Callithrix and Leontopithecus exhibit ecological differences that have implications for the patterns of infant care. In C. jacchus, which uses a small home range because it depends mainly on plant exudates, infants can forage independently early in their life. L. chrysomelas, which feeds mainly on fruits and insects, needs larger home ranges and, therefore, its infants have a more extensive period of dependence. Three families of C. jacchus and four families of L. chrysomelas were studied in captivity. The animals were observed starting from the birth of the infants up to their 8th week of age. Our results suggest that the pattern of infant transfer in L. chrysomelas did not follow the one reported for L. rosalia in that transfers from the mother occurred much earlier. L. chrysomelas infants were carried for about 15% of total time during the 8th week of life against less than 1% in C. jacchus in the same week. Infant care seems to be more extensive in L. chrysomelas than in C. jacchus, and the period of exclusive mother carrying in L. chrysomelas is shorter than that observed in L. rosalia.

The study of behavioural gender differences among Callitrichid primates has been generally neglected. We describe evidence from experimental studies in which adult female tamarins (Saguinus) and marmosets (Callithrix) demonstrate priority of access to food that is spatially and temporarily restricted. Differences in behavioural strategies between both reproductive and non-reproductive females, and males, are consistent with differences between the genera in their feeding ecology and social organisation. They are also functionally plausible. A recent study gives preliminary data to show that, although mated females in family groups of common marmosets demonstrate priority of access to food sources, overall there are differences in responsiveness that may be influenced by factors such as the time of feeding, energy content and preference of food.Gender differences among the primates in their feeding behaviour include examples in which adult females demonstrate a priority of access to food (eg Jolly, 1984;Richard, 1987). This is unusual among primates and raises a number of interesting theoretical questions. For example, considerations of functional hypotheses to account for such phenomena include reproductive exclusivity within a small number of adult males and females. The case is most easily explained in the context of monogamy, as in some lemurs and in which paternity is relatively certain. The argument is that male deference to a breeding or potentially breeding female will benefit the future survival of the offspring of that female (eg Richard, 1987).