Higher Critical Thermal Maxima Research Articles

Characterization of genes encoding heat shock proteins reveals a differential response to temperature in two geographic populations of Liriomyza trifolii (Diptera: Agromyzidae)

Liriomyza trifolii is a significant, invasive pest that damages horticultural crops and vegetables. The distribution of L. trifolii is influenced by temperature, and prior research has demonstrated that variations in thermal adaptability differ among geographic populations of the insect. Heat shock proteins (Hsps) are involved in adaptation to temperatures; however, the underlying molecular mechanism for thermal adaption in different L. trifolii populations remains unclear. This study examines the temperature adaptability of two L. trifolii populations from Hainan (HN) and Jiangsu (JS) provinces. The results indicate that the HN population has a higher survival rate and a higher critical thermal maximum (CTmax) than the JS population under high temperature stress. Transcriptome data at 42 °C revealed that the JS population has more differentially expressed genes (DEGs) than the HN population, while the HN population has more upregulated DEGs. The two populations were similar in functional annotation of DEGs, and a large number of Hsps were upregulated. However, the HN population had larger numbers and higher expression levels of Hsps during heat stress as compared to the JS population. Additionally, the expression patterns of differentially expressed Hsps varied between the HN and JS populations in response to different elevated temperatures. Notably, the transcription levels of Hsp70s were higher in the HN population as compared to the JS population, while the expression level of genes encoding small heat shock proteins was higher in the JS population. These findings have significant scientific value in understanding the underlying mechanism of temperature adaption in L. trifolii and provide a fresh perspective on the distribution of this invasive pest.

Thermal tolerance and vulnerability to warming differ between populations of wild Oncorhynchus mykiss near the species’ southern range limit

Fish habitat temperatures are increasing due to human impacts including climate change. For broadly distributed species, thermal tolerance can vary at the population level, making it challenging to predict which populations are most vulnerable to warming. Populations inhabiting warm range boundaries may be more resilient to these changes due to adaptation or acclimatization to warmer temperatures, or they may be more vulnerable as temperatures may already approach their physiological limits. We tested functional and critical thermal tolerance of two populations of wild Oncorhynchus mykiss near the species’ southern range limit and, as predicted, found population-specific responses to temperature. Specifically, the population inhabiting the warmer stream, Piru Creek, had higher critical thermal maxima and higher functional thermal tolerance compared to the population from the cooler stream, Arroyo Seco. Arroyo Seco O. mykiss are more likely to experience a limitation of aerobic scope with warming. Piru Creek O. mykiss, however, had higher resting metabolic rates and prolonged exercise recovery, meaning that they could be more vulnerable to warming if prey or dissolved oxygen become limited. Temperature varies widely between streams near the O. mykiss southern range limit and populations will likely have unique responses to warming based on their thermal tolerances and metabolic requirements.

Plasticity of salmonfly (Pteronarcys californica) respiratory phenotypes in response to changes in temperature and oxygen.

Like all taxa, populations of aquatic insects may respond to climate change by evolving new physiologies or behaviors, shifting their range, exhibiting physiological and behavioral plasticity, or going extinct. We evaluated the importance of plasticity by measuring changes in growth, survival and respiratory phenotypes of salmonfly nymphs (the stonefly Pteronarcys californica) in response to experimental combinations of dissolved oxygen and temperature. Overall, smaller individuals grew more rapidly during the 6-week experimental period, and oxygen and temperature interacted to affect growth in complex ways. Survival was lower for the warm treatment, although only four mortalities occurred (91.6% versus 100%). Nymphs acclimated to warmer temperatures did not have higher critical thermal maxima (CTmax), but those acclimated to hypoxia had CTmax values (in normoxia) that were higher by approximately 1°C. These results suggest possible adaptive plasticity of systems for taking up or delivering oxygen. We examined these possibilities by measuring the oxygen sensitivity of metabolic rates and the morphologies of tracheal gill tufts located ventrally on thoracic segments. Mass-specific metabolic rates of individuals acclimated to warmer temperatures were higher in acute hypoxia but lower in normoxia, regardless of their recent history of oxygen exposure during acclimation. The morphology of gill filaments, however, changed in ways that appeared to depress rates of oxygen delivery in functional hypoxia. Our combined results from multiple performance metrics indicate that rising temperatures and hypoxia may interact to magnify the risks to aquatic insects, but that physiological plasticity in respiratory phenotypes may offset some of these risks.

