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204 results for “Thermal tolerance”
Data from: Broad thermal tolerance is negatively correlated with virulence in an opportunistic bacterial pathogen
Predicting the effects of global increase in temperatures on disease virulence is challenging, especially for environmental opportunistic bacteria, because pathogen fitness may be differentially affected by temperature within and outside host environment. So far, there is very little empirical evidence on the connections between optimal temperature range and virulence in environmentally growing pathogens. Here we explored if the virulence of an environmentally growing opportunistic fish pathogen, Flavobacterium columnare, is malleable to evolutionary changes via correlated selection on thermal tolerance. To this end, we experimentally quantified the thermal performance curves (TPCs) for maximum biomass of 49 F. columnare isolates from eight different geographic locations in Finland over ten years (2003-2012). We also characterized virulence profiles of these strains in a zebra-fish (Danio rerio) infection model. We show that virulence among the strains increased over the years, but tolerance to higher temperatures was negatively associated with virulence. Our data suggest that temperature has a strong effect on the pathogen genetic diversity, and therefore presumably also on disease dynamics. However, the observed increase in frequency and severity of F. columnare epidemics over the last decade cannot be directly linked to bacterial evolution due to increased mean temperature, but is most likely associated with factors related to increased length of growing season, or other time dependent change in environment. Our study demonstrates that complex interactions between the host, the pathogen and the environment influence disease virulence of environmentally growing opportunistic pathogen.
Data from: Cardiac plasticity influences aerobic performance and thermal tolerance in a tropical, freshwater fish at elevated temperatures
Fishes faced with novel thermal conditions often modify physiological functioning to compensate for elevated temperatures. This physiological plasticity (thermal acclimation) has been shown to improve metabolic performance and extend thermal limits in many species. Adjustments in cardiorespiratory function are often invoked as mechanisms underlying thermal plasticity because limitations in oxygen supply have been predicted to define thermal optima in fishes, however few studies have explicitly linked cardiorespiratory plasticity to metabolic compensation. Here we quantify thermal acclimation capacity in the commercially harvested Nile perch (Lates niloticus) of East Africa, and investigate mechanisms underlying observed changes. We reared juvenile Nile perch for 3 months under two temperature regimes, and then measured a series of metabolic traits (e.g., aerobic scope, AS) and critical thermal maximum (CTmax) upon acute exposure to a range of experimental temperatures. We also measured morphological traits of heart ventricles, gills, and brains to identify potential mechanisms for compensation. We found that long-term (3-months) exposure to elevated temperature induced compensation in upper thermal tolerance (CTmax) and metabolic performance (SMR, MMR and AS), and induced cardiac remodeling in Nile perch. Furthermore, variation in heart morphology influenced variations in metabolic function and thermal tolerance. These results indicate that plastic changes enacted over longer exposures lead to differences in metabolic flexibility when acutely exposed to temperature variation. Furthermore, we established functional links between cardiac plasticity, metabolic performance, and thermal tolerance, providing evidence that plasticity in cardiac capacity may be one mechanism for coping with climate change.
Data from: Hotter nests produce hatchling lizards with lower thermal tolerance
In many regions, the frequency and duration of summer heatwaves is predicted to increase in future. Hotter summers could result in higher temperatures inside lizard nests, potentially exposing embryos to thermally stressful conditions during development. Potentially, developmentally plastic shifts in thermal tolerance could allow lizards to adapt to climate warming. To determine how higher nest temperatures affect the thermal tolerance of hatchling geckos, we incubated eggs of the rock-dwelling velvet gecko, Amalosia lesueurii, at two fluctuating temperature regimes to mimic current nest temperatures (mean 23.2°C, range 10–33°C, 'cold') and future nest temperatures (mean 27.0°C, range 14–37°C, 'hot'). Hatchlings from the hot incubation group hatched 27 days earlier and had a lower critical thermal maximum (CTmax 38.7°C) and a higher critical thermal minimum (CTmin 6.2°C) than hatchlings from cold incubation group (40.2 and 5.7°C, respectively). In the field, hatchlings typically settle under rocks near communal nests. During the hatching period, rock temperatures ranged from 13 to 59°C, and regularly exceeded the CTmax of both hot- and cold-incubated hatchlings. Because rock temperatures were so high, the heat tolerance of lizards had little effect on their ability to exploit rocks as retreat sites. Instead, the timing of hatching dictated whether lizards could exploit rocks as retreat sites; that is, cold-incubated lizards that hatched later encountered less thermally stressful environments than earlier hatching hot-incubated lizards. In conclusion, we found no evidence that CTmax can shift upwards in response to higher incubation temperatures, suggesting that hotter summers may increase the vulnerability of lizards to climate warming.
