Functional morphology of the masticatory musculature of the rodent subfamily microtinae
01 Aug 1980-Journal of Morphology (Wiley Subscription Services, Inc., A Wiley Company)-Vol. 165, Iss: 2, pp 205-222
TL;DR: Dissections of the masticatory musculature of the 12 genera and subgenera of North American microtines show an increase in the potential anterior vector component and the potential vertical vector component of these muscles relative to the molar tooth row, leading to the formulation of a propalinal “swing” hypothesis which is supported by vector analyses of the musculatures.
Abstract: Voles and lemmings are the most successful group of graminivorous rodents, but the adaptations allowing them to enter this niche are not fully known. Dissections of the masticatory musculature of the 12 genera and subgenera of North American microtines show an increase in the potential anterior vector component and in the potential vertical vector component of these muscles relative to the molar tooth row. The result is a separation of the compressive and propulsive functions of the masticatory muscles during the power stroke of mastication. This has led to the formulation of a propalinal “swing” hypothesis which is supported by vector analyses of the musculature.
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TL;DR: This work examined several potential developmental and functional explanations of character covariation throughout ontogeny using known‐age samples of the cotton rat to identify the causes of covariation and to assess the variability of patterns of covariance throughout postnatal growth.
Abstract: Patterns of variation and covariation within populations can influence how characters respond to natural selection and random genetic drift and so constrain the ability of natural selection to modify the phenotype. We examined several potential developmental and functional explanations of character covariation throughout ontogeny using known-age samples of the cotton rat (Sigmodon fulviventer) to identify the causes of covariation and to assess the variability of patterns of covariation throughout postnatal growth. Competing developmental and functional models were fit to samples of orofacial and neurocranial measures by confirmatory factor analysis and evaluated for their ability to reconstruct observed variance-covariance matrices. Samples of successive ages were simultaneously fit to a common model to test the hypothesis that the patterns of developmental and functional integration were invariant between ages. Orofacial characters derived from the same branchial-arch primordium covary early in ontogeny. Subsequently, there is a repatterning of integration that may reflect a transition from developmental to functional sources of integration. Neurocranial characters exhibit even more variation in patterns of covariation: initially, characters appear to comprise a single integrated unit; before puberty, they appear to respond to localized bone growth; after puberty, they form separate calvarial and basicranial components. This ontogenetic variation in patterns of covariation suggests that developmental constraints are transient and flexible and that the consequences of selection may depend upon the age at which it acts.
115 citations
01 Jan 1994
TL;DR: The diversity of mammalian masticatory systems has attracted considerable attention for a long time and numerous descriptive studies appeared, including comparative ones, e.g. Fiedler (1953, Insectivora); Starck (1933, platyrrhine primates); Storch (1968, Chiroptera); later, significant studies were published by Gaspard et al.
Abstract: The diversity of mammalian masticatory systems has attracted considerable attention for a long time. In the first half of this century, numerous descriptive studies appeared, including comparative ones, e.g. Fiedler (1953, Insectivora); Starck (1933, platyrrhine primates; 1935, ursids); Storch (1968, Chiroptera); later, significant studies were published by Gaspard et al. (1976), Schumacher (1961) and Turnbull (1970). Bluntschli (1929) and followers (Muller 1933; Zey 1939) published morphological papers, taking into account postnatal development.
95 citations
01 Jan 2002
TL;DR: In this paper, the shape and size of the mandible of the European wood mouse (Apodemus sylvaticus) were investigated across the latitudinal range of the mouse in order to address the relative importance of genetic structure, insularity and geographical gradient in patterning morpho-logical variation.
