Thermal Optimum Research Articles

Paleohydrological history of Lake Allos (2200 m a.s.l) since 13 500 cal a bp in the Mediterranean Alps inferred from an ostracod δ18O record

ABSTRACTThis paper presents the first Lateglacial/Holocene (the last 13 500 cal a bp) ostracod δ18O record to infer hydroclimate variability in the Southern French Alps. Cytherissa lacustris (δ18Osp) shells extracted from the sediments of Lake Allos allowed a reconstruction of δ18Olake water (δ18Olw) except for the interval 5800–2800 cal a bp. The shape of the Younger Dryas (YD) clearly differed from records documented in the northern Alps. First, δ18Olw values remained close to modern values before a marked drop ca. 12 000 cal a bp. Then, after several oscillations, δ18Olw values increased, reaching the highest value of the record ca. 6100 cal a bp during a thermal optimum for this latitude. Finally, low δ18Olw values occurred from 450 to 100 cal a bp during the Little Ice Age (LIA) following the Medieval Climate anomaly. At the beginning of the YD, δ18Olw probably reflected changes in local glacier dynamics and precipitation sources. The following decrease in δ18Olw values was associated with higher freshwater inputs during the second half of the YD. During the LIA, the low δ18O values are consistent with a higher torrential activity and lower air temperatures.

Summer temperature drives the lake ecosystem during the Late Weichselian and Holocene in Eastern Europe: A case study from East European Plain

East European lake-river systems have hydrological regimes typical for continental climate zones. The Postglacial development of the basins and regional palaeoclimatic pattern in the Holocene implied a specific succession of biota communities passing through lakes’ subsequent stages in the water level, trophic state and habitat availability. The Great Serteya Palaeolake Basin is the largest palaeolake within the Serteyka lake-river system, which has been functioning since the Late Weichselian (Vistulian). Presented below is a multi-proxy study on the sequence from the paleolake within the present-day valley. During the Late Weichselian, it formed an astatic, and later a permanent, water body of Postglacial origin. The associated melting, flooding and aeolian processes acted as sources of various Late Weichselian sediments. Summer mean air temperature drove the lake ecosystem development. The Holocene Thermal Optimum in 8.5–7.7 kyr cal BP was followed by subsequent lower temperature. There is weak evidence of coole oscillations at 8.2 kyr cal BP, 7.0–6.8 kyr cal BP and 5.8–5.9 kyr cal BP and the Little Ice Age (480–395 yr cal BP), until modern time (−65 yr cal BP). Five stages of lake ecosystem development were identified based on the biota: 1) an initial stage during the Late Weichselian with glaciolacustrine and later lacustrine accumulation of inorganic deposits, 2) the stage with Cladocera as a leading indicators of mesotrophic water body with a well-developed pelagic zone supplied by early spring floods of the Serteyka River, carrying melting snow and ice floes to the lake basin, 3) the stage dominated by Chironomidae and diatoms typical to high trophic states reflecting widespread open bottom sediment and macrophyte habitats 4) a stage with distinct Neolithic community impact reflected by macrofossils remain after pile-dwelling settlement, fish and aquatic plants consumption 5) a final stage dominated by diatoms typical to shallow, semi-permanent, eutrophic bulrush swamp.

The evolution of thermal performance in native and invasive populations of Mimulus guttatus.

