Male capuchin monkeys are seen in mating ritual – 06/19/2023 – Science

The complex mating ritual typical of capuchin monkeys can also be practiced by two individuals of the same sex, shows a study signed by researchers from USP (University of São Paulo).

The data, which were obtained during the observation of the animals in the Atlantic forest of southern Bahia, are yet another example of how homosexual behavior is relatively common among primates and other animals.

“In the case of capuchin monkeys, there are still few studies on the subject, but it is very likely that we will identify several other similar cases”, he told the Sheet the first author of the study, Irene Delval, who is currently a postdoctoral researcher at the Department of Experimental Psychology at USP.

She signs the work with three colleagues from the São Paulo university (Marcelo Fernández-Bolaños, Patrícia Izar and Jaroslava Varella Valentova) and with Elisabetta Visalberghi, a primatologist at the Italian National Research Council.

Delval is Spanish and says that she always wanted to study primates in the wild, which brought her to Brazil, where she also completed her master’s and doctorate, starting at the beginning of the last decade. One of the researcher’s interests is the development of personality in primates from the first months of life, in a process that has many similarities with the same process in humans.

“We manage to accompany the puppies from birth, in the most varied aspects, such as breastfeeding, the relationship between mother and puppy, interactions and games between the puppies”, he explains. One of the places where the team monitors is the Una Biological Reserve, near Ilhéus (BA), where there is a group of about 30 yellow-breasted capuchin monkeys (Sapajus xanthosternos), a critically endangered species.

Capuchin monkeys are famous for their intelligence and behavioral flexibility, being able to use tools (such as round stones and chopsticks) to obtain food in a variety of ways. The animals’ love lives are similarly intricate, involving a long “courtship” ritual in which the females take the initiative.

While courting the male over several hours and days, the female capuchin monkey adopts a series of ritualized behaviors, including typical vocalizations and facial expressions (raising her eyebrows and giving “smiles”, for example), as well as displaying her genitalia.

At first, it is common for the male to ignore these invitations and even be rude, before finally giving in and copulating with the suitor. To date, the few cases of homosexual behavior recorded for capuchin monkeys have only involved males “mounting” each other.

The situation caught by the researchers in the new study, which is in the specialized journal Archives of Sexual Behavior, is much more complex. The data are recorded in a 15-minute video in which two young males appear —Dumbo, aged between 5 and 6 years, and Pimenta, aged about a year and a half.

When the researchers started recording, the sexual interactions had already started, with Pimenta “riding” Dumbo. Both males took turns in this role and showed erections during the process, but much of the behavioral repertoire of the mating ritual was also present.

To be exact, the researchers accounted for 16 of the 20 typical capuchin “courtship” movements, including facial expressions (though without the initial “rejection” phase of one animal by the other).

The team also observed behaviors that are not usually part of this traditional repertoire, but which seem to denote intimacy between young males, such as hugging, positioning the head of one animal close to the chest of the other, sniffing it, mutual caresses on the chest and the intertwining of tails during “mounting”.

“In many species of primates and other animals, it is common for homosexual behavior to be seen as a way of managing or minimizing conflicts between group members, but that doesn’t seem to be the case here,” says Delval.

Several other possible explanations exist for the interaction between Pepper and Dumbo, but follow-up to the group indicates that they were already quite close to each other and had a friendly relationship.

“Because of this, they could simply be showing affection, even more so because, in the case of Pimenta, it is an age when sexual activity is not expected”, says the Spanish researcher.

It is possible to speculate that the friends were even saying goodbye, since, shortly afterwards, Dumbo transferred to another pride, which is common in the case of males his age.

On the other hand, the behavior could be linked to the learning of mating rituals, with young males copying actions practiced by the females of the species. There are still no records of a pair of females acting in this way among capuchin monkeys, but Delval says that this possibility cannot be ruled out.