Isopods failed to acclimate their thermal sensitivity of locomotor performance during predictable or stochastic cooling

Higher temperature and substrate vibrations as stress factors for terrestrial isopods - model species matter

This study was focused on behaviour of the Common Rough Woodlouse (Porcellioscaber) and the Plum Woodlouse (Porcellionidespruinosus) under the influence of stressors in the form of increased temperature, the vibrating surface, or their combination. Two types of experiments were performed. First, woodlice placed in a labyrinth were observed, to determine the degree of turn alternation, the speed of passing through the labyrinth, and the corrections of turn alternation, when exposed to stressors. In the second experiment how woodlice aggregate in the aforementioned potential stressors was recorded and whether the change in aggregation behaviour can be an indicator of the degree of stress. Increased temperature and the combination of increased temperature and vibrations were stressors only for P.scaber. The results show that vibrations are not a stress factor for P.scaber or P.pruinosus. Porcellioscaber passed through the labyrinth more slowly at increased temperatures, and although they made more turn-corrections, they alternated turns less intensely. Its aggregation behaviour was mainly influenced by temperature, which confirms that the aggregation behaviour of P.scaber actually indicates a degree of stress.

Developmental temperature affects thermal dependence of locomotor activity in Drosophila

In their natural environments, animals have to cope with fluctuations in numerous abiotic and biotic factors, and phenotypic plasticity can facilitate survival under such variable conditions. However, organisms may differ substantially in the ability to adjust their phenotypes in response to external factors. Here, we investigated how developmental temperature affects the thermal performance curve for locomotor activity in adult fruit flies (Drosophila melanogaster). We examined the thermal dependence of spontaneous activity in individuals originating from two natural populations (from tropical (India) and temperate climate zone (Slovakia)) that developed at three different temperatures (19 °C, 25 °C, and 29 °C). Firstly, we found that developmental temperature has a significant impact on overall activity - flies that developed at high temperature (29 °C) were, on average, less active than individuals that developed at lower temperatures. Secondly, developmental acclimation had a population-specific effect on the thermal optimum for activity. Whereas the optimal temperature was not affected by thermal conditions experienced during development in flies from India, developmental temperature shifted thermal optimum in flies from Slovakia. Thirdly, high developmental temperature broadened performance breadth in flies from the Indian population but narrowed it in individuals from the Slovak population. Finally, we did not detect a consistent effect of acclimation temperature on circadian rhythms of spontaneous activity. Altogether, our results demonstrate that developmental temperature can alter different parameters (maximum performance, thermal optimum, performance breadth) of the thermal performance curve for spontaneous activity. Since adult fruit flies are highly vagile, this sensitivity of locomotion to developmental conditions may be an important factor affecting fitness in changing environments.

Acclimation temperature affects thermal reaction norms for energy reserves in Drosophila

Organisms have evolved various physiological mechanisms to cope with unfavourable environmental conditions. The ability to tolerate non-optimal thermal conditions can be substantially improved by acclimation. In this study, we examined how an early-life acclimation to different temperatures (19 °C, 25 °C and 29 °C) influences thermal reaction norms for energy stores in Drosophila adults. Our results show that acclimation temperature has a significant effect on the amount of stored fat and glycogen (and their relative changes) and the optimal temperature for their accumulation. Individuals acclimated to 19 °C had, on average, more energy reserves than flies that were initially maintained at 25 °C or 29 °C. In addition, acclimation caused a shift in optimal temperature for energy stores towards acclimation temperature. We also detected significant population differences in this response. The effect of acclimation on the optimal temperature for energy stores was more pronounced in flies from the temperate climate zone (Slovakia) than in individuals from the tropical zone (India). Overall, we found that the acclimation effect was stronger after acclimation to low (19 °C) than to high (29 °C) temperature. The observed sensitivity of thermal reaction norms for energy reserves to acclimation temperature can have important consequences for surviving periods of food scarcity, especially at suboptimal temperatures.