Data from: Potential fitness tradeoffs for thermal tolerance in the intertidal copepod Tigriopus californicus
Thermal adaptation to spatially varying environmental conditions occurs in a wide range of species, but what is less clear is the nature of fitness trade-offs associated with this temperature adaptation. Here, populations of the intertidal copepod Tigriopus californicus are examined at both local and latitudinal scales to determine whether these populations have evolved differences in their survival under high temperature stress. A clear pattern of increasing high temperature stress tolerance is seen with decreasing latitude, consistent with temperature adaptation. Additionally, there is also evidence for significant variation in thermal tolerance on a smaller scale. The competitive fitness of pairs of northern and southern copepod populations were also examined under a series of lower, more moderate temperatures. These fitness assays show that the southern populations that have the best survival under extreme high temperatures have lowered competitive fitness at the lower temperatures tested, whereas the fitness of the southern populations exceeded that of the northern populations at the highest temperatures tested. Combined, these results suggest that there may be evolutionary trade-offs between performance at high and stressful temperatures and fitness at moderate temperatures in this species.
Data from: Evolution of thermal tolerance and its fitness consequences: parallel and non-parallel responses to urban heat islands across three cities
The question of parallel evolution—what causes it, and how common it is—has long captured the interest of evolutionary biologists. Widespread urban development over the last century has driven rapid evolutionary responses on contemporary timescales, presenting a unique opportunity to test the predictability and parallelism of evolutionary change. Here we examine rapid urban evolution in an acorn-dwelling ant species, focusing on the urban heat island signal and the ant's tolerance of these altered urban temperature regimes. Using a common-garden experimental design with acorn ant colonies collected from urban and rural populations in three cities and reared under five temperature treatments in the laboratory, we assessed plastic and evolutionary shifts in the heat and cold tolerance of F1 offspring worker ants. In two of three cities, we found evolved losses of cold tolerance, and compression of thermal tolerance breadth. Results for heat tolerance were more complex: in one city, we found evidence of simple evolved shifts in heat tolerance in urban populations, though in another, the difference in urban and rural population heat tolerance depended on laboratory rearing temperature, and only became weakly apparent at the warmest rearing temperatures. The shifts in tolerance appeared to be adaptive, as our analysis of the fitness consequences of warming revealed that while urban populations produced more sexual reproductives under warmer laboratory rearing temperatures, rural populations produced fewer. Patterns of natural selection on thermal tolerances supported our findings of fitness tradeoffs and local adaptation across urban and rural acorn ant populations, as selection on thermal tolerance acted in opposite directions between the warmest and coldest rearing temperatures. Our study provides mixed support for parallel evolution of thermal tolerance under urban temperature rise.
Data from: Thermal tolerance patterns across latitude and elevation
Linking variation in species' traits to large-scale environmental gradients can lend insight into the evolutionary processes that have shaped functional diversity and future responses to environmental change. Here, we ask how heat and cold tolerance vary as a function of latitude, elevation and climate extremes, using an extensive global dataset of ectotherm and endotherm thermal tolerance limits, while accounting for methodological variation in acclimation temperature, ramping rate and duration of exposure among studies. We show that previously reported relationships between thermal limits and latitude in ectotherms are robust to variation in methods. Heat tolerance of terrestrial ectotherms declined marginally towards higher latitudes and did not vary with elevation, whereas heat tolerance of freshwater and marine ectotherms declined more steeply with latitude. By contrast, cold tolerance limits declined steeply with latitude in marine, intertidal, freshwater and terrestrial ectotherms, and towards higher elevations on land. In all realms, both upper and lower thermal tolerance limits increased with extreme daily temperature, suggesting that different experienced climate extremes across realms explain the patterns, as predicted under the Climate Extremes Hypothesis. Statistically accounting for methodological variation in acclimation temperature, ramping rate and exposure duration improved model fits, and increased slopes with extreme ambient temperature. Our results suggest that fundamentally different patterns of thermal limits found among the earth's realms may be largely explained by differences in episodic thermal extremes among realms, updating global macrophysiological 'rules'.