High thermal plasticity, and vulnerability, in extreme environments at the warm distributional edge: The case of a tidepool shrimp

Climate change threatens the resilience of species, especially at their warm distributional edge in extreme environments. We investigated the thermal vulnerability of the tidepool shrimp, Palaemon elegans in the fast-warming southeastern Mediterranean Sea, its warm distributional edge. Tidepool organisms experience strong and fast thermal fluctuations. This might make them more resilient to change, but also bring them closer to their thermal limits during extreme conditions. To examine the shrimp's resilience, we tested three hypotheses: (1) P. elegance in the southeast Mediterranean has higher critical thermal maximum (CTMax) than in cooler regions, (2) the shrimp possess seasonal acclimatization, but (3) long exposure to extreme summer temperatures might erode its thermal performance making it vulnerable to future climate change. In a series of field observations and laboratory experiments we characterized the shrimp's thermal environment and population dynamics, determined its CTMax and tested diverse physiological performance attributes (respiration, digestion, activity, growth) under a wide range of temperatures during winter and summer. The thermal performance curves show that peak respiration rates occur at higher temperatures in the summer compared to winter, indicating seasonal acclimatization. The shrimp's CTMax was 38.1 °C; higher than its Atlantic counterparts, and an indication of biogeographic adaptation. However, its warming tolerance (the thermal safety margin: distance between maximum pool temperatures and CTMax) was only 0.3 °C, indicating low capacity for dealing with further warming in mostly isolated pools, compared to northeast Atlantic populations that have a wider safety margin. Performance also eroded with increase in exposure duration to high temperatures, and the optimum temperature reduces with time. We predict that prolonged exposure to current (~ 32 °C) and future mean summer values in open water would significantly reduce its performance and increase its mortality. Further, juvenile P. elegans were found to be more vulnerable to extreme (cold and hot) temperatures than adults. Together, these findings indicate that the population viability of this robust coastal water shrimp would eventually be reduced under continuous regional warming and the intensification of extreme events.

Mimicking Transgenerational Signals of Future Stress: Thermal Tolerance of Juvenile Chinook Salmon Is More Sensitive to Elevated Rearing Temperature Than Exogenously Increased Egg Cortisol

Elevated temperatures resulting from climate change are expected to disproportionately affect ectotherms given their biological function has a direct link to environmental temperature. Thus, as climate change leads to rapid increases in water temperatures in rivers, aquatic ectotherms such as fish may be highly impacted. Organisms can respond to these stressors through flexible and rapid phenotypic change induced via developmental and/or transgenerational plasticity. In oviparous species, gravid females may translate environmental stress across generations via increased exposure of eggs to maternally-derived glucocorticoids (i.e., maternal stress), which has been shown to result in diverse phenotypic effects in offspring. Recent studies suggest these phenotypic changes from maternal glucocorticoids may elicit predictive adaptive responses, where offspring exposed to maternal stress may be better prepared for the stressful environment they will encounter (i.e., environmental match hypothesis). We applied the environmental match hypothesis to examine whether a prenatal exogenous increase in egg cortisol may prepare Chinook salmon offspring (Oncorhynchus tshawytscha) to cope with thermal challenges after being reared in chronically elevated temperatures. Specifically, we exposed eggs to aqueous bath of cortisol-dosed (1000ng/mL) or control (0ng/ml) solutions, and then raised both treatments at current (+0°C—contemporary ambient river temperature) or elevated (+3°C—projected future river temperature) thermal regimes. We quantified thermal performance in fish 7-9 month post fertilization using two methods: via critical thermal maximum (CTMax), and energetic responses (in plasma cortisol, glucose, and lactate) to environmentally relevant, but challenging thermal spikes over 3 days. Overall, we found that exposure to elevated rearing temperatures had a large impact on thermal tolerance, where elevated-temperature reared offspring had significantly higher CTMax. In comparison, egg cortisol treatment had little to no clear effects on CTMax and blood energetic response. Our study demonstrates the importance of elevated water temperatures as an inducer of offspring phenotypes (via early developmental cues), and highlights the significance of examining offspring performance in environments with ecologically relevant stressors.

