Aaron A. King, Ph.D.

Nelson G. Hairston Collegiate Professor of Ecology, Evolutionary Biology,
and Complex Systems, University of Michigan
External Professor, Santa Fe Institute
Fellow of the American Association for the Advancement of Science

Running for your life or running for your dinner: what drives fiber-type evolution in lizard locomotor muscles?

J. A. Scales, A. A. King, and M. A. Butler
The American Naturalist 173(5): 543–553, 2009.
Running for your life vs running for your dinner....

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; ΔAIC_c=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 (ΔAIC_c=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.

The official version of the paper is here.   Please contact Prof. King if you'd like a reprint.

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