Data from: Protein expression parallels thermal tolerance and ecologic changes in the diversification of a diving beetle species complex
Physiological changes associated with evolutionary and ecological processes such as diversification, range expansion or speciation are still incompletely understood, especially for non-model species. Here we study differences in protein expression in response to temperature in a western Mediterranean diving beetle species complex, using two-dimensional differential gel electrophoresis with one Moroccan and one Iberian population each of Agabus ramblae and Agabus brunneus. We identified proteins with significant expression differences after thermal treatments comparing them with a reference EST library generated from one of the species of the complex (A. ramblae). The colonisation during the Middle Pleistocene of the Iberian peninsula by A. ramblae, where maximum temperatures and seasonality are lower than in the ancestral north African range, was associated with changes in the response to 27 °C in proteins related to energy metabolism. The subsequent speciation of A. brunneus from within populations of Iberian A. ramblae was associated with changes in the expression of several stress-related proteins (mostly chaperons) when exposed to 4 °C. These changes are in agreement with the known tolerance to lower temperatures of A. brunneus, which occupies a larger geographical area with a wider range of climatic conditions. In both cases, protein expression changes paralleled the evolution of thermal tolerance and the climatic conditions experienced by the species. However, although the colonisation of the Iberian peninsula did not result in morphological change, the speciation process of A. brunneus within Iberia involved genetic isolation and substantial differences in male genitalia and body size and shape.
Data from: Evolutionary potential of multiple measures of upper thermal tolerance in Drosophila melanogaster
Thermal tolerance influences the distribution and abundance of many species, but the adaptive capacity of species to increase upper thermal tolerance is poorly understood. Given that patterns of heat tolerance can strongly depend on assay method, it is crucial to get a better understanding of genetic variances and correlations among different heat tolerance components. This study tests for correlated responses in different heat tolerance assays in Drosophila melanogaster lines selected for increased heat tolerance following exposure to a static high temperature. Traits tested included heat tolerance measured under static (basal and hardened) and ramping assays (using different starting temperatures and ramping rates), with lines exposed to fluctuating conditions (3 days of a cycling temperature regime) and a variable food treatment. Selected lines had higher heat tolerance than control lines in all static and ramping assays. The upper thermal tolerance was up to 0·5 °C higher in the selected compared to control lines after ten generations of strong selection. Selection using a static assay therefore leads to correlated responses in other heat-resistant components, suggesting that traits are genetically correlated and not influenced strongly by assay conditions. While the D. melanogaster population we studied harboured additive genetic variation to evolve increased upper thermal tolerance, the level detected may be insufficient to keep up with temperature increases predicted under climate change.
Data from: Evolutionary potential of thermal preference and heat tolerance in Drosophila subobscura
Evolutionary change of thermal traits (i.e. heat tolerance and behavioral thermoregulation) is one of the most important mechanisms exhibited by organisms to respond to global warming. However, the evolutionary potential of heat tolerance, estimated as narrow-sense heritability, depends on the methodology employed. An alternative adaptive mechanism to buffer extreme temperatures is behavioral thermoregulation, although the association between heat tolerance and thermal preference is not clearly understood. We suspect that methodological effects associated with the duration of heat stress during thermal tolerance assays are responsible for missing this genetic association. To test this hypothesis, we estimated the heritabilities and genetic correlations for thermal traits in Drosophila subobscura, using high-temperature static and slow ramping assays. We found that heritability for heat tolerance was higher in static assays (h2 = 0.134) than in slow ramping assays (h2 = 0.084), suggesting that fast assays may provide a more precise estimation of the genetic variation of heat tolerance. In addition, thermal preference exhibited a low heritability (h2 = 0.066), suggesting a reduced evolutionary response for this trait. We also found that the different estimates of heat tolerance and thermal preference were not genetically correlated, regardless of how heat tolerance was estimated. In conclusion, our data suggest that these thermal traits can evolve independently in this species. In agreement with previous evidence, these results indicate that methodology may have an important impact on genetic estimates of heat tolerance and that fast assays are more likely to detect the genetic component of heat tolerance.
