Chromosomal and C-heterochromatin Characterization of Arvicanthis niloticus (Rodentia: Murinae) in Egypt

摘要

The karyotype and C-banding pattern of the unstriped grass rat Arvicanthis niloticus from four localities in Egypt are presented. All individuals karyotyped, as a rule, have the same diploid number of 2n = 62 and autosomal Fundamental Number of aFN = 62. In addition, all chromosomes have a large centromeric block of fairly uniform size. However, an additional interstitial or telomeric small C-band is scored in some chromosomes. Nevertheless, frequent heteromorphism in the morphology and heterochromatin content of both the homologous chromosomes of the pair No. 1 and the X chromosome are scored in some individuals from the four localities and led to an aFN = 63. Accordingly, four forms or cytotypes, namely ANI-1a, ANI-1b, ANI-1c and ANI-1d, are recognized based on this variation, which is mostly attributed either to addition or deletion of a heterochromatic segment as a result of pericentric inversions. Of these four forms, the ANI-1a is considered ancestral for A . niloticus in Egypt and is closely similar to that of the Ethiopian A . dembeensis , regardless the contradiction concerned with nomenclature of the X chromosome, while the karyotypes of the other forms are synapomorphy of the form ANI-1a and showed as well a relative resemblance to those of the Ethiopian A . abyssinicus and A . blicki . Therefore, it is concluded that the genus Arvicanthis would be represented by an Egyptian-Ethiopian radiation ( A . niloticus , A . dembeensis , A . abyssinicus and A . blicki ) and by a Central-Western African one, including the karyotypes described as A . centralis and A . solatus . Moreover, A . niloticus should be regarded no longer as a single species but as a cluster of several proper species.