Hypoxia causes woodlice (Porcellio scaber) to select lower temperatures and impairs their thermal performance and heat tolerance

Environmental temperatures and oxygen availability are important for the balance between oxygen supply and demand. Terrestrial organisms are generally perceived to be less limited by access to oxygen than their aquatic counterparts. Nevertheless, even terrestrial environments can be deficient in oxygen, especially for organisms occurring in soil, litter, wood, rotten fruit or at high elevations. While isopods are the best adapted to a terrestrial lifestyle among crustaceans, many species, including woodlice, occupy environmental gradients of temperature and oxygen. To investigate whether mismatches between oxygen supply and demand can result in a loss of performance in a terrestrial organism, we studied the effects of atmospheric oxygen concentration on the thermal performance of the common rough woodlouse (Porcellio scaber). We compared the thermal preference, thermal sensitivity of running speed, and tolerance to extreme temperatures of woodlice exposed to one of two oxygen concentrations (21% - normoxia, 7% - hypoxia). Under hypoxia, P. scaber preferred microhabitats with temperatures that were on average 3°C lower than those preferred under normoxia. The running speed tended to reach its maximum at a lower temperature under hypoxia than under normoxia (25.13°C vs 28.87°C, respectively, although p was equal to 0.09), and normoxic woodlice ran approximately 1.5-fold faster than hypoxic woodlice at the point of maximum speed. Heat tolerance was significantly lower under hypoxia (38.9°C) than under normoxia (40.7°C), but there was no difference in cold tolerance (5.81°C under normoxia and 5.44°C under hypoxia). Overall, our results indicate that environmental gradients of temperature and oxygen may shape the physiological performance of terrestrial ectotherms, likely via their effects on the balance between oxygen supply and demand, which may have fitness consequences for these organisms in nature.

An intertidal fish shows thermal acclimation despite living in a rapidly fluctuating environment

The co-evolution of acclimation capacity and thermal performance breadth has been a contentious issue for decades, and little is known regarding the extent to which acclimation alters the shape of acute thermal performance curves. Current acclimation theory suggests that when daily variation is large and unpredictable ectotherms should not acclimate but should evolve wide performance breadths, allowing maintenance of performance across a wide thermal range. The subtropical intertidal zone, however, experiences a large amount of daily thermal variation, but daily means and ranges shift in predictable ways with season, where daily and seasonal variation is roughly equal. We predicted that animals in this habitat would maintain their capacity to acclimate and that performance breadth would not be altered by acclimation to maintain function with rapidly fluctuating daily temperatures. We tested our prediction using a subtropical goby, Bathygobius cocosensis, which lives in tide pools that vary widely, over days and seasons. We exposed B. cocosensis to winter (12-17 °C) and summer (30-35 °C) thermal conditions for six weeks and then measured the thermal dependence of burst swimming speed, routine and maximum metabolic rate, and ventilation rate between 12 and 36 °C. B. cocosensis exhibited an acclimation response for burst swimming speed, maximum metabolic rate and metabolic scope, but acclimation did not alter the shape of acute thermal performance curves. These results indicate that thermal acclimation can occur when short-term thermal variability is large and equal to seasonal variation, and wide performance breadths can be maintained with acclimation in heterogeneous environments.

Host choice, settling and folding leaf behaviors of the larval rice leaf folder under heat stress

Extreme high-temperature events are the key factor to determine population dynamics of the rice leaf folder, Cnaphalocrocis medinalis (Guenée), in summer. Although we know that adult of this insect can migrate to avoid heat stress, the behavioral response of larva to high temperature is still unclear. Therefore, impacts of high temperature on behavioral traits of C. medinalis including host choice, settling and folding leaf were observed. The results revealed that these behavioral traits were clearly influenced by high temperature. The larvae preferred maize leaves rather than rice and wheat at normal temperature of 27°C, but larvae experienced a higher temperature of 37 or 40°C for 4 h preferred rice leaves rather than maize and wheat. Capacity of young larvae to find host leaves or settle on the upper surface of leaves significantly reduced when they were treated by high temperature. High temperature of 40°C reduced the leaf-folding capacity of the third instar larvae, but no effects were observed on the fourth and fifth instar larvae. Short-term heat acclimation could not improve the capacity of the third instar larvae to make leaf fold under 40°C.

