Previous studies have shown that guppies, Poecilia reticulata, can learn the route to a food source by shoaling with knowledgeable conspecifics, and prefer to shoal with experienced foragers and familiar fish. We tested the hypothesis that guppies would learn more effectively from (1) familiar than unfamiliar demonstrators and (2) well-trained than poorly trained demonstrators. Demonstrator fish were given experience in swimming a route to a food source and then introduced into shoals of untrained observer guppies; the spread of this foraging skill was recorded over 15 trials. The demonstrators were either familiar or unfamiliar to the observers and either well trained or poorly trained. Observers performed significantly better when the demonstrators were familiar. The training of the demonstrators made no overall difference to the performance of naïve observers. However, whilst observers in shoals exposed to well-trained demonstrators did better initially than those with poorly trained ones, the latter learned the route to the feeder faster. Our results suggest that familiarity may generate a form of directed social learning in guppy shoals, in which fish learn more effectively from familiar conspecifics. An analysis of who follows whom suggests that well-trained demonstrators can provide a 'tip-off' as to the location of the hole but poorly trained demonstrators were more likely to be followed. The results suggest that while observers are able to shoal with poorly trained demonstrators, well-trained demonstrators swim the maze route too quickly to be followed, but may attract attention to the maze route.

Low intensity, non-noxious, stimulation of cutaneous somatosensory nerves has been shown to trigger oxytocin release and is associated with increased social motivation, plus reduced physiological and behavioural reactivity to stressors. However, to date, little attention has been paid to the specific nature of the mechanosensory nerves which mediate these effects. In recent years, the neuroscientific study of human skin nerves (microneurography studies on single peripheral nerve fibres) has led to the identification and characterisation of a class of touch sensitive nerve fibres named C-Tactile afferents. Neither itch nor pain receptive, these unmyelinated, low threshold mechanoreceptors, found only in hairy skin, respond optimally to low force/velocity stroking touch. Notably, the speed of stroking which c-tactile afferents fire most strongly to is also that which people perceive to be most pleasant. The social touch hypothesis posits that this system of nerves has evolved in mammals to signal the rewarding value of physical contact in nurturing and social interactions. In support of this hypothesis, in this paper we review the evidence that cutaneous stimulation directly targeted to optimally activate c-tactile afferents reduces physiological arousal, carries a positive affective value and, under healthy conditions, inhibits responses to painful stimuli. These effects mirror those, we also review, which have been reported following endogenous release and exogenous administration of oxytocin. Taken together this evidence suggests c-tactile afferent stimulation may mediate oxytocin release during affiliative tactile interactions.

Mammalian imprinted genes are generally thought to have evolved as a result of conflict between parents; however, recent knockout studies suggest that coadaptation between mother and offspring may have been a significant factor. We present evidence that the same imprinted gene that regulates mammalian maternal care and offspring development also regulates male sexual behavior and olfaction. We have shown that the behavior of male mice carrying a knockout of the imprinted gene Peg3 does not change with sexual experience and that the mice are consequently unable to improve their copulatory abilities or olfactory interest in female odor cues after mating experience. Forebrain activation, as indexed by female odor-induced c-Fos protein induction, fails to increase with sexual experience, providing a neural basis for the behavioral deficits that the male mice display. The behavioral and neural effects of the Peg3 knockout show that this imprinted gene has evolved to regulate multiple and varied aspects of reproduction, from male sexual behavior to female maternal care, and the development of offspring. Moreover, sexual experience-driven behavioral changes may represent an adaptive response that enables males to increase their reproductive potential over their lifespan, and the effects we have found suggest that the evolution of genomic imprinting has been influenced by coadaptation between males and females as well as between females and offspring.accessory olfactory system ͉ coadaptation ͉ mammalian brain ͉ reward ͉ sexual behavior T he expression of certain mammalian autosomal genes in a parent-of-origin fashion was first demonstrated in the 1980s and termed ''genomic imprinting'' (1); since then, close to 100 maternally and paternally expressed imprinted genes have been identified (2). Over the last 20 years, the essential roles that imprinted genes play in development, particularly that of the brain, have become clear (3, 4), suggesting that imprinted genes might have enabled the evolutionary expansion of the mammalian brain (5). Most imprinted genes are strongly expressed in the placenta (6) and are involved in regulating fetal development (7). These developmental roles, in particular those of Igf2, Igf2r, Igf2AS, and H19, have been cited as evidence to support the conflict theory for the evolution of genomic imprinting (8). This theory posits that imprinted genes evolved with placentation in mammals as a result of parental conflict over offspring investment. The fetus/placenta is a genetically half-paternal structure that provides the father with an opportunity to manipulate the mother's investment in his offspring to the possible detriment of her potential future offspring. Thus, paternally expressed genes are predicted to enhance offspring growth, whereas maternally expressed genes are predicted to resist this as a result of an evolutionary ''arms race'' over levels of investment in offspring. However, work by our group on the paternally expressed gene Peg3 has shown that as well as regulating pup development...

Small-brained rodents have been the principle focus for pheromonal research and have provided comprehensive insights into the chemosensory mechanisms that underpin pheromonal communication and the hugely important roles that pheromones play in behavioural regulation. However, pheromonal communication does not start or end with the mouse and the rat, and work in amphibians reveals much about the likely evolutionary origins of the chemosensory systems that mediate pheromonal effects. The dual olfactory organs (the main olfactory epithelium and the vomeronasal organ), their receptors and their separate projection pathways appear to have ancient evolutionary origins, appearing in the aquatic ancestors of all tetrapods during the Devonian period and so pre-dating the transition to land. While the vomeronasal organ has long been considered an exclusively pheromonal organ, accumulating evidence indicates that it is not the sole channel for the transduction of pheromonal information and that both olfactory systems have been co-opted for the detection of different pheromone signals over the course of evolution. This has also led to great diversity in the vomeronasal and olfactory receptor families, with enormous levels of gene diversity and inactivation of genes in different species. Finally, the evolution of trichromacy as well as huge increases in social complexity have minimised the role of pheromones in the lives of primates, leading to the total inactivation of the vomeronasal system in catarrhine primates while the brain increased in size and behaviour became emancipated from hormonal regulation.