Unexpected hard‐object feeding in Western lowland gorillas

Abstract

Objectives: Gorilla diets are characterized by large amounts of fruit and tough fibrous plant material. Hard-object feeding is not generally associated with this genus as the high crests on their molar teeth would be at risk of damage from the mechanically challenging woody endocarp. This study aims to demonstrate that at least one population of western lowland gorillas are seasonal hard-object feeders, orally processing the seeds of Coula edulis. Materials and methods:Feeding behavior of habituated western lowland gorillas and phenology of fruiting trees was observed over a 4-year period to determine the extent they exploited the seeds of C. edulis. Additionally, the endocarps of C. edulis were subjected to testing to determine their mechanical properties.Results: Our results demonstrate that during the fruiting season (January, February, and December) gorillas consistently opened the seeds of C. edulis using their postcanine dentition. The protective endocarp is composed of a very stiff material, presenting a substantial mechanical challenge to a gorilla. However, the high ratio between elastic modulus and toughness will facilitate brittle, cataclysmic fracture of the seed shell given a high enough load.Discussion: Although a rich energy source, C. edulis likely tax gorilla dentitions to their upper limit. The rarity of such behavior at sites where it could be observed may indicate a degree of social learning or culture driving its occurrence. This shows a greater breadth of gorilla diets than previously described and suggests gorillas may be a useful model for interpreting the dietary mechanics that necessitated robust craniodental morphology in australopiths. K E Y W O R D Sfood mechanical properties, gorilla, hard-object feeding

Extractive foraging on hard‐shelled walnuts and variation of feeding techniques in wild Japanese macaques (Macaca fuscata)

“…Therefore, a small mouth and the feeble occlusal force of immatures may be the major constraint for not feeding on large and hard walnuts. Such a requirement of sufficient physical strength and dental development in extractive foraging is also reported in tufted capuchin monkeys to feed on Maximailiana maripa fruit (Gunst et al, 2010), larvae in a bamboo stalk (Gunst et al, 2010), and in western lowland gorillas ( G. gorilla gorilla ) to feed on the hard seeds of Coula edulis (van Casteren et al, 2019). A five‐year‐old female ( Mb ) was the youngest monkey that showed complete cracking.…”

“…I found some sex‐specific differences in walnut feeding behavior in wild Japanese macaques. Sexual differences in feeding efficiency are reported in some primate species and are likely to be observed when species with large sexual dimorphism feed on foods which require physical strength (van Casteren et al, 2019; Gunst et al, 2010; Nakagawa, 1999; Post et al, 1980). Additionally, in such cases, the food processing pattern also seems to be different between sexes.…”

“…Some primate species, for instance, show a dental adaptation for the consumption of mechanically protected foods (Daegling et al, 2011; Martin et al, 2003; McGraw et al, 2011, McGraw et al, 2014; Norconk and Veres, 2011). Wild western lowland gorillas’ robust masticatory apparatus enables them to access the nutrient endosperm of C. edulis (van Casteren et al, 2019). Aye‐ayes ( Daubentonia madagascariensis ) have an unusually thin middle finger for tap‐scanning behavior to excavate insects from deadwoods (Erickson, 1994).…”

“…Furthermore, most previous studies have focused only on manual food processing for the consumption of prickly foods, including in great apes (e.g., Byrne and Byrne, 1993; Corp and Byrne, 2002; Stokes and Byrne, 2001; Tan et al, 2016; Trébouet et al, 2018). As to hard‐object feeding, on the other hand, although many researchers investigated morphological adaptations to oral processing of hard foods in an array of primate species (e.g., van Casteren et al, 2019; Daegling et al, 2011; Martin et al, 2003; McGraw et al, 2011; Norconk and Veres, 2011), there is no published study that describes hard food processing in detail and refers to the presence of certain feeding techniques against the type of food defense.…”

Tooth chipping patterns inParanthropusdo not support regular hard food mastication

“…In H. neanderthalensis , the high rate of fractures is thought to be caused by non-masticatory activities, but in H. naledi it likely relates to ingesting environmental contaminants, such as grit (Fiorenza & Kullmer, 2013; Fox & Frayer, 1997; Towle et al, 2017). Grit is also masticated by many extant primates, and likely influences chipping rates in certain species (e.g., Van Casteren et al, 2019; Fannin et al, 2020).…”