| During the development period, social environment plays an important role in shaping individual differences in behavior and neuroendocrine system at adult. In mammals, the early social environment mainly consists of parent-offspring (often mother-infant) and peers. Parent-offspring interactions are very intense and span a considerable period of offspring development. In addition to providing of warmth and nutrition, the high amount of physical contact with parents is also important for the infant maturation in behavior and physiology. Social interactions with peers are also essential for the development of social skills of the offspring. In some social families, older juvenile offspring may provide care-giving toward younger siblings and this is considered as a form of alloparenting. According to the inclusive fitness theory, alloparenting experience may increase future parental behavior and reproductive success. As an important social experience during development period, whether this experience exerts any effect on other behaviors, and whether effects of alloparental care provided by older juvenile helpers on behavioral expression is similar to that of parental care are still unknown. In addition, high levels of alloparental behavior are an important property of the monogamy. Whether alloparenting can alter monogamy relevant behaviors, and whether it plays an important role in the formation and maintenance monogamy, remain unclear. Oxytocin (OT) has been found to regulate close social attachment, while dopamine (DA) is involved in the reward and strengthen, as well as the expression of prosocial behavior. It is suggested that early social environment has the potential to shape OT and DA systems, which, in turn, will alter the expression and regulation of social behavior throughout life. Thus, it is worth investigating the involvement of OT and DA in this process. Here, we investigated the effects of alloparenting experience and care on social behaviors, OT and DA systems using socially monogamous mandarin voles with alloparenting. The present study investigated the effects of alloparenting on the social behaviors such as social interaction, parental care, social recognition and partner preference; the central levels OT and TH, OT receptor (OTR) and DA receptor mRNA expression were also measured.If older juvenile offspring provide care-giving to younger siblings, they should live with parents after weaning. There may be superimposed effect of alloparenting experience and post-weaning living with parents. Only one study has investigated the effect of post-weaning mother-offspring interaction on adult explorative behavior and social behavior. Little is known about the effect of post-weaning parent-offspring interaction on anxiety and the monogamy relevant behaviors, and whether these effects are associated with OT and DA system.(1) The effects of post-weaning living with parents on adult behaviors, OT and DA system:Mandarin vole offspring are generally weaned at21d of age, and some disperse and leaving the natal cage nest in the wild. However, some juveniles remain in the natal nest for45-50d. In the present study, voles were assigned to living with parents and siblings until45d (natural dispersal time) or to live with sibling from the same litter after weaning. We found that voles that live with parents during post-weaning period engaged in less locomotor activity and rearing behavior in the open field test. The cohabitation also decreased the sniffing to novel individual, and delayed the formation of partner preference. However, this living condition increased the social recognition and the levels of parental care. On the other hand, post-weaning living with parents increased the levels of central OT in PVN and MeA, and the expression of OTR mRNA in the MeA. Increased OT-ir cells were also found in MPOAp and MPOAa in male voles. However, this living condition decreased TH-ir neurons in MPOAp, PVN and SN, as well as D2R mRNA expression in the NAcc. These results indicate that post-weaning living with parents alters the monogamy related behaviors, and these changes may be associated with OT and DA release in the specific regions, as well as the level of OTR and D2R.(2) The effects of alloparenting experience on adult behaviors, OT and DA system: Mandarin voles that had cared for younger siblings displayed significantly more locomotor activity in a novel environment and engaged in more social investigation of unfamiliar same-sex individuals. Females of this group also provided more parental care compared to control voles. Alloparenting experience decreased the levels of the social recognition, but promoted the pair-bonding formation. In addition, this experience decreased the synthesis of OT in the PVN of both sexes, and the release of OT in the AH and LH of female voles. However, increased TH-ir cells were found in the PVN and AH in the females from the alloparenting animals. It also increased the levels of D2R mRNA expression in the NAcc. Alloparenting experience alterd the levels of OTR mRNA expression in a region-specific way, increased OTR in the NAcc and decreased OTR in the MeA. These data illustrate the effects of alloparenting experience on other social behavior relevant to monogamy. The levels of OTR and D2R in the NAcc, and the release of DA in specific regions have been implicated in the regulation of these behaviors.(3) The effects of alloparental care on adult behaviors, OT and DA system: individuals cared by older siblings demonstrated lower levels of anxiety and aggression, and higher levels of parental investment at adulthood, compared to control animals. In addition, there was no difference in social recognition between them. However, alloparental care could enhance the formation of partner preference in female mandarin voles. Correspondingly, the effect of alloparental care on neuroendocrine parameters was sex-specific. Female voles received alloparental care possessed significantly more OT-ir cells in MPOAa, PVN, MeA and AH, and more TH-ir in MPOAa, PVN and VTA. These voles also had more D2R mRNA expression in the MeA, and less OTR and D2R mRNA expression in the NAcc. Such care induced reduced OT in the AH and decreased DR mRNA expression on male voles. These results indicate that alloparental care changes the expression behavior and neuroendocrine parameters in a gender-specific manner.Taken together, this study concluded that post-weaning living with parents, alloparenting experience, alloparental care could affect the behaviors related to mating system at adulthood. The effects of these experiences on social behaviors are closely associated with central lelvels of OT and DA release, as well as the expression of OTR and DR in the NAcc and MeA. In addition, variations in other neuroendocrine substrate induced by these experiences may also involve in the behavioral regulation. Giving and receiving alloparental care have clear benefits in mandarin voles and suggests that alloparental care may increase the inclusive fitness of both givers and receivers. Alloparenting plays a very important role in the formation of monogamy related behaviors. These findings can provide new ideas for prevention and intervention of physical and psychological disorders induced by only one child policy. It is also very significant for further studies on resolving of the social problems caused by China only one child policy to some extent.
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