Abstract: Aim Size and shape of the mandible are investigated across the latitudinal range of theEuropean wood mouse (Apodemus sylvaticus), in order to address the relative import-ance of genetic structure, insularity, and geographical gradient in patterning morpho-logical variation. Results are compared with those on two Asiatic species of wood mice,A. argenteus and A. speciosus.Location The European wood mouse is sampled by a set of trapping localities includingboth, islands and mainland populations, as well as the four genetic groups identified inprevious studies. The localities cover a latitudinal gradient from 55 Nto36 N.Methods Different Fourier methods are applied to the outlines of mandibles and theirresults compared in the case of A. sylvaticus. All provide similar results and allow aquantification of the size and shape variations across the geographical range of theEuropean wood mouse. Using the method allowing for the best reduction of theinformative data set, a comparison of the European wood mouse with the two Asiaticspecies was performed.Results Within the European wood mouse A. sylvaticus, a strong latitudinal gradient inmandible shape overrides the influence of insularity and genetic structure. Yet, randommorphological divergence in insular conditions can be identified as a secondary processof shape differentiation. Size displays no obvious pattern of variation, neither withinsularity or latitude. A comparison with two other species of wood mice suggests that asimilar latitudinal gradient in mandible shape exists in different species, mandibles beingflatter in the north and wider in the south.Main conclusion The latitudinal gradient in mandible shape observed in the threespecies of wood mice is interpreted as an intraspecific adaptive response to gradualchanges in feeding behaviour.KeywordsShape, size, mandible, Apodemus, Rodentia, latitude, island biogeography, morpho-metrics, Fourier analysis.INTRODUCTIONSize of organisms has long been recognized to displayimportant biogeographical variations. The trend towards anincrease in size with latitude, or Bergmann’s rule (Bergmann,1847; Mayr, 1942), has been demonstrated in mammals andinvertebrates (Ray, 1960; Chapelle & Peck, 1999). Sizechanges can also be the consequence of isolation such as inthe islands, where small mammals like rodents will tend tobecome larger, whereas large mammals tend to be smaller(Foster, 1964; Lomolino, 1985; Michaux et al., 2002b).Apart from size, the shape of organs is of prime import-ance in the interaction of the organism with its environment.Taxonomic differentiation is commonly associated withmorphological divergence, but patterns of intraspecificvariation are less investigated. Still, genetic structure(Auffray et al., 1996; Corti & Rohlf, 2001) and insularity
77 citations
TL;DR: The latitudinal gradient in mandible shape observed in the threespecies of wood mice is interpreted as an intraspecific adaptive response to gradualchanges in feeding behaviour and should be interpreted as a secondary process of shape differentiation.
Abstract: Aim Size and shape of the mandible are investigated across the latitudinal range of theEuropean wood mouse (Apodemus sylvaticus), in order to address the relative import-ance of genetic structure, insularity, and geographical gradient in patterning morpho-logical variation. Results are compared with those on two Asiatic species of wood mice,A. argenteus and A. speciosus.Location The European wood mouse is sampled by a set of trapping localities includingboth, islands and mainland populations, as well as the four genetic groups identified inprevious studies. The localities cover a latitudinal gradient from 55 Nto36 N.Methods Different Fourier methods are applied to the outlines of mandibles and theirresults compared in the case of A. sylvaticus. All provide similar results and allow aquantification of the size and shape variations across the geographical range of theEuropean wood mouse. Using the method allowing for the best reduction of theinformative data set, a comparison of the European wood mouse with the two Asiaticspecies was performed.Results Within the European wood mouse A. sylvaticus, a strong latitudinal gradient inmandible shape overrides the influence of insularity and genetic structure. Yet, randommorphological divergence in insular conditions can be identified as a secondary processof shape differentiation. Size displays no obvious pattern of variation, neither withinsularity or latitude. A comparison with two other species of wood mice suggests that asimilar latitudinal gradient in mandible shape exists in different species, mandibles beingflatter in the north and wider in the south.Main conclusion The latitudinal gradient in mandible shape observed in the threespecies of wood mice is interpreted as an intraspecific adaptive response to gradualchanges in feeding behaviour.KeywordsShape, size, mandible, Apodemus, Rodentia, latitude, island biogeography, morpho-metrics, Fourier analysis.INTRODUCTIONSize of organisms has long been recognized to displayimportant biogeographical variations. The trend towards anincrease in size with latitude, or Bergmann’s rule (Bergmann,1847; Mayr, 1942), has been demonstrated in mammals andinvertebrates (Ray, 1960; Chapelle & Peck, 1999). Sizechanges can also be the consequence of isolation such as inthe islands, where small mammals like rodents will tend tobecome larger, whereas large mammals tend to be smaller(Foster, 1964; Lomolino, 1985; Michaux et al., 2002b).Apart from size, the shape of organs is of prime import-ance in the interaction of the organism with its environment.Taxonomic differentiation is commonly associated withmorphological divergence, but patterns of intraspecificvariation are less investigated. Still, genetic structure(Auffray et al., 1996; Corti & Rohlf, 2001) and insularity
77 citations
Cites background from "Functional morphology of the mastic..."
...Studies on interspecific differences in rodents have nevertheless shown that coronoid and angular processes are zones of attachment of the muscles involved in biting and mastication, whereas the condylar process plays a pivotal role in the articulation with the skull (Kesner, 1980; Satoh, 1997)....
