Environmental and Social Determinants of Sexual Function in the Male Lesser Mouse Lemur (Microcebus murinus)

Abstract

Environmental factors that regulate the sexual activity of male lesser mouse lemurs have been studied experimentally with more than 60 captive animals over an 8-year period. In this nocturnal Malagasy prosimian, variation in day length is the primary factor controlling seasonal sexual activity. Plasma testosterone concentrations were low (= 9 ng/ml) during short days and reached 60 ng/ml during long days (>12-hour day). This cyclic pattern persists unchanged when artificial photoperiodic rhythms are applied and is not altered by ageing. The timing of puberty is also regulated by photoperiodic changes. Nevertheless, the sexual activity of the male lesser mouse lemur can be dramatically modified by the social environment. In heterosexual groups, behavioural and physiological components of sexual activity are depressed in all males except the dominant one, whose aggressive interactions are always successful. Intermale sexual inhibition was shown to be mediated by chemical cues present in the urine of dominant or isolated males but not in urine of subordinate individuals. The inhibitory signals possess lipophilic properties and are not contingent on the gonadal activity of the urine donor but are linked to adrenocortical activity. By contrast, chemical signals stimulating the reproductive function of all males are found in the urine of females, the presence of which is required for the establishment of clear dominance among grouped males. Endocrine mechanisms underlying intermale sexual inhibition by chemical cues were analysed. Variations in prolactin strongly suggest that olfaction interacts with the photoperiodic regulation of reproductive function, leading to changes in the sensitivity of the negative feedback effect of testosterone on gonadotrophin secretion. Inhibitory or stimulatory effects of chemical signals are discussed in the context of their functional significance for wild populations.

Senescence or selective disappearance? Age trajectories of body mass in wild and captive populations of a small-bodied primate

“…Microcebus murinus have a long potential lifespan relative to their body size and life-history characteristics [75,76], yet a distinctly shorter average lifespan in nature. While high EM may be associated with evolutionary processes that shorten lifespan, these processes might be partially counteracted in M. murinus by their lifelong reproduction [45,51] and ability to efficiently fatten and use torpor in late adulthood. Overall, our results support the view that conditiondependent EM may shape FS and, eventually, lifespan.…”

Attenuated effect of increased daylength on activity rhythm in the old mouse lemur, a non-human primate

“…The lamps were placed on the side of the cage, at 10 cm from a wooden nest, where the animal could retire during the entire sleeping period, until it started its activity. All animals were tested after at least 1 month of exposure to a given photoperiod, a time lapse necessary for their complete physiological adaptation to the photoperiod (Perret, 1992). The recording period began at least 3 weeks after surgery.…”

“…This primate exhibits photoperiod-dependent seasonal and daily rhythms in most of its biological functions. Daily exposure to light for longer than 12 h promotes sustained behavioral activity, whereas daily exposure to light for less than 12 h reduces behavioral activity and leads to an increase in fat deposits (Perret, 1992). The life span of this species is about 8 -10 years in captivity (Perret, 1997).…”

Females go where the food is: does the socio-ecological model explain variation in social organisation of solitary foragers?

“…Specifically, we hypothesised that (1) M. berthae experience high levels of scramble competition and little potential for female-female association because they use small and quickly depleting resources (Dammhahn Wimmer et al 2002;Radespiel et al 2003;Fredsted et al 2005 d Sleeping associations (Radespiel et al 2001;Wimmer et al 2002) and communal breeding units (Eberle and Kappeler 2006) e In captivity : Perret 1992 and Kappeler 2008b). In contrast, because M. murinus use a wider variety of food sources, also including larger and higher quality resources (Dammhahn and Kappeler 2008b), we hypothesised that (2) they will experience high levels of contest competition as well as an increased potential for female-female association.…”