Thermal Habitat Research Articles

High temperature events shape the broadscale distribution of juvenile Atlantic salmon (Salmo salar)

Abstract Summer water temperatures within many temperate rivers regularly surpass the incipient lethal temperature for juvenile Atlantic salmon (c. 27°C), causing widescale abandonment of territory in favour of areas of cooler water (thermal refuges). This study aims to highlight the influence of thermal refuges on river‐scale abundance patterns. That is, do salmon parr adjust their distribution over time according to proximity to thermal refuges? Twelve reaches (seven reference: five refuge) were chosen along a 17‐km section of the Little Southwest Miramichi River in Canada. Reaches were sampled throughout the 2011 and 2012 summer periods; high temperature events were recorded during summer 2012 but not summer 2011. Multivariate principal component analyses indicated no discernible difference in habitat characteristics between the reach‐types under normal thermal conditions. However, reaches containing a thermal refuge had a significant increase in relative abundance of parr immediately after a series of high temperature events (water temperature >26°C) in 2012 (p = 0.034). This increase in relative abundance in refuge reaches was not present during the summer of 2011 when no temperature events occurred (p = 0.088), prior to the event of 2012 (p = 0.999), or at the late autumn survey following the 2012 event (p = 0.999). Difference in temperature between refuge and mainstem reaches significantly influenced the suitability of a tributary as a thermal refuge habitat (R2 = 0.84), with preference shown for cooler refuges. River‐wide thermal heterogeneity therefore plays a critical role in survival of juvenile salmon throughout summer months and is likely to become necessary under future climate change scenarios.

Recent and projected climate change–induced expansion of Atlantic halibut in the Northwest Atlantic

With the influence of climate change on marine systems expanding, climate adaptation will be fundamental for the future of fisheries management. An exponential increase in Atlantic halibut Hippoglossus hippoglossus landings over the past decade has coincided with warming ocean temperatures. Here, we explore how historical changes in abundance have been linked to changing thermal habitat conditions and project trends with a warming climate under different emissions scenarios. From 1990 to 2018, available thermal habitat increased by 11.6 ± 7.35% and growing degree days have increased by 13.5 ± 7.86 °C·days across the region. With warming, the probability of occurrence is projected to increase up to 20.5% in Canada by 2085 under RCP 8.5 for Atlantic halibut. Our results suggest that shifting patterns of halibut distribution and abundance are linked to thermal conditions and that continued warming will likely continue to enhance habitat conditions, leading to increased abundance in the Canadian range. Collectively, these results illustrate the influence of shifting environmental conditions on population dynamics and emphasize the importance of adaptive management practices in a dynamic future climate.

Aerobic metabolic scope mapping of an invasive fish species with global warming.

Climate change will exacerbate the negative effects associated with the introduction of non-indigenous species in marine ecosystems. Predicting the spread of invasive species in relation to environmental warming is therefore a fundamental task in ecology and conservation. The Baltic Sea is currently threatened by several local stressors and the highest increase in sea surface temperature of the world's large marine ecosystems. These new thermal conditions can further favour the spreading of the invasive round goby (Neogobius melanostomus), a fish of Ponto-Caspian origin, currently well established in the southern and central parts of the Baltic Sea. This study aims to assess the thermal habitat suitability of the round goby in the Baltic Sea considering the past and future conditions. The study combines sightings records with known physiological models of aerobic performance and sea surface temperatures. Physiological models read these temperatures, at sighting times and locations, to determine their effects on the aerobic metabolic scope (AMS) of the fish, a measure of its energetic potential in relation to environmental conditions. The geographical mapping of the AMS was used to describe the changes in habitat suitability during the past 3 decades and for climatic predictions (until 2100) showing that the favourable thermal habitat in the Baltic Sea has increased during the past 32 years and will continue to do so in all the applied climate model predictions. Particularly, the predicted new thermal conditions do not cause any reduction in the AMS of round goby populations, while the wintertime cold ranges are likely expected to preserve substantial areas from invasion. The results of this research can guide future monitoring programs increasing the chance to detect this invader in novel areas.

A heated rock crack captures and polymerizes primordial DNA and RNA.

