Patterns of karyotype evolution in complexes of sibling species within three genera of African murid rodents inferred from the comparison of cytogenetic and molecular data.

Here we report on the analysis of three rodent sibling species complexes belonging to the African genera Arvicanthis, Acomys and Mastomys. Using cytogenetic and molecular approaches we set out to investigate how karyotype and molecular evolution are linked in these muroid sibling species and, in particular, to what extent chromosomal changes are relevant to cladogenic events inferred from molecular data. The study revealed that each complex is characterized by a distinct pattern of karyotype evolution (karyotypic orthoselection), and a specific mutation rate. However we found that the general pattern may be considerably modified in the course of evolution within the same species complex (Arvicanthis, Acomys). This observation suggests that karyotypic orthoselection documented in numerous groups is not so much a reflection of selection of a definite type of chromosomal mutation, as suggested by the classical concept, but is due to genome structure of a given species. In particular, karyotypic change appears related to the quantity and chromosomal location of repeated sequences. The congruence between the chromosomal and molecular data shows that chromosomal changes are often valuable phylogenetic characters (Arvicanthis and Mastomys, but not Acomys). However, most importantly the approach underscores the value of incorporating both in order to gain a better understanding of complex patterns of evolution. Moreover, the fact that every cladogenetic event in Mastomys is supported by two pericentric inversions allowed us to hypothesize that genetic differentiation is initiated by the suppression of recombination within inverted segments, and that the accumulation of multiple pericentric inversions reinforces genetic isolation leading to subsequent speciation. Finally, the low sequence divergences distinguishing karyotypically distinct sibling species within Arvicanthis and Mastomys emphasizes the power of combining cytogenetic and molecular approaches for the characterization of unrecognized components of biodiversity.