Data from: Can physiological engineering/programming increase multi-generational thermal tolerance to extreme temperature events?
Organisms increasingly encounter higher frequencies of extreme weather events as a consequence of global climate change. Currently, few strategies are available to mitigate climate change effects on animals arising from acute extreme high temperature events. We tested the capacity of physiological engineering to influence the intra- and multi-generational upper thermal tolerance capacity of a model organism Artemia, subjected to extreme high temperatures. Enhancement of specific physiological regulators during development could affect thermal tolerances or life-history attributes affecting subsequent fitness. Using experimental Artemia populations we exposed F0 individuals to one of four treatments; heat hardening (28 &[deg]C to 36 &[deg]C, 1 &[deg]C per 10 minutes), heat hardening plus serotonin (0.056 μg ml-1), heat hardening plus methionine (0.79 mg ml-1), and a control treatment. Regulator concentrations were based on previous literature. Serotonin may promote thermotolerance, acting upon metabolism and life-history. Methionine acts as a methylation agent across generations. For all groups, measurements were collected for three performance traits of individual thermal tolerance (upper sublethal thermal limit, lethal limit, and dysregulation range) over two generations. Results showed no treatment increased upper thermal limit during acute thermal stress, although serotonin-treated and methionine-treated individuals outperformed controls across multiple thermal performance traits. Additionally, some effects were evident across generations. Together these results suggest phenotypic engineering provides complex outcomes; and if implemented with heat hardening can further influence performance in multiple thermal tolerance traits, within and across generations. Potentially, such techniques could be up-scaled to provide resilience and stability in populations susceptible to extreme temperature events.
Data from: Elevational and microclimatic drivers of thermal tolerance in Andean Pristimantis frogs
Aim: We analysed elevational and microclimatic drivers of thermal tolerance diversity in a tropical mountain frog clade to test three macrophysiological predictions: less spatial variation in upper than lower thermal limits (Bretts' heat invariant hypothesis); narrower thermal tolerance ranges in habitats with less variation in temperature (Janzen´s climatic variability hypothesis); and higher level of heat impacts at lower altitudes. Location: Forest and open habitats through a 4230 m elevational gradient across the tropical Andes of Ecuador. Method: We examined variability in critical thermal limits (CTmax, and CTmin), and thermal breadth (CTmax-CTmin) in 21 species of Pristimantis frogs. Additionally, we monitored maximum and minimum temperatures at the local-scale (tmax, tmin), and estimated vulnerability to acute thermal stress from heat (CTmax-tmax) and cold (tmin – CTmin), by partitioning thermal diversity into elevational and microclimatic variation. Results: Our results were consistent with Brett's hypothesis: altitude promotes more variation in CTmin and tmin than in CTmax and tmax. Frogs inhabiting thermally variable open habitats have higher CTmax and tmax and greater thermal breadths than species restricted to forest habitats, which show less climatic overlap across the elevational gradient (Janzen´s hypothesis). Vulnerability to heat stress was higher in open than forest habitats and did not vary with altitude. Main conclusions: We suggest a mechanistic explanation of thermal tolerance diversity in elevational gradients by including microclimatic thermal variation. We propose that the unfeasibility to buffer minimum temperatures locally may explain the rapid increase in cold tolerance (lower CTmin) with elevation. In contrast, the relative invariability in heat tolerance (CTmax) with elevation may revolve around the organisms' habitat selection of open and canopy buffered habitats. Secondly, on the basis of microclimatic estimates, lowland and upland species may be equally vulnerable to temperature increase, which is contrary to the pattern inferred from regional interpolated climate estimators.
