Sociality in Callithrix penicillata: II. Individual Strategies During Intergroup Encounters

In social animals, intergroup interactions, whether through agonistic and competitive behaviors or affiliative ones, can influence important parameters such as home range, territory sizes, and access to resources, which may directly affect both female and male fitness. We studied the intergroup interaction patterns of a wild group of black-tufted-ear marmosets (Callithrix penicillata) in central Brazil. Agonistic interactions occurred at low frequencies during intergroup encounters. The marmosets directed agonistic interactions without physical aggression primarily against same-sex individuals, suggesting that male and female aggression patterns are shaped by their sexual interests. However, females of the focal group also directed agonistic behavior toward extragroup males that attempted copulation. The marmosets appeared to use intergroup encounters to gather information about possible partners and extragroup reproductive opportunities. Intergroup sexual interactions occurred mainly in the form of copulations or attempted copulations by all adults, with the exception of the dominant female. Our results suggest that a possible reproductive strategy used by males is to attempt fertilization of extragroup females. Adult males copulated with the same extragroup female during several opportunities, which suggests sperm competition or the establishment of social bonds with neighboring females.