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Substantial variation exists in the mechanical properties of foods consumed by primate species. This variation is known to influence food selection and ingestion among non-human primates, yet no large-scale comparative study has examined the relationships between food mechanical properties and feeding strategies. Here, we present comparative data on the Young's modulus and fracture toughness of natural foods in the diets of 31 primate species. We use these data to examine the relationships between food mechanical properties and dietary quality, body mass, and feeding time. We also examine the relationship between food mechanical properties and categorical concepts of diet that are often used to infer food mechanical properties. We found that traditional dietary categories, such as folivory and frugivory, did not faithfully track food mechanical properties. Additionally, our estimate of dietary quality was not significantly correlated with either toughness or Young's modulus. We found a complex relationship among food mechanical properties, body mass, and feeding time, with a potential interaction between median toughness and body mass. The relationship between mean toughness and feeding time is straightforward: feeding time increases as toughness increases. However, when considering median toughness, the relationship with feeding time may depend upon body mass, such that smaller primates increase their feeding time in response to an increase in median dietary toughness, whereas larger primates may feed for shorter periods of time as toughness increases. Our results emphasize the need for additional studies quantifying the mechanical and chemical properties of primate diets so that they may be meaningfully compared to research on feeding behavior and jaw morphology., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Our aim is general: we want to illustrate how much can be gleaned from mechanical measurement in the field. We ask how mechanics may constrain foraging and feeding on both plants and animals, and how various aspects of mechanical behavior could affect the feeding choices that primates make. Here, we present novel methods for the measurement of the material properties and also the employment of tried and tested methods in novel settings. This review demonstrates how mechanical investigation methods can quantify the environmental factors affecting primate locomotion to and from food, which makes up a large part of a primate's daily energy budget. We indicate that, despite the accumulation of much data on the material properties of primate foods, the introduction of new methods is allowing researchers to pursue new avenues of research and change paradigms in primate feeding ecology. Field methods are presented that could aid in the understanding of the extra-oral processing of foodstuffs by primates and enrich further studies into cognition and culture surrounding these types of behavior. We conclude that the use of in-field measurements and a greater understanding of the physics of primate environments are vital and exciting themes integral to the continued understanding of primate evolution and biology., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Primate teeth adapt to the physical properties of foods in a variety of ways including changes in occlusal morphology, enamel thickness, and overall size. We conducted a comparative study of extant primates to examine whether their teeth also adapt to foods through variation in the mechanical properties of the enamel. Nanoindentation techniques were used to map profiles of elastic modulus and hardness across tooth sections from the enamel-dentin junction to the outer enamel surface in a broad sample of primates including apes, Old World monkeys, New World monkeys, and lemurs. The measured data profiles feature considerable overlap among species, indicating a high degree of commonality in mechanical properties. These results suggest that differences in the load-bearing capacity of primate molar teeth are more a function of morphology-particularly tooth size and enamel thickness-than of underlying mechanical properties., (Copyright © 2012 Wiley Periodicals, Inc.)

A number of living primates feed part-year on seemingly hard food objects as a fallback. We ask here how hardness can be quantified and how this can help understand primate feeding ecology. We report a simple indentation methodology for quantifying hardness, elastic modulus, and toughness in the sense that materials scientists would define them. Suggested categories of fallback foods-nuts, seeds, and root vegetables-were tested, with accuracy checked on standard materials with known properties by the same means. Results were generally consistent, but the moduli of root vegetables were overestimated here. All these properties are important components of what fieldworkers mean by hardness and help understand how food properties influence primate behavior. Hardness sensu stricto determines whether foods leave permanent marks on tooth tissues when they are bitten on. The force at which a food plastically deforms can be estimated from hardness and modulus. When fallback foods are bilayered, consisting of a nutritious core protected by a hard outer coat, it is possible to predict their failure force from the toughness and modulus of the outer coat, and the modulus of the enclosed core. These forces can be high and bite forces may be maximized in fallback food consumption. Expanding the context, the same equation for the failure force for a bilayered solid can be applied to teeth. This analysis predicts that blunt cusps and thick enamel will indeed help to sustain the integrity of teeth against contacts with these foods up to high loads.

Evolution of the red-green visual subsystem in trichromatic primates has been linked to foraging advantages, namely the detection of either ripe fruits or young leaves amid mature foliage. We tested competing hypotheses globally for eight primate taxa: five with routine trichromatic vision, three without. Routinely trichromatic species ingested leaves that were "red shifted" compared to background foliage more frequently than species lacking this trait. Observed choices were not the reddest possible, suggesting a preference for optimal nutritive gain. There were no similar differences for fruits although red-greenness may sometimes be important in close-range fruit selection. These results suggest that routine trichromacy evolved in a context in which leaf consumption was critical.

