Phenotypic variation is channeled by adaptation to local environments and phylogenetic constraints. The morphology of the obligatorily subterranean African mole-rats of the genus Fukomys has been shaped within the context of their underground habitat, posing particular limits on the animals' morphology. Especially the biting apparatus has likely evolved within severe evolutionary constraints, as it is used for feeding on hard geophytes, for digging complex tunnel systems, and for defensive purposes and social interactions in a colony. We studied interspecific differences in bite performance among three taxa, in relation to their skull anatomy and skull shape. Data on biting performance were gathered by in vivo measurements and compared with model simulations. It is shown that the model simulation is a good proxy for in vivo measurement. Scaling of bite force is positively allometric relative to head size. Moreover, differences in biting performance exist between taxa, which may be linked to differences in their ecology. This study will eventually enable us to analyze the evolutionary pattern behind the variation in structure and performance of the biting apparatus in Fukomys mole-rats.

The genus Cryptomys contains a number of social, subterranean rodents that are widely distributed throughout subSaharan Africa. Specimens of Cryptomys from 23 localities in south-west Zambia were karyotyped using a standard staining protocol. A minimum of five metaphases per specimen was scored for 2n and the fundamental number (NF) was determined in females. Nine new karyotypes, which may represent several new species, were identified: (1) 2n = 42, NF = 78 (Dongo, Southern Province); (2) 2n = 44, NF = 76 (Salujinga, North-western Province); (3) 2n = 45, NF = 78 (Lochinvar, Southern Province); (4) 2n = 52, NF = 86 (Chinyingi, North-western Province); (5) 2n = 54, NF = 78 (Monze, Southern Province); (6) 2n = 56, NF = 76 (Watopa, North-western Province); (7) 2n = 58, NF = 80 (Livingstone, Southern Province); (8) 2n = 58, NF = 86 (Senanga, Western Province); (9) 2n = 60, NF = 82 (Kataba, Western Province; type locality of C. damarensis micklemi). Contrary to previous reports, the specimens from Kataba and Senanga on the left bank of the Zambezi do not correspond to C. damarensis and should be considered a separate species: C. micklemi (as confirmed by molecular analyses; Ingram, Burda & Honeycutt, 2004). According to the karyotype, C. damarensis occurs only on the right bank of the Zambezi River in the Western Province. In contrast to the high karyotypic variability on the right bank of the Kafue River, it was found that C. anselli (2n = 68) is widely distributed throughout the Central province on the left bank of the Kafue River. The resulting pattern of occurrence of the different karyotypes correlates well with the extant river system configuration that separates most karyotypes. We hypothesize that geomorphological changes and in particular river system dynamics in recent geological times have played an important role in the chromosomal diversification and may have provided opportunities for speciation to occur.

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