Ontogenetic Dietary Shifts and Microscopic Tooth Wear in Western Chimpanzees

Julia Stuhlträger,Kornelius Kupczik,Roman M Wittig,Ellen Schulz-Kornas

doi:10.3389/fevo.2019.00298

Abstract

Microscopic tooth wear studies on primates have largely focused on interspecific dietary comparisons, while few have addressed intraspecific variations such as those among age groups. Here, we examined to what extent dietary shifts during ontogeny can be revealed from microscopic tooth wear in a western chimpanzee population using 3D surface texture (3DST) analysis. To this end, we analyzed feeding observation data of 14 chimpanzees of the Taї National Park (Ivory Coast) and matched them to 3DST data analyzed on two wear facets (f9, f3) of deciduous fourth premolars and permanent molars of 41 specimens (infants, juveniles, adolescents, adults) of the same population. We expected to find an age-dependent increase in texture complexity resulting from the more frequent consumption of seeds and insects in older compared to younger individuals. Furthermore, we expected the introduction of phytolith-producing plants to the diet of post-weaned individuals to result in many small and parallel-orientated 3DST features in juveniles, adolescents and adults compared to infants. We found that the 3DST pattern did not mirror the observed increase in dietary breadth from infants to adults. However, we found that age-dependent differences in the consumption of phytolith-producing plants were reflected to some extent in the 3DST pattern: infants and adolescents who spent more time feeding on phytolith-producing plants than older individuals had more parallel orientated 3DSTs with higher peaks, while adults had flatter and more randomly orientated 3DST features. Our results suggest that phytoliths as small abrasive particles may be of greater importance for the 3DST formation than food categories such as fruits, leaves or seeds. However, compared to the variation in the feeding data, 3DST results show only little variation among age groups. We conclude that 3DST does not explicitly reflect ontogenetic dietary changes in chimpanzees. Rather, other factors, such as individual- or sex-based feeding habits as well as seasonal variation in dust accumulation, may be of greater importance for 3DST formation.

Highlights

In western chimpanzees (P. t. verus) of the Taï National Park (Ivory Coast) post-weaned individuals commonly feed on phytolith-producing plants, while it was suggested that individuals up to 3 years complement their nutritional needs with a phytolith-free diet (Power et al, 2015)
While such studies have generally focused on dietary proclivities of individuals within a single species using predominantly permanent teeth, the aim of the present study was to assess whether the distinct dietary preferences observed among four age groups in the western chimpanzee Taï forest population are reflected in their microscopic tooth wear patterns (3DST data)
We found some evidence that the proportion of time spent feeding on phytolith-producing plants has a larger influence on 3D surface texture (3DST) than large hard objects, such as seeds

Summary

Introduction

The diet of chimpanzees (Pan troglodytes) includes mostly fruits, and leaves, piths and other vegetative plant parts as well as animal resources (e.g., Hiraiwa-Hasegawa, 1990a; Tutin et al, 1991; Boesch and Boesch-Achermann, 2000; Morgan and Sanz, 2006; Pruetz, 2006; Fahy et al, 2013). Other than the reported differences in fruit content in the diet among chimpanzee subspecies, several authors have reported age-related feeding preferences within populations as well (e.g., Hiraiwa-Hasegawa, 1990a,b; Matsumoto, 2017). A continuous increase in the feeding bouts on seed-rich Ficus fruits until an age of

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