What kinds of fractures do teeth sustain and how do they resist disintegration? This study involved the mechanical loading of extracted human and sea otter teeth using hard and soft indenters to simulate hard and soft diets. The tests were accompanied by real-time imaging. At least three types of fracture were seen in the enamel - median, radial and margin cracks. Each kind of fracture appears to have a different cause, although the distinction between median and radial cracks blurs as they propagate. Only margin cracks appear to form under soft indenters. Several aspects of tooth form can be described as devices to limit damage to a tooth crown against the onslaught of hard or soft foods. The damage modes of teeth are paralleled by the behavior of some bilayered hard foods. [ABSTRACT FROM AUTHOR]

Ateles spp. and Alouatta spp. are often sympatric, and although they are mainly frugivorous and folivorous, respectively, they consume some of the same fruit species. However, they differ in terms of color vision, which is thought to be important for fruit detection. Alouatta spp. have routine trichromatic color vision, while Ateles spp. presents the classic polymorphism of platyrrhines: heterozygous females have trichromatic color vision, and males and homozygous females have dichromatic vision. Given these perceptual differences, one might expect Alouatta spp. to consume more reddish fruits than Ateles spp., since trichromats have an advantage for detecting fruits of that hue. Furthermore, since Ateles spp. have up to six different color vision phenotypes, as do most other platyrrhines, they might be expected to include fruits with a wider variety of hues in their diet than Alouatta spp. To test these hypotheses we studied the fruit foraging behavior of sympatric Alouatta palliata and Ateles geoffroyi in Costa Rica, and modeled the detectability of fruit via the various color vision phenotypes in these primates. We found little similarity in fruit diet between these two species (Morisita=0.086). Furthermore, despite its polymorphism, A. geoffroyi consumed more reddish fruits than A. palliata, which consumed more greenish fruits. Our modeling results suggest that most fruit species included in the diet of A. geoffroyi can be discriminated by most color vision phenotypes present in the population. These findings show that the effect of polymorphism in platyrrhines on fruit detection may not be a disadvantage for frugivory. We suggest that routine trichromacy may be advantageous for other foraging tasks, such as feeding on young leaves. Am. J. Primatol. 67:399–409, 2005. © 2005 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Although most arguments explaining the predominance of polymorphic color vision in platyrrhine monkeys are linked to the advantage of trichromacy over dichromacy for foraging for ripe fruits, little information exists on the relationship between nutritional reward and performance in fruit detection with different types of color vision. The principal reward of most fruits is sugar, and thus it seems logical to investigate whether fruit coloration provides a long-distance sensory cue to primates that correlates with sugar content. Here we test the hypothesis that fruit detection performance via trichromatic color vision phenotypes provides better information regarding sugar concentration than dichromatic phenotypes (i.e., is a color vision phenotype with sufficient red-green (RG) differentiation necessary to “reveal” the concentration of major sugars in fruits?). Accordingly, we studied the fruit foraging behavior of Ateles geoffroyi by measuring both the reflectance spectra and the concentrations of major sugars in the consumed fruits. We modeled detection performance with different color phenotypes. Our results provide some support for the hypothesis. The yellow-blue (YB) color signal, which is the only one available to dichromats, was not significantly related to sugar concentration. The RG color vision signal, which is present only in trichromats, was significantly correlated with sugar content, but only when the latter was defined by glucose. There was in fact a consistent negative relationship between fruit detection performance and sucrose concentration, although this was not significant for the 430 nm and 550 nm phenotypes. The regular trichromatic phenotypes (430 nm, 533 nm, and 565 nm) showed higher correlations between fruit performance and glucose concentration than the other two trichromatic phenotypes. Our study documents a trichromatic foraging advantage in terms of fruit quality, and suggests that trichromatic color vision is advantageous over dichromatic color vision for detecting sugar-rich fruits. Am. J. Primatol. 67:411–423, 2005. © 2005 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Here we describe correlations among visual ecology and the physiochemical properties of fruits and leaves consumed by four species of catarrhine primate: Cercopithecus ascanius, Colobus guereza, Pan troglodytes, and Piliocolobus badius. Collectively, their diet was diverse, with each species relying on fruits and leaves to different extents. The mean chromaticity of both foods, as perceived by the green-red and yellow-blue signals that catarrhines decode, was distinct from background foliage. However, selection on the basis of color was evident only for leaves. Primates consumed leaves with higher green-red values than the leaves they avoided–sensory mechanism that correlated with key nutritional variables, such as increased protein and reduced toughness. Moreover, the monkeys ingested leaves near dusk, when reddish targets may be more salient. Similar patterns were never observed with respect to edible fruits, the chromaticities of which did not differ from unconsumed fruits or correlate with nutritional properties. We also found that primate biomass is higher in seasonal sites. We conclude that these findings are consistent with the notion that routine trichromatic vision evolved in a context where seasonal folivory was pivotal to survival. Am. J. Primatol. 62:189-207, 2004. © 2004 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Reports on an experiment to determine the value of the capacity to discriminate red-green colors in primates. Statement that trichromatic primate species in Kibale Forest, Uganda, eat leaves that are color discriminated only by red-greenness; Methods; Results; Conclusion that trichromacy is valuable to primates foraging for leaves.