The long-term impact of infant rearing background on the behavioural and physiological stress response of adult common marmosets (Callithrix jacchus)

Although triplet litters are increasing in captive colonies of common marmosets, parents can rarely rear more than two infants without human intervention. There is however much evidence that early life experience, including separation from the family, can influence both vulnerability and resilience to stress. The current study investigated the behavioural and hypothalamic pituitary adrenal (HPA) axis response to the routine stressor of capture and weighing in adult common marmosets (Callithrix jacchus), reared as infants under 3 different conditions: family-reared twins (n=6 individuals), family-reared animals from triplet litters where only 2 remain (2stays: n=8) and triplets receiving supplementary feeding from humans (n=7). In the supplementary feeding condition, infants remained in contact with each other when they were removed from the family. There were no significant differences (P>0.5) in cortisol level or behaviour between the rearing conditions. In all conditions, salivary cortisol decreased from baseline to post-capture, which was accompanied by increases in agitated locomotion. Family reared 2stays demonstrated significant cortisol decreases from baseline to post capture (post 5 mins: P=0.005; post 30 mins: P=0.018), compared to the other conditions. Family reared twins displayed significantly more behavioural changes following the stressor than the other conditions, including significant increases in scent marking (post 5 mins and post 30 mins: P=0.028) and significant decreases in inactive alert (post 5 mins: P=0005; post 30 mins: P=0.018), calm locomotion (post 5 mins: P=0.028; post 30 mins: P=0.046) and proximity to partner (post 5 mins: P=0.046). There were increases in behaviour suggesting reduced anxiety, including significantly more exploration post-capture in supplementary fed triplets (post 5 mins: P=0.041), and significantly more foraging post capture in family reared 2stays (post 5 mins and post 30 mins: P=0.039). However, as differences between rearing conditions were minimal, supplementary feeding of large litters of marmosets at this facility did not have a major effect on stress vulnerability, suggesting that this rearing practice may be the preferred option if human intervention is necessary to improve survival of large litters