Transgenerational plasticity of reproduction depends on rate of warming across generations

Predicting the impacts of climate change to biological systems requires an understanding of the ability for species to acclimate to the projected environmental change through phenotypic plasticity. Determining the effects of higher temperatures on individual performance is made more complex by the potential for environmental conditions experienced in previous and current generations to independently affect phenotypic responses to high temperatures. We used a model coral reef fish (Acanthochromis polyacanthus) to investigate the influence of thermal conditions experienced by two generations on reproductive output and the quality of offspring produced by adults. We found that more gradual warming over two generations, +1.5°C in the first generation and then +3.0°C in the second generation, resulted in greater plasticity of reproductive attributes, compared to fish that experienced the same increase in one generation. Reproduction ceased at the projected future summer temperature (31.5°C) when fish experienced +3.0°C for two generations. Additionally, we found that transgenerational plasticity to +1.5°C induced full restoration of thermally affected reproductive and offspring attributes, which was not possible with developmental plasticity alone. Our results suggest that transgenerational effects differ depending on the absolute thermal change and in which life stage the thermal change is experienced.

Life in the Frequency Domain: the Biological Impacts of Changes in Climate Variability at Multiple Time Scales

Over the last few decades, biologists have made substantial progress in understanding relationships between changing climates and organism performance. Much of this work has focused on temperature because it is the best kept of climatic records, in many locations it is predicted to keep rising into the future, and it has profound effects on the physiology, performance, and ecology of organisms, especially ectothermic organisms which make up the vast majority of life on Earth. Nevertheless, much of the existing literature on temperature-organism interactions relies on mean temperatures. In reality, most organisms do not directly experience mean temperatures; rather, they experience variation in temperature over many time scales, from seconds to years. We propose to shift the focus more directly on patterns of temperature variation, rather than on means per se, and present a framework both for analyzing temporal patterns of temperature variation and for incorporating those patterns into predictions about organismal biology. In particular, we advocate using the Fourier transform to decompose temperature time series into their component sinusoids, thus allowing transformations between the time and frequency domains. This approach provides (1) standardized ways of visualizing the contributions that different frequencies make to total temporal variation; (2) the ability to assess how patterns of temperature variation have changed over the past half century and may change into the future; and (3) clear approaches to manipulating temporal time series to ask "what if" questions about the potential effects of future climates. We first summarize global patterns of change in temperature variation over the past 40 years; we find meaningful changes in variation at the half day to yearly times scales. We then demonstrate the utility of the Fourier framework by exploring how power added to different frequencies alters the overall incidence of long-term waves of high and low temperatures, and find that power added to the lowest frequencies greatly increases the probability of long-term heat and cold waves. Finally, we review what is known about the time scales over which organismal thermal performance curves change in response to variation in the thermal environment. We conclude that integrating information characterizing both the frequency spectra of temperature time series and the time scales of resulting physiological change offers a powerful new avenue for relating climate, and climate change, to the future performance of ectothermic organisms.

Contrasting environments shape thermal physiology across the spatial range of the sandhopper Talorchestia capensis

