The effect of thermal microenvironment in upper thermal tolerance plasticity in tropical tadpoles. Implications for vulnerability to climate warming

• Published in: Journal of experimental zoology. Part A, Ecological and integrative physiology Ecological and integrative physiology, 2022-08, Vol.337 (7), p.746-759
• Main Authors: Turriago, Jorge L., Tejedo, Miguel, Hoyos, Julio M., Bernal, Manuel H.
• Format: Article
• Language: English
• Subjects: Acclimation; acclimation capacity; Acclimatization; Ambient temperature; Aquatic reptiles; Climate change; Extreme heat; Global warming; Habitats; Heat; Heat stress; Heat tolerance; Heating; Heating rate; heating rates; Juveniles; Microenvironments; Plastic properties; Plasticity; Plastics; Population decline; Shade; Species; Temperature tolerance; Thermal environments; thermal fluctuations; Thermal stress; Tolerances; Tolerances (dimensional); Tropical climate; tropical tadpoles; upper critical thermal limits; Vulnerability; warming tolerances
• ISSN: 2471-5638; 2471-5646
• DOI: 10.1002/jez.2632

Current climate change is generating accelerated increase in extreme heat events and organismal plastic adjustments in upper thermal tolerances, (critical thermal maximum ‐CTmax) are recognized as the quicker mitigating mechanisms. However, current research casts doubt on the actual mitigating role of thermal acclimation to face heat impacts, due to its low magnitude and weak environmental signal. Here, we examined these drawbacks by first estimating maximum extent of thermal acclimation by examining known sources of variation affecting CTmax expression, such as daily thermal fluctuation and heating rates. Second, we examined whether the magnitude and pattern of CTmax plasticity is dependent of the thermal environment by comparing the acclimation responses of six species of tropical amphibian tadpoles inhabiting thermally contrasting open and shade habitats and, finally, estimating their warming tolerances (WT = CTmax – maximum temperatures) as estimator of heating risk. We found that plastic CTmax responses are improved in tadpoles exposed to fluctuating daily regimens. Slow heating rates implying longer duration assays determined a contrasting pattern in CTmax plastic expression, depending on species environment. Shade habitat species suffer a decline in CTmax whereas open habitat tadpoles greatly increase it, suggesting an adaptive differential ability of hot exposed species to quick hardening adjustments. Open habitat tadpoles although overall acclimate more than shade habitat species, cannot capitalize this beneficial increase in CTmax, because the maximum ambient temperatures are very close to their critical limits, and this increase may not be large enough to reduce acute heat stress under the ongoing global warming. Critical thermal maximum (CTmax) variation for shade and open habitat anurans at different thermal treatments and estimated at two heating rates. Highlights Tadpoles from open habitats, had higher and more plastic critical thermal maximum (CTmax) than shade habitats. Fluctuating acclimation temperatures increased the CTmax in all examined species. Slower heating rate increased the CTmax only in species from open habitats.