegetation biomes or bioregions. The distributional ranges of eight of these lineages showed some correspondence with the type localities of previously described subspecies of M. namaquensis. Some clades displayed considerable within-lineage variation indicating possible fine-scale population structuring, while others showed very little differentiation. Divergence times between lineages varied between 7.26 MYA and 2.70 MYA, corresponding to a Late Miocene to Pliocene radiation. Cytochrome b sequences alone do not fully resolve the evolutionary relationships among the lineages and the phylogenetic analysis was thus supplemented with nuclear Recombination Activating Gene 1 (RAG1) sequences. This gene was successfully sequenced for 11 of the identified lineages. Independent analyses of the two genes were not congruent possibly as a result of incomplete lineage sorting of the nuclear gene. The combined dataset yielded good support for six of the lineages. Finally, a more detailed phylogeographic analysis was conducted among ten localities of the Eastern Kalahari Bushveld lineage based on mitochondrial cyt b sequences to elucidate processes underlying diversification in this species complex. A genetic pattern of phylogenetic continuity with a lack of spatial separation was observed. The mismatch distribution analysis suggests that the lineage has expanded its population size and the geographical expansion may have followed environmental changes in the recent past. Estimates of female gene flow indicate connectivity among localities but not to the extent expected for a panmictic population. Instead a combination of a stepping-stone model and metapopulation dynamics may be applicable to this lineage. Examination of type material of described subspecies is needed to resolve the identity of the unique lineages which will allow us to better understand the phylogeography and mode of speciation in M. namaquensis. In addition, localities of sympatry (lineages in sympatry) should also be studied in more detail in order to help resolve the current taxonomic uncertainties within M. namaquensis. Future research should therefore include a multidisciplinary approach, such as cytogenetics, morphology and more gene regions. Copyright
Thesis (PhD)--University of Pretoria, 2010.
Genetics
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Phylogeographic mitochondrial DNA (mtDNA) population structure was determined for Aethomys namaquensis and A. ineptus from southern Africa and Swaziland. It was evident from the study that A. namaquensis reflected a pattern of phylogenetic discontinuity with and without spatial separation between populations. Previously documented mtDNA phylogeographic patterns recorded in the rock hyrax, Procavia capensis and the red rock rabbit species, Pronolagus rupestris and P. randensis, coincided with the phylogeographic break that was detected in one of the mtDNA lineages (C) within A. namaquensis. Similar vicariant events may have been responsible for shaping evolutionary processes in the independent Procavia, Pronolagus and Aethomys lineages. In contrast, A. ineptus showed a pattern of shallow phylogeographic structuring. The marked genetic differences detected in A. namaquensis and A. ineptus may reflect the influences of habitat specificity, its fragmentation and the effects of life history on mtDNA gene flow. The study also revealed three genetically well-supported lineages within A. namaquensis: a lineage (A) found in the Limpopo valley, a lineage (B) widely distributed across the Karoo and a lineage (C) found across the grasslands of the North-West, Limpopo and Mpumalanga Provinces. These spatial distributions broadly coincided with the ranges of four previously proposed morphologically defined subspecies. From the present sample sizes, there is only good support, from a molecular point of view, for the subspecies A. n. lehocla (lineage B). In addition to the three well-supported lineages, six geographically restricted lineages were identified that could not be assigned to any of the four previously proposed subspecies, A. n. namaquensis, A. n. monticularis, A. n. alborarius and A. n. lehocla. Molecular techniques, specifically the analysis of the mtDNA cytochrome b gene, have been useful in the identification of sibling species. This technique has also proved to be useful in the identification of two cryptic species, A. chrysophilus and A. ineptus in this study. Phylogenetic analysis revealed two maternal groups corresponding to A. chrysophilus and A. ineptus. Distributional data of these two species, suggest that A. chrysophilus occupies the low elevations of the Limpopo River drainage, while A. ineptus occupies the remainder of South Africa at higher elevations, but expands into lower elevations in the southern portion of its range. Phylogenetic relationships among four southern African species of Aethomys suggest the presence of two clades that included: 1) A. chrysophilus and A. ineptus and 2) A. namaquensis and A. granti. This study, however, revealed that Aethomys may be paraphyletic, suggesting that the allocation of A. namaquensis and A. granti to the subgenus Micaelamys needs to be investigated further.
Dissertation (MSc (Genetics))--University of Pretoria, 2006.
Genetics
unrestricted

Since the energy available to an animal for cell growth, thermoregulation, reproduction and other physiological functions is highly dependent on seasonal environmental changes many small mammals breed seasonally during times when environmental conditions are most favourable for growth and survival of the young. In the tropics and sub-tropics, seasonal rainfall appears to be the main reason for seasonal breeding. In order to maximize fitness, it is important for an animal to be able to anticipate these seasonal changes and to trigger reproductive events at the correct time. Photoperiod is used to time reproduction in many temperate mammalian species, but is also used by several seasonally breeding sub-tropical and tropical mammals. The neuroendocrine system is crucial in relaying these environmental signals to the reproductive system. A number of recent studies have suggested that kisspeptin may play a major part in the regulation of the hypothalamo-pituitary-gonadal axis and ultimately reproduction. The exact role of kisspeptin signalling in seasonal breeders is, however, unclear. The present study investigated the seasonality of reproduction and the reproductive photoresponsiveness of two southern hemisphere species, the spiny mouse (Acomys spinosissimus) and the Eastern rock elephant-shrew (Elephantulus myurus) from South Africa. Furthermore, it compared hypothalamic kisspeptin expression in males and females of both species between the breeding and non-breeding seasons to ascertain if kisspeptin had any potential role in seasonal breeders under natural conditions. Both A. spinosissimus and E. myurus breed seasonally in South Africa. The breeding season extended through the spring and summer months, whereas the gonads were regressed and steroid hormone levels of both sexes were low during the autumn and winter months of the southern hemisphere. Testes mass and volume of A. spinosissimus were smaller and plasma testosterone concentrations lower under short-day than long-day photoperiods which implies that male spiny mice are reproductively photoresponsive. In contrast, male E. myurus did not appear to be responsive to changing photoperiods and testes size and seminiferous tubule diameter did not differ between photoperiods. It may be possible that other environmental factors such as changes in food availability and/or social factors influence seasonal reproduction in E. myurus. In E. myurus and male A. spinosissimus, kisspeptin-immunoreactivity was significantly lower during the non-breeding than the breeding seasons suggesting that kisspeptin may be important for the regulation of the reproductive axis to seasonal environmental changes. In contrast, kisspeptin-immunoreactivity did not differ between the breeding and non-breeding seasons in female A. spinosissimus, but was higher in pregnant than in non-pregnant females implying a differential regulation of the reproductive system of males and females of this species by kisspeptin. In conclusion, seasonal environmental changes trigger similar reproductive responses in these two phylogenetically very distinct species. However, A. spinosissimus may be energetically more restricted than E. myurus because of its small body size and judging from the lack of responsiveness to photoperiod, E. myurus may follow a more opportunistic breeding strategy. In both species, kisspeptin seems to be important in the regulation of the reproductive system to environmental changes.
Thesis (PhD)--University of Pretoria, 2011.
Zoology and Entomology
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