The effect of alloparental experience and care on anxiety-like, social and parental behaviour in adult mandarin voles

Providing or receiving alloparental care promote partner preference and alter central oxytocin and dopamine systems in adult mandarin voles

Juveniles of cooperative breeding species usually remain in the natal area and provide care to younger siblings, a behavior considered one form of alloparenting in the natural condition. Previous studies have demonstrated the effects of providing or receiving alloparental care on adult behaviors, including anxiety-like behavior, social interaction, and parental behavior, but little is known about the influences on species-typical bonding behaviors, such as pair-bond formation. In this study, we explored this concept using socially monogamous mandarin voles (Lasiopodomys mandarinus). As the oxytocin (OT) and dopamine systems are involved in alloparental and pair-bonding behaviors, we also examined the levels of central OT and tyrosine hydroxylase (TH), as well as OT receptor (OTR) and dopamine D1-type and D2-type receptors (D1R and D2R) mRNA expression in the nucleus accumbens (NAcc) and amygdala to investigate the underlying mechanisms. Our results show that mandarin voles providing alloparental care to younger siblings displayed facilitation of partner preference formation, lower levels of OT expression in the paraventricular nucleus of the hypothalamus (PVN) and lateral hypothalamus (LH), and increased OTR and D2R mRNA expression in the NAcc compared to controls. Individuals receiving alloparental care also demonstrated facilitation of partner preference formation in adult voles. Additionally, alloparental care enhanced OT expression in the PVN, anterior medial preoptic nucleus (MPOAa), medial amygdala (MeA), and TH expression in the ventral tegmental area (VTA) and zona incerta (ZI). Furthermore, males displayed decreased D1R mRNA expression in the NAcc, whereas females showed slightly increased D2R expression in the amygdala. These results demonstrate that providing or received alloparental care can promote partner preference formation in monogamous species and that these changes are associated with altered OT and dopamine levels and their receptors in specific brain regions.

Predator odor exposure increases social contact in adolescents and parental behavior in adulthood in Brandt's voles

Research suggests that predation risk during adolescence can program adult stress response and emotional behavior; however, little is known about the short-term and lasting residual effects of this experience on social behavior. We explored this concept in social Brandt's voles (Lasiopodomys brandtii). Adolescent male and female voles were exposed to distilled water, rabbit urine (as a non-predator stimulus), and cat urine for 60 min daily from postnatal day (PND) 28-49. Social play tests were conducted immediately following exposure on PND 28, 35, 42, and 49. In the social play test, repeated cat odor (CO) exposure enhanced the contact behavior of voles with their cagemate. Adolescent exposure to CO did not affect behavioral responses toward unrelated pups in the alloparental behavior test or same-sex individuals in the social interaction test. However, exposure to CO significantly enhanced the licking/grooming behavior of voles towards their own pups in the home cage parental behavior test. Repeated CO exposure significantly inhibited weight gain in male voles during adolescence. This effect was transmitted to the next generation, with lower weight gain in offspring before weaning. Following repeated CO exposure, males tended to have more female offspring whereas females produced more offspring, suggesting an adaptive strategy to increase inclusive fitness under predatory risk. These findings demonstrate that adolescent exposure to predatory risk augments adolescent social contact and adult parental behavior and suggest a role for improved inclusive fitness in mediating long-term outcomes.

The neurobiological causes and effects of alloparenting

Alloparenting, defined as care provided by individuals other than parents, is a universal behavior among humans that has shaped our evolutionary history and remains important in contemporary society. Dysfunctions in alloparenting can have serious and sometimes fatal consequences for vulnerable infants and children. In spite of the importance of alloparenting, they still have much to learn regarding the underlying neurobiological systems governing its expression. Here, they review how a lack of alloparental behavior among traditional laboratory species has led to a blind spot in our understanding of this critical facet of human social behavior and the relevant neurobiology. Based on what is known, they draw from model systems ranging from voles to meerkats to primates to describe a conserved set of neuroendocrine mechanisms supporting the expression of alloparental care. In this review we describe the neurobiological and behavioral prerequisites, ontogeny, and consequences of alloparental care. Lastly, they identified several outstanding topics in the area of alloparental care that deserve further research efforts to better advance human health and wellbeing. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 214-232, 2017.

Development-dependent behavioral change toward pups and synaptic transmission in the rhomboid nucleus of the bed nucleus of the stria terminalis

Sexually naïve male C57BL/6 mice aggressively bite unfamiliar pups. This behavior, called infanticide, is considered an adaptive reproductive strategy of males of polygamous species. We recently found that the rhomboid nucleus of the bed nucleus of the stria terminalis (BSTrh) is activated during infanticide and that the bilateral excitotoxic lesions of BSTrh suppress infanticidal behavior. Here we show that 3-week-old male C57BL/6 mice rarely engaged in infanticide and instead, provided parental care toward unfamiliar pups, consistent with observations in rats and other rodent species. This inhibition of infanticide at the periweaning period is functional because the next litter will be born at approximately the time of weaning of the previous litter through maternal postpartum ovulation. However, the mechanism of this age-dependent behavioral change is unknown. Therefore, we performed whole-cell patch clamp recordings of BSTrh and compared evoked neurotransmission in response to the stimulation of the stria terminalis of adult and 3-week-old male mice. Although we were unable to detect a significant difference in the amplitudes of inhibitory neurotransmission, the amplitudes and the paired-pulse ratio of evoked excitatory postsynaptic currents differed between adult and 3-week-old mice. These data suggest that maturation of the synaptic terminal in BSTrh that occurred later than 3 weeks after birth may mediate by the adaptive change from parental to infanticidal behavior in male mice.

Two of a Kind or a Full House? Reproductive Suppression and Alloparenting in Laboratory Mice

Alloparenting, a behavior in which individuals other than the actual parents act in a parental role, is seen in many mammals, including house mice. In wild house mice, alloparental care is only seen when familiar sibling females simultaneously immigrate to a male's territory, so in the laboratory, when a pair of unfamiliar female wild mice are mated with a male, alloparenting does not occur because one female will typically be reproductively suppressed. In contrast, laboratory mice are assumed to alloparent regardless of familiarity or relatedness and are therefore routinely trio bred to increase productivity. Empirical evidence supporting the presence of alloparental care in laboratory mice is lacking. Albino and pigmented inbred mice of the strain C57BL/6NCrl (B6) and outbred mice of the stock Crl:CF1 (CF1) were used to investigate alloparenting in laboratory mice since by mating pigmented and albino females with albino males of the same stock or strain, maternal parentage was easily determined. We housed pairs (M:F) or trios (M:2F) of mice in individually ventilated cages containing nesting material and followed reproductive performance for 16 weeks. Females in trios were tested to determine dominance at the start of the experiment, and again 5 days after the birth of a litter to determine if a female's dominance shifted with the birth of pups. Results showed a significant and expected difference in number of offspring produced by B6 and CF1 (p < 0.0001). Pigmented mice nursed and nested with albino pups and vice-versa, confirming empirical observations from many that group nesting and alloparenting occurs in unrelated laboratory mice. When overall production of both individual mice and cages was examined, reproductive suppression was seen in trio cages. Dominance testing with the tube test did not correlate female reproduction with female dominance in a female-female dyad. Due to the reproductive suppression noted in trios, on a per-mouse basis, pair mating outperformed trio mating (p = 0.02) when the measure was weaned pups/female/week. No infanticide was seen in any cages, so the mechanism of reproductive suppression in trio matings may occur before birth.