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We here present an inventory of rodents from Niger, mainly based on cytotaxonomic data because of the presence of many groups providing sibling species. A total of 39 species are listed, one of which is a new chromosomal form (Talerillus sp.). Moreover, three other cytotypes already described but still not specifically attributed were found (Mastomys sp., Acomys sp. and Tatera sp). New karyotypic data are presented for Gerbillus nancillus, Graphiurus cf. pan^us, Massouteria mzabi, and Xerus erythropus. Once again, the efficiency of cytotaxonomy for small mammals inventories is enhanced.Specific distribution maps of poorly known species are thus completed. No clear gradients could be observed between what is currently defined as the West and the East African faunas. The distributions are mainly structured in a latitudinal manner. The Air massif appears as a continuous prolongation of the Sahelian area, rather than as a Sahelian refuge in the Sahara. Five biogeographical groups of species were distinguished: 1) a Sudanian group in the area receiving less than 700 mm rainfall, 2) a group of very widespread species largely overlapping the Sudanian (more than 700 mm rainfall) and the Sahelian areas, and sometimes including some Saharan localities, 3) a typical Saharan group, 4) some species infeoded to the mountainous Saharan area, and 5) few strictly commensal species. A global southward extension of several taxa confirms the desertification of the Sahel, as a result of both natural global warming and human activities.Resume. -Nous avons realise un inventaire des rongeurs du Niger qui s'appuie essentiellement sur des donnees cytotaxonomiques non ambigues ä cause de la presence de nombreux complexes d'especes jumelles. Trente neuf especes ont pu etre recensees, Tune d'entre-elles correspondant ä une nouvelle forme chromosomique de Taterillus. De plus, 3 cytotypes toujours sans attribution specifique ont ete retrouves (Mastomys sp., Tatera sp. et Acomys sp.) et des donnees caryotypiques nouvelles sont presentees pour Gerbillus nancillus, Graphiurus cf. parvus, Massouteria mzabi et Xerus erythropus. Les cartes de repartition de nombreuses especes peu connues Mammalia, t. 66, n° 4, 2002: 495-523. Brought to you by | The University of Auckland Library Authenticated Download Date | 5/27/15 5:28 AM 496 MAMMALIA sont completees. Aucun gradient n'est observe entre les faunes cTAfrique occidentale et celles d'Afrique Orientale, les especes se repartissant essentiellement en fonction de la latitude. Le massif de 1'A'ir apparait plutot comme un prolongement de la zone sahelienne que comme un refuge sahelien dans le Sahara. Parmi les especes de rongeurs inventoriees, cinq grands groupes biogeographiques peuvent etre distingues: 1) des especes infeodees ä la zone soudanienne recevant moins de 700 mm; 2) un groupe d'especes tres largement reparties de la zone soudanienne (plus de 700 mm) au nord de la zone sahelienne, et incluant parfois des localites sahariennes; 3) des especes typiquement sahariennes; 4) des especes infeodees ...

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Acomys species phylogeny was reconstructed from the sequences of the cytochrome b mitochondria! gene (1141 base pairs). Tree topologies obtained with different algorithms were mostly congruent and clades are well supported, although some relationships remain unresolved. The species included in the controversial « cahirinus-dimidiatus complex » cluster together in a terminal multifurcation, the lack of resolution of which is not caused by saturation of the marker. This suggest an adaptive radiation, and a redefinition of the « cahirinus-dimidiatus complex » is proposed.A tentative phylogeographic scenario was drawn from the phylogeny, using a molecular clock to roughly estimate dates of the cladogenetic events. In this scenario, Acomys lineages successively individualize from the presumed center of origin of the genus in East Africa, towards the rest of the African continent, Arabic Peninsula and Near East. The most ancient of these events would have occurred around 9.7 to 13.7 million years ago, while the most recent is the dispersion of Acomys cahirinus across the Mediterranean Sea by humans.Resume. -La phylogenie des especes tfAcomys a ete reconstruite ä partir des sequences du gene mitochondria! du cytochrome b (1141 nucleotides). Les topologies des arbres obtenus avec differents algorithmes sont pour la plupart congruentes et les clades sont robustes, bien que certaines relations restent irresolues. Les especes du «complexe cahirinus-dimidiatus» se regroupent dans une multifurcation terminale, dont le manque de resolution n'est pas du ä la saturation du marqueur. Ce resultat suggere qu'une radiation evolutive s'est produite, et une redefinition du complexe est proposee.Un scenario phylogeographique hypothetique est tire de la phylogenie, en utilisant une horloge moleculaire pour estimer approximativement les dates des cladogeneses. Dans le scenario propose, les lignees d'Acomys s'individualisent successivement ä partir de PAfrique de 1'Est, centre d'origine presume du genre, vers le reste du continent africain ainsi que vers la Peninsule Arabique et le Proche-Orient. Le plus ancien de ces evenements se serait produit il y a 9,7 ä 13,7 millions d'annees, tandis que le plus recent est la dispersion o'Acomys cahirinus ä travers la Mer Mediterranee par FHomme.

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