Life is based on informational polymers such as DNA or RNA. For their polymerization, high concentrations of complex monomer building blocks are required. Therefore, the dilution by diffusion poses a major problem before early life could establish a non-equilibrium of compartmentalization. Here, we explored a natural non-equilibrium habitat to polymerize RNA and DNA. A heat flux across thin rock cracks is shown to accumulate and maintain nucleotides. This boosts the polymerization to RNA and DNA inside the crack. Moreover, the polymers remain localized, aiding both the creation of longer polymers and fostering downstream evolutionary steps. In a closed system, we found single nucleotides concentrate 104-fold at the bottom of the crack compared to the top after 24 hours. We detected enhanced polymerization for 2 different activation chemistries: aminoimidazole-activated DNA nucleotides and 2',3'-cyclic RNA nucleotides. The copolymerization of 2',3'-cGMP and 2',3'-cCMP in the thermal pore showed an increased heterogeneity in sequence composition compared to isothermal drying. Finite element models unravelled the combined polymerization and accumulation kinetics and indicated that the escape of the nucleotides from such a crack is negligible over a time span of years. The thermal non-equilibrium habitat establishes a cell-like compartment that actively accumulates nucleotides for polymerization and traps the resulting oligomers. We argue that the setting creates a pre-cellular non-equilibrium steady state for the first steps of molecular evolution.

The invasive blue crab Callinectes sapidus thermal response: Predicting metabolic suitability maps under future warming Mediterranean scenarios

One of the consequences of climate change and globalization is the recent proliferation of the invasive blue crab Callinectes sapidus in the Mediterranean Sea. In this study, C. sapidus thermal tolerance was investigated through experiments based on species metabolic response (measuring respiration rates) to a wide temperature range. Based on metabolic rates, Thermal Habitat Suitability (THS) maps were performed on current and futures temperature conditions in the Mediterranean Sea. Thermal Performance Curve showed a CTmax at 40°C and an optimum at 24°C. Respiration rate increased between 12°C and 24°C and decreased until 30°C. At the highest temperatures (> to 30°C) a pointed increase in the respiration rate values was observed from 32°C before the organisms’ death at 40°C. Predictive maps showed that the whole basin shows suitable conditions for population maintenances of C. sapidus in all used warming scenarios. The future scenarios show a mean increase of +0.2 of the THS over the year. The present study increases the understanding of the ecological performance and potential distribution of C. sapidus. This information will contribute to the design and implementation of risk assessment and management plans of this impactful crustacean in the Mediterranean Sea.

Thermal physiology integrated species distribution model predicts profound habitat fragmentation for estuarine fish with ocean warming

Species distribution models predict a poleward migration for marine ectotherms with ocean warming. However, a key limitation in current species distribution models (SDM) is that they do not account for population-specific heterogeneity in physiological responses to temperature change resulting from local adaptations and acclimatization. To address this gap, we developed a novel, Physiology Integrated BioClimate Model (PIBCM) that combines habitat-specific metabolic thermal physiological tolerance of a species into a bioclimate envelope model. Using a downscaling approach, we also established a fine-resolution coastal sea-surface temperature data set for 2050–2080, that showed a high degree of location-specific variability in future thermal regimes. Combining predicted temperature data with the PIBCM model, we estimated habitat distribution for a highly eurythermal intertidal minnow, the Atlantic killifish (Fundulus heteroclitus), a species that likely presents a best-case-scenario for coastal vertebrates. We show that the killifish northern boundary shifts southwards, while distinct habitat fragmentation occurs in the southern sub-population (due to migration of adjacent fish populations to the nearest metabolically optimal thermal habitat). When compared to current SDMs (e.g., AquaMaps), our results emphasize the need for thermal physiology integrated range shift models and indicate that habitat fragmentation for coastal fishes may reshape nursery habitats for many commercially and ecologically important species.

Testing the predictability of morphological evolution in contrasting thermal environments.

