Physiological responses of ectotherms to daily temperature variation

Abstract

Daily thermal fluctuations (DTFs) impact the capacity of ectotherms to maintain performance and energetic demands because of thermodynamic effects on physiological processes. Mechanisms that reduce the thermal sensitivity of physiological traits may buffer ectotherms from the consequences of DTFs. Species that experience varying degrees of DTFs in their environments may differ in their responses to thermally variable conditions, if thermal performance curves reflect environmental conditions. We tested the hypothesis that in response to DTFs, tadpoles from habitats characterised by small DTFs would show greater plasticity in the thermal sensitivity of physiological processes than tadpoles from environments characterised by large DTFs. We tested the thermal sensitivity of physiological traits in tadpoles of three species that differ naturally in their exposure to DTFs, raised in control (24°C) and DTF treatments (20-30°C and 18-38°C). DTFs reduced growth in all species. Development of tadpoles experiencing DTFs was increased for tadpoles from highly thermally variable habitats (∼15%), and slower in tadpoles from less thermally variable habitats (∼30%). In general, tadpoles were unable to alter the thermal sensitivity of physiological processes, although DTFs induced plasticity in metabolic enzyme activity in all species, although to a greater extent in species from less thermally variable environments. DTFs increased upper thermal limits in all species (between 0.89 and 1.6°C). Our results suggest that the impact of increased thermal variability may favour some species while others are negatively impacted. Species that cannot compensate for increased variability by buffering growth and development will probably be most affected.

The role of stochastic thermal environments in modulating the thermal physiology of an intertidal limpet, Lottia digitalis

“…4). Our results are at odds with previous studies that have found higher thermal tolerance of organisms when exposed to greater magnitudes of fluctuating temperatures (Schaefer and Ryan, 2006;Oliver and Palumbi, 2011;Kern et al, 2015;Giomi et al, 2016). Temperature tolerance was only increased with acclimation to unpredictable heating regimes in one trial of the unpredictable treatments, but only in comparison to the predictable low and predictable high treatments.…”

“…This phenomenon, known as heat hardening (Bowler, 2005), is a very important inducible stress tolerance mechanism in many organisms, both terrestrial and aquatic, inhabiting variable environments (Maness and Hutchinson, 1980;Rutledge et al, 1987;Middlebrook et al, 2008;Bilyk et al, 2012). Previous studies have shown fluctuating thermal environments increase thermal tolerance (Feldmeth et al, 1974;Otto, 1974;Threader and Houston, 1983;Woiwode and Adelman, 1992;Schaefer and Ryan, 2006;Oliver and Palumbi, 2011;Manenti et al, 2014;Kern et al, 2015), with intertidal species exposed to tidal cycle fluctuations being more stress-tolerant than those that are exposed to constant temperatures (Tomanek and Sanford, 2003;Podrabsky and Somero, 2004;Todgham et al, 2006;Giomi et al, 2016). Taken together, these studies suggest that the thermal physiology of intertidal organisms is likely modulated by the natural variability inherent with the ebb and flow of tides.…”

“…Stress response mechanisms are energetically costly and require animals to increase metabolic rates (Sokolova et al, 2012). Under heat stress, the activity of metabolic enzymes, such as citrate synthase, can also increase, which allows for a higher aerobic capacity (Sokolova and Pörtner, 2001;Morley et al, 2009;Kern et al, 2015). Increased metabolic rates under stressful conditions can cause animals to deplete glycogen energy stores (Santini and Chelazzi, 1995;Lim et al, 1996;Leung and Furness, 2001;Palais et al, 2011;Bjelde and Todgham, 2013;Goh and Lai, 2014) and increase the production of reactive oxygen species (Abele et al, 2002;Kültz, 2005;Han et al, 2013;Zhang et al, 2014).…”

Impacto de las variaciones de temperatura diaria en la historia natural de los anuros tropicales

“…Studies incorporating thermal variations may represent more natural field conditions, since temperature fluctuations are typical of most of the shallow and ephemeral pools where tadpoles live in. Despite the remarkable plasticity of amphibians through the embryonic and larval periods (Álvarez, & Nicieza, 2002;Moore, 1939), environmental temperature is well documented as one of the most predominant abiotic factor to influence the anuran development and growth (Atkinson, 1996;Bradford, 1990;Kern, Cramp, & Franklin, 2015;Smith-Gill, & Berven, 1979). Growth is the trajectory of increase in the somatic mass owned by the uptake, transformation and allocation of materials, while development is the trajectory of differentiation from a fertilized egg or some later stage to its adulthood, which is regulated by gene-by-environment interactions (Zuo, Moses, West, Hou, & Brown, 2011).…”

Physiological responses to daily temperature variation and ultraviolet radiation in amphibian larvae

“…The final experimental chapter (Chapter 4) investigates the interaction between temperature variability and UVR exposure on oxidative damage, antioxidant activity, the induction of Hsps and upper thermal limits. Chapters 2 and 3 are published in the Journal of Experimental Biology (Kern et al, 2015a;Kern et al, 2014), and Chapter 4 is published in Comparative Biochemistry and Physiology -Part A (Kern et al, 2015b). As such, each chapter is written as a complete scientific manuscript with an abstract, introduction, methods, results and discussion.…”