The rise of globalization has spread organisms beyond their natural range, allowing further opportunity for species to adapt to novel environments and potentially become invaders. Yet, the role of thermal niche evolution in promoting the success of invasive species remains poorly understood. Here, we use thermal performance curves (TPCs) to test hypotheses about thermal adaptation during the invasion process. First, we tested the hypothesis that if species largely conserve their thermal niche in the introduced range, invasive populations may not evolve distinct TPCs relative to native populations, against the alternative hypothesis that thermal niche and therefore TPC evolution has occurred in the invasive range. Second, we tested the hypothesis that clines of TPC parameters are shallower or absent in the invasive range, against the alternative hypothesis that with sufficient time, standing genetic variation, and temperature‐mediated selection, invasive populations would re‐establish clines found in the native range in response to temperature gradients. To test these hypotheses, we built TPCs for 18 native (United States) and 13 invasive (United Kingdom) populations of the yellow monkeyflower, Mimulus guttatus. We grew clones of multiple genotypes per population at six temperature regimes in growth chambers. We found that invasive populations have not evolved different thermal optima or performance breadths, providing evidence for evolutionary stasis of thermal performance between the native and invasive ranges after over 200 years post introduction. Thermal optimum increased with mean annual temperature in the native range, indicating some adaptive differentiation among native populations that was absent in the invasive range. Further, native and invasive populations did not exhibit adaptive clines in thermal performance breadth with latitude or temperature seasonality. These findings suggest that TPCs remained unaltered post invasion, and that invasion may proceed via broad thermal tolerance and establishment in already climatically suitable areas rather than rapid evolution upon introduction.

Laboratory Investigation of Microwave Healing Characteristic of Hot Mix Asphalt Incorporating Steel Slag and Fly Ash

Abstract: This research aims to analyze the usage of fly ash (FA) as filler and Steel slag as coarse aggregate in hot mix asphalt concrete to monitor its healing characteristic under microwave heat. Both fly ash and steel slag are the industrial by-products. Using Marshall, Hot mix asphalt (HMA) mixtures were prepared for control and three different modified specimens having 10%, 20% and 30% steel slag as coarse aggregate, and 75% optimum fly ash content (OFC) as filler. Then thermal distribution and optimum healing time of test specimens were recorded using infrared thermometer. A three-point bending (TPB) tests were applied to the samples before and after the microwave healing procedures. Test results demonstrated that adding steel slag and fly ash in asphalt concrete mixtures increases the heating rates and improve the healing performance of hot mix asphalt using microwave heat. The replacement of natural coarse aggregate by 30% steel aggregate is extremely promising since it has not only improved healing results but also enhance the load-displacement relationship of the HMA mixtures with more ductile behavior. Overall, the use of steel slag and fly ash in hot mix asphalt is a significant option that helps to the sustainable pavement construction as it improves healing and cracking resistance. Keywords: Fly ash, Steel slag, Hot mix asphalt, Microwave heating, Three-point Bending

Molecular Response of the Brain to Cross-Generational Warming in a Coral Reef Fish

Ocean warming is a threat to marine biodiversity, as it can push marine species beyond their physiological limits. Detrimental effects can occur when marine poikilotherms are exposed to conditions beyond their thermal optima. However, acclamatory mechanisms, such as plasticity, may enable compensation of detrimental effects if warming is experienced during development or across generations. Studies evaluating the molecular responses of fishes to warming have mostly focused on liver, muscle, and gonads, and little is known about the effects on other vital organs, including the brain. This study evaluated the transcriptional program of the brain in the coral reef fish Acanthochromis polyacanthus, exposed to two different warming scenarios: +1.5°C and +3.0°C, across successive generations. Fish were exposed to these conditions in both developmental (F1 and F2) and transgenerational settings (F2 only), as well as a treatment with step-wise warming between generations. The largest differences in gene expression were between individuals of the first and second generation, a pattern that was corroborated by pairwise comparisons between Control F1 and Control F2 (7,500 DEGs) fish. This large difference could be associated with parental effects, as parents of the F1 generation were collected from the wild, whereas parents of the F2 generation were reared in captivity. A general response to warming was observed at both temperatures and in developmental and transgenerational treatments included protein folding, oxygen transport (i.e., myoglobin), apoptosis and cell death, modification of cellular structure, mitochondrial activity, immunity and changes in circadian regulation. Treatments at the highest temperature showed a reduction in synaptic activity and neurotransmission, which matches previous behavioral observations in coral reef fishes. The Transgenerational +3.0°C treatment showed significant activation of the gene pls3, which is known for the development of neuro-muscular junctions under heat-stress. F2 samples exposed to step-wise warming showed an intermediate response, with few differentially expressed genes compared to developmental and transgenerational groups (except for Transgenerational +1.5°C). In combination with previous studies on liver gene expression, this study indicates that warming produces a molecular signature of stress response in A. polyacanthus that is influenced both by the intensity of warming as well as the duration of exposure.

