title: Function and position determine relative proportions of different fiber types in limb muscles of the lizard Tropidurus psammonastes.
abstract: Skeletal muscles can be classified as flexors or extensors according to their function, and as dorsal or ventral according to their position. The latter classification evokes their embryological origin from muscle masses initially divided during limb development, and muscles sharing a given position do not necessarily perform the same function. Here, we compare the relative proportions of different fiber types among six limb muscles in the lizard Tropidurus psammonastes. Individual fibers were classified as slow oxidative (SO), fast glycolytic (FG) or fast oxidative-glycolytic (FOG) based on mitochondrial content; muscles were classified according to position and function. Mixed linear models considering one or both effects were compared using likelihood ratio tests. Variation in the proportion of FG and FOG fibers is mainly explained by function (flexor muscles have on average lower proportions of FG and higher proportions of FOG fibers), while variation in SO fibers is better explained by position (they are less abundant in ventral muscles than in those developed from a dorsal muscle mass). Our results clarify the roles of position and function in determining the relative proportions of the various muscle fibers and provide evidence that these factors may differentially affect distinct fiber types.
authors.affiliation: Department of Biology, FFCLRP, University of São Paulo, Avenida Bandeirantes, 3900, Bairro Monte Alegre, Ribeirão Preto, SP, Brazil; Department of Genetics, Federal University of Rio de Janeiro, Prof. Rodolpho Paulo Rocco, S/N, Rio de Janeiro, RJ, Brazil.
authors.forename: Anieli G
authors.initials: AG
authors.lastname: Pereira
authors.affiliation: Instituto de Biodiversidad Neotropical - CONICET, Miguel Lillo 205, Tucumán, Argentina.
authors.forename: Virginia
authors.initials: V
authors.lastname: Abdala
authors.affiliation: Department of Biology, FFCLRP, University of São Paulo, Avenida Bandeirantes, 3900, Bairro Monte Alegre, Ribeirão Preto, SP, Brazil. Electronic address: tiana@usp.br.
authors.forename: Tiana
authors.initials: T
authors.lastname: Kohlsdorf
mesh_terms: D000818:Animals; D006614:Hindlimb / Q000166:cytology / Q000502:physiology; D016014:Linear Models; D008116:Lizards / Q000033:anatomy & histology* / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000166:cytology*; D018482:Muscle, Skeletal / Q000166:cytology*
keywords: Fiber types; Limb muscles; Muscle function; Muscle position; Tropidurus psammonastes