Gaining the ability to predict population responses to climate change is a pressing concern. Using a "natural experiment," we show that testing for divergent evolution in wild populations from contrasting thermal environments provides a powerful approach, and likely an enhanced predictive power for responses to climate change. Specifically, we used a unique study system in Iceland, where freshwater populations of threespine sticklebacks (Gasterosteus aculeatus) are found in waters warmed by geothermal activity, adjacent to populations in ambient-temperature water. We focused on morphological traits across six pairs from warm and cold habitats. We found that fish from warm habitats tended to have a deeper mid-body, a subterminally orientated jaw, steeper craniofacial profile, and deeper caudal region relative to fish from cold habitats. Our common garden experiment showed that most of these differences were heritable. Population age did not appear to influence the magnitude or type of thermal divergence, but similar types of divergence between thermal habitats were more prevalent across allopatric than sympatric population pairs. These findings suggest that morphological divergence in response to thermal habitat, despite being relatively complex and multivariate, are predictable to a degree. Our data also suggest that the potential for migration of individuals between different thermal habitats may enhance nonparallel evolution and reduce our ability to predict responses to climate change.

Combined tracers reveal the multi‐dimensionality of resource partitioning among sympatric forage fish

Abstract Quantifying the multi‐dimensional nature of resource partitioning in‐situ represents a fundamental challenge for understanding how environmental conditions contribute to the co‐existence of sympatric species. For aquatic poikilotherms, the availability of temperatures at or near optima generally define the ranges and limitations of species biology and ecology. Specifically, how poikilotherms partition this abiotic resource remains a broader unknown in aquatic ecology. Alewife (Alosa pseudoharengus), deepwater sculpin (Myoxocephalus thompsonii), rainbow smelt (Osmerus mordax), and round goby (Neogobius melanostomus) co‐occur throughout Lake Ontario and are known to share common prey resources. Here, we used a combination of trophic tracers (stable isotopes), pollutants (polychlorinated biphenyls, PCBs), and bioenergetic modelling to illustrate resource partitioning of diet items and thermal habitat among Lake Ontario prey fish species. We predicted that the combined use of δ13C, δ15N, and PCBs will capture the multi‐dimensional nature of resource partitioning among coexisting species inhabiting similar compartments within this ecosystem. The δ13C and δ15N values confirmed our understanding of trophic relationships among these species. A bioenergetic model predicted temperature occupancies for each species and for individuals during the open water growing season when prey consumption rates are likely to be maximised and the PCB congener profiles were highly correlated with these predictions. Three‐dimensional niche modelling demonstrated that ecological tracer assimilation is probably a direct result of species behavioural thermoregulation during the open water growing season when temperatures are at or near physiological optima. These results demonstrate that the ability of aquatic poikilotherms to track optimal temperatures and exploit habitat and food resources is captured by their PCB congener profiles. Consumer PCB congener profiles integrate not only the specific prey resources consumed, but also the predominant thermal conditions under which those resources were acquired and assimilated and that subsequently regulate individual and species growth. Given their global ubiquity and capacity for interpretation under the assumptions applied to ecological tracers, consumer PCB profiles could greatly advance our understanding of the mechanisms regulating resource partitioning, especially among aquatic poikilotherms.

Magnitude–duration relationships of physiological sensitivity and environmental exposure improve climate change vulnerability assessments

Integrating thermal physiology with environmental temperature is essential to understanding distributions of species and vulnerability to climate change. Warming tolerance – the difference between an organism's maximum thermal tolerance (Tmax) and maximum habitat temperature (Thab) – is frequently used to integrate organismal sensitivity and environmental exposure. Traditionally, applications of warming tolerance define Tmax and Thab as invariable magnitudes, yet tolerance magnitude depends on exposure duration, and diel temperature cycles expose organisms to a range of temperature magnitudes and durations. How traditional (i.e. acute) estimates of warming tolerance compare to estimates from prolonged exposures remains poorly understood. In this study, magnitude–duration curves for tolerances of one cold‐water, two cool‐water and one warm‐water species of freshwater fish were compiled from the literature and compared to magnitude–duration exposures from 66 streams across the eastern United States. Warming tolerances were estimated for exposure durations spanning 0.01–24 h. Current acute (0.01 h) warming tolerances ranged from median 6.30°C for the cold‐water species to 9.68°C for the warm‐water species. The lowest warming tolerances corresponded to prolonged exposures lasting median 3.85–5.30 h among species and were 2.51–4.38°C lower than acute estimates. Although acute estimates remained positive in historically occupied and unoccupied streams (6.30 versus 2.33°C), estimates based on prolonged exposure were positive at occupied streams of the cold‐water species but transitioned to negative in unoccupied streams (2.19 versus −1.12°C). Acute warming tolerances for the cold‐water species also remained positive under future climate (6.29–4.23°C) but approached zero at prolonged durations (2.19–0.09°C) and transitioned to negative for 47.2% of streams. Results demonstrate that acute measures of Tmax and Thab overestimate warming tolerances and therefore underestimate climate change vulnerability. Integrating magnitude–duration relationships into warming tolerance estimates can elucidate physiological mechanisms underlying species distributions and can improve accuracy of climate change vulnerability assessments.

