Species with fuzzy borders: the taxonomic status and species limits of Saunders' vlei rat, Otomys saundersiae Roberts, 1929 (Rodentia, Muridae, Otomyini)

Abstract

The taxonomic status and species limits of the South African-endemic rodent species Otomys saundersiae were revised using G-banding karyotypic analysis, assessment of pelage colour and craniodental traits, multivariate analysis of eight cranial distance measurements, and geometric morphometric analysis of 11 landmarks of the dorsal image of the skull. In the Western Cape, the recognized subspecies Otomys saundersiae karoensis differed in karyotype from sympatrically-occurring populations of O. irroratus (cytotype "C") in having six (as opposed to four) pairs of biarmed chromosome pairs and in the absence of pair number 14. Discriminant analysis of linear craniometric variables in positively identified (karyotyped) samples of Otomys irroratus and Otomys s. karoensis separated the two species without any overlap, as did pelage colour and certain qualitative cranial characters such as nasal angle; such clear-cut differences however were not apparent between unkaryotyped samples of O. s. saundersiae and O. irroratus from the Eastern Cape. Centroid size (from geometric morphometric analysis of cranial landmarks) was significantly correlated with both non-affine and affine components of skull shape, indicating strong allometric effects. Both cranial shape and size differed significantly between Western Cape O. s. karoensis and O. irroratus; size, but not shape, varied significantly between Eastern Cape O. s. saundersiae and O. irroratus. Within both currently recognized species, significant geographical differences in cranial shape were detected between eastern and western Cape populations occupying distinct ecological biomes. Problems with defining species limits in this complex case were discussed with reference to available data and alternative species concepts.