Integrating thermal physiology and species range extent can contribute to a better understanding of the likely effects of climate change on natural populations. Generally, broadly distributed species show variation in thermal physiology between populations. Within their distributional ranges, populations at the edges are assumed to experience more challenging environments than central populations (fundamental niche breadth hypothesis). We have investigated differences in thermal tolerance and thermal sensitivity under increasing/decreasing temperatures among geographically separated populations of the sandhopper Talorchestia capensis along the South African coasts. We tested whether the thermal tolerance and thermal sensitivity of T. capensis differ between central and marginal populations using a non-parametric constraint space analysis. We linked thermal sensitivity to environmental history by using historical climatic data to evaluate whether individual responses to temperature could be related to natural long-term fluctuations in air temperatures. Our results demonstrate that there were significant differences in the thermal response of T. capensis populations to both increasing/decreasing temperatures. Thermal sensitivity (for increasing temperatures only) was negatively related to temperature variability and positively related to temperature predictability. Two different models fitted the geographical distribution of thermal sensitivity and thermal tolerance. Our results confirm that widespread species show differences in physiology among populations by providing evidence of contrasting thermal responses in individuals subject to different environmental conditions at the limits of the species' spatial range. When considering the complex interactions between individual physiology and species ranges, it is not sufficient to consider mean environmental temperatures, or even temperature variability; the predictability of that variability may be critical.

Progeny of Osmia lignaria from distinct regions differ in developmental phenology and survival under a common thermal regime

Many insects, including some bees, have extensive subcontinental distributions that can differ in climatic conditions. Within and beyond these distributions, humans intentionally transport beneficial insects, including bees, to non-natal geographic locations. Insects also are experiencing unprecedented climatic change in their resident localities. For solitary bees, we know very little about the adaptive plasticity and geographic variation in developmental physiology that accommodates the different climates experienced within distributional ranges. Osmia lignaria Say (Hymenoptera: Megachilidae) is a widely distributed North American spring-emerging bee being developed as a managed pollinator for tree fruit crops, including almonds. We examined the development and survival of O. lignaria progeny that were descended from populations sourced from southern California, western Washington, and northern Utah, and then were reared together under an hourly and weekly temperature regime simulating those of a California almond-growing region. We found that developmental physiologies of Washington and Utah progeny were generally similar. However, California progeny developed slower, were more metabolically active, and survived better under California conditions than did populations native to regions at higher latitudes. Regardless of geographic origin, cocooned adults managed under prescribed thermal regimes emerged faster and lived longer after wintering. Progeny of parents from different regions exhibited some acclimatory plasticity in developmental phenologies to a novel climatic regime, but overall their responses reflected their geographic origins. This outcome is consistent with their developmental phenologies being largely heritable adaptations to regional climates.

Differential responses to thermal variation between fitness metrics

Temperature is a major factor affecting population abundance and individual performance. Net reproductive rate (R₀) and intrinsic rate of increase (r) differ in their response to different temperature regimes, and much of the difference is mediated by generation time (Tg). Here, we evaluate the effects of thermal mean and variability on R₀, r and Tg, at four population densities in Drosophila melanogaster. The results show that R₀, r and Tg present differential responses to thermal variation. Although temperature effects on R₀ and Tg are non-linear, r response was negligible. R₀ and Tg comprise a generational time scale, while r is at a chronological time scale. Thus, we argue that individuals growing under different thermal environments perform similarly on a chronological scale, but differently on a generational scale.

Variation in thermal sensitivity and thermal tolerances in an invasive species across a climatic gradient: lessons from the land snail Cornu aspersum

The ability of organisms to perform at different temperatures could be described by a continuous nonlinear reaction norm (i.e., thermal performance curve, TPC), in which the phenotypic trait value varies as a function of temperature. Almost any shift in the parameters of this performance curve could highlight the direct effect of temperature on organism fitness, providing a powerful framework for testing thermal adaptation hypotheses. Inter-and intraspecific differences in this performance curve are also reflected in thermal tolerances limits (e.g., critical and lethal limits), influencing the biogeographic patterns of species' distribution. Within this context, here we investigated the intraspecific variation in thermal sensitivities and thermal tolerances in three populations of the invasive snail Cornu aspersum across a geographical gradient, characterized by different climatic conditions. Thus, we examined population differentiation in the TPCs, thermal-coma recovery times, expression of heat-shock proteins and standard metabolic rate (i.e., energetic costs of physiological differentiation). We tested two competing hypotheses regarding thermal adaptation (the "hotter is better" and the generalist-specialist trade-offs). Our results show that the differences in thermal sensitivity among populations of C. aspersum follow a latitudinal pattern, which is likely the result of a combination of thermodynamic constraints ("hotter is better") and thermal adaptations to their local environments (generalist-specialist trade-offs). This finding is also consistent with some thermal tolerance indices such as the Heat-Shock Protein Response and the recovery time from chill-coma. However, mixed responses in the evaluated traits suggest that thermal adaptation in this species is not complete, as we were not able to detect any differences in neither energetic costs of physiological differentiation among populations, nor in the heat-coma recovery.

