title: Running for your life or running for your dinner: what drives fiber-type evolution in lizard locomotor muscles?
abstract: Despite its role in whole-animal performance, the adaptation of muscle physiology related to terrestrial locomotion remains underexplored. We tested evolutionary models based on predator escape and foraging strategies of lizards to assess whether fiber-type composition of a leg muscle is adaptive for behavior. The best-fitting model for fast-twitch fiber-type evolution was one based on predator-escape strategy, while the foraging-mode model fared poorly (Akaike Information Criterion with small sample size correction; DeltaAICc=29.7). According to the predator-escape model, lizards relying on sprints to avoid predators are predicted to have relatively higher proportions of fast glycolytic (FG) fibers (70%), while cryptic lizards are predicted to have relatively higher fast oxidative glycolytic (FOG) fiber proportions (77%). This pattern suggests an evolutionary trend toward greater FG (FOG) fiber composition among lizards that specialize in sprinting (crypsis). The best-fitting model for slow-twitch fibers had a single optimum, suggesting a common selective pressure across these lizards. The second-best model explaining slow-twitch fiber-type evolution was Brownian motion (DeltaAICc=0.80), indicating some support for neutral evolution. We find evidence suggesting that different fiber types occurring in the same muscle can evolve under different evolutionary pressures.
authors.affiliation: Department of Zoology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA. jscales@hawaii.edu
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Scales
authors.forename: Aaron A
authors.initials: AA
authors.lastname: King
authors.forename: Marguerite A
authors.initials: MA
authors.lastname: Butler
mesh_terms: D000220:Adaptation, Biological; D000818:Animals; D005075:Biological Evolution; D004924:Escape Reaction; D005247:Feeding Behavior; D040961:Genetic Drift; D008116:Lizards / Q000033:anatomy & histology / Q000502:physiology*; D008954:Models, Biological; D009043:Motor Activity; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology*; D012641:Selection, Genetic