Testing the Pace-of-Life Syndrome in the Tree Lizard, Urosaurus ornatus

Abstract

The pace-of-life syndrome (POLS) describes covariation between behavioral, physiological, and in some instances thermal traits. The POLS predicts that bolder, more exploratory individuals should have higher metabolic rates, higher physiological performance, and prefer and perform better at high temperatures. Evidence supporting the POLS has been mixed. The goal of this study was to test the POLS in the color polymorphic tree lizard (Urosaurus ornatus) by comparing behavioral, thermal, and physiological performance traits, among all individuals, between the sexes, and among color morphs. We measured behavioral traits using laboratory-based estimates of boldness and exploration, thermal preference traits using a thermal gradient, and used stamina as a measure of locomotor performance. We described the patterns of covariation among the physiological, behavioral, and thermal traits using a principal component analysis. Bolder lizards were more exploratory, but selected cooler body temperatures, which contradicts the relationship predicted by the POLS. We also found that stamina was unrelated to either behavioral or thermal traits. Only boldness and exploration differed among the color morphs: blue and yellow/blue throated males were more exploratory than yellow males and yellow/blue males were bolder than yellow and orange/yellow males. Our results provide little support for the POLS in tree lizards. This study emphasizes the importance of not overgeneralizing the prevalence of the POLS and that in some populations, local conditions and selection pressures may play a larger role in trait correlations than suites of generalized traits.

Some like it hotter: differential thermal preferences among lizard color morphs

“…We randomized lane assignments and ran experiments with sets of individuals that varied by morph, sex, and reproductive status. After the acclimation period, we took external body temperature measurements with a FLIR TG5 temperature gun (Hare et al, 2007; Trochet et al, 2018; George & Miles, 2022) every 5 min for 1 h (N = 50), 3 h (N = 24), and 6 h (N = 21). We ran trials of different lengths due to time constraints in the field and tested if individual Tpref differed between the 60 min timepoint and final timepoint in experiments lasting 3 h and 6 h. To keep body temperature measurements consistent among individuals, we took temperature readings on the dorsal surface between the lizard’s shoulders.…”

“…Color morph Tpref was calculated as the 50% IQR of all individual Tpref calculations for each color morph. We calculated a shuttling variable by summing the absolute values of the change in body temperature at 5-min intervals (George & Miles, 2022). This measurement describes the thermoregulatory behavior of individuals during the experiment.…”

“…Intraspecific color morphs with morph-associated morphology, social behaviors, and microhabitat associations have evolved in many species across the tree of life (Hugall & Stuart-Fox, 2012; Brock et al, 2022c), particularly in lizards (Stuart-Fox et al, 2020). Yet, relatively little is known about intraspecific color morph variation in preferred body temperature (but see Paranjpe et al, 2013; George & Miles, 2022). Indeed, animal color morphs are expected to use different subsets of available resources and occupy, on average, different environmental niches due to morph-associated morphological and microhabitat differences (Forsman et al, 2008).…”