Data from: Ecological novelty by hybridization: experimental evidence for increased thermal tolerance by transgressive segregation in Tigriopus californicus
Early generations of hybrids can express both genetic incompatibilities and phenotypic novelty. Insights into whether these conflicting interactions between intrinsic and extrinsic selection persist after a few generations of recombination require experimental studies. To address this question, we use interpopulation crosses and recombinant inbred lines (RILs) of the copepod Tigriopus californicus, and focus on two traits that are relevant for the diversification of this species: survivorship during development and tolerance to thermal stress. Experimental crosses between two population pairs show that most RILs between two heat-tolerant populations show enhanced tolerance to temperatures that are lethal to the respective parentals, whereas RILs between a heat-tolerant and a heat-sensitive population are intermediate. Although interpopulation crosses are affected by intrinsic selection at early generational hybrids, most of the sampled F9 RILs have recovered fitness to the level of their parentals. Together, these results suggest that a few generations of recombination allows for an independent segregation of the genes underlying thermal tolerance and cytonuclear incompatibilities, permitting certain recombinant lineages to survive in niches previously unused by parental taxa (i.e., warmer thermal environments) without incurring intrinsic selection.
Data on heat tolerance for D latus from: Does plasticity in thermal tolerance trade off with inherent tolerance? The influence of setal tracheal gills on thermal tolerance and its plasticity in a group of European diving beetles
<h3>Dataset on heat tolerance used in the study by Verberk et al., (2018).</h3><h3>Method description</h3><p>We assessed the impact of mode of respiration on heat tolerance under different oxygen conditions in one of the 15 species: <i>D. latus</i>, the most tolerant species in our comparison, using previously described methods (<a href="https://www.sciencedirect.com/science/article/pii/S0022191017302044#b0170">Verberk and Calosi, 2012</a>, <a href="https://www.sciencedirect.com/science/article/pii/S0022191017302044#b0185">Verberk and Bilton, 2015</a>). Briefly, individuals were placed in flow-through chambers, whose water supply could be heated. For one group of animals, we used chambers where the animals were completely submerged and had no access to air, while for a second group of animals chambers were used with a small head space holding a layer of air, meaning that these animals could obtain oxygen either from the air compartment by surfacing or from the water with oxygen diffusing directly into their tracheal system <i>via</i> the setae or oxygen diffusing into their subelytral air reservoir <i>via</i> their physical gill. Individuals were left to settle for 1 h at the equilibration temperature of 10 °C, after which the temperature was ramped up at 0.25 °C min−1. The CTmax was defined as the point at which animals lost coordinated swimming, hence losing their ability to escape from the conditions that will lead to their death (<a href="https://www.sciencedirect.com/science/article/pii/S0022191017302044#b0095">Lutterschmidt and Hutchison, 1997</a>). The heating rate, endpoint and starting temperature all therefore differed from the methodology described above, meaning that the critical thermal temperatures from both methods cannot be compared directly. CTmax was assessed under <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/normoxia">normoxia</a>, <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/hypoxemia">hypoxia</a> and <a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/hyperoxia">hyperoxia</a> conditions (5, 20, 60 kPa O2 respectively) and adults were assessed with and without access to air. Oxygen tension of both the water and the air in the headspace was altered to produce hypoxia and hyperoxia, as described by <a href="https://www.sciencedirect.com/science/article/pii/S0022191017302044#b0185">Verberk and Bilton (2015)</a>.</p>
The effect of urbanization and temperature on thermal tolerance, foraging performance, and competition in cavity dwelling ants
<p>Human disturbance including rapid urbanization and increased temperatures can have profound effects on the ecology of local populations. Eusocial insects, such as ants, have adapted to stressors of increasing temperature and urbanization, however these evolutionary responses are not consistent among populations across geographic space. Here we asked how urbanization and incubation temperature influence critical thermal maximum (CT<sub>max</sub>) and various ecologically relevant behaviors in three ant species in urban and rural locations in Worcester, MA, USA. We did this by incubating colonies of three species of cavity dwelling ant (<em>Aphaenogaster picea, Tapinoma sessile, </em>and <em>Temnothorax longispinosus</em>) from 2 habitat types (Rural and Urban), for 60-days at multiple temperatures. We found that incubation temperature, urbanization and species of ant all significantly affected overall colony critical thermal maximum. We also found that recruitment time, colonization time and defense response were significantly affected by incubation temperature and varied between species of ant, while recruitment and colonization time were additionally affected by urbanization. These variable changes in performance and competitive traits across species suggest that responses to urbanization and shifting temperatures are not universal across species. Changes in behavioral responses caused by urbanization may disrupt biodiversity, creating unusual competitive environments as a consequence of natural adaptations and cause both direct and indirect mechanisms for which human disturbance can lead to local species extinction.</p> <p> </p>
