[Influence of social grouping on seasonal sexual activation in male Microcebus murinus (Miller 1777)].

Comparative studies were made on different heterosexual groups of Microcebus murinus during the period of sexual activation, which is determined by the photoperiod. In pairs (1 male--1 female), the sexual activation of the males occurs during January. This is accompanied by a loss of body weight and by an increase in basal oxygen consumption. The testes are maximal in size by the beginning of March. In groups of 8 individuals (4 males--4 females) only one male exhibits normal sexual activity. He is the heaviest and mates with males. The 3 other males of the group show delayed activation and their testes are reduced in size. Two subordinate males died under the social pressure of severe diseases (e.g. renal failure) normally associated with overcrowding.