Behavioral thermoregulation is highly repeatable and unaffected by digestive status in Agama atra

Abstract

The precision and the extent of behavioral thermoregulation are likely to provide fitness benefits to ectotherms. Yet the factors driving variation in selected or preferred body temperature (T ) and its usefulness as a proxy for optimal physiological temperature (T ) are still debated. Although T is often conserved among closely related species, substantial variation at the individual, population, and species level has also been reported but repeatability (sensu the intra-class correlation coefficient, ICC) of T is generally low. One factor that influences T is feeding status, with fed reptiles typically showing higher T , a process thought to aid meal digestion. Here using experiments simulating realistic ranges of feeding and fasting regimes in Agama atra, a heliothermic lizard from southern Africa, we test if T and its repeatability under these two states significantly differ. Daily T ranged from 33.7 to 38.4° C, with a mean (± SE) of 36.7 ± 0.1° C for fed and 36.6 ± 0.1° C for unfed individuals. Comparisons of repeatability showed that females tend to be more consistent in the selection of body temperature than males, but not significantly so regardless of feeding status. We report some of the highest repeatability estimates of T to date (full range: 0.229 - 0.642), and that the weak positive effects of feeding status on T detected here do not hinder obtaining relatively high repeatability estimates. In conclusion, one of the major prerequisites for natural selection, consistent among-individual variation, is present, making the adaptive significance of T considerably more plausible. This article is protected by copyright. All rights reserved.

Sex-specific microhabitat use is associated with sex-biased thermal physiology in Anolis lizards

“…We then recorded body temperatures every 30 s for the ensuing hour. By design, laboratory thermal arenas are free of physical or ecological barriers to movement and therefore the body temperatures that individuals achieve are assumed to be optimal for physiological performance (Camacho and Rusch, 2017;Gilbert and Miles, 2017;Neel and McBrayer, 2018;Sannolo and Carretero, 2019;van Berkel and Clusella-Trullas, 2018). We included the mean (often referred to as 'preferred temperature'), minimum and maximum body temperatures achieved in the thermal arenas as traits to be included in subsequent analyses of sexual dimorphism in thermoregulatory behavior.…”

The Bogert Effect and environmental heterogeneity

“…A thermoconforming population is represented by a strong correlation between T b and T e . Thus, we take the deviation of this relationship from 1:1 and the extent to which T b overlaps with the preferred temperature range of A. atra [measured in a laboratory thermal gradient for a third population (S31°46.614′; E18°46.447′) as part of a previous study; van Berkel and Clusella-Trullas 2018)] to approximate the accuracy of behavioral thermoregulation in each population (Angilletta 2009;Hertz et al 1993). This approach is essentially a visual representation of the model presented by Hertz et al (1993).…”

Environmental temperature alters the overall digestive energetics and differentially affects dietary protein and lipid use in a lizard

“…Waldschmidt et al, 1986;Alexander et al, 2001;McConnachie and Alexander, 2004;Lei and Booth, 2014;Miller et al, 2014). Agama atra is known to only eat at temperatures above 19°C, and its selected body temperature in a laboratory thermal gradient varies between 32 and 36°C (Bruton, 1977;Van Berkel and Clusella-Trullas, 2018). The increase in gut passage time at low temperatures may cause decay of food in the stomach.…”