Proximity and grooming patterns reveal opposite-sex bonding in Rwenzori Angolan colobus monkeys (Colobus angolensis ruwenzorii)

Abstract

Close proximity and social grooming are important bonding mechanisms in primates. These behaviors show the social structure of a species and many studies have found positive correlations between the degree of kinship and grooming and proximity. We used 1 year of data collected via instantaneous scan sampling on a large "supertroop" of Colobus angolensis ruwenzorii at Lake Nabugabo, Uganda, to examine partner preferences for grooming and nearest neighbors in each age-sex class. Little is known about this species, so we based our hypotheses on congeners. Of the five species of black-and-white colobus, data on sex-biased dispersal patterns are available for three (C. guereza, C. vellerosus, and C. polykomos), all of which show male-biased dispersal with occasional female dispersal. We thus predicted that female C. a. ruwenzorii would be more strongly bonded than males, showing greater proximity and grooming. We did not expect bonding between the sexes since congeners do not show this pattern. We found that among adult dyads, males and females were more likely to be found in loose proximity, and to groom, than would be expected given group composition. Conversely, both males and females had relatively weak same-sex relationships. Between the sexes, adult males had higher proximity and grooming indices with adult females without infants than with females with infants. These observations indicate that this subspecies is cross-bonded and that both sexes may disperse. Furthermore, our findings suggest that the social organization and social structure of C. a. ruwenzorii differ greatly from other black-and-white colobus species.

A multi-level society comprised of one-male and multi-male core units in an African colobine (Colobus angolensis ruwenzorii)

“…This aligns with what is known about their dispersal patterns, as males tend to disperse from their natal band prior to sexual maturity, limiting the opportunities for this sex to form long-term bonds with other core unit members 66–68 (although see 68–69 ). Previous work on our study population found that cross-sex bonding is stronger than bonding among the sexes 52 , a pattern associated with bi-sexual dispersal in other primates 80 . Bi-sexual dispersal is supported in this subspecies, as over the course of the year, we observed a total of eight dispersals, four females and four males.…”

“…where groups typically average less than 20 individuals (reviewed by Fashing 51 ). Rwenzori Angolan colobus at our study site at Lake Nabugabo, Uganda form large groups of about 200 individuals and exhibit a greater degree of fission-fusion dynamics than reported at Nyungwe 52 . The aims of this study were 1) to determine if Rwenzori Angolan colobus at Nabugabo are forming a multi-level society and if so, 2) to determine the core unit composition and tier number.…”

“…These groups of individuals were referred to as ‘core units’. Individuals within a core unit were not only spatially cohesive, but also socially cohesive; direct interactions (e.g., grooming 52 , copulations) were only ever observed to occur between members of the same core unit. Note that all adult males in multi-male/multi-female core units were seen to mate with females, with the exception of one seemingly very old male in core unit PS, who sometimes trailed his unit.…”

Anogenital distance as a measure of male competitive ability in Rwenzori Angolan colobus

“…We are just beginning to understand the social organization and social structure of C. angolensis ruwenzorii (Stead & Teichroeb, 2019) and the form of male relationships is still unclear. We know that within their unique multilevel society, adult males and adult females groom most frequently within core units (Arseneau‐Robar et al, 2018), which is supported by the bisexual dispersal we have observed from natal units (Stead & Teichroeb, 2019). However, the distance of dispersal between the sexes appears to differ.…”

Spatiotemporal association patterns in a supergroup of Rwenzori black‐and‐white colobus (Colobus angolensis ruwenzorii) are consistent with a multilevel society

“…; Rawson, 2009), proboscis monkeys ( Nasalis larvatus ; Yeager, 1990), snub‐nosed monkeys ( Rhinopithecus spp. ; Kirkpatrick & Grueter 2010; Qi et al, 2014), and recently Rwenzori colobus ( Colobus angolensis ruwenzorii ), which form temporary associations of more than 100 individuals at a lowland site in Uganda (Lake Nabugabo) (Arseneau‐Robar, Joyce, Stead, & Teichroeb, 2018; Stead & Teichroeb, 2019), are confirmed to have a multilevel society with three social tiers (Stead & Teichroeb, 2019). A study at the same site on proximity and grooming patterns reveals opposite‐sex bonding and weak same‐sex bonds within dyads of the Rwenzori colobus (Arseneau‐Robar et al, 2018).…”