Thermal niche and habitat use by co-occurring lake trout (Salvelinus namaycush) and brook trout (S. fontinalis) in stratified lakes

Thermal niche and habitat use by co-occurring lake trout (Salvelinus namaycush) and brook trout (S. fontinalis) in stratified lakes

Winners and losers in a warming Arctic: Potential habitat gain and loss for epibenthic invertebrates of the Chukchi and Bering Seas, 2008–2100

Our goal was to examine how the epibenthic invertebrate community in the Pacific Arctic Region might be affected by continued increases in ocean temperatures. We used epibenthic invertebrate catch and bottom temperature data collected on groundfish assessment and ecosystem surveys in the Bering and Chukchi seas from 2009 to 2018 to determine the “preferred” temperature of all taxa. We grouped taxa into five clusters according to their similarity in median temperature and temperature range. We then used an ensemble of eight climate models under Representative Concentration Pathway 8.5 (RCP8.5) scenarios to project bottom temperature from present (2008) to mid-century (2050) and end of the century (2100). Based on these projections, we show how the amount and distribution of cluster-specific thermal habitat might change with ocean warming. We found that by mid-century there was a 50% decrease in thermal habitat for all clusters except for the most eurythermic cluster, and that thermal habitat contracted to the north. By the end of the century there was very little thermal habitat for all clusters, except the most eurythermic cluster, and habitat was further contracted to the north. The cold-water and stenothermic cluster, hypothesized to be the most vulnerable to ocean warming, had virtually no projected thermal habitat by the end of the century. These “losers” were primarily gastropods and the bivalve mussel Musculus sp. These taxa are some of the primary prey to the endangered Pacific walrus (Odobenus rosmarus), which is harvested as a food resource in native Alaskan communities. Bivalves are prey for commercial flatfish such as yellowfin sole (Limanda aspera) and Alaska plaice (Pleuronectes quadrituberculatus). By 2100 the most eurythermic cluster, hypothesized to be the least vulnerable to warming, had projected suitable thermal habitat throughout most of the Bering and Chukchi seas, except nearshore coastal regions. The most abundant species of these “winners” was the basketstar Gorgonocephalus cf. arcticus. The loss of thermal habitat for all but the “winners” could impact the species diversity of the Bering and Chukchi seas because the “winner” cluster accounted for only 26 taxa or 8% of all taxa observed. Although temperature is a key determinant of habitat, a full habitat and ecosystem model is needed to provide more detailed predictions. In addition, more laboratory studies of thermal acclimation potential of Arctic benthic invertebrates are needed. Our results provide the first indications that the epibenthic invertebrate community in the Bering and Chukchi seas, which supports marine mammals, seabirds and human communities, may be seriously impacted by future ocean warming.

Draft genome of six Cuban Anolis lizards and insights into genetic changes during their diversification

BackgroundDetecting genomic variants and their accumulation processes during species diversification and adaptive radiation is important for understanding the molecular and genetic basis of evolution. Anolis lizards in the West Indies are good models for studying evolutionary mechanisms because of the repeated evolution of their morphology and the ecology. We performed de novo genome assembly of six Cuban Anolis lizards with different ecomorphs and thermal habitats (Anolis isolepis, Anolis allisoni, Anolis porcatus, Anolis allogus, Anolis homolechis, and Anolis sagrei). We carried out a comparative analysis of these genome assemblies to investigate the genetic changes that occurred during their diversification.ResultsWe reconstructed novel draft genomes with relatively long scaffolds and high gene completeness, with the scaffold N50 ranging from 5.56 to 39.79 Mb and vertebrate Benchmarking Universal Single-Copy Orthologs completeness ranging from 77.5% to 86.9%. Comparing the repeat element compositions and landscapes revealed differences in the accumulation process between Cuban trunk-crown and trunk-ground species and separate expansions of several families of LINE in each Cuban trunk-ground species. Duplicated gene analysis suggested that the proportional differences in duplicated gene numbers among Cuban Anolis lizards may be associated with differences in their habitat ranges. Additionally, Pairwise Sequentially Markovian Coalescent analysis suggested that the effective population sizes of each species may have been affected by Cuba’s geohistory.ConclusionsWe provide draft genomes of six Cuban Anolis lizards and detected species and lineage-specific transposon accumulation and gene copy number changes that may be involved in adaptive evolution. The change processes in the past effective population size was also estimated, and the factors involved were inferred. These results provide new insights into the genetic basis of Anolis lizard diversification and are expected to serve as a stepping stone for the further elucidation of their diversification mechanisms.

