Characterizing Behavioural Measures of Age-Related Physical Decline in Wild White-Faced Capuchins (Cebus imitator)

Abstract

Aging research in animals promotes better understanding of the biology of aging and evolution of life history traits including longevity. It can also inform interventions that support physical functioning into advanced ages. Nonhuman primates are excellent models for human aging, but research is biased toward a few species in captivity. While capuchins are of enduring interest given their convergent evolution with humans, their aging patterns are poorly known. In this thesis, I led a cross-sectional study of behavioural aspects of physical aging in wild white-faced capuchins (Cebus imitator) at Santa Rosa, Costa Rica, asking whether age is associated with differences in the activity budget, posture and locomotion, microhabitat use, and food intake rates and preferences among adults; I also explored sex differences in these relationships. Using generalized additive mixed models to analyze 13 months of behavioural data collected from adults in five social groups (44 females and 25 males aged 6-30 years), I found partial support for my hypothesis that aging-associated physical declines decrease activity levels and abilities to engage in physically demanding behaviours. Older adults were more likely to rest and use the upper canopy but less likely to cling, run, suspend, and use vertical supports than younger adults. They also demonstrated shorter leap distances, lower intake rates of overall invertebrates, and reduced feeding preferences for extracted invertebrates. However, age was not significantly associated with frequencies of foraging, socializing, traveling, climbing, leaping, or ground use; intake rates for extracted invertebrates, mobile invertebrates, overall fruits, or encased fruits; or feeding preferences for mobile invertebrates or encased fruits. Across all behaviours, there were no significant sex differences in age patterns. This study is the first to report detailed behavioural patterns across adulthood in wild white-faced capuchins, establishing non-invasive measures of physical function for subsequent work on socioecological modifiers of the pace of biological aging in this system. Moreover, this research expands the taxonomic breadth of primate datasets for comparative aging research to include a remarkably long-lived platyrrhine.