Maternal investment in a cooperatively breeding primate, Wied\u27s black tufted -ear marmoset (Callithrix kuhlii)

The present series of studies was designed to investigate the expression, regulation, and extent of maternal investment in a cooperatively breeding primate, Wied\u27s black tufted-ear marmoset (Callithrix kuhlii ). First, I examined the possibility that marmoset females might be sensitive to litter-to-litter changes in the immediate energetic demands of reproduction and that they might make tradeoffs between current versus future offspring by reducing investment in their current litters. As reported for other callitrichid primates, C. kuhlii females reduced their investment in offspring across the postpartum period. However, the magnitude and timing of this reduction varied as a function of females\u27 ability to delegate the care of their infants to other family members, and as a function of the timing of the postpartum conception. Second, I assessed the relationship between hormonal factors and litter-to-litter variation in patterns of maternal investment. When females had experienced alloparents to assist them with the rearing of offspring, they had significantly lower levels of urinary cortisol during the pre- and postpartum period than when they only had assistance from their male partners. However, urinary cortisol was not correlated with postpartum carrying effort. When females conceived during the early postpartum period, they had significantly higher postpartum urinary estradiol levels than when they conceived later in the postpartum period. Postpartum estradiol was significantly and negatively correlated with infant carrying effort. Third, I observed maternal behavior during the nighttime hours to determine whether disrupted sleep is associated with parent-infant co-sleeping in marmosets. Females caring for newborns were awake more than twice as often as females without infants. Furthermore, breeding females exhibited more nighttime wakefulness than their male partners across the first nine weeks of infant life. The results of these studies indicated that the expression of maternal investment in marmosets is more flexible than previously reported, and that the costs of rearing callitrichid infants may be even more costly than previously recognized