SHORT COMMUNICATION
Demographic and Reproductive Patterns in Moustached Tamarin Monkeys (Saguinus mystax): Implications for Reconstructing Platyrrhine Mating Systems
P.A. GARBER1, F. ENCARNACION2, L. MOVA3, AND J.D. PRUETZ1
Department of Anthropology, University of Illinois, Urbana, Illinois; 2Proyecto Peruano de
Primatologia, Iquitos, Peru; 3Ministerio de Agricultura y Alimentación, Iquitos, Peru)
ABSTRACT. In this paper we address a series of questions concerning reproductive opportunities, kinship, dispersal, and mating patterns in free-ranging moustached tamarin monkeys (Saguinus mystax). Between 1980 and 1990 information on group size, composition, and migration patterns was collected on marked groups of moustached tamarins inhabiting Padre Isla, an island in the Amazon Basin of northeastern Peru. In 1990, 86% of 114 animals residing in 16 social groups were trapped, examined, and re-leased. Mean group size was 7.0, including 2.2 adult males and 2.0 adult females. None of these groups was characterized by a single adult male-female pair. In groups with more than one adult female, only the oldest female produced offspring.
An examination of dispersal patterns indicates that transfers between groups were common and fell into several categories, including immigra-tion of individual males and females, simultaneous transfer of pairs of subadult and/or adult males (sometimes relatives) into the same social groups, and group fissioning in which males and females of the splinter group join another small social group. We have no unambiguous cases of adult/subadult females migrating together into the same social group. All 6 groups for which reproductive data were available were characterized by either a polyandrous or polygynous (polygyandrous) mating pattern.
The results of this study indicate that moustached tamarins reside in small multimale multifemale groups that are likely to contain both re-lated and unrelated adult group members. Kinship and social ties among males appear to be stronger and more longlasting than kinship and social ties among females. We contend that the modal mating system of mous-tached and many other tamarins is not monogamous, and offer the possi-bility that cooperative infant care and mating system flexibility in cal-litrichines evolved from a polygynous mating pattern-© 1993 Wiley-Liss, Inc.
Key Words: Key words: dispersal, reproduction, demography
Received for publication August 19, 1991; revision accepted October 31, 1992. Address reprint requests to Dr. Paul A. Garber, Department of Anthropology, 109 Davenport Hall, University of Illinois, Urbana, IL 61801 © MW Wiley-Liss, Inc.INTRODUCTION
Tamarins and their close relatives the marmosets are unusual among higher primates in the production of twin offspring and the degree to which several adults within a group (helpers) participate in infant care- Among certain species there is evidence that fathers, other adult males, and nonreproductive adult females ex-pend considerable time and effort carrying arid exchanging food with the young [Box, 1977; Epple, 1975; Garber, 1986; Garber et al., 1984; Goldizen, 1987a, 1989; Snowdon&Soini, 1988; Stevenson & Rylands, 1988; Tardif et al., 1990]. Although in captive settings older siblings frequently participate in infant care, in free--ranging groups it remains uncertain the degree to which cooperative caregiving is kin based, and whether male and female helpers are closely related to the young [Goldizen, 1989; Sussman & Garber, 1987].
In callitrichines [sensu Rosenberger, 1981], the evolution of cooperative infant care is associated with a social group composed of 1-4 adult males, 1-4 adult females, and a small number of subadults and young. Regardless of the number of females present in a group, however, only a single female gives birth. Evidence from laboratory investigations indicates that in groups containing more than I adult female, generally only a single female exhibits hormonal levels indicative of a normal ovarian cycle [Epple & Katz, 1984; French et al., 1984]. Although there are indications that in certain settings the ovarian cycle of daughters may not be suppressed [Abbott, 1984; Tardif, 19841, the ability of an alpha female to control the reproductive opportunities of subordinate females represents a highly special-ized behavioral-endocrine mechanism that effectively limits the number of breed-ing females in the population as well as the number of offspring born into a group at one time.
Traditionally, tamarin and marmoset breeding systems have been described as monogamous extended family social units [Kleiman, 1977; Kleiman et al., 1988; Snowdon & Soini, 1988]. This interpretation has been questioned recently in light of more extensive field data on group size and composition, frequency of migration, and evidence of what appears to be a highly variable system of mating [Ferrari & Lopes Ferrari, 1989; Garber et al., 1984; Goldizen, 1987a,b, 1989, 1990; Stevenson & Rylands, 1988, Sussman & Garber, 1987; Sussman & Kinzey, 1984; Terborgh & Goldizen, 1985]. In particular, long-term field investigations of S. fuscicollis, the saddle-back tamarin, indicate that groups within a single population exhibit mat-ing patterns that are described as functionally monogamous, polyandrous, polyg-ynous, and/or polygynandrous [Goldizen, 1990; Goldizen & Terborgh, 19891. Poly-androus and/or polygynous, matings have also been observed in S. mystax [Pruetz & Garber, 1991; Ruth, 1991] and Callithrix humeralifer [Rylands, 1982, 1986], and are suspected in other tamarin species including S. imperator (Goldizen, 1987b] and S. geoffroyi [Garber & Zeigler, in preparation]. A breeding system character-ized by intense female competition, reproductive suppression, twinning, and high costs of infant care places severe constraints on individual reproductive opportu-nities. If the reproductive success of male and female tamarins is dependent on the cooperative rearing efforts of group helpers, then proximate conditions such as the number, age, sex, relatedness, and reproductive condition of animals residing in the same social group, as well as individual opportunities for dispersal into neigh-boring groups, are likely to regulate the expression and effectiveness of particular mating patterns. In this regard, Goldizen [1990:79) has suggested that the mating system of tamarins "appear[s] to be more directly affected by demographic factors ... than by ecological conditions."
In this paper we present demographic information collected over the course of 10 years on an island population of moustached tamarin monkeys, Saguinus mys-tax mystax, in Amazonian Peru, and address a series of questions regarding repro-ductive opportunities, dispersal, patterns of mating, and the role of kinship in primate social interactions. These questions are as follows:
As used here, the term mating to refers to copulatory behavior. A mating system therefore represents the pool of potential gene donors or the individuals within a group that copulate. In contrast, a breeding system refers only to those individuals that are successful gene donors and produce viable offspring. The term tamarin is restricted to callitrichines of the genus Saguinus.