Thermal tolerance varies with age and sex for the nonnative Italian Wall Lizard (Podarcis siculus) in Southern California

Temperature has a substantial effect on both the physiology and behavior of ectothermic animals such as lizards. Physiology and behavior can also be influenced by ontogenetic and sex differences, but these effects are largely understudied in lizards. We examined ontogenetic and sex-based differences in thermal tolerances, preferred temperature, and temperature-dependent evaporative water loss rates in Italian Wall Lizards, Podarcis siculus, collected from an introduced population near Los Angeles, California, USA that were acclimated to laboratory conditions. Podarcis siculus has been introduced to multiple localities in the USA and the Mediterranean region and has demonstrated remarkable ability to adapt to novel climatic conditions. In the California population, adults of both sexes had a higher critical thermal maximum (CTmax) than juveniles, and adult females had a lower critical thermal minimum (CTmin) than juveniles and adult males. Thus, adult females had a significantly wider thermal breadth (CTmax - CTmin) compared to adult males and juveniles. Mass-specific evaporative water loss was higher in juveniles compared to adult males at intermediate temperatures. There was no significant difference among groups for preferred temperature. This implies that thermal tolerance, a physiological characteristic, varies with age and sex for this population, whereas thermal preference, a behavioral characteristic, does not. Interestingly, CTmin for all age and sex classes was above temperatures likely experienced by some nonnative populations in winter, suggesting individuals need to find urban thermal retreats. These results add to the growing literature demonstrating that thermal tolerances and breadths can vary between sexes and across age classes in squamate species.

Evidence of rapid spread and establishment of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in semi-arid Botswana

BackgroundTuta absoluta (Meyrick), a major invasive pest of Solanaceous plants, was recently detected in Botswana. Abiotic and biotic factors, together with a suite of population demographic traits are likely key for species propensity and invasion success. First, we determined the movement of T. absoluta from its core detection centre to new invasion areas using pheromone baiting and established likely biotic dispersal drivers. Second, we measured thermal tolerance vis critical thermal limits and lower and upper lethal limits to determine how these traits shape population establishment.ResultsWe detected T. absoluta in all 67 pristine sites across nine districts of Botswana. Within-district trap catches varied between cultivated and wild hosts but were generally not statistically significant (P > 0.001). We report three major wild host plants for T. absoluta as biotic dispersal drivers: Solanum coccineum (Jacq.), Solanum supinum (Dunal) and Solanum aculeatissimum (Jacq.). Solanum coccineum and S. supinum were omnipresent, while S. aculeatissimum distribution was sporadic. Thermal tolerance assays showed larvae were more heat tolerant, with a higher critical thermal maxima (CTmax) than adults (P < 0.001), whereas the adults were more tolerant to cold with a significantly lower (P < 0.001) critical thermal minima (CTmin) compared to larvae. The upper lethal temperatures ranged from 37–43 °C, whereas the lower lethal temperatures ranged from − 1 to − 12 °C for 0–100% mortality, respectively. In the light of prevailing environmental (habitat) temperatures (Thab), warming temperature (7.29 °C) and thermal safety margin (22.39 °C) were relatively high.ConclusionTuta absoluta may not be under abiotic physiological or biotic constraint that could limit its geographical range extension within Botswana. The ubiquity of wild Solanaceous plants with the bridgehead of year-round intensive monocultures of Solanaceous crops within a favourable climatic framework may mean that environmental suitability aided the rapid spread of T. absoluta.