Conjugate Natural Convection: A Study of Optimum Fluid Flow and Heat Transfer in Eccentric Annular Channels

Laminar natural convection-conduction heat transfer in vertically positioned annular channels with inherent eccentricity is investigated for optimum solid-fluid thermal conductivity ratio and optimum cylinder walls thicknesses allowing maximum induced fluid flow rate and heat transfer under varying geometry parameters, i.e., annulus eccentricity and radius ratio. A finite-difference technique is employed to solve the coupled momentum and energy equations for the cylindrical annulus walls and the annular fluid with Prandtl number 0.7. As part of the results, fluctuations in the induced fluid flow rate and heat transfer in the eccentric annular channel due to the conjugate effect, governed by the ratios of the solid and fluid thermal conductivities and thicknesses of outer and inner circular cylinder walls, are obtained for the boundary conditions of one wall heated isothermally and the other kept adiabatic. Commonly encountered ratios of the solid and fluid thermal conductivities and cylinder walls thicknesses are utilized in the present analysis. Results reveal that the optimum conductivity ratio and cylinder walls thicknesses increase nonlinearly with eccentricity and radius ratio. Such results can be very useful in effectively designing the heat transfer equipment for optimum performance.

Effects of elevated temperature on the performance and survival of pacific crown-of-thorns starfish (Acanthaster cf. solaris)

Population irruptions of Pacific crown-of-thorns starfish (Acanthaster cf. solaris) have caused substantial damage to coral reefs, but it is largely unknown how this asteroid will fare in a warmer ocean. We exposed these starfish to one of four thermal treatments, with final temperatures of 26 °C (control, annual average), 28 °C (summer average), 30 °C (summer maximum) and 32 °C (predicted summer maximum by 2100). We measured the righting time, movement rate, standard metabolic rate and probability of survival of the crown-of-thorns starfish at various timepoints over ~ 60 days. We found that while temperature did not affect righting time, it did significantly affect movement rate. The movement rate of starfish increased across the 26 to 30 °C range, with those at 28 °C and 30 °C moving 18 and 27% faster than those at the control temperature. Similarly, the standard metabolic rate of starfish increased from 26 to 30 °C, with metabolism 100% and 260% faster at 28 °C and 30 °C compared to those at the 26 °C control. At 32 °C, individual starfish exhibited a 14% slower movement rate, a 33% slower metabolic rate, and also exhibited a fourfold lower probability of survival than those at 30 °C. These results indicate that 32 °C is above the thermal optimum of crown-of-thorns starfish, suggesting that prolonged exposure to temperatures that are expected to be regularly exceeded under near-future climate change may be detrimental to this species.

Staying in place and moving in space: Contrasting larval thermal sensitivity explains distributional changes of sympatric sea urchin species to habitat warming.

