Dietary consistency and plasticity of masseter fiber architecture in postweaning rabbits

Taylor, Andrea B.; Jones, Kelly E.; Kunwar, Ravinder; Ravosa, Matthew J.

doi:10.1002/ar.a.20382

Cited by 29 publications

(31 citation statements)

References 39 publications

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“…Even though we speculated above that these zoological animals shared broadly similar diets in captivity, this remains unproven. Studies comparing rabbits fed different diets show that the group masticating the more obdurate diet increased their masseter mass without changes in fiber length (Taylor et al, 2006) as well as had larger muscle fibers (Kiliaridis et al, 1988). Our results do not point to either an evolutionary mechanism or a physiological response as the predominant contributing factor in the larger PCSA and enlarged jaw muscles of C. apella .…”

Section: Discussionmentioning

confidence: 99%

“…These and all other linear measurements were taken with digital calipers to the nearest 0.01 mm. Fiber length and pinnation angle were measured for both muscles following Taylor and Vinyard (2004) and Taylor et al (2006). Depending on the size of the muscle, we sectioned the masseter and temporalis muscles along their lengths to produce a minimum of two and a maximum of five segments, each segment approximately 1.5 cm in thickness (Fig.…”

Section: Methodsmentioning

confidence: 99%

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

Taylor

Vinyard

2009

Journal of Human Evolution

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105

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Cebus apella is renowned for its dietary flexibility and capacity to exploit hard and tough objects. Cebus apella differs from other capuchins in displaying a suite of craniodental features that have been functionally and adaptively linked to their feeding behavior, particularly the generation and dissipation of relatively large jaw forces. We compared fiber architecture of the masseter and temporalis muscles between the tufted capuchin (C. apella; n = 12 ) and two "untufted" capuchins (C. capuchinus, n = 3; C. albifrons, n = 5). These three species share broadly similar diets, but tufted capuchins occasionally exploit mechanically challenging tissues. We tested the hypothesis that C. apella exhibits architectural properties of their jaw muscles that facilitate relatively large forces, including relatively greater physiologic cross-sectional areas (PCSA), more pinnate fibers, and lower ratios of mass to tetanic tension (Mass/P 0 ). Results show some evidence supporting these predictions, as C. apella has relatively greater superficial masseter, whole masseter, and temporalis PCSAs, significantly so only for the temporalis following Bonferroni adjustment. Capuchins did not differ in pinnation angle or Mass/P 0 . As an architectural trade-off between maximizing muscle force and muscle excursion/contraction velocity, we also tested the hypothesis that C. apella exhibits relatively shorter muscle fibers. Contrary to our prediction, there are no significant differences in relative fiber lengths between tufted and untufted capuchins. Therefore, we attribute the relatively greater PCSAs in C. apella primarily to their larger muscle masses. These findings suggest that relatively large jaw-muscle PCSAs can be added to the suite of masticatory features that have been functionally linked to the exploitation of a more resistant diet by C. apella. By enlarging jaw-muscle mass to increase PCSA, rather than reducing fiber lengths and increasing pinnation, tufted capuchins appear to have increased jaw-muscle and bite forces without markedly compromising muscle excursion and contraction velocity. One performance advantage of this morphology is that it promotes relatively large bite forces at wide jaw gapes, which may be useful for processing large food items along the posterior dentition. We further

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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

Taylor

Vinyard

2009

Journal of Human Evolution

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105

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“…Once weaned, mammals ingest 'adult' food items (e.g. Watts, 1985;Tarnaud, 2004) and develop 'adult' jaw-adductor activity patterns (Herring and Wineski, 1986;Weijs et al, 1987;Herring et al, 1991;Iinuma et al, 1991;Langenbach et al, 1991;Langenbach et al, 1992;Westneat and Hall, 1992;Huang et al, 1994), with associated skeletal and soft-tissue responses to 'adult' jaw-loading regimes (Ravosa, 1991a;Ravosa, 1992;Ravosa, 1996;Ravosa, 1999;Cole, 1992;Biknevicius and Leigh, 1997;Vinyard and Ravosa, 1998;Taylor et al, 2006).…”

Section: Adaptive Plasticity and Degradation In Masticatory Tissuesmentioning

confidence: 99%

Pushing the limit: masticatory stress and adaptive plasticity in mammalian craniomandibular joints

