Locomotor Compensation Creates a Mismatch Between Laboratory and Field Estimates of Escape Speed in Lizards: A Cautionary Tale for Performance-to-Fitness Studies

Abstract

A key assumption in evolutionary studies of locomotor adaptation is that standard laboratory measures of performance accurately reflect what animals do under natural circumstances. One widely examined measure of performance is maximum sprint speed, which is believed to be important for eluding predators, capturing prey, and defending territories. Previous studies linking maximum sprint speed to fitness have focused on laboratory measurements, and we suggest that such analyses may be appropriate for some species and intraspecific classes, but not others. We provide evidence for a general inverse relationship between maximum laboratory sprint speed and the percentage of maximum capacity that animals use when escaping from a threat in the field (the model of locomotor compensation). Further, absolute values of field escape speed and maximum laboratory speed are not significantly related when comparing across a diverse group of Anolis and lacertid lizards. We show that this pattern of locomotor compensation holds both within (i.e., among intraspecific classes) and among lizard species (with some exceptions). We propose a simple method of plotting field escape speed (y-axis) versus maximum laboratory speed (x-axis) among species and/or intraspecific classes that allows researchers to determine whether their study organisms are good candidates for relating laboratory performance to fitness. We suggest that species that reside directly on, or near the "best fitness line" (field escape speed = maximum laboratory speed) are most likely to bear fruit for such studies.

An experimental test of the role of predators in the maintenance of a genetically based polymorphism

“…It is possible that the equipment and conditions used in our collection of performance data (e.g. a motorized treadmill and an enclosed sprint track under ambient field temperatures) were not sufficient to produce ecologically relevant measures of endurance and escape speed (Irschick et al ., ,b). However, we have previously detected statistically significant and ecologically intuitive patterns of natural selection acting on variation in endurance and sprint speed measured with identical methods in male anoles (Calsbeek & Irschick, ).…”

Evidence of Circadian Rhythm, Oxygen Regulation Capacity, Metabolic Repeatability and Positive Correlations between Forced and Spontaneous Maximal Metabolic Rates in Lake Sturgeon Acipenser fulvescens

“…While maximal performance is crucial for a wide range of behaviours tightly connected to fitness (e.g. [62], [63]), animals may not exercise at maximal intensity very often [64]–[66]. Therefore, measurements of maximal performance could have more pronounced functional importance if maximal performance correlated positively with spontaneous performance, which is used more frequently.…”

Linking genotypes to phenotypes and fitness: how mechanistic biology can inform molecular ecology

“…However, laboratory‐based measures of phenotypes, performance and fitness may not translate directly to field measures of fitness (e.g. Irschick 2003; Irschick et al. 2005), so they should, whenever possible, be complemented with experiments performed under natural or semi‐natural conditions.…”