For marine ectotherms, larval success, planktonic larval duration and dispersal trajectories are strongly influenced by temperature, and therefore, ocean warming and heatwaves have profound impacts on these sensitive stages. Warming, through increased poleward flow in regions with western boundary currents, such as the East Australia Current (EAC), provides opportunities for range extension as propagules track preferred conditions. Two sea urchin species, Centrostephanus rodgersii and Heliocidaris tuberculata, sympatric in the EAC warming hotspot, exhibit contrasting responses to warming. Over half a century, C. rodgersii has undergone marked poleward range extension, but the range of H. tuberculata has not changed. We constructed thermal performance curves (TPC) to determine if contrasting developmental thermal tolerance can explain this difference. The temperatures tested encompassed present-day distribution and forecast ocean warming/heatwave conditions. The broad and narrow thermal optimum (Topt) ranges for C. rodgersii and H. tuberculata larvae (7.2 and 4.7°C range, respectively) matched their realized (adult distribution) thermal niches. The cool and warm temperatures for 50% development to the feeding larva approximated temperatures at adult poleward range limits. Larval cool tolerances with respect to mean local temperature differed, 6.0 and 3.8°C respectively. Larval warm tolerances were similar for both species as are the adult warm range edges. The larvae of both species would be sensitive to heatwaves. Centrostephanus rodgersii has stayed in place and shifted in space, likely due to its broad cold-warm larval thermal tolerance and large thermal safety margins. Phenotypic plasticity of the planktonic stage of C. rodgersii facilitated its range extension. In contrast, larval cold intolerance of H. tuberculata explains its restricted range and will delay poleward extension as the region warms. In a warming ocean, we show that intrinsic thermal biology traits of the pelagic stage provide an integrative tool to explain species-specific variation in range shift patterns.

Thermal tolerance of Hypnea pseudomusciformis ecotypes (Cystocloniaceae, Rhodophyta) related to different floristic provinces along the Brazilian coast

SUMMARYStudies on the effects of temperature on physiological processes are essential to model macroalgae biogeographic distribution. Tetrasporophytes of Hypnea pseudomusciformis were collected from three floristic provinces (tropical, transition and warm temperate) along the Brazilian coast (~3.000 km), representing three ecotypes. Specimens were cultured under 20°C, 24°C, 28°C and 32°C for 21 days, then physiological parameters (growth rates, photosynthesis and pigments content) were analyzed. H. pseudomusciformis specimens tolerated a temperature variation from 20°C to 32°C. However, all ecotypes displayed a significant decrease in physiological performance at 32°C in all parameters analyzed. We hypothesized that the H. pseudomusciformis ecotype from the tropical province is already living at its thermal physiological limit, reaching its maximum growth only in the winter months (June to September), whereas a warm temperate ecotype reaches maximum growth in the summer months (December to March). This wide thermal optimum may be the reason for the widespread distribution of this species along the Brazilian coast, allowing it to occupy different thermal environments.

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.

Resident lobsters dominate food competition with range-shifting lobsters in an ocean warming hotspot

Species redistributions are one of the most prevalent changes observed in oceans worldwide due to climate change. One of the major challenges is being able to predict temperature-driven changes to species interactions and the outcome of these changes for marine communities due to the complex nature of indirect effects. In the ocean-warming hotspot of south-east Australia, the ranges of many species have shifted poleward. The range of the eastern rock lobster Sagmariasus verreauxi has extended into warming Tasmanian waters inhabited by the resident southern rock lobster Jasus edwardsii, which may lead to increased competitive interactions between the species. Using video monitoring, we investigated how the 2 species compete for food at current (18°C), future (21°C) and future heatwave (24°C) summer temperatures. Behavioural competition occurred in 80% of experiments, during which J. edwardsii won 84% of competitive interactions and showed more aggressive behaviour at all temperatures. This indicates that resident J. edwardsii is not only more dominant in direct food competition than the range-shifting S. verreauxi but, surprisingly, also sustains competitive dominance beyond its physiological thermal optimum under predicted future ocean warming and heatwave scenarios.

The effect of temperature on the growth of acaropathogenic fungi from Hirsutella genus

The aim of the study was to determine the effect of temperature on the growth of four species of acaropathogenic fungi of the genus Hirsutella (isolated from mites) grown in vitro on Sabouraud (SDA) and Czapek-Dox media. The effects of seven temperature ranges (5–35°C) were tested under laboratory conditions. Observations of colony growth were carried out every 5 days until day 25 by measuring the diameter of the colonies in mm. The growth rate of the test isolates was calculated in mm per day. The conducted studies showed that the thermal optimum of most of the tested isolates of acaropathogenic fungi of the genus Hirsutella was between 20°C and 25°C, with individual values varying depending on the type of medium on which the inoculum was developed. The fungus species with the highest temperature range of colony growth was Hirsutella thompsonii var. synnematosa. It was the only acaropathogenic fungus strain tested that developed on both types of culture medium, also at 35°C. The fastest growth rate of the tested isolates of acaropathogenic fungi was at 25°C. The cultures of the tested species of fungi reached larger sizes on the SDA medium rather than on Czapek-Dox medium.

