Comparative studies of social behavior in Callicebus and Saimiri: Heterosexual jealousy behavior

Abstract

1. In nature, titi monkeys (Callicebus moloch) are typically found in small ‘family-type’ groups, the nucleus of which is an adult male and female that form strong and abiding emotional attachments to one another. 2. To further understand the behavioral basis for this monogamous patern, the present experiment investigated the possibility that a mechanism tending to prevent accretions to the minimal male-female unit is ‘jealous behavior,’ defined as a specific set of spatial and agonistic responses occurring when a subject encounters its mate in proximity to a perceived competitor or rival. Ten adult titi monkeys housed in heterosexual pairs were observed in three sets of test conditions, one of which (Cagemate vs. Intruder) presented the subject's mate in three levels of increasing proximity to a stranger of the subject's sex (intruder). A parallel set of ‘control’ conditions (Opposite-Sex Stranger vs. Intruder) and three Single-Stimulus conditions were also presented. To provide comparative data on jealousy behavior in a nonmonogamous primate, ten adult squirrel monkeys (Saimiri sciureus) housed in malefemale pairs were tested in the same circumstances. 3. Results from the jealousy conditions indicated a large, unanticipated sex difference in Callicebus. Male titis displayed a marked enhancement of attraction to the mate and an increment in agonism toward the intruder as a function of increasing proximity of intruder and mate (Fig. 3a). Female titis, however, showed an opposite reaction, displaying highest levels of attraction to the mate when the intruder was most distant (Fig. 3b). Neither sex of Saimiri showed significant jealousy reactions (Fig. 3c and d). Results from the Single-Stimulus conditions corroborated previous data indicating that basic attractions between male-female cagemates are both stronger and more specific in Callicebus than in Saimiri (Fig. 2). 4. The sex difference in reactions to jealousy conditions found for titis in our experiment is consistent with available field notes on their behavior in the wild, and is interpreted in terms of the particular contingencies of male and female reproductive success in a monogamous social system. In particular, it is suggested that jealousy behavior in monogamous males reduces the likelihood of being cuckolded.