Habitat Use for Two Heliothermic Lizards in Longleaf Pine Savannas

Heliothermic lizards, like Aspidoscelis sexlineata (Six-lined Racerunner) and Sceloporus undulatus (Eastern Fence Lizard), use direct solar radiation to maintain high body temperatures needed to fulfill their basic life functions. These lizards are often found in frequently burned Pinus palustris (Longleaf Pine) savannas that provide open, high-quality thermal habitat and foraging opportunities. We examined microhabitat features surrounding 42 locations where we captured lizards using drift-fences within Longleaf Pine savannas from March to May 2017 to better understand the fine-scale habitat components important for these 2 species. We used negative binomial regression, model selection (AICc), and model averaging to identify important variables associated with lizard habitat use. We found both Six-lined Racerunners (n = 52) and Eastern Fence Lizards (n = 38) used microhabitats that were characteristic of open-canopied sites (i.e., more bare ground and grass, and less litter, midstory, and canopy cover). However, their use of sites differed in the forest structure selected. The surface-dwelling Six-lined Racerunner selected sites with more stumps and the arboreal Eastern Fence Lizard selected sites with greater Quercus (oak) basal area. Management for these lizards should include activities that promote their habitat, foraging, and thermoregulatory requirements, such as frequent prescribed fire to maintain savanna-like conditions and the retention of forest structures for basking and refuge.

A warmer environment can reduce sociability in an ectotherm.

The costs and benefits of being social vary with environmental conditions, so individuals must weigh the balance between these trade-offs in response to changes in the environment. Temperature is a salient environmental factor that may play a key role in altering the costs and benefits of sociality through its effects on food availability, predator abundance, and other ecological parameters. In ectotherms, changes in temperature also have direct effects on physiological traits linked to social behaviour, such as metabolic rate and locomotor performance. In light of climate change, it is therefore important to understand the potential effects of temperature on sociality. Here, we took the advantage of a 'natural experiment' of threespine sticklebacks from contrasting thermal environments in Iceland: geothermally warmed water bodies (warm habitats) and adjacent ambient-temperature water bodies (cold habitats) that were either linked (sympatric) or physically distinct (allopatric). We first measured the sociability of wild-caught adult fish from warm and cold habitats after acclimation to a low and a high temperature. At both acclimation temperatures, fish from the allopatric warm habitat were less social than those from the allopatric cold habitat, whereas fish from sympatric warm and cold habitats showed no differences in sociability. To determine whether differences in sociability between thermal habitats in the allopatric population were heritable, we used a common garden breeding design where individuals from the warm and the cold habitat were reared at a low or high temperature for two generations. We found that sociability was indeed heritable but also influenced by rearing temperature, suggesting that thermal conditions during early life can play an important role in influencing social behaviour in adulthood. By providing the first evidence for a causal effect of rearing temperature on social behaviour, our study provides novel insights into how a warming world may influence sociality in animal populations.