Climate change impacts on seabirds and marine mammals: the importance of study duration, thermal tolerance and generation time
Understanding climate change impacts on top predators is fundamental to marine biodiversity conservation, due to their increasingly threatened populations and their importance in marine ecosystems. We conducted a systematic review of the effects of climate change (prolonged, directional change) and climate variability on seabirds and marine mammals. We extracted data from 484 studies (4808 published studies were reviewed), comprising 2215 observations on demography, phenology, distribution, diet, behaviour, body condition and physiology. The likelihood of concluding that climate change had an impact increased with study duration. However, the temporal thresholds for the effects of climate change to be discernible varied from 10 to 29 years depending on the species, the biological response and the oceanic study region. Species with narrow thermal ranges and relatively long generation times were more often reported to be affected by climate change. This provides an important framework for future assessments, with guidance on response- and region-specific temporal dimensions that need to be considered when reporting effects of climate change. Lastly, we found that tropical regions and non-breeding life stages were poorly covered in the literature, a concern that should be addressed to enable a better understanding of the vulnerability of marine predators to climate change.
Heterogeneous environmental seascape across a biogeographic brake influences the thermal physiology and tolerances to ocean acidification in an ecosystem
<p><b>Aim:</b> Understanding how spatio-temporal environmental variability influences stress tolerance, local adaptation, and phenotypic variation among populations is a key challenge for evolutionary ecology and climate change biology. Coastal biogeographic breaks are natural laboratories to explore this fundamental research question due to the contrasting environmental conditions experienced by natural populations across these regions.</p> <p><b>Location:</b> In the South East Pacific (SEP) coast a major break (30º-32ºS) is characterized by extreme natural variability in sea surface temperature (SST) and carbonate chemistry parameters related to temporal and spatial dynamics in upwelling events. Calcifying organisms inhibiting this zone are exposed to marked fluctuations and clines in SST that together with naturally acidified waters can impact their metabolism, calcification and fitness, making them particularly prone to the effects of climate change (e.g., ocean acidification, OA). We investigated to what extent the spatial and temporal environmental variability (in SST and seawater carbonate conditions) that characterizes the biogeographic break in the SEP, influences intra-specific differences in the thermal ecology and the tolerances to OA of the limpet <i>Scurria araucana</i>.</p> <p><b>Methods: </b>During two years, we conducted field surveys of limpet populations at sites across the SEP break (27ºS, 30ºS and 32ºS). We collected individuals from each population to test for geographic differences in morphometric (e.g., total buoyancy weight, shell length) and physiological (e.g., oxygen consumption rate, cardiac activity, and thermal performance curves; TPC) responses to local environmental conditions (Tº and pH/pCO<sub>2</sub>) and to simulated OA scenarios.</p> <p><b>Results:</b> Populations of <i>S. Araucana </i>exhibit high tolerance to OA with no signal of geographic influence on this attribute. However, inter-population differences in thermal physiology (metabolic rates and performances) where found across the biogeographic break in the SEP coast. Limpets from the central part of the break (30ºS) exhibit higher thermal performance compared to limpets from populations at both sides of the break.</p> <p><b>Main conclusions:</b> Variation in SST has a greater effect shaping inter-population differences in thermal physiology of the limpet <i>S. araucana</i>. These physiological differences<i> </i>are aligned the thermal heterogenous seascape along the biogeographic break in the SEP. Contrary, temporal and spatial variation in seawater carbonate conditions does not influence inter-population differences in phenotypic response populations, but an overall high tolerance to OA.</p>
Thermal tolerance of fish to heatwaves in agricultural streams: What does not kill you makes you stronger?
