Mastomys natalensis (Smith, 1834)

Denys, Christiane, Lalis, Aude, Lecompte, Émilie, Cornette, Raphaël, Moulin, Sibyle, Makundi, Rhodes H., Machang, Robert S., Volobouev, Vitaly & Aniskine, Vladimir M., 2011, A faunal survey in Kingu Pira (south Tanzania), with new karyotypes of several small mammals and the description of a new Murid species (Mammalia, Rodentia), Zoosystema 33 (1), pp. 5-47 : 19

Mastomys natalensis (Smith, 1834)

Mus coucha natalensis Smith, 1834: 156 .

In Tanzania, Mastomys is very abundant, especially in cultivated areas (Leirs et al. 1990; Lima et al. 2003). Different studies have shown that only M. natalensis is present in Tanzania.

This very common species was represented in our sample from KP by 217 individuals, of which 108 females and 109 males. Mastomys was found in all the trapping lines except the Kichi forest (F) and the open woodland (G). Some specimens were also trapped in houses. Among the females there are many juvenile specimens (eight with mass <13 g and tooth wear stage 1), 29 had visible mammae with a weight greater than 34 g, and none was pregnant. Among the males only four specimens reached a mass of 50 g and only two had scrotal testes. The composition of the present sampling reflects the biological cycle of the species in Tanzania ( Lalis et al. 2006).

The results of microsatellite analyses revealed the absence of rupture in gene flow between individuals of Morogoro and Kingu Pira indicating that the Rufiji river and its swamp does not constitute a geographic barrier important enough to limit the crossing of Mastomys . They exchanged high gene flows by migration phenomenon and could belong to a single panmictic unit. This migratory flow contributed to genetic mixing which tends to homogenize the populations and to limit their genetic diversification ( Lalis et al. 2009).

The karyotype of M. natalensis has been described repeatedly (Britton-Davidian et al. 1995; Granjon et al. 1997; Corti et al. 2005). It contains 32 chromosomes and FNa varying from 54 to 52, due to pericentric inversion of chromosome pair 14. In addition, this species is characterized by appreciable heteromorphism of two submetacentric pairs of autosomes resulting from addition/ deletion of C heterochromatin on the entirely heterochromatic short arms (Britton-Davidian et al. 1995). Four out of five KP specimens possess typical M. natalensis karyotype with 2n = 32 and FNa = 54. However the fifth individual appeared unusual by having variable chromosome number in different cells, namely 78% possess 33 and 12% 34 chromosomes (the remaining 10% have 2n = 32). This variation is caused by the presence of supernumerary or B chromosomes which often display intercellular variation or mosaicism ( Volobouev 1980). In addition, the sizes of both X and Y chromosomes was variable, due to polymorphism for addition/deletion of C heterochromatin ( Fig. 8 ) never revealed before.

Figures

FIG. 8. — Standard karyotype of different Mastomys natalensis Smith, 1834 KP specimens displaying variability: A, specimen MNHN- CG2007-1015 (2n = 33,FNa = 56,B:supplementary chromosome);B, variability of the2n number with arrowsindicating the supernumerary chromosomes; C, variability of the sexual chromosomes of specimens (MNHN-CG2007-1016, 2007-1144, 2007-1205, 2007-1237).