Habitat compression indices for monitoring ocean conditions and ecosystem impacts within coastal upwelling systems

Upwelling ecosystems are characterized by intense seasonal productivity that supports highly dynamic species populations, high diversity of mid and upper trophic levels, and a myriad of important fisheries. Climate variability and long-term change will impact upwelling intensity, timing and persistence, thereby potentially threatening resilience of coastal food webs and stability of ecosystem services. The spatial footprint of cool upwelled waters in the surface mixed-layer supports trophic transfer and ultimately the productivity of fisheries. The spatial area of upwelled water in eastern boundary upwelling systems can vary dramatically in response to both local and remote atmospheric forcing. These variations contribute to dynamic habitats that impact the structure, function, and spatial characteristics of marine ecosystems. We quantified the variability in “cool-water thermal habitat” area as a new ecological indicator, the Habitat Compression Index (HCI), for the nearshore (within 150 km of the coast) waters of the California Current Large Marine Ecosystem (CCLME). The HCI can be easily updated from ocean model products and satellite observations of sea surface temperature. We describe standardization of the HCI, regional variability, and evaluate HCI relationships with other indicators commonly used to inform ecosystem context within the CCLME. Importantly, our approach to calculating the HCI is easily extendable to other upwelling ecosystems. Further, we discuss the management context of the HCI such as assessing risk of whale entanglement in a highly profitable fishery, and implications for monitoring ecosystem shifts in coastal upwelling systems and the fisheries they support.

Connectivity among thermal habitats buffers the effects of warm climate on life-history traits and population dynamics.

Contemporary climate change affects population dynamics, but its influence varies with landscape structure. It is still unclear whether landscape fragmentation buffers or amplifies the effects of climate on population size and the age and body size of individuals composing these populations. This study aims to investigate the impacts of warm climates on lizard life-history traits and population dynamics in habitats that vary in their connectivity. We monitored common lizard Zootoca vivipara populations for 3 years in an experimental system in which both climatic conditions and connectivity among habitats were simultaneously manipulated. We considered two climatic treatments (i.e. present-day climate and warm climate [+1.4°C than present-day climate]) and two connectivity treatments (i.e. a connected treatment in which individuals could move from one climate to the other and an isolated treatment in which movement between climates was not possible). We monitored survival, reproduction, growth, dispersal, age and body size of each individual in the system as well as population density through time. We found that the influence of warm climates on life-history traits and population dynamics depended on connectivity among thermal habitats. Populations in warm climates were (i) composed of younger individuals only when isolated; (ii) larger in population size only in connected habitats and (iii) composed of larger age-specific individuals independently of the landscape configuration. The connectivity among habitats altered population responses to climate warming likely through asymmetries in the flow and phenotype of dispersers between thermal habitats. Our results demonstrate that landscape fragmentation can drastically change the dynamics and persistence of populations facing climate change.

Metabolic responses to increased temperatures in three semi-aquatic turtle species from the southeastern United States

Physiological maintenance of ectotherms is largely dependent on temperature. Abrupt changes in environmental conditions can cause shifts in energy budgets, with higher temperatures requiring more energy be devoted to maintenance functions, making less energy available for other activities. As a group, freshwater turtles are of conservation concern; thus, it is important to understand their physiological responses to temperature shifts, particularly given current climate change predictions. We quantified metabolic rates (MR) for three species of semi-aquatic turtles that vary in their degree of terrestriality and propensity to aestivate: chicken turtles (Deirochelys reticularia), eastern mud turtles (Kinosternon subrubrum), and eastern musk turtles (Sternotherus odoratus). Metabolic trials were performed using a flow-through respirometer at three environmentally-relevant temperatures: 25 °C, 30 °C, and 35 °C. As expected, MRs of turtles were significantly and positively associated with increases in mass and temperature. Pairwise comparisons revealed that D. reticularia exhibited significantly higher oxygen consumption rates (VO2) relative to K. subrubrum, which had significantly higher VO2 than S. odoratus. The combination of higher metabolic rates, the tendency to terrestrially aestivate, and declining quantity of high quality thermal habitats may place some semi-aquatic turtles at a disadvantage when considering future climate scenarios. Our findings, when combined with knowledge of other ecological traits, may be a useful tool for predicting relative sensitivities of turtle species to predicted climate change, particularly those species inhabiting seasonal wetlands.

