Early life experience and alterations of group composition shape the social grooming networks of former pet and entertainment chimpanzees (Pan troglodytes)

Abstract

The long-term effects of early life adversities on social capacities have been documented in humans and wild-caught former laboratory chimpanzees (Pan troglodytes). However, former pet and entertainment chimpanzees have received little attention to date. This study aimed to investigate the long-term effects of early life experience on 18 former pet and entertainment chimpanzees, based on social grooming data collected at a primate rescue centre over a 12year period. Moreover, we also focused on the possible short-term effects that alterations to group composition might have on grooming patterns. For this purpose, we compared stable and unstable periods (i.e. where alterations to group composition occurred). We used two individual social network measures to analyse the grooming activity and the distribution of grooming among group mates for each individual. We could show that wild-caught chimpanzees were significantly more selective regarding their grooming partners and spent less time grooming when compared to their captive born companions. We also found that individuals who were predominantly housed without conspecifics during infancy spent less time grooming compared to those who were predominantly housed with conspecifics during infancy. Furthermore, we found that alterations to the group composition had short-term effects on the distribution of social grooming from a more equal distribution during periods with a stable group composition towards a more unequal and selective distribution during unstable periods. Thus, we conclude that the social grooming networks of former pet and entertainment chimpanzees are shaped not only by long-term effects such as early life experience, but also by short-term effects such as alterations to group composition. Remarkably, we found not only captive born chimpanzees but also wild-caught individuals to adjust their grooming to socially challenging situations by modifying their grooming distribution in a similar way.

Personality, cognition and behavior in chimpanzees: a new approach based on Eysenck’s model

“…Hierarchical personality models, like Eysenck’s or the FFM, describe higher order traits which include several specific traits; and these lower traits are characterized by several behavioral responses ( Eysenck, 1990 ; DeYoung, 2006 ; DeYoung, 2010 ). Finally, it should be noted than we only had a small sample of chimpanzees, all coming from the same site (a primate rescue centre), with some of them having been exposed to traumatic past experiences which most likely shaped their personality ( Ortín et al, 2019 ) and their behavior ( Crailsheim et al, 2020 ).…”

Assessing the sociability of former pet and entertainment chimpanzees by using multiplex networks

“…Our latest long-term study on grooming networks in former pet and entertainment chimpanzees demonstrated variations in the grooming activity on an individual level based on the chimpanzees’ biographical background 30 . More precisely, we found wild-caught chimpanzees as well as chimpanzees who were predominantly housed without conspecifics during infancy to be more affected in their grooming activity and their distribution of grooming compared to those who were captive born as well as those who were predominantly housed with conspecifics during infancy.…”

“…In previous studies 26 , 30 we assessed chimpanzees sociability by looking into how their atypical life history affected their grooming activities based on their individual centrality scores. In this study, however, we chose a relational approach by taking the atypical life history not only of the individual but also of his/her partner into account when investigating their directed dyadic interactions.…”

“…We do not expect to find an interlayer correlation between stationary vicinity, representing a low-level interaction type, and either allogrooming or passive close proximity, representing high-level interaction types. Based on findings of long-term observations on this study population over a period of 12 years 30 and on ex-laboratory chimpanzees 49 , 50 , we also expected the chimpanzees’ biographical background to have an effect on the four different social interaction types. Here, we predict allogrooming as well as passive close proximity to be affected by early life history, as the toleration of permanent body contact and the ability to perceive the group members as trust-worthy may be impaired in adversely reared chimpanzees.…”

“…One of the most relevant social behaviours of chimpanzees is allogrooming 22,23 , which beside its hygienic function 24 is used to establish and maintain relationships, bonds and coalitions 25 . As such, many studies investigating the social networks of chimpanzees focus on social grooming as their edge variable [26][27][28][29][30] . In cases where allogrooming is rare or difficult to observe, information might be limited to spatial or temporal co-occurrences of two individuals 31 .…”