<p>Heatwaves are increasing in frequency and intensity under climate change. Freshwater ecosystems are among the most thermally impacted systems, within which agricultural streams are experiencing the most extreme heatwaves and deserve prioritized focus. Heatwaves are approaching the upper thermal limits of many fishes but have received little attention to date.</p> <p>To study whether and how fish tolerate heatwaves from a physiological perspective, we simulated single, multiple, and extended heatwaves at 32 and 34 °C in the laboratory, based on high-resolution summer temperatures recorded in agricultural vs. forested streams in Illinois, USA.</p> <p>By investigating the effects of heatwaves on 25 °C acclimated fathead minnow <i>Pimephales promelas</i>, an important prey species across North America, we witnessed its high thermal resilience, including a rapid return to metabolic homeostasis after single and multiple heatwaves, measured by oxygen consumption rate (<i>Ṁ</i>O<sub>2</sub>). During extended heatwave, fathead minnow were still able to lower <i>Ṁ</i>O<sub>2</sub> after the initial exposure, despite without complete thermal compensation. We also found transient increases in their critical thermal maximum (CT<sub>max</sub>), especially after higher intensity and frequency of heatwaves. However, the thermal resilience of fathead minnow did come with costs, including reduced anaerobic capacity indicated by decreased lactate dehydrogenase activity and impaired antioxidant defense indicated by reduced superoxide dismutase in white muscle.</p> <p>By monitoring metabolic costs and physiological adjustments of fish during and after heatwaves, we showed that fathead minnow were resilient to simulated current and near-future heatwaves, which may allow them to cope with thermal extremes expected in agricultural streams.</p> <p>Overall, the real-time monitoring of fish responses to heatwaves incorporates natural dynamics of thermal patterns. It facilitates the mechanistic understandings of how fish react to thermal challenges in the real world and offers opportunities to incorporate high-resolution metabolic costs into future bioenergetic modeling.</p>
No consistent effect of daytime versus night-time measurement of thermal tolerance in nocturnal and diurnal lizards
<p>While essential in understanding impacts of climate change for organisms, diel variation remains an understudied component of temporal variation in thermal tolerance limits (i.e. the critical thermal minimum (CTmin) and maximum (CTmax)). For example, a higher Ctmax might be expected for an individual if the measurement is taken during the day (when heat stress is most likely to occur) instead of at night. We measured thermal tolerance (Ctmin and Ctmax) during both the daytime and night-time in 101 nocturnal and diurnal geckos and skinks in Hong Kong and in South Africa, representing six species, and covering a range of habitats. We found that period of measurement (day vs. night) only affected Ctmin in South Africa (but not in Hong Kong) and that Ctmax was unaffected. Body size and species were important factors for determining Ctmax in Hong Kong and Ctmin in South Africa, respectively. Overall, however, we did not find consistent diel variation of thermal tolerance and suggest that measurements of critical thermal limits may be influenced by timing of measurement – but that such effects, when present, are likely to be context-dependent.</p>
Thermal tolerance of Arbacia lixula
<p>As the ocean warms, the thermal tolerance of marine invertebrates is key to determining their distributional change, where acclimation to low pH may impact the thermal range of optimal development. We compared thermal tolerance of progeny from a low pH-acclimated sea urchin (<em>Arbacia lixula</em>) population from the CO2 vents of Ischia (Italy), and a nearby population living at ambient pH. The percentage of normally developing gastrulae and two-armed larvae were determined across 10 temperatures representing present and future temperature conditions (16-34 ˚C). Vent-acclimated sea urchins showed a greater percentage of normal development at 24 hours, with a larger optimal developmental temperature range than control sea urchins (12.3 ˚C vs 5.4 ˚C range, respectively). At 48 hours, upper lethal temperatures for 50% survival with respect to ambient temperatures were similar between control (+6.8 ˚C) and vent (+6.2 ˚C) populations. Thus, acclimation to low pH did not impact the broad thermal tolerance of <em>A. lixula</em> progeny. With<em> A. lixula</em>'s barrens forming abilities, its wide thermotolerance and its ability to acclimate to low pH, this species will continue to be an important ecological engineer in Mediterranean macroalgal ecosystems in a changing ocean.</p>
Data and code for: Heat tolerance and its plasticity in freshwater and marine fishes are linked to their thermal regimes (v0.1).
<p>Data and code for: Heat tolerance and its plasticity in freshwater and marine fishes are linked to their thermal regimes (v0.1).</p>
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