Day/night upper thermal limits differ within Ectatomma ruidum ant colonies

In the tropics, daily temperature fluctuations can pose physiological challenges for ectothermic organisms, and upper thermal limits may affect foraging activity over the course of the day. Variation in upper thermal limits can occur among and within species, and for social insects such as ants, within colonies. Within colonies, upper thermal limits may differ among individuals or change for an individual throughout the day. Daytime foragers of the Neotropical ant Ectatomma ruidum have higher critical thermal maxima (CTmax) than nocturnal foragers, but whether these differences occur among or within colonies was not previously known. We investigated the potential mechanisms accounting for day/night variation in CTmax of E. ruidum foragers by testing whether CTmax varied among or within colonies or due to individuals within colonies acclimating to changes in temperature over a short time scale (3 h). We found within- but not among-colony differences in CTmax on a diel cycle, and we found no evidence for among- or within-colony partitioning of foraging times by individual workers. Individuals did not acclimate to experimental manipulations of temperature, although additional experiments with more ecologically relevant temperature manipulations are needed to rule out this mechanism. In summary, we have shown that day/night differences in upper thermal limits can occur within ant colonies, but further investigation is needed to elucidate the mechanisms driving this variation.

Thermal physiology of native cool-climate, and non-native warm-climate Pumpkinseed sunfish raised in a common environment

Contemporary evolution of thermal physiology has the potential to help limit the physiological stress associated with rapidly changing thermal environments; however it is unclear if wild populations can respond quickly enough for such changes to be effective. We used native Canadian Pumpkinseed (Lepomis gibbosus) sunfish, and non-native Pumpkinseed introduced into the milder climate of Spain ~100 years ago, to assess genetic differences in thermal physiology in response to the warmer non-native climate. We compared temperature performance reaction norms of two Canadian and two Spanish Pumpkinseed populations born and raised within a common environment. We found that Canadian Pumpkinseed had higher routine metabolic rates when measured at seasonally high temperatures (15°C in winter, 30°C in summer), and that Spanish Pumpkinseed had higher critical thermal maxima when acclimated to 30°C in the summer. Growth rates were not significantly different among populations, however Canadian Pumpkinseed tended to have faster growth at the warmest temperatures measured (32°C). The observed differences in physiology among Canadian and Spanish populations at the warmest acclimation temperatures are consistent with the introduced populations being better suited to the warmer non-native climate than native populations. The observed differences could be the result of either founder effects, genetic drift, and/or contemporary adaptive evolution in the warmer non-native climate.

Silk moth larvae suffer more than pupae in heat

Striking a deal with the environment, ectotherms have come up with a low-cost lifestyle compromise by hitching their body temperature to that of their surroundings. However, as climate change takes a grip and the equilibrium begins shifting, this compromise may come unstuck if conditions become uncomfortably hot. Leigh Boardman and John Terblanche from Stellenbosch University, South Africa, explain that as temperatures rise, aquatic ectotherms are unable to meet the oxygen demands of their warmer bodies, but it wasn't clear whether insects suffered the same fate. Knowing that oxygen availability should alter the thermal tolerance of animals if it is the factor limiting their ability to adapt to hotter conditions, Boardman and Terblanche decided to test the impact of altering the oxygen supply on the metabolism and activity of silk moth larvae and sluggish pupae as the mercury rises.Gently increasing the environmental temperature from 25 to 60°C over 2 h 20 min, the duo measured the metabolic rates and breathing activity of silk moth larvae and pupae in air ranging from hypoxic (with ∼2.5% O2) to normoxic (21% O2) and hyperoxic (40% O2) to find out whether oxygen availability affected the insects’ thermal tolerance. They also tested the effects of changing the density of normoxic air (replacing some of the nitrogen with low density helium) and the air humidity to see whether physical changes to the air altered how hard the insects had to work to breathe in order to alter their thermal tolerance.Surprisingly, the team found that the effects of oxygen availability depended on the insects’ life stage. While the pupae seemed unaffected by oxygen availability – maintaining a critical thermal maximum of 50°C at all oxygen levels – the larvae's critical thermal maximum fell from 53°C in normoxic air to 51°C in hypoxic air: the larvae were oxygen limited while the pupae, with a lower metabolic rate, were not. And the larvae required more oxygen to sustain metabolism than pupae at the same temperature, as well as having a higher critical thermal maximum (53°C) than pupae (50°C) in normoxic air. Next, the team analysed the impact of humidity and density on the insects’ thermal tolerance, and found that humidified hypoxic air increased the larval critical thermal limit, suggesting that the water vapour may have somehow increased delivery of oxygen through the larvae's tracheal system. However, altering the air density did not seem to affect how hard the insects had to breathe and did not affect their thermal tolerance.So, different insect life stages respond to thermal stress in different ways, with oxygen supply determining the thermal limits of fifth instar larvae, while it has little impact on the thermal tolerance of metamorphosing pupae. Realising that some insect life stages may therefore be more susceptible to the detrimental effects of climate change than others Boardman and Terblanche say, ‘Further investigation into life stage-related oxygen safety margins is urgently needed’.

