title: Sexual communication in mice: linking male signals, female learning and adult neurogenesis
Creators: name: Hoffman, Emma
Publisher: name: University of Liverpool Repository
Year: 2014

description: For many species sexually selected signals are essential for communication between conspecifics. These signals produced by males are attractive to females and may reliably reflect competitive ability, health status and genetic identity. There is high diversity in the types of auditory, visual and olfactory signals that males produce, and males of many species invest in multiple signals. In mice, adult males invest in scent-marks and ultrasonic calls as sexual signals. Ultrasonic calls are emitted during encounters with female conspecifics, primarily during pre-copulatory sniffing and investigation. As a result, this sexually dimorphic and individually variable behaviour has been suggested to serve a specific courtship function in mice. Scent marks are also important for communication with conspecifics and provide long lasting signals of identity, health status and competitive ability to potential mates. Both male signals are therefore important in sexual communication, but it is unclear whether scent marking and calling serve separate functions. To address this, male scent marking and calling was recorded in response to female odours, a female behind a mesh barrier, a direct interaction with a female or no female cues. Male signalling investment varied according to female cue type. Further, cues that elicited a high rate of calling differed from those that elicited a high rate of scent marking. Ultrasonic calls were primarily emitted in interactions suggesting an important role in direct courtship. By contrast, the greatest number of scent marks was deposited when males were not in direct contact with female conspecifics. Consistent with the results obtained in the first experiment, scent marks are known to provide information to females in the absence of a male through long lasting cues present in urine. The distribution of scent marks also provides an honest signal of a male’s competitive ability to defend its territory. Females are highly attracted to spend time near male scent marks and are subsequently more attracted to the owners of these familiar scent marks than to equivalent unfamiliar males. Male scent can also condition a preference for its location, stimulated by a specific sex pheromone present in male urine. These acquired memories of male scent mark locations and individual scent signatures are likely to be important in allowing females to be selective and approach preferred males when ready to mate. In a natural context, females investigate multiple scent marks when territories of competing males are encountered. To reflect the complexity of scents encountered in a natural context and to assess how differences in male expression of specific scent components influence female spatial learning, conditioned place preference tests comprising multiple scents and locations were used. When multiple scents were presented simultaneously, females formed a learned preference for multiple locations of male but not female scents; darcin, a male-specific pheromone, was also required for male scent to condition a preference for its remembered location. Further, the relative amount of darcin influenced the strength of a remembered preference. The comparative composition of individual scents may therefore be important in determining female learned preferences for locations scent marked by competing males. Male scent from dominant territory owners also stimulates neurogenesis in the hippocampus and olfactory bulbs of female mice, areas of the mammalian brain associated with spatial learning and olfactory processing. In hippocampal neurogenesis, neurons are generated and remain in their mature form within this same structure; by contrast, the germinal area for olfactory neurons is present in the forebrain and newly generated cells must migrate over long distances before being incorporated into existing circuits. To investigate whether scent components that stimulate spatial learning also stimulate neurogenesis in females, immature hippocampal neurons and proliferating cells in the forebrain were quantified in female mice exposed to different male scents or scent components. The results suggest darcin, a male specific MUP that stimulates spatial learning, also stimulates hippocampal and olfactory neurogenesis in females. This male pheromone therefore appears to play a role in the immediate behavioural response and the long-term neurological change associated with exposure to male scents.