Social and Ecological Challenges in Female Geladas: A Test of the Vocal Grooming Hypothesis

[摘要] Maintaining social bonds is an important and time-consuming part of primate life. Strong social bonds provide individuals with fitness benefits, yet grooming – the primary way in which primates socialize – requires a significant investment of time and energy. Vocalizations, in contrast, could furnish a different and efficient means of socializing, a strategy that may have been adopted by humans in their use of language. The hypothesis that calls serve to cement social bonds, known as the vocal grooming hypothesis, has yet to be tested empirically. This research presents a thorough test of the vocal grooming hypothesis in a highly social and exceptionally vocal primate, the gelada (Theropithecus gelada). Among geladas, an herbivorous primate that must spend much of their day feeding, time budgets are extremely strained. In this dissertation, I address each of the following components of the vocal grooming hypothesis: (1) I identify when and why social time is most constrained for female geladas; (2) I assess the impact of these constraints on individual reproductive fitness; (3) I identify when and how vocalizations are used as potential substitutes for grooming. To do so, I combine longitudinal behavioral and demographic data with extensive hormonal sampling, allowing me to capture variation across seasons, social contexts, and individuals.This research has 4 main findings that further our understanding of the role of vocalizations in primate social behavior. First, I identify two distinct kinds of social relationships that female geladas maintain: primary social partners and secondary social partners. Second, I demonstrate that both ecological and social factors can shape female reproductive timing. Third, I demonstrate that the optimal unit size for female gelada reproductive performance is larger than the number of grooming partners an individual female can maintain. Finally, I provide evidence that a specific kind of vocalization, the affiliative grunt or contact call, is used primarily between secondary social partners and is used more frequently when social time is most constrained. These results provide support for the idea that vocalizations may substitute for grooming. Specifically, I highlight how vocal grooming allows females to socialize with more individuals than they can through grooming alone, perhaps contributing to the stability of optimally-sized units.

[发布机构] University of Michigan

[效力级别] endocrinology

[关键词] primate behavior;endocrinology;evolution of social behavior;socio-ecology;reproduction;Ecology and Evolutionary Biology;Anthropology and Archaeology;Science;Social Sciences;Anthropology