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References
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339 citations
TL;DR: It is argued that the primitive adaptation of the rodent mandibulo-dental apparatus was for an omnivorous diet rather than a herbivorous one, and that the versatility of the feeding adaptation was the primary factor in the highly successful adaptive radiation in the order.
Abstract: The rodents have been generally regarded as basically herbivorous animals. A review of the literature of the natural history of the feeding habits of rodents shows many species in all major lines of rodent evolution to be, to a surprising degree, carnivorous, piscivorous, or insectivorous. It is argued, therefore, that the primitive adaptation of the rodent mandibulo-dental apparatus was for an omnivorous diet rather than a herbivorous one, and that, indeed, the versatility of the feeding adaptation was the primary factor in the highly successful adaptive radiation in the order. A functional-morphological study of the rodent gnawing adaptation supports the argument.
225 citations
TL;DR: The masticatory apparatus in the albino rat was studied by means of electromyography and subsequent estimation of muscular forces.
Abstract: The masticatory apparatus in the albino rat was studied by means of electromyography and subsequent estimation of muscular forces. The activity patterns of the trigeminal and suprahyoid musculature and the mandibular movements were recorded simultaneously during feeding. The relative forces of the individual muscles in the different stages of chewing cycles and biting were estimated on the basis of their physiological cross sections and their activity levels, as measured from integrated electromyograms. Workinglines and moment arms of these muscles were determined for different jaw positions. In the anteriorly directed masticatory grinding stroke the resultants of the muscle forces at each side are identical; they direct anteriorly, dorsally and slightly lingually and pass along the lateral side of the second molar. Almost the entire muscular resultant force is transmitted to the molars while the temporo-mandibular joint remains unloaded. A small transverse force, produced by the tense symphyseal cruciate ligaments balances the couple of muscle resultant and molar reaction force in the transverse plane. After each grinding stroke the mandible is repositioned for the next stroke by the overlapping actions of three muscle groups: the pterygoids and suprahyoids produce depression and forward shift, the suprahyoids and temporal backward shift and elevation of the mandible while the subsequent co-operation of the temporal and masseter causes final closure of the mouth and starting of the forward grinding movement. All muscles act in a bilaterally symmetrical fashion. The pterygoids contract more strongly, the masseter more weakly during biting than during chewing. The wide gape shifts the resultant of the muscle forces more vertically and moreposteriorly. The joint then becomes strongly loaded because the reaction forces are applied far anteriorly on the incisors. The charateristic angle between the almost horizontal biting force and the surface of the food pellet indicates that the lower incisors produce a chisel-like action. Tooth structure reflects chewing and biting forces. The transverse molar lamellae lie about parallel to the chewing forces whereas perpendicular loading of the occlusal surfaces is achieved by their inclination in the transverse plane. The incisors are loaded approximately parallel to their longitudinal axis, placement that avoids bending forces during biting. It is suggested that a predominantly protrusive musculature favors the effective force transmission to the lower incisors, required for gnawing. By grinding food across transversely oriented molar ridges the protrusive components of the muscles would be utilized best. From the relative weights of the masticatory muscles in their topographical relations with joints, molars and incisors it may be concluded that the masticatory apparatus is a construction adapted to optimal transmission of force from muscles to teeth.
217 citations
Book•
03 Sep 2011
TL;DR: A monograph of the Voles and Lemmings (Microtinæ), Living and Extinct, one which will serve the needs of systematic zoologists for many years to come.
Abstract: THERE is no group of mammals so likely to throw light on the manner in which new species arise as the Microtinae, a subfamily of rodents represented by voles and lemmings, and there is certainly no one so well qualified as Mr. Martin A. C. Hinton, of the Zoological Department of the British Museum (Natural History), to bring together and to systematise all that is known concerning the distribution in space and time, the structure and habit, of this highly specialised group. It may be said at once that Mr. Hinton is producing a monograph—for the volume noted here is only the first part—of the very highest order, one which will serve the needs of systematic zoologists for many years to come. In the present volume 14 genera, including 120 species, are defined and described, a score of the species having been discovered and named by the author. Great and abiding as is the service which Mr. Hinton is thus rendering to systematic zoologists, he is doing even more for the student of evolution, and it is to this aspect of his inquiries which we desire to direct attention now.Monograph of the Voles and Lemmings (Microtinæ), Living and Extinct.By Martin A. C. Hinton. Vol. 1. Pp. xvi + 488 + 15 plates. (London: British Museum (Natural History), 1926.) 30s.
152 citations
152 citations