Thermal stress and mutation accumulation increase heat shock protein expression in Daphnia

Understanding the short- and long-term consequences of climate change is a major challenge in biology. For aquatic organisms, temperature changes and drought can lead to thermal stress and habitat loss, both of which can ultimately lead to higher mutation rates. Here, we examine the effect of high temperature and mutation accumulation on gene expression at two loci from the heat shock protein (HSP) gene family, HSP60 and HSP90. HSPs have been posited to serve as ‘mutational capacitors’ given their role as molecular chaperones involved in protein folding and degradation, thus buffering against a wide range of cellular stress and destabilization. We assayed changes in HSP expression across 5 genotypes of Daphnia magna, a sentinel species in ecology and environmental biology, with and without acute exposure to thermal stress and accumulated mutations. Across genotypes, HSP expression increased ~ 6× in response to heat and ~ 4× with mutation accumulation, individually. Both factors simultaneously (lineages with high mutation loads exposed to high heat) increased gene expression ~ 23×—much more than that predicted by an additive model. Our results corroborate suggestions that HSPs can buffer against not only the effects of heat, but also mutations—a combination of factors both likely to increase in a warming world.

Increasing Temperature Facilitates Polyp Spreading and Medusa Appearance of the Invasive Hydrozoan Craspedacusta sowerbii.

Simple SummaryThe jellyfish Craspedacusta sowerbii is one of the most widespread freshwater invasive species. The aim of this study is to analyze polyp and medusa responses to different temperatures using experimental studies on polyp colony growth and medusae to develop a model capable of predicting the Thermal Habitat Suitability (THS) for the polyp and medusa stages. Temperature had a significant effect on the total number of polyps and colonies over time and on the structure of polyp colonies. Polyp and colony numbers were greater at high temperature while colonies were composed of more polyps per colony at 19 °C compared to 29 °C. The thermal tolerance of the medusa stage showed that temperature will favor the expansion of the species in the future to higher latitudes.The freshwater jellyfish Craspedacusta sowerbii is among the most widespread invasive species, observed across a wide temperature range. The aim of this study is to analyze the polyp and medusa stages response to different temperatures by using (i) an experimental study on the polyp colony growth at 19 and 29 °C, and (ii) prediction of the Thermal Habitat Suitability (THS) based on the thermal tolerance of the medusa stage. The total number of polyps and colonies was greater at high temperature. At 19 °C, colonies with 1 to 5 polyps were present, with colonies of 1 to 3 polyps numerically dominating. At 29 °C, colonies were 80% composed of 1- to 2-polyps. Based on the published medusa pulsation rhythm data, a Thermal Performance Curve (TPC) regression was performed and used to monthly predict the THS for current and future (2050 and 2100) scenarios. The southern hemisphere offered optimal conditions (THS > 0.6) year-round. In the northern hemisphere, the optimum period was predicted to be between June and September. The future THS were considerably larger than at present with an increase in optimal THS at higher latitudes (up to 60° N). The combination of experimental and modeling approaches allows to identify the optimal thermal conditions of the polyp and medusa stages and to predict their invasive capacities.

Functional analysis of thermo-sensitive TRPV1 in an aquatic vertebrate, masu salmon (Oncorhynchus masou ishikawae)

Transient receptor potential vanilloid 1 (TRPV1) is mainly expressed in nociceptive primary sensory neurons and acts as a sensor for heat and capsaicin. The functional properties of TRPV1 have been reported to vary among species and, in some cases, the species difference in its thermal sensitivity is likely to be associated with thermal habitat conditions. To clarify the functional properties and physiological roles of TRPV1 in aquatic vertebrates, we examined the temperature and chemical sensitivities of TRPV1 in masu salmon (Oncorhynchus masou ishikawae, Om) belonging to a family of salmonids that generally prefer cool environments. First, behavioral experiments were conducted using a video tracking system. Application of capsaicin, a TRPV1 agonist, induced locomotor activities in juvenile Om. Increasing the ambient temperature also elicited locomotor activity potentiated by capsaicin. RT-PCR revealed TRPV1 expression in gills as well as spinal cord. Next, electrophysiological analyses of OmTRPV1 were performed using a two-electrode voltage-clamp technique with a Xenopus oocyte expression system. Heat stimulation evoked an inward current in heterologously expressed OmTRPV1. In addition, capsaicin produced current responses in OmTRPV1-expressing oocytes, but higher concentrations were needed for its activation compared to the mammalian orthologues. These results indicate that Om senses environmental stimuli (heat and capsaicin) through the activation of TRPV1, and this channel may play important roles in avoiding environments disadvantageous for survival in aquatic vertebrates.