Climate change effects on macrofaunal litter decomposition: the interplay of temperature, body masses and stoichiometry

Macrofauna invertebrates of forest floors provide important functions in the decomposition process of soil organic matter, which is affected by the nutrient stoichiometry of the leaf litter. Climate change effects on forest ecosystems include warming and decreasing litter quality (e.g. higher C : nutrient ratios) induced by higher atmospheric CO(2) concentrations. While litter-bag experiments unravelled separate effects, a mechanistic understanding of how interactions between temperature and litter stoichiometry are driving decomposition rates is lacking. In a laboratory experiment, we filled this void by quantifying decomposer consumption rates analogous to predator-prey functional responses that include the mechanistic parameters handling time and attack rate. Systematically, we varied the body masses of isopods, the environmental temperature and the resource between poor (hornbeam) and good quality (ash). We found that attack rates increased and handling times decreased (i) with body masses and (ii) temperature. Interestingly, these relationships interacted with litter quality: small isopods possibly avoided the poorer resource, whereas large isopods exhibited increased, compensatory feeding of the poorer resource, which may be explained by their higher metabolic demands. The combination of metabolic theory and ecological stoichiometry provided critically important mechanistic insights into how warming and varying litter quality may modify macrofaunal decomposition rates.

Thermal tolerance breadths among groundwater crustaceans living in a thermally constant environment

Abstract: The climate variability hypothesis assumes that the thermal tolerance breadth of a species is primarily determined by temperature variations experienced in its environment. If so, aquatic invertebrates living in thermally-buffered environments would be expected to exhibit narrow thermal tolerance breadths (stenothermy). We tested this prediction by studying the thermal physiology of 3 isopods (Asellidae, Proasellus) colonizing groundwater habitats characterized by annual amplitude of temperature less than 1°C. The species responses to temperature variation were assessed in the laboratory using five physiological variables: survival, locomotor activity, aerobic respiration, immune defense and concentrations of total free amino acids and sugars. The three species exhibited contrasted thermal physiologies although all variables were not equally informative. In accordance with the climate variability hypothesis, two species were extremely sensitive even to moderate changes in temperature (2°C) below and above their habitat temperature. In contrast, the third species exhibited a surprisingly high thermal tolerance breadth (11°C). Differences in response to temperature variation among Proasellus species indicated that their thermal physiology was not solely shaped by the current temperature seasonality in their natural habitats. More particularly, recent gene flow among populations living in thermally constant yet contrasted habitats might explain the occurrence of eurytherm species in thermally buffered environments.

Temperature-dependent growth of Geomyces destructans, the fungus that causes bat white-nose syndrome

White-nose syndrome (WNS) is an emergent disease estimated to have killed over five million North American bats. Caused by the psychrophilic fungus Geomyces destructans, WNS specifically affects bats during hibernation. We describe temperature-dependent growth performance and morphology for six independent isolates of G. destructans from North America and Europe. Thermal performance curves for all isolates displayed an intermediate peak with rapid decline in performance above the peak. Optimal temperatures for growth were between 12.5 and 15.8°C, and the upper critical temperature for growth was between 19.0 and 19.8°C. Growth rates varied across isolates, irrespective of geographic origin, and above 12°C all isolates displayed atypical morphology that may have implications for proliferation of the fungus. This study demonstrates that small variations in temperature, consistent with those inherent of bat hibernacula, affect growth performance and physiology of G. destructans, which may influence temperature-dependent progression and severity of WNS in wild bats.