The morphology of the masticatory apparatus facilitates muscle force production at wide jaw gapes in tree-gouging common marmosets (Callithrix jacchus)

Abstract

SUMMARYCommon marmosets (Callithrix jacchus) generate wide jaw gapes when gouging trees with their anterior teeth to elicit tree exudate flow. Closely related cotton-top tamarins (Saguinus oedipus) do not gouge trees but share similar diets including exudates. Maximizing jaw opening theoretically compromises the bite forces that marmosets can generate during gouging. To investigate how jaw-muscle architecture and craniofacial position impact muscle performance during gouging, we combine skull and jaw-muscle architectural features to model muscle force production across a range of jaw gapes in these two species. We incorporate joint mechanics, resting sarcomere length and muscle architecture estimates from the masseter and temporalis to model muscle excursion, sarcomere length and relative tension as a function of joint angle. Muscle excursion from occlusion to an estimated maximum functional gape of 55deg. was smaller in all regions of the masseter and temporalis of C. jacchus compared with S. oedipus except the posterior temporalis. As a consequence of reduced muscle excursion distributed over more sarcomeres in series (i.e. longer fibers), sarcomere length operating ranges are smaller in C. jacchus jaw muscles across this range of gapes. This configuration allows C. jacchus to act on a more favorable portion of the length-tension curve at larger gapes and thereby generate relatively greater tension in these muscles compared with S. oedipus. Our results suggest that biting performance during tree gouging in common marmosets is improved by a musculoskeletal configuration that reduces muscle stretch at wide gapes while simultaneously facilitating comparatively large muscle forces at the extremes of jaw opening.

Jaw-muscle fiber architecture in tufted capuchins favors generating relatively large muscle forces without compromising jaw gape

“…Additionally, this architectural configuration may allow C. apella to maintain bite forces at large gapes as well as the jaw gape where maximal bite force is achieved. These last two functional outcomes follow from observations that most jaw-muscle sarcomeres stretch with increasing gape, and this stretching eventually decreases their contractile force as sarcomeres are lengthened past the plateau of the length-tension curve (Nordstrom et al, 1974; Nordstrom and Yemm, 1974; Hertzberg et al, 1980; Eng et al, 2007). …”

Quantifying the effect of gape and morphology on bite force: biomechanical modelling and in vivo measurements in bats

“…Furthermore, differences in sarcomere lengths across species and among muscle fibres within a muscle can also impact length‐force relationships (Rassier, MacIntosh & Herzog ; Eng et al . ). Data on muscle fibre length exist for several of the species studied here (Herrel et al .…”

Comparative Biomechanical Modeling of Metatherian and Placental Saber-Tooths: A Different Kind of Bite for an Extreme Pouched Predator

“…Typically, maximum force is generated when fibers are only moderately stretched, and maximizing gape will theoretically compromise bite forces. However, the musculoskeletal configuration of saber-tooths may have allowed them to operate within a more favorable portion of the length–tension curve at larger gapes, as has been demonstrated in some other mammalian taxa [46]. Among living felids there is evidence for increased fiber length in the jaw adductors of species that have wider gapes and that take relatively large prey [47].…”