Behaviour 2019
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The effects of maternal presence, rank and investment on offspring muscle development in wild chimpanzees
Patrick Tkaczynski1, Liran Samuni1,2, Tobias Deschner1, Therese L÷hrrich3,4, Pawel Fedurek1,5, Roman Wittig1,2, Catherine Crockford1,2. 1Max Planck Institute for Evolutionary Anthropology, Leipzig, Sachsen, Germany; 2Ta´ Chimpanzee Project, Centre Suisse de Recherches Scientifiques, Abidjan, , Cote d Ivoire; 3World Wide Fund for Nature, Dzanga Sangha Protected Areas, Bangui, , Central African Republic; 4Epidemiology of Highly Pathogenic Microorganisms, Robert Koch Institute, Berlin, , Germany; 5Department of Psychology, University of Stirling, Stirling, , United Kingdom

Maternal care and provisioning during immaturity may optimize offspring growth patterns. The prolonged juvenile dependence and maternal care seen in humans is a distinctive life history adaptation likely adaptively selected to enable sustained somatic and brain development. In chimpanzees, immature individuals continue to associate with their mothers years beyond weaning, however, whether this prolonged association influences growth patterns is not clear. Urinary creatinine concentration has been validated as a non-invasive measure of muscle mass in wild chimpanzees. In our study, we examined how maternal presence and characteristics influence urinary creatinine concentrations in wild chimpanzees from the Ta´ population aged 0-15 years. The dataset included repeated sampling of 93 individuals (1509 samples). Maternal presence positively influenced offspring muscle mass throughout ontogeny such that orphaned chimpanzees had less muscle mass than non-orphans. For offspring with mothers, those with top-ranking mothers had greater muscle mass. Male offspring with greater levels of maternal investment (using inter-birth interval as a proxy measure) also had greater muscle mass.