Meeting Abstract
Western fence lizards have a broad thermal performance range, achieving nearly the same maximal accelerations and velocities between 25 and 40° C, despite a significant decrease in maximal muscle power across this temperature range. Thermal breadth is not unique to these lizards, as it is a common feature in ectotherm performance. However, previous studies have found that lizard muscles are just powerful enough to attain peak acceleration performance at optimal temperatures, which should indicate a performance decline with decreasing temperature, and not the thermal robustness that has been observed. We hypothesize that the thermal breadth in lizards results from their use of elastic energy storage to amplify muscle power during the first few steps of acceleration. We tested this prediction using a combination of in vitro muscle experiments and kinematic analyses of lizard running. Peak accelerations required estimated muscle powers in excess of those measured in vitro, which indicates that lizards may be amplifying muscle power. Additionally, by measuring muscle fiber shortening and aponeurosis lengthening during isometric contractions of isolated ankle extensors, we found that hindlimb muscles can store a substantial amount of elastic energy, which may account for more than a third of the total work used during acceleration. To get more detailed view of the distribution of mechanical power in the hindlimb, we will use inverse dynamics to quantify joint-level power requirements during acceleration across temperatures. This work aims to understand the role of elastic elements in broadening thermal performance in locomoting ectotherms.
