The genus Mastomys in the Ivory Coast.

The genus Mastomys in the Ivory Coast L. BELLIER Dr L. Bellier presented a detailed paper on the above subject including an extensive treatise on mathematical methodology relating the chromo- somal characteristics of Mastomys to the morpho- logical features of the cranium. A summary of the paper is given below. Ecological and taxonomic studies on Mastomys have been carried out in West Africa for over ten years, mainly in the Ivory Coast. Specimens were obtained from a wide variety of biotypes and in- cluded domestic and peridomestic village rodents. In earlier studies several thousand specimens were examined and a basic sample of 677 Mastomys skulls from 28 localities in the Ivory Coast, 6 in the Upper Volta, and 1 in the Niger were studied quantitatively, and an attempt was made to correlate chromosome numbers with cranial measurements. In this pre- sentation the author emphasized studies on four population groups involving 197 specimens. The author was able to show that at least two dif- ferent morphological forms have a chromosome number of 38. His observations indicated that Mastomys captured in houses or in villages, including purchased specimens, have a chromosome number of 32, whereas those captured quite far from villages -in the savanna, in forest, or in cultivated or aban- doned plantations-have a chromosome number of 38. It proved possible, in approximately 90°/ of cases, to distinguish on morphological grounds by visual inspection individuals representing popula- tions with different chromosome numbers. However, for the two forms that probably have chromosome numbers of 38, skulls could be distinguished by visual inspection in only 50%. of the cases. Individuals in the populations possessing a chro- mosome number of 32 are described as having dull grey or chocolate-grey undersides with the fur on the dorsum varying from dull red-brown to almost slate grey. Melanic forms were never seen in the Ivory Coast. In addition, this type was also more aggressive than other Mastomys and had a tail more densely covered with short hard hairs. The author suggests that these groups, which now represent true species of Mastomys, originated during the Pleistocene by successive periods of isola- tion between savanna and forested areas. He further points out that it will be necessary in future studies of Mastomys populations to define more clearlythe chro- mosome number of the population involved; in areas endemic for Lassa virus there may be a difference in susceptibility and therefore in the reservoir status of populations with different chromosome numbers. BULL. WORLD HEALTH ORGAN., Vol. 52, 1975-6653397