Warm microhabitats drive both increased respiration and growth rates of intertidal consumers

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 522:127-143 (2015) - DOI: https://doi.org/10.3354/meps11117 Warm microhabitats drive both increased respiration and growth rates of intertidal consumers Luke P. Miller1,*, Bengt J. Allen2, Felicia A. King1, Daisy R. Chilin2, Vanessa M. Reynoso2, Mark W. Denny1 1Hopkins Marine Station, Stanford University, 120 Ocean View Blvd., Pacific Grove, California 93950, USA 2Department of Biological Sciences, California State University Long Beach, 1250 Bellflower Blvd., Long Beach, California 90840, USA *Corresponding author: contact@lukemiller.org ABSTRACT: Rocky intertidal organisms are often exposed to broadly fluctuating temperatures as the tides rise and fall. Many mobile consumers living on the shore are immobile during low tide, and can be exposed to high temperatures on calm, warm days. Rising body temperatures can raise metabolic rates, induce stress responses, and potentially affect growth and survival, but the effects may differ among species with different microhabitat preferences. We measured aerial and aquatic respiration rates of 4 species of Lottia limpets from central California, and estimated critical thermal maxima. In a variety of microhabitats in the field, we tracked body temperatures and measured limpet growth rates on experimental plates colonized by natural microalgae. Limpet species found higher on the shore had lower peak respiration rates during high temperature aerial exposure, and had higher critical thermal maxima. Using our long-term records of field body temperatures, we estimated cumulative respiration to be 5 to 14% higher in warm microhabitats. Growth rates in the field appear to be driven by an interaction between available microalgal food resources, low tide temperature, and limpet species identity, with limpets from warmer microhabitats responding positively to higher food availability and higher low tide temperatures. Stressful conditions in warm microhabitats make up a small portion of the total lifetime of these limpets, but the greater proportion of time spent at non-stressful, but warm, body temperatures may result in enhanced growth compared to limpets living in cooler microhabitats. KEY WORDS: Intertidal zone · Limpet · Microalgae · Shore height · Temperature stress · Thermotolerance Full text in pdf format Supplementary material PreviousNextCite this article as: Miller LP, Allen BJ, King FA, Chilin DR, Reynoso VM, Denny MW (2015) Warm microhabitats drive both increased respiration and growth rates of intertidal consumers. Mar Ecol Prog Ser 522:127-143. https://doi.org/10.3354/meps11117 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 522. Online publication date: March 02, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

The effects of dissolved oxygen and triploidy on critical thermal maximum in brook charr (Salvelinus fontinalis)

This study examined the effect of dissolved oxygen (DO) level on critical thermal maximum (CTMax) in diploid and triploid brook charr (Salvelinus fontinalis) exposed to a temperature increase of 3°C/h. Because gas solubility is inversely proportional to temperature, DO declines during standard CTMax tests. With this treatment as a baseline, oxygen or nitrogen injection was used to provide three other DO conditions during CTMax tests: two hyperoxic (maintenance at initial 10mg/L and increase from 10mg/L at 2mg/L/h) and one hypoxic (decrease from 10mg/L at 2mg/L/h). Hyperoxia had no effect on temperature at CTMax or time taken to reach CTMax. Hypoxia, on the other hand, resulted in a significantly lower CTMax and shorter time to CTMax than under standard or hyperoxic conditions, with both indices affected by triploidy but not in a consistent fashion: in one experiment triploids had a lower CTMax and shorter time to CTMax than diploids and in a second experiment they had a higher CTMax and longer time to CTMax than diploids. Indices of the secondary stress response (plasma glucose and ions) during CTMax tests under hypoxia responded as would be predicted for an acute stress, with no difference between triploids and diploids.

Foraging by forest ants under experimental climatic warming: a test at two sites

Climatic warming is altering the behavior of individuals and the composition of communities. However, recent studies have shown that the impact of warming on ectotherms varies geographically: species at warmer sites where environmental temperatures are closer to their upper critical thermal limits are more likely to be negatively impacted by warming than are species inhabiting relatively cooler sites. We used a large-scale experimental temperature manipulation to warm intact forest ant assemblages in the field and examine the impacts of chronic warming on foraging at a southern (North Carolina) and northern (Massachusetts) site in eastern North America. We examined the influence of temperature on the abundance and recruitment of foragers as well as the number of different species observed foraging. Finally, we examined the relationship between the mean temperature at which a species was found foraging and the critical thermal maximum temperature of that species, relating functional traits to behavior. We found that forager abundance and richness were related to the experimental increase in temperature at the southern site, but not the northern site. Additionally, individual species responded differently to temperature: some species foraged more under warmer conditions, whereas others foraged less. Importantly, these species-specific responses were related to functional traits of species (at least at the Duke Forest site). Species with higher critical thermal maxima had greater forager densities at higher temperatures than did species with lower critical thermal maxima. Our results indicate that while climatic warming may alter patterns of foraging activity in predictable ways, these shifts vary among species and between sites. More southerly sites and species with lower critical thermal maxima are likely to be at greater risk to ongoing climatic warming.

Recent thermal history influences thermal tolerance in freshwater mussel species (Bivalvia:Unionoida)

AbstractUnderstanding species’ temperature tolerances in the context of concurrent environmental stressors is critical because thermal regimes of freshwater ecosystems are changing. We evaluated the critical thermal maximum (CTM) of 3 freshwater mussel species (Alasmidonta varicosa, Elliptio complanata, and Strophitus undulatus) acclimated to 2 temperatures (15 and 25°C) and exposed to 2 aeration treatments (aerated vs unaerated) during CTM testing. Responses varied by species, but mussels acclimated to 25°C generally had a higher CTM than mussels acclimated to 15°C. For E. complanata, the effects of acclimation temperature and aeration were interactive, such that CTM was highest at 15°C but only under aerated conditions. Our results indicate that recent thermal history affects thermal tolerance, combinations of environmental stressors may influence thermal tolerance, and such responses vary among species.

The Critical Thermal Maximum of Juvenile Red Drum Reared for Out‐of‐Season Stocking in Texas

AbstractHatchery‐propagated red drum Sciaenops ocellatus are released by the Texas Parks and Wildlife Department (TPWD) during the spring, summer, and fall to supplement natural stocks. Reported success of red drum stocked out of season in summer has been low or nonexistent; several potential causes, including mortality due to high temperatures, have been suggested. The present study was devised to determine the critical thermal maximum (CTM) of pond‐raised juvenile red drum that had previously been exposed to diurnal temperatures of the summer season. Laboratory studies designed to mimic the rate of temperature increase (0.25°C per hour) typical of TPWD rearing ponds were used to examine rates of mortality in juvenile red drum that were collected from three separate ponds exposed to the ambient fluctuating temperatures of the summer season. The CTM (temperature that was lethal to 50% of the test fish [LT50]) was significantly lower (P &lt; 0.0001) for two of the fish trials (LT50 = 37.1°C and 37.0°C) than for a third trial (LT50 = 38.7°C). This difference correlated with the size of fish in each trial; the two trials with smaller‐sized fish (range = 18–32 mm total length) had the lower CTMs, whereas the trial with larger‐sized fish (range = 31–50 mm total length) had the higher CTM, suggesting positive size dependence in the CTM. The CTMs obtained here are higher than the maximum temperatures encountered in grow‐out ponds during summer, indicating that high temperature exposure may not be the sole cause for the low success of red drum stocked out of season.

The acute temperature tolerance of green sturgeon (Acipenser medirostris) and the effect of environmental salinity

We investigated the effect of environmental salinity on the upper thermal tolerance of green sturgeon (Acipenser medirostris), a threatened species whose natural habitat is vulnerable to temperature and salinity variation as a result of global climate change. Freshwater (FW)-reared sturgeon were gradually acclimated to salinities representing FW, estuary water (EST), or San Francisco Bay water (BAY) at 18 degrees C, and their critical thermal maximum (CTMax) was measured by increasing temperature 0.3 degrees C/min until branchial ventilation ceased. CTMax was 34.2+/-0.09 degrees C in EST-acclimated fish, with FW- and BAY-acclimated fish CTMax at 33.7+/-0.08 and 33.7+/-0.1 degrees C, respectively. Despite the higher CTMax in EST-acclimated fish, FW-acclimated sturgeon ventilation rate reached a peak that was 2 degrees C higher than EST- and BAY-acclimated groups and had a greater range of temperatures within which they exhibited normal ventilatory function as assessed by Q10 calculation. The osmoregulatory consequences of exposure to near-lethal temperatures were assessed by measuring plasma osmolality and hematocrit, as well as white muscle, brain, and heart tissue water contents. Hematocrit was increased following CTMax exposure, most likely owing to the elevated metabolic demands of temperature increase, and plasma osmolality was significantly increased in EST- and BAY-acclimated fish, which was likely the result of a greater osmotic gradient across the gill as metabolism increased. To our knowledge, this represents the first evidence for an effect of salinity on the upper thermal tolerance of sturgeon, as well as the first investigation of the osmoregulatory consequences of exposure to near-lethal temperatures.

Thermal Tactics of Air-breathing and Non Air-breathing Gobiids Inhabiting Mangrove Tidepools on Pulau Hoga, Indonesia

Air-breathing and non air-breathing gobiids inhabiting mangal tidepools on Pulau Hoga, Sulawesi, Indonesia, displayed differing types and degrees of behavioral and physiological adaptations to mitigate daily thermal and oxic stress. Non air-breathing Dusky Frillfin Goby, Bathygobius fuscus, and an undescribed sandflat goby species, Bathygobius sp., had higher critical thermal maxima, CTMax, (41.2 and 41.6 C, respectively) and lower critical thermal minima, CTMin, (11.0 and 11.4 C, respectively) than amphibious Common Mudskipper, Periopthalmus kalolo (40.8 and 12.8 C, respectively). During hypoxia, Common Mudskipper CTMax decreased significantly (38.8 C) and fish displayed a pronounced escape response, while Dusky Frillfin Goby showed no significant CTMax decrease (40.8 C). Neither bathygobiid attempted to escape during CTM trials. Common Mudskipper, however, attempted escape at temperatures significantly lower than their normoxic and hypoxic CTMax (36.4 and 35.0 C, respectively), and at temperatures higher than their normoxic CTMin (18.7 C). Temperature quotients (ratio of metabolic rates or oxygen consumption at two temperatures) for all species approached unity and ranged from 1.00 to 1.37 when exposed to a temperature increase of 6 C. Oxygen insensitive CTMaxima and a wide thermal scope allow bathygobiids to remain in tidepools during the most extreme conditions. In contrast, amphibious Common Mudskipper use a well developed behavioral escape response to avoid unfavorable environments. A sharply reduced temperature quotient response for these gobies diminishes the metabolic costs typically associated with diel temperature increases.

Thermal Physiology and Reproductive Phenology of Buergeria japonica (Rhacophoridae) Breeding in a Stream and a Geothermal Hotspring in Taiwan

Abstract We compared the reproductive phenology and tadpole thermal physiology of two populations of Buergeria japonica in Taiwan. The population in Jentse breeds in a geothermal hot spring whose water is a warm, over 35°C year-round, whereas the population in Chukou breeds in a stream whose water temperature is closely correlated with fluctuations in air temperature and averages 23°C. The B. japonica population in Jentse breeds year-round, but the Chukou population breeds only from March to October. Tadpoles from Jentse that reared at 32°C attained larger sizes than tadpoles from Chukou that reared at 32°C, whereas tadpoles from both sites attained similar body size when reared at 22°C. Chukou tadpoles reared at 40°C died within 1–2 d, whereas Jentse tadpoles survived for 9 d at 40°C. All tadpoles tolerated heat well, but Jentse tadpoles had higher critical thermal maxima (CTMax) than Chukou tadpoles. Tadpoles from Jentse showed no metabolic compensation but those from Chukou showed an “inverse” metaboli...

Comparative environmental tolerances of threatened delta smelt (Hypomesus transpacificus) and introduced wakasagi (H. nipponensis) in an altered California estuary.

In California's Sacramento-San Joaquin estuary, environmental protection and habitat restoration efforts directed at a threatened native osmerid, the delta smelt (Hypomesus transpacificus), are complicated by the presence of a morphologically similar non-native congener, the wakasagi (H. nipponensis), transported to the estuary from upstream reservoirs. In order to better define delta smelt critical habitat and to evaluate the potential for habitat overlap by these two species, we compared the tolerances of the two species to temperature, salinity, and water velocity, environmental factors that vary spatially and temporally within the estuary. For fishes acclimated to 17°C and fresh water (0 ppt), we measured critical thermal maxima and minima, chronic upper salinity tolerance limits, and critical swimming velocities. Wakasagi had higher critical thermal maxima (29.1°C vs. 25.4°C for delta smelt), lower critical thermal minima (2.3°C vs. 7.5°C for delta smelt), higher upper salinity tolerances (26.8 ppt vs. 19.1 ppt for delta smelt), and swam faster (for 6-6.9 cm SL fish, 43.3 cm s-1 vs. 28.2 cm s-1 for delta smelt) than delta smelt. This suggests that the wide seasonal and year-to-year fluctuations in temperature, salinity, and flow typical in the estuary would not exclude wakasagi, although their eggs and larvae may be less tolerant. With respect to these factors, the native delta smelt may be at a physiological disadvantage, particularly in habitats with suboptimal environmental conditions, and may be excluded from shallow-water habitat restoration sites, which are characterized by poor circulation, low flows, and more environmentally extreme conditions. The low abundance of wakasagi in the estuary recorded to date may indicate that factors other than temperature, salinity, and flow determine wakasagi distribution.

Temperature Tolerance in Three Mycophagous Drosophila Species: Relationships with Community Structure

Patterns of host use at several spatial and temporal scales suggest that temperature tolerance may influence the structure of mycophagous fly communities. For instance, Drosophila putrida is more abundant than D. falleni and D. tripunctata in dry sites, at dry periods, and in small, desiccation-prone mushrooms. In this experiment, we acclimated flies from these species at different temperatures (15°C, 20°C, 25°C, and 30°C) for 5 d, and then measured their responses to acute thermal stress (increasing temperature 0.5°C/min). ANOVA were used to describe the effects of sex, species, and acclimation temperature on: 1) survivorship after 5 d, and 2) Critical Thermal Maxima (CTMax). Critical Thermal Maximum was measured as the temperature at which 50% of the flies in a sample were incapable of righting themselves. Survivorship was uniformly high for all species from 15°C to 25°C. However, at 30°C, D. putrida survival (74%) was significantly higher than either D. falleni (39%) or D. tripunctata (23%). When averaged across all acclimation temperatures, D. putrida also had a higher CTMax than the other species (40.7°C, compared to 40.2°C for D. falleni and 39.9°C for D. tripunctata). D. putrida was the only species with a CTMax that increased significantly after acclimation at 30°C. Thus, D. putrida was more tolerant to chronic and acute thermal stress than the other species, and was the only species to show an adaptive physiological response to high temperature exposure. These species differences are consistent with spatial and temporal abundance patterns, and may contribute to patterns in community structure.