Le cycle saisonnier des lipides de réserve chez deux espèces de rongeurs du Sénégal

The seasonal cycle of lipid deposition has been studied for two consecutive years in populations of Mastomys erythroleucus and Taterillus gracilis from a sahelo-sudanian woodland in Senegal. At the beginning of the dry season young Mastomys, 2 to 3 months old, feed mostly upon the temporarily superabundant seeds and store fat. These fat deposits, largely made of oleic acid, are used during the long dry season, when food is scarce. During the rains, Mastomys diet changes, as does the nature of their lipids tores which then contain a larger percentage of linoleic acid. This last fatty acid is quite likely provided to the animais by Cucumis melo seeds, which are frequently consumed by Mastomys at this time of the year, when breeding takes place. The seasonal cycle of fat deposition in Taterillus gracilis is similar to that of Mastomys erythroleucus, but less marked. The diet of this gerbilid is also more varied, and its breeding season spread over a longer time interval. The above observations were made at the end of the 1975- 1977 rodent outbreak in Northern Senegal. However, fat deposits remained very substantial in January 1976, at the time when population densities reached their peak values. Similarly, the rodents still maintained sizable fat deposits during the "crash" period, from August 1976 to the end of 1977. In the present situation, at least, population fluctuations were clearly not dependent upon the nutritional status of the rodents studie