Socioecological factors and patterns of growth and development in two gorilla species

George Washington University, Washington DC

Investigators

Abstract

A central challenge in human evolutionary studies is to understand when, how and in what social and ecological context unique features of modern human life history evolved, including our early age at weaning, prolonged period of slow childhood growth, and late age at first reproduction. These key elements of our life histories are proposed underlie key shifts in human cognitive and behavioral evolution. Our closest living relatives, the great apes, provide critical comparisons for investigating human life history evolution, but current knowledge of their physical growth patterns remains overwhelmingly derived from captive studies and from chimpanzees. This project uses non-invasive methods to study growth and development in two long-term study populations of wild gorillas, for which there are very few existing data. The outcome of this research will significantly advance our understanding of comparative great ape development and will critically inform fundamental questions about the evolutionary origins of modern human life history. In addition, the research will result in a valuable new dataset of interest to researchers across several disciplines, and support important efforts in primate conservation, student training, research infrastructure, and international collaboration. This research employs a novel combination of non-invasive methods to integrate morphological, physiological, and behavioral data to generate a comprehensive understanding of the manner in which observed differences in life history and socioecology interact with variation in physical ontogeny within and among ecologically distinct populations of wild gorillas. Data to be collected from Karisoke mountain gorillas (N=115; 0-18 years, N=80 based on current demographics) include measures of morphological growth and development (dental emergence, linear body dimensions, muscle mass via urinary creatinine), maternal and offspring energetics and diet (urinary C-peptide, suckling rate and bout duration, diet composition and nutritional content), maternal dominance status and parity, and other measures of behavior (e.g., activity budgets, daily travel distance) and health. These data will be partnered with measures of dental and somatic growth determined from a naturally accumulated skeletal sample at this site. Comparative morphological and behavioral data for wild western lowland gorillas are from the Mbeli Bai Study, Republic of Congo (N=140; 0-18 years, N=50). The project aims to: 1) provide the first data on physical ontogeny in wild mountain gorillas of known age, and test hypothesized socioecological factors influencing variation in development and life history between mountain and western gorillas; 2) test maternal energetics, nutrition and other effects on variation in offspring dental and somatic development within mountain gorillas; 3) test relationships between measures of morphological development and key behavioral and reproductive life history measures in mountain gorillas; and 4) test whether the timing of developmental milestones assessed from skeletal remains differs significantly from those determined from surviving members of the same population. Results will yield a more comprehensive understanding of how and why dental, somatic, reproductive, and behavioral milestones co-vary in closely-related great ape taxa, and by shedding light on how individual variability in life history may be mediated by offspring growth, improve our understanding of reproductive (and thus, evolutionary) outcomes of ontogenetic variation. Further, by generating a comprehensive model of development and life history in these extant populations, and testing the accuracy of our life history inferences from an associated skeletal assemblage, our results are expected to significantly inform approaches to studying life history in fossil contexts.