Correspondence between thermal biology and locomotor performance in a liolaemid lizard from the southeastern coastal Pampas of Argentina

The behavioral and physiological mechanisms of thermoregulation and the morphological traits of lizards result in a particular range of body temperatures, which influence performance and ultimately fitness. We studied the thermal biology and locomotor performance of the lizard Liolaemus wiegmannii from the coastal dunes in the southeastern Pampas of Argentina. During the austral summer, we examined the link between thermoregulation and optimal locomotor performance. Liolaemus wiegmannii faced a stressful environment due to high risk of overheating; despite this, the species was able to achieve field body temperatures (Mean Tb ± SD = 35.58 ± 2.86 °C) than expected by chance (i.e., the null model) and suitable for sustaining its physiological performance. Locomotion in this species was thermally-sensitive, with lizards showing high-performance bouts at a relatively wide range of body temperatures (30–38 °C). Lizards exhibited a mean maximum running speed of 1.30 m/s at 37.3 °C (i.e., optimal temperature for locomotion) which was within the set point range of preferred temperature (Tset = 35.4–37.5 °C). Therefore, we found a correspondence between thermal optimum and preferred temperature. Our findings suggest that L. wiegmannii, like other lizard species with a broad distribution, is capable of performing well across a wide range of temperatures despite the spatiotemporal thermal fluctuations of the environment.

Resilience of cold-water coral holobionts to thermal stress.

Cold-water corals are threatened by global warming, especially in the Mediterranean Sea where they live close to their upper known thermal limit (i.e. 13°C), yet their response to rising temperatures is not well known. Here, temperature effects on Lophelia pertusa and Madrepora oculata holobionts (i.e. the host and its associated microbiome) were investigated. We found that at warmer seawater temperature (+2°C), L. pertusa showed a modification of its microbiome prior to a change in behaviour, leading to lower energy reserves and skeletal growth, whereas M. oculata was more resilient. At extreme temperature (+4°C), both species quickly lost their specific bacterial signature followed by lower physiological activity prior to death. In addition, our results showing the holobionts' negative response to colder temperatures (-3°C), suggest that Mediterranean corals live close to their thermal optimum. The species-specific response to temperature change highlights that global warming may affect dramatically the main deep-sea reef-builders, which would alter the associated biodiversity and related ecosystem services.

Behavioral Interactions between a Native and an Invasive Fish Species in a Thermally Heterogeneous Experimental Chamber

Mechanisms of the displacement of native fish by nonnative fish can include agonistic behaviors that push native fish species out of their preferred habitat, including their thermal optima. To examine these interactions, we built an experimental thermal preference chamber to evaluate: (1) the thermal preference of native, glacial relict northern redbelly dace Chrosomus eos; (2) if the thermal preference and movement changed in the presence of the invasive western mosquitofish Gambusia affinis; and (3) the direction of agonistic interactions. We hypothesized that G. affinis would express agonistic behavior toward C. eos, because G. affinis is widely recognized as an aggressive invader. Given the temperature range of the experimental chamber, i.e., 20–30 °C, C. eos selected an average of 24.3 °C as its thermal preference. After G. affinis’ introduction, the thermal preference of C. eos increased by 1.7 °C and the movement, given by distance (cm) travelled, increased by 21%. Contrary to our prediction, more agonistic interactions were observed in C. eos toward G. affinis. These results indicate that agonistic behavior of G. affinis toward native fish species may be species- and condition-specific, and may not always be the primary mechanism of native species’ displacement. Biological invasions are a global issue and altered thermal regimes are expected to continue. This study provided the novel approach using of a thermally heterogeneous thermal chamber to examine thermal preferences and aggressive interactions between a native and an invasive species. Future research should examine other life history traits that may be conveying the competitive advantage to G. affinis.

