Homage to Santa Anita: Thermal Sensitivity of Sprint Speed in Agamid Lizards

Abstract

Ectotherms can compensate for geographical and temporal changes in the thermal environment in several ways: by behavioral regulation, by physiological acclimatization, and by genetic differentiation among populations. Most lizards (Bogert, 1949;Huey, 1982a) compensate by using fast-acting behavioral shifts (e.g., changes in time of activity and in basking activity), and many species also show supplementary (and slower) acclimatory responses (Corn, 1971;Spellerberg, 1972;Hertz, 1981). Whether closely related lizards living in thermally distinctive environments also show genetic adaptation in thermal physiology (Hertz et aI., 1979) has frequently been debated-often in the pages of this journal. Two competing views have emerged over the last three decades.(i) The "static" view, based largely on studies of desert lizards (Bogert, 1949; see also Ushakov, 1964;Brown and Feldmeth, 1971;Hutchison, 1976), emphasizes that thermal physiology is evolutionarily conservative and thus relatively insensitive to directional selection. This view is derived from the empirical generalization that aspects of thermal physiology of lizards typically show little differentiation within or among closely related taxa from climatically distinctive habitats. Because these taxa effectively adjust their thermoregulatory behaviors to local environmental conditions, geographic variation in body temperatures during activity-and

Estimating maximum performance: effects of intraindividual variation

“…We measured sprint speed following the procedures of Hertz et al (Hertz et al, 1983). Prior to each run, lizards were held individually in 1·l plastic containers within a constant-temperature chamber at either 35°C or 20°C for at least 1·h; 35°C is the optimal temperature for sprint locomotion in this species, and is approximately the mean body temperature of field-active animals, whereas 20°C is at the lower end of the field body temperature distribution for these populations (Bennett, 1980;Marsh and Bennett, 1986;van Berkum, 1988;Adolph, 1990).…”

“…We removed each lizard from the chamber and chased it along a horizontal racetrack (2.5·m longϫ28·cm wide) that had a rough particle board surface. Photocells spaced every 0.25·m were connected to a computer that recorded elapsed times (Huey et al, 1981;Hertz et al, 1983). We gave each lizard five training runs several days prior to the experiment (Bennett, 1980).…”

The Behavior-Physiology Nexus: Behavioral and Physiological Compensation Are Relied on to Different Extents between Seasons

“…Typically, the performance traits of an ectotherm described as a function of body temperature have an asymmetrical shape that peaks at the preferred body temperature (targeted temperature selected in a thermal gradient devoid of biotic factors, T pref ) but rapidly drops at temperatures higher than T pref . At T pref , most (but not all) physiological and biological processes are optimized (enzyme activity, energy assimilation, sprinting ;Licht 1964;Hertz et al 1983; but see Angilletta et al 2002) and likely enhance individual fitness (Cowles and Bogert 1944;Huey and Bennett 1987;Angilletta et al 2006). However, when targeting T pref , thermoregulatory behaviors can rapidly become energetically expensive, especially during periods or in habitats of poor thermal quality (Huey and Slatkin 1976;Lee 1980).…”

AN EXPERIMENTAL CONFIRMATION OF MORPHOLOGICAL ADAPTATION: TOE FRINGES IN THE SAND‐DWELLING LIZARD UMA SCOPARIA

“…The first two are complex functional units, and, as with any such morphological system, manipulations (altering limb length or removing toe pads) to demonstrate their significance in increasing locomotor performance are problematic, as it is difficult to establish appropriate controls. Numerous intraspecific studies have quantified differential running performance in lizards (e.g., Ballinger et aI., 1973;Bennett, 1980;Huey, 1982;Punzo, 1982;Hertz, 1983;Huey and Hertz, 1984), but none have studied characters presumed to have evolved specifically to aid locomotion (Laerm [1973] anecdotally reported reduced locomotor effectiveness in uncontrolled fringe removal experiments with water-running Basiliscus).…”