groups of cotton-top tamarins (Saquinus oedipus) ranging in size from 2 to ... KEY WORDS: cotton-top tamarins; Saguinus oedipus; infant care; reproductive ...
International Journal of Pdrnatology, VoL 13, No. 2, 1992
Contributions to Infant Care in Captive Cotton-Top Tamarins (Saguinus oedipus): The Influence of Age, Sex, and Reproductive Status Eluned C. Price 1,2 Received December 10, 1990; revised May 8, 1991
Marmosets and tamarins are characterized by a reproductive strategy that includes twinnin& and a communal rearing system in which infant care is shared among all group members, both breeders and nonbreeding helpers (oj~en older offspring). In order to test some predictions about the extent to which different age-sex classes should invest in infants, contributions to infant carrying and food-sharing by all family members were measured in captive groups of cotton-top tamarins (Saquinus oedipus) ranging in size from 2 to 12 independent individuals. Fourteen litters were observed from birth to 12 weeks. Carrying by mothers decreased steadily over the study period, while carrying by fathers and other offspring increased for 3-5 weeks, then declined. Infants spent more time carried by siblings than by either parent, but parents did more carrying than individual siblings and, also, shared more food with infants. Older siblings contributed more care than younger siblings did Adult sons carried infants more than adult daughters did, but immature daughters carried more than immature sons did. However, adult daughters actively offered food to infants more than any other class of helper did These results were interpreted in the light of hypotheses concerning the reproductive and dispersal strategies of callitrichid species. KEY WORDS: cotton-top tamarins; Saguinus oedipus; infant care; reproductive strategy;
dispersal.
1Department of Psychology, University of Stifling, Stirling, FK9 4LA, UK. 2present address: Jersey Wildlife Preservation Trust, Les Augr~s Manor, Trinity, Jersey, Channel lslands. 125 0164.-0291/92~400-0125506.50/00 1992Plenum"PublishingCorporation
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INTRODUCTION The Callitrichidae (marmosets and tamarins) typically produce twin offspring that are reared communally, i.e., fathers, older offspring and sometimes nonrelatives help the mother with infant care (Cleveland and Snowdon, 1984; Rylands, 1985; Goldizen, 1987; Savage, 1990). Communal rearing systems may have benefits both for the breeders that receive assistance and for the helpers that give it (Emlen, 1984; Price, 1991a,b). Breeders may benefit from increased survival rates either for themselves (because their energetic costs are reduced) or for their infants (because they receive more care). Helpers may also gain, perhaps by acquiring experience in parental care, developing affiliative bonds with infants, which may later assist the helper when it starts to breed, or increasing the chance that the breeders will tolerate the helpers' continuing presence on the group's territory and, therefore, the probability that the helpers may eventually inherit part or all of the area. The aim of this study was to test some specific predictions about the relative contributions to infant care of different family members in captive groups of cotton-top tamarins (Saguinus oedipus). There are several factors that might be important in determining the benefits a given individual has to gain and, therefore, the extent to which it invests in infants. Age and experience may have considerable effects on the amount of care invested by an individual. Ingram (1977) suggested that juveniles are likely to carry relatively little, first, because they have no previous experience and need to acquire the necessary skills before becoming proficient and, second, because they are smaller and less able to bear the load of an infant. As they grow older and more experienced, they would be expected to help more, I therefore predicted a positive correlation between age and contributions to infant care. Sex might be expected to affect parental contributions to care since lactation imposes an additional burden on the mother. This may mean that she can afford to invest less in infants in other ways. I therefore expected mothers to carry and share food with infants less than other family members. Sex might also affect the contributions of older offspring. Gaston (1978) hypothesized that investment in infants by siblings could be seen as "payment" extracted by parents for "allowing" older offspring to remain on their territory. Adopting this idea, McGrew and McLuckie (1986) predicted that eldest sons in families of cotton-top tamarins should invest most in infants, as an experiment simulating dispersal suggested that sons might stay longer than daughters on the natal territory and, perhaps, be more likely to inherit it eventually. However, there are reasons why daughters might also be expected to invest in infants. Experience with infant siblings
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is of considerable importance to later successful reproduction in callitrichids (Epple, 1975; Hoage, 1978; Ingram, 1978; Tardif et aL, 1984)and appears to be particularly crucial for females. Accordingly, daughters would be expected to try to gain as much experience as possible before emigrating, so I predicted an interaction between age and sex in care by siblings, with older sons carrying more than daughters of similar age but younger daughters carrying more than younger sons. Finally, reproductive status (whether an individual is a parent/breeder or a nonbreeding helper) may affect its contributions. Mumme and de Queiroz (1985) suggested that since nonbreeding helpers do not realize a direct reproductive reward, they must profit less than breeders from any contribution to cooperative behavior and, therefore, should contribute less than breeders do. In several studies of communally rearing species, breeders have been reported to contribute more than helpers to behavior such as care and feeding of offspring and resource defence [coyotes, Canis iatrans (Bekoff and Wells, 1982); acorn woodpeckers, Melanerpes formicivorus (Mumme and de Queiroz, 1985)]. However, in other species, at least some categories of helper may contribute as much as or more than breeders [dwarf mongooses, Helogale parvula (Rood, 1978); Florida scrub jays, Aphelocoma c. coendescens (Stallcup and Woolfenden, 1978)]. Therefore no specific predictions were made about the relative contributions to care by parents versus helpers in cotton-top tamarins.
METHODS
Subjects and Housing The subjects were 21 infant cotton-top tamarins and their families. Groups consisted of a breeding pair and older offspring and ranged in size from 2 to 12 individuals, excluding the infants themselves (Table I). Two of the seven twin litters were originally triplets, and five of the seven singleton infants were also born into multiple litters, but the additional infants all died before the age of 10 days. At the age of 4-7 days, one infant in each set of twins was marked with a yellow dye- on the head. Infants were remarked once during the observation period if necessary. Groups lived in cages or rooms (3-41 m 3) with access to outside areas (mean, 29 m3). They were fed three times daily, at approximately 0930, 1200 and 1600. Further details of housing and husbandry are given by Evans (1984) and Price and McGrew (1990).
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Behavioral Categories and Recording Methods
Each infant was observed for three to five 30-min observation sessions each week from birth to the age of 12 weeks. Sessions each week were spread evenly between 1000 and 1730. Data were collected on Check,sheets using 15-sec time intervals. The identities of the carriers of each infant were recorded using instantaneous sampling. A caretaker was given a score of 1 if carrying one infant at a 15-sec point and a score of 2 if it was carrying both infants in a twin litter. An infant not being carried was scored as "off." Mothers nursing infants were also scored as carrying. Each infant was observed at the midday fruit feed on 1 day each week. During this session, all occurrences of food-sharing involving the focal infant were recorded. The identity of the possessor of the food, the behavior of the infant and the possessor, and the outcome of the episode were noted. Foodsharing events were classed as begging (initiated by the infant) or offering (initiated by the possessor (Feistner and Chamove, 1986; Feistner and Price, 1990)). The possessor's response to an infant beg was termed positive if the infant received the food and resistance if the infant did not receive the food. Analysis of Data
Caretakers were described in terms of their sex and age class (parent; adult offspring, >24 months; subadult offspring, 13-24 months; juvenile offspring,
