The functional correlates of jaw-muscle fiber architecture in tree-gouging and nongouging callitrichid monkeys.

Published

Journal Article

Common (Callithrix jacchus) and pygmy (Cebuella pygmaea) marmosets and cotton-top tamarins (Saguinus oedipus) share broadly similar diets of fruits, insects, and tree exudates. Marmosets, however, differ from tamarins in actively gouging trees with their anterior dentition to elicit tree exudates flow. Tree gouging in common marmosets involves the generation of relatively wide jaw gapes, but not necessarily relatively large bite forces. We compared fiber architecture of the masseter and temporalis muscles in C. jacchus (N = 18), C. pygmaea (N = 5), and S. oedipus (N = 13). We tested the hypothesis that tree-gouging marmosets would exhibit relatively longer fibers and other architectural variables that facilitate muscle stretch. As an architectural trade-off between maximizing muscle excursion/contraction velocity and muscle force, we also tested the hypothesis that marmosets would exhibit relatively less pinnate fibers, smaller physiologic cross-sectional areas (PCSA), and lower priority indices (I) for force. As predicted, marmosets display relatively longer-fibered muscles, a higher ratio of fiber length to muscle mass, and a relatively greater potential excursion of the distal tendon attachments, all of which favor muscle stretch. Marmosets further display relatively smaller PCSAs and other features that reflect a reduced capacity for force generation. The longer fibers and attendant higher contraction velocities likely facilitate the production of relatively wide jaw gapes and the capacity to generate more power from their jaw muscles during gouging. The observed functional trade-off between muscle excursion/contraction velocity and muscle force suggests that primate jaw-muscle architecture reflects evolutionary changes related to jaw movements as one of a number of functional demands imposed on the masticatory apparatus.

Full Text

Cited Authors

  • Taylor, AB; Eng, CM; Anapol, FC; Vinyard, CJ

Published Date

  • July 2009

Published In

Volume / Issue

  • 139 / 3

Start / End Page

  • 353 - 367

PubMed ID

  • 19140215

Pubmed Central ID

  • 19140215

Electronic International Standard Serial Number (EISSN)

  • 1096-8644

Digital Object Identifier (DOI)

  • 10.1002/ajpa.20991

Language

  • eng

Conference Location

  • United States