Los Viejos Project: Aging in white-faced capuchins

Principal Investigators: Dr. Katharine Jack, Dr. Amanda Melin, and Dr. Fernando Campos 
Co-Investigators: Dr. Michael Gurven, Dr. James Highman; Consultant: Dr. Noah Synder-Mackler; Collaborators: Dr. Joe Orkin, Dr. Eva Wikberg, Dr. Yeonjoo Park 

Chronological age is a strong predictor of health and lifespan, but the pace of biological aging varies greatly between individuals. Some retain good health into advanced ages, while others experience age-related disease onset while relatively young. Much variation in the progression of human aging processes remains poorly explained, but a growing body of literature highlights the contributions of both the social and physical environment. Studies of human health and pace of aging are limited by the difficulty of collecting detailed within-subject longitudinal data on lived experience and health outcomes. Studies of humans also have numerous confounds, including individual variation in lifestyle, early-life experience, and access to health care. Accumulating evidence has revealed that longitudinal studies of wild nonhuman primates can provide invaluable insights into how social and physical environmental factors influence natural aging processes and the human healthspan. However, current sampling techniques and assessment tools used to study aging in primate models often rely on invasive sampling methods that are incompatible with many wild populations. Accordingly, most insights about aging from primate models come from captivity.

In this project, we are able to leverage our established population-based, longitudinal study of wild, white-faced capuchins (Cebus imitator) to generate insights into how social and physical environmental factors contribute to heterogeneity in rates of aging and health disparities. We have refined existing methods of observational data collection and develop new techniques for non-invasive, population-level sampling of wild animals to identify and study hallmarks of aging across behavioral, physiological, and molecular domains. The study of capuchin physical health in situ, when combined with our detailed dataset of lifetime social and environmental experiences, will allow us to holistically assess the impact of lived and intergenerational experiences on health outcomes and the pace of aging across individuals. Capuchins are medium-sized, platyrrhine primates that live in multi-male multi-female social groups, and females remain in their birth groups for life. If they survive into adulthood in the wild (6 years), they can expect to live another 11 years on average, yet they can live over 50 years in captivity. This potential for extended longevity and their similarities to humans, including large brains and complex social relationships, make capuchins well suited for translational studies of human health and aging 1.

At close to 30 years old, Legolas was one of our population’s oldest individuals.

The Scent of an Alpha Male: The Role of Urinary Volatiles in Male Dimorphism of Capuchins

Principal Investigators: Dr. Katharine Jack and Dr. Amanda Melin (with Dr. Anja Widdig, PI, and Dr. Jacinta Beehner, Co-I). Funded by the National Science Foundation (NSF BCS-2051573).

The existence of two physically and behaviorally distinct types of males in a single species is extremely rare in mammals but has now been documented in a number of primates. In species that display these alternative male morphologies, the larger, socially dominant, alpha male morph has higher testosterone and sires more offspring than the smaller subordinate male morph. This project investigates a potential role of olfactory communication in the development and maintenance of alternative male morphologies in a species of wild primate. The study’s integrative approach measures variation among males and advance a comprehensive understanding of this phenomenon while providing insight into the importance of olfactory communication in the biology and behavior of wild primates. Through this longitudinal and cross-sectional study, we are integrating methods from behavioral ecology with non-invasive measures of endocrinology, morphology, and chemical ecology to quantify and investigate the potential role of olfactory signaling in enforcing male rank.

A photograph of alpha male, Barty Crouch, with photogrammetric landmarks applied.

Making an alpha male: the behavior, endocrinology, and genetics of dominance in male white-faced capuchin monkeys (Cebus capucinus). 

One of my current research projects in Santa Rosa examines behavioral, endocrinological, and genetic correlates (including kinship, reproductive success, and the major histocompatibility complex [MHC]) of male life history and reproductive strategies. The main goal of this longitudinal project is to understand how hormonal and social factors influence the emergence, from puberty into adulthood, of dominance status in male white-faced capuchins (e.g. Jack et al., 2014). My collaborators (Stacey Tecot, and Eva Wikberg) and I have several current grants (Leakey Foundation, Nacey Maggioncalda Foundation, National Geographic Society) that enabled us to continue data collection for this project through 2017, thereby providing a decade of behavioral data and hormone samples from male capuchins residing in five study groups (2007-2017). Identifying traits and processes influencing individual variability in reproductive success is fundamental to understanding evolutionary processes. In our capuchins, like many other socially living mammals including humans, there is a strong association between dominance status and reproductive success, however we still know very little about how and why some males attain alpha status while others do not. These data, along with our ongoing studies of the role of the major histocompatibility in male dispersal and mate choice decisions (funded by the LA Board of Regents, with Jessica Lynch Alfaro), will provide us with a holistic picture for examining male dominance and reproductive biology.

Legolas has been the alpha male in our CP study group since 2007 (an impressive 10 years during which time he sired >20 offspring). This male has been studied since his birth in our LV study group in 1994. Update: Legolas is no longer alpha male as of Nov. 2018, though he remains on in the group as a subordinate male.

The effects of forest protection, forest regeneration, and climate change on primate populations.

My second major project in Santa Rosa involves an on-going examination of the long-term population trends of the capuchin and howler monkeys (e.g. Fedigan and Jack, 2012). We have been conducting park-wide censuses of these two primates since the project began in 1983, the most recent of which I co-directed with Fernando Campos in 2017. Several interesting trends have emerged from our analyses of these long-term data, the least of which is that if forest is protected and allowed to regenerate primate populations will return and thrive. To this end, we have documented that the population size more than doubled for both capuchin and howler monkeys between 1983 and 1999 (from <300 to > 600 individuals). However, between 1999 and 2007, the howler population experienced zero population growth, likely having reached the carrying capacity of the environment with regards to the state of forest regeneration. This population plateau was followed by an abrupt crash to ~300 howlers between the 2007 and 2011 censuses. We are currently exploring a variety of explanations for this dramatic decline (e.g. climate change and pesticide use), which was sustained in the 2013 and 2015 censuses 

Santa Rosa National Park at the end of the dry season. Photo taken by K. Jack in April 2015.