1. ¹Muséum National d'Histoire Naturelle, Laboratoire Origine, Structure et Evolution de la Biodiversité, FRE CNRS 2695, 55, rue Buffon, Paris F75005, France
2. ²Russian Academy of Sciences, Severtsov Institute of Ecology and Evolution, Moscow, Russia
3. ³Institut de Recherche pour le Développement, Laboratoire de Mammalogie (CBGP, UMR 022), BP 2528, Bamako, Mali

Correspondence: G Dobigny, Current address: Institut de Recherche pour le Développement, Centre de Biologie et de Gestion des Populations, Campus de Baillarguet, CS30016, 34988 Montferrier-sur-Lez Cedex, France. E-mail: dobigny@mpl.ird.fr

Received 7 February 2005; Accepted 18 July 2005; Published online 17 August 2005.

Abstract

West African gerbils of the genus Taterillus constitute a complex of seven sibling species distributed from sudano-guinean to saharo-sahelian regions. They display radically rearranged karyotypes despite low genic divergence and a very recent differentiation, that is, within the last 0.4 Myr for the six most derived species. We here provide a comparison of the seven specific karyotypes and perform a cladistic analysis using chromosomal rearrangements character states. When a posteriori polarized mutations were mapped onto the phylogenetic tree, 38 rearrangements were identified as fixed during the evolution of these rodents. This makes Taterillus one of the most striking examples of accelerated chromosomal evolution within placental mammals. Taking into account the types of chromosomal changes involved, divergence times between lineages, genetic distances, as well as reassessed geographic distributions, we suggest that (1) speciation in West African Taterillus was driven by chromosomal changes, and (2) the paleoclimatic oscillations of the Sahara desert have played a major role in their evolution. In particular, elevated plasticity of the Taterillus genome, as suggested by the patterns observed for some repetitive elements, would have led to a higher probability of mutation. We hypothesize that the process underpinning cladogenesis most probably involved highly underdominant genomic rearrangements that were fixed following pronounced populational bottlenecks resulting from drastic climatic and subsequent environmental changes. Major African rivers formed significant barriers to dispersal, limiting expansion during the more moist and so favorable periods. This scenario would explain the current parapatric species distributions and their relationship to the West African hydrographic features.