Disentangling direct and indirect effects of local temperature on abundance of mountain birds and implications for understanding global change impacts.

Unravelling the environmental factors driving species distribution and abundance is crucial in ecology and conservation. Both climatic and land cover factors are often used to describe species distribution/abundance, but their interrelations have been scarcely investigated. Climatic factors may indeed affect species both directly and indirectly, e.g., by influencing vegetation structure and composition. We aimed to disentangle the direct and indirect effects (via vegetation) of local temperature on bird abundance across a wide elevational gradient in the European Alps, ranging from montane forests to high-elevation open areas. In 2018, we surveyed birds by using point counts and collected fine-scale land cover and temperature data from 109 sampling points. We used structural equation modelling to estimate direct and indirect effects of local climate on bird abundance. We obtained a sufficient sample for 15 species, characterized by a broad variety of ecological requirements. For all species we found a significant indirect effect of local temperatures via vegetation on bird abundance. Direct effects of temperature were less common and were observed in seven woodland/shrubland species, including only mountain generalists; in these cases, local temperatures showed a positive effect, suggesting that on average our study area is likely colder than the thermal optimum of those species. The generalized occurrence of indirect temperature effects within our species set demonstrates the importance of considering both climate and land cover changes to obtain more reliable predictions of future species distribution/abundance. In fact, many species may be largely tracking suitable habitat rather than thermal niches, especially among homeotherm organisms like birds.

Do Differences in Latitudinal Distributions of Species and Organelle Haplotypes Reflect Thermal Reaction Norms Within the Emiliania/Gephyrocapsa Complex?

The cosmopolitan phytoplankterEmiliania huxleyicontrasts with its closest relatives that are restricted to narrower latitudinal bands, making it interesting for exploring how alternative outcomes in phytoplankton range distributions arise. Mitochondrial and chloroplast haplogroups withinE. huxleyiare shared with their closest relatives: SomeE. huxleyishare organelle haplogroups withGephyrocapsa parvulaandG. ericsoniiwhich inhabit lower latitudes, while otherE. huxleyishare organelle haplogroups withG. muellerae, which inhabit high latitudes. We investigated whether the phylogeny ofE. huxleyiorganelles reflects environmental gradients, focusing on the Southeast Pacific where the different haplogroups and species co-occur. There was a high congruence between mitochondrial and chloroplast haplogroups withinE. huxleyi. Haplogroup II ofE. huxleyiis negatively associated with cooler less saline waters, compared to haplogroup I, both when analyzed globally and across temporal variability at the small special scale of a center of coastal upwelling at 30° S. A new mitochondrial haplogroup Ib detected in coastal Chile was associated with warmer waters. In an experiment focused on inter-species comparisons, laboratory-determined thermal reaction norms were consistent with latitudinal/thermal distributions of species, withG. oceanicaexhibiting warm thermal optima and tolerance andG. muelleraeexhibiting cooler thermal optima and tolerances.Emiliania huxleyihaplogroups I and II tended to exhibit a wider thermal niche compared to the otherGephyrocapsa, but no differences among haplogroups withinE. huxleyiwere found. A second experiment, controlling for local adaptation and time in culture, found a significant difference betweenE. huxleyihaplogroups. The difference between I and II was of the expected sign, but not the difference between I and Ib. The differences were small (≤1°C) compared to differences reported previously withinE. huxleyiby local adaptation and even in-culture evolution. Haplogroup Ib showed a narrower thermal niche. The cosmopolitanism ofE. huxleyimight result from both wide-spread generalist phenotypes and specialist phenotypes, as well as a capacity for local adaptation. Thermal reaction norm differences can well explain the species distributions but poorly explain distributions among mitochondrial haplogroups withinE. huxleyi. Perhaps organelle haplogroup distributions reflect historical rather than selective processes.

