Age related variation in male–male relationships in wild spider monkeys (Ateles geoffroyi yucatanensis)

Abstract

In social organizations characterized by male philopatry, social relationships between males are argued to be the strongest. Little is known about the social relationships of philopatric male spider monkeys. To address this limitation, we investigated social relationships among individually recognized wild adult male spider monkeys from two well-habituated communities in the Yucatan Peninsula, Mexico, focusing on affiliative behaviors important in regulating male social relationships, including grooming, embracing, arm-wrapping, and grappling. We examined whether behaviors were reciprocated between male partners and whether age was a factor in how the behaviors were distributed or reciprocated, by examining differences between younger adult males (<10 years) and older adult males (≥14 years). Although we found evidence that affiliative behaviors were overall reciprocated between spider monkey adult males, there were pronounced differences in the interactions depending on their relative age. Reciprocation in grooming and embraces between same-age males suggests their relationships are valuable to both partners. Among different-age dyads, younger males gave more embraces than they received, were the initiators of grappling and arm-wrapped more often than with same-age males, suggesting relationships between younger and older males are more risky. This confirms that younger males are attracted to older males, probably because they value relationships with older males more than the reverse, but they are also at risk.

Male philopatry in spider monkeys revisited

“…Male–male social relationships within the same community appear as the strongest because of the highest levels of affiliation (Fedigan and Baxter, ; van Roosmalen and Klein, ; Symington, ; Slater et al, ) and because of males' cooperation with one another in dangerous activities associated with between‐community interactions, such as border patrols and raids (Aureli et al, ; Wallace, ). However, at some level philopatric males are also rivals in within‐community competition, despite sometimes being closely‐related to one another, and interactions between males, especially between younger and older males, can be risky and may have lethal consequences (Campbell, ; Valero et al, ; Vick, ; Rebecchini et al, ; Schaffner et al, ).…”

“…A combination of sampling methods (Altmann, ) was used to collect behavioral data on activity and social interactions: 10‐minutes instantaneous sampling of all visible subgroup members in which their activities and proximity (within an arm reach) with other individuals were scored; all‐occurrence sampling of conspicuous events, such as fissions, fusions, and escalated aggression; and ad libitum sampling of approaches, grooming, play, and three additional typical spider monkey behaviors, “embraces,” “arm‐wrapping,” and “grappling” (van Roosmalen and Klein, ; Slater et al, ; Schaffner et al, ). “Embraces” (i.e., where an individual places its arm around the neck or back of another individual while facing the recipient, typically lasting only a few seconds) are most commonly observed at times when animals are at greater risk of aggression from conspecifics, such as during fusion events (when aggression is more likely: Aureli and Schaffner, ) or when mothers with vulnerable infants are approached by other adults (Schaffner and Aureli, ; Slater et al, ).…”

“…“Arm‐wrapping” (i.e., where each individual places an arm around the partner's back while both are facing forward and jointly threatening a third party) is a coalitionary behavior manifest during aggressive situations. “Grappling” (i.e., where animals engage in a prolonged exchange of physical contact that can involve facial greeting, face touching, tail wrapping, pectoral sniffing, genital contact, and embraces) appears to occur typically between males when there is strong attraction on the part of a younger male toward an older male, in conjunction with a substantial risk to the younger male (Aureli and Schaffner, ; Vick, ; Schaffner et al, ) due to aggression it can receive from older males, which can even have lethal consequences (Campbell, ; Valero et al, ; Vick, ). All of these types of data were recorded into a dictaphone and then transcribed into a computer database within 1–3 days of being collected.…”

“…Recent field observations, however, suggest that male–male relationships may not be as consistently and uniformly strong as previously thought (Aureli and Schaffner, ). For example, in A. geoffroyi some male–male social relationships are tenuous and prone to risk, as evidenced by relatively high rates of exchanges between males of behaviors associated with appeasement and aggression (Rebecchini et al, ; Schaffner et al, ).…”

Seasonal changes in social cohesion among males in a same‐sex primate group

“…In some primate species (e.g., patas monkeys [ Erythrocebus patas ] (Cords, ; Harding & Olson, )), male intrasexual relationships are highly adversarial and intolerant. In other taxa (e.g., chimpanzees [ Pan troglodytes ] (Mitani, ), spider monkeys [ Ateles geoffroyi ] (Schaffner, Slater, & Aureli, ), Assamese macaques [ Macaca assamensis ] (Schülke, Bhagavatula, Vigilant, & Ostner, ), bonnet macaques [ M. radiata ] (Adiseshan, Adiseshan, & Isbell, )), adult males form strong, and persistent social affiliations. Given that many primate species live in stable multimale multifemale groups, a lone male may profit from the presence of additional males – both related and unrelated – through the services they provide, e.g., vigilance, cooperative hunting, resource defense, and cooperative defense of females against rivals inside and outside the group (Bissonnette et al, ; Díaz‐Muñoz et al, ; Ostner & Kappeler, ; van Hooff, ).…”