Cellular and whole‐organism effects of prolonged versus acute heat stress in a montane, desert lizard

Abstract

Global climate change involves both prolonged periods of higher‐than‐normal temperatures and short but extreme heat waves. Both types of temperature increases are likely to be detrimental to ectotherms, and even if such temperature increases do not cause mortality directly, compensating for such temperature increases will likely entail costs to organisms. We tested the effects of prolonged periods of higher‐than‐average temperatures and short‐term, acute heat stress in wild populations of greater short‐horned lizards (Phrynosoma hernandesi), a temperate, montane lizard of the Colorado Plateau, UT, USA. We transplanted one group of lizards from a high‐ to a low‐elevation site, exposing them to a prolonged period of warmer temperatures. These lizards, exposed to prolonged periods of higher‐than‐average temperatures, experienced no change in sprint speed, endurance, or heat shock protein (HSP) production after treatment compared to baseline levels; however, they had lower water content after the transplant to a warmer climate compared to before the transplant. We exposed a second group of lizards to acute heat stress by exposing them to thermally stressful temperatures for 4 h. These lizards, exposed to a short period of acute heat stress, had no change in endurance, water content, or HSP production following acute heat stress; however, lizards exposed to acute heat stress had slower sprint speeds than control lizards. Our results demonstrate that both prolonged temperature increases and acute heat stress, each of which are predicted to occur with climate change, had different cellular and/or whole organismal‐level effects on lizards.

Effects of Simulated Heat Wave on Oxidative Physiology and Immunity in Asian Yellow Pond Turtle (Mauremys mutica)

“…Unexpectedly, in the present study, heat waves did not induce significant upregulation in the expression of hsp gene in the liver of M. mutica, even though the turtles experienced 37-39 • C for nearly 5 h daily during the heat wave (Supplementary Figure 2). A similar phenomenon was also observed in a montane lizard (Phrynosoma hernandesi) exposed to acute heat stress at 36 • C for 4 h (Refsnider et al, 2021) and in a skink after 24 h exposure to 35 • C (Plestiodon chinensis) (Dang et al, 2018). One possible explanation was exhaustion of the cellular stress responses indicated by the decreased hepatosomatic index as described above.…”

Plasticity in thermal hardening of the invasive Asian house gecko

“…Dipteran insects have served as models to study thermal hardening studies for decades (Berrigan and Hoffmann 1998;Hoffmann et al 2003;Hu et al 2014;Loeschcke and Hoffmann 2007;Overgaard and Sørensen 2008;Sejerkilde et al 2003;van Heerwaarden et al 2016). By contrast, until recently, there have been fewer studies on hardening responses in reptiles (Deery et al 2021;Gilbert and Miles 2019;Phillips et al 2016;Refsnider et al 2021).…”

Mitochondrial Protein-Coding Gene Expression in the Lizard Sphenomorphus incognitus (Squamata:Scincidae) Responding to Different Temperature Stresses

“…There was a downregulation of genes at 34 • C, but this did not occur at the higher temperature of 38 • C. We proposed that, in contrast to the adaptation to gradual longterm temperature changes, organisms exposed to extremely high temperatures had a transient increase in individual heat tolerance. This increase was primarily attributed to the production of heat shock proteins (HSP70) [67]. The temperature change for S. incognitus from 34 • C to 38 • C necessitated a higher heat tolerance, resulting in the allocation of more energy towards costly physiological activities, such as the activation of heat shock proteins.…”