Increasing temperature weakens the positive effect of genetic diversity on population growth.

Genetic diversity and temperature increases associated with global climate change are known to independently influence population growth and extinction risk. Whether increasing temperature may influence the effect of genetic diversity on population growth, however, is not known. We address this issue in the model protist system Tetrahymena thermophila. We test the hypothesis that at temperatures closer to the species’ thermal optimum (i.e., the temperature at which population growth is maximal, or T opt), genetic diversity should have a weaker effect on population growth compared to temperatures away from the thermal optimum. To do so, we grew populations of T. thermophila with varying levels of genetic diversity at increasingly warmer temperatures and quantified their intrinsic population growth rate, r. We found that genetic diversity increases population growth at cooler temperatures, but that as temperature increases, this effect weakens. We also show that a combination of changes in the amount of expressed genetic diversity (G) in r, plastic changes in population growth across temperatures (E), and strong G × E interactions underlie this temperature effect. Our results uncover important but largely overlooked temperature effects that have implications for the management of small populations with depauperate genetic stocks in an increasingly warming world.

Zooplankton body size is filtered by a thermo‐oxygenic niche at the regional scale

AbstractAimThere is ongoing debate regarding the extent to which body size is selected by the environment. To address this issue, we assessed how thermo‐oxygenic conditions select body size of rotifer species composing a regional species pool.LocationApproximately 600 different water bodies in Sweden.TaxonRotifers (188 species).MethodsData were acquired from previously published studies. For the environmental parameters, we conducted principal component analysis (PCA) to recognize the pattern among the species‐specific thermal and oxygenic preferences of rotifers of different ecology. We assigned a standard body length to each species. We performed phylogenetically correlated analyses to evaluate the relationships between body length and the parameters that were selected as PCA drivers.ResultsThermal and oxygenic tolerance ranges, designated by the differences between the minimum and maximum of species occurrence, were grouped separately from the optima designated by the conditions referring to the highest species abundance, according to PC1 versus PC2. The parameters representing temperature and oxygen occupied opposite positions on the PC2 axis. Body size selection was driven by both temperature and oxygen, but the cues for this selection differed; species with higher thermal optima were smaller, while species with wider oxygen tolerance ranges were larger.Main conclusionThe body sizes of rotifer species are filtered by both thermal and oxygenic conditions. Selection is driven by tolerance ranges and optima. Oxygenic conditions are as important as thermal conditions in body size selection within a species assemblage.

Thermal Performance Curves Are Shaped by Prior Thermal Environment in Early Life.

Understanding links between thermal performance and environmental variation is necessary to predict organismal responses to climate change, and remains an ongoing challenge for ectotherms with complex life cycles. Distinct life stages can differ in thermal sensitivity, experience different environmental conditions as development unfolds, and, because stages are by nature interdependent, environmental effects can carry over from one stage to affect performance at others. Thermal performance may therefore respond to carryover effects of prior thermal environments, yet detailed insights into the nature, strength, and direction of those responses are still lacking. Here, in an aquatic ectotherm whose early planktonic stages (gametes, embryos, and larvae) govern adult abundances and dynamics, we explore the effects of prior thermal environments at fertilization and embryogenesis on thermal performance curves at the end of planktonic development. We factorially manipulate temperatures at fertilization and embryogenesis, then, for each combination of prior temperatures, measure thermal performance curves for survival of planktonic development (end of the larval stage) throughout the performance range. By combining generalized linear mixed modeling with parametric bootstrapping, we formally estimate and compare curve descriptors (thermal optima, limits, and breadth) among prior environments, and reveal carryover effects of temperature at embryogenesis, but not fertilization, on thermal optima at completion of development. Specifically, thermal optima shifted to track temperature during embryogenesis, while thermal limits and breadth remained unchanged. Our results argue that key aspects of thermal performance are shaped by prior thermal environment in early life, warranting further investigation of the possible mechanisms underpinning that response, and closer consideration of thermal carryover effects when predicting organismal responses to climate change.