Ravosa

Kunwar

Stock

et al. 2007

Journal of Experimental Biology

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151

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SUMMARY Excessive, repetitive and altered loading have been implicated in the initiation of a series of soft- and hard-tissue responses or `functional adaptations' of masticatory and locomotor elements. Such adaptive plasticity in tissue types appears designed to maintain a sufficient safety factor, and thus the integrity of given element or system, for a predominant loading environment(s). Employing a mammalian species for which considerable in vivo data on masticatory behaviors are available, genetically similar domestic white rabbits were raised on diets of different mechanical properties so as to develop an experimental model of joint function in a normal range of physiological loads. These integrative experiments are used to unravel the dynamic inter-relationships among mechanical loading, tissue adaptive plasticity, norms of reaction and performance in two cranial joint systems:the mandibular symphysis and temporomandibular joint (TMJ). Here, we argue that a critical component of current and future research on adaptive plasticity in the skull, and especially cranial joints, should employ a multifaceted characterization of a functional system, one that incorporates data on myriad tissues so as to evaluate the role of altered load versus differential tissue response on the anatomical, cellular and molecular processes that contribute to the strength of such composite structures. Our study also suggests that the short-term duration of earlier analyses of cranial joint tissues may offer a limited notion of the complex process of developmental plasticity, especially as it relates to the effects of long-term variation in mechanical loads, when a joint is increasingly characterized by adaptive and degradative changes in tissue structure and composition. Indeed, it is likely that a component of the adaptive increases in rabbit TMJ and symphyseal proportions and biomineralization represent a compensatory mechanism to cartilage degradation that serves to maintain the overall functional integrity of each joint system. Therefore, while variation in cranial joint anatomy and performance among sister taxa is, in part, an epiphenomenon of interspecific differences in diet-induced masticatory stresses characterizing the individual ontogenies of the members of a species,this behavioral signal may be increasingly mitigated in over-loaded and perhaps older organisms by the interplay between adaptive and degradative tissue responses.

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“…Employing this experimental design, a number of studies have observed changes in the phenotypic properties of the jaw muscles related to changes in masticatory function brought about by changing the ordinary hard diet to a soft one (Kitagawa et al, 2004;Taylor et al, 2006). It has been suggested that the changes in the jaw-muscle properties are signs of a structural adaptation caused by a reduction in the neuromuscular activity of the muscles involved (Miyata et al, 1993).…”

Section: Introductionmentioning

confidence: 99%

Changes in rabbit jaw-muscle activity parameters in response to reduced masticatory load

Grünheid

Brugman

Zentner

et al. 2010

Journal of Experimental Biology

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SUMMARYMechanical food properties influence the neuromuscular activity of jaw-closing muscles during mastication. It is, however, unknown how the activity profiles of the jaw muscles are influenced by long-term alterations in masticatory load. In order to elucidate the effect of reduced masticatory load on the daily habitual activity profiles of three functionally different jaw muscles, the electromyograms of the masseter, temporalis and digastric muscles were recorded telemetrically in 16 male rabbits between seven and 20 weeks of age. Starting at eight weeks of age the experimental animals were fed significantly softer pellets than the control animals. Daily muscle activity was quantified by the relative duration of muscle use (duty time), burst number and burst length in relation to multiple activity levels. The daily duty time and burst number of the masseter muscle were significantly lower in the experimental group than in the control group at 5% and 10% of the maximum activity during the two weeks following the change in food hardness. By contrast, altered food hardness did not significantly influence the activity characteristics of the temporalis and digastric muscles. The findings suggest that a reduction in masticatory load decreases the neuromuscular activity of the jaw-closing muscles that are primarily responsible for force generation during mastication. This decrease is most pronounced in the weeks immediately following the change in food hardness and is limited to the activity levels that reflect muscle contractions during chewing. These findings support the conclusion that the masticatory system manifests few dietspecific long-term changes in the activity profiles of jaw muscles.

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Dietary consistency and plasticity of masseter fiber architecture in postweaning rabbits

Cited by 29 publications

References 39 publications

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

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

Pushing the limit: masticatory stress and adaptive plasticity in mammalian craniomandibular joints

Changes in rabbit jaw-muscle activity parameters in response to reduced masticatory load

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