Heat Coma Temperatures Research Articles

Thermal tolerance does not explain the altitudinal segregation of lowland and alpine aquatic insects

Elevation gradients provide powerful study systems for examining the influence of environmental filters in shaping species assemblages. High-mountain habitats host specific high-elevation assemblages, often comprising specialist species adapted to endure pronounced abiotic stress, while such harsh conditions prevent lowland species from colonizing or establishing. While thermal tolerance may drive the altitudinal segregation of ectotherms, its role in structuring aquatic insect communities remains poorly explored. This study investigates the role of thermal physiology in shaping the current distribution of high-mountain diving beetles from the Sierra Nevada Iberian mountain range and closely related lowland species. Cold tolerance of five species from each altitudinal zone was measured estimating the supercooling point (SCP), lower lethal temperature (LLT) and tolerance to ice enclosure, while heat tolerance was assessed from the heat coma temperature (HCT). Alpine species exhibited wider fundamental thermal niches than lowland species, likely associated with the broader range of climatic conditions in high-mountain areas. Cold tolerance did not seem to prevent lowland species from colonizing higher elevations, as most studied species were moderately freeze-tolerant. Therefore, fundamental thermal niches seem not to fully explain species segregation along elevation gradients, suggesting that other thermal tolerance traits, environmental factors, and biotic interactions may also play important roles.

Thermal tolerances of littorinid snails from temperate and subtropical South Africa

Environmental temperature affects ectotherm performance and fitness because physiological performance increases up to a sublethal optimum temperature; this is not fixed, but depends on the species and individual history. We explored the influence of species identity, size and thermal history on thermal tolerance in four species of littorinid snails in South Africa. As expected, heat coma temperature (HCT) was lower than the lethal temperatures (LT50), and was greater for juveniles, while LT50 was greater for adults. The ranking by both metrics was Echinolittorina natalensis > Littoraria glabrata > Afrolittorina africana > A. knysnaensis, reflecting their biogeographical distributions. No species showed an effect of laboratory acclimation for 14 days at temperatures from 20 to 35 °C, though HCT was lower for field fresh individuals than for all other treatments. Nor was there acclimatisation of LT50 between seasons. Bioregion is a proxy for lifetime acclimatisation yet the Afrolittorina species showed nonsignificant differences between conspecifics from different regions. The effect of size differed between the two metrics, and field fresh individuals showed lower HCT values than laboratory-treated individuals—which taken together indicates the need for care when interpreting the results of lab work. The thermal tolerances of these species reflect their biogeography and appear fixed with little or no plasticity, rendering these littorinids vulnerable to future climate warming.

Thermal biology of aquatic insects in alpine lakes: Insights from diving beetles

Abstract High mountain areas are especially vulnerable to global warming, as they experience faster temperature changes than lowlands in a climate change context. Notably, increased temperatures and frequency of extreme flooding and droughts, and the consequent decrease in ice cover and water availability fluctuations, will induce important physical changes in alpine freshwater systems. Thus, assessing thermal limits and exploring overwintering strategies of aquatic alpine insects is pivotal to understanding how aquatic communities of high‐mountain fresh waters will respond to climate change. However, knowledge on these topics is still scarce for aquatic alpine insects. Here, the thermal biology of adults of five diving beetle species from alpine lakes located in the Sierra Nevada mountain range (southern Iberia) was studied. Cold tolerance was measured estimating the supercooling point (SCP), lower lethal temperature (LLT), tolerance to ice enclosure and to submersion, whereas heat tolerance was assessed from the heat coma temperature and upper lethal temperature. All of the species survived ice enclosure for 3 h. Furthermore, three of the studied species had SCPs higher than their LLTs, suggesting that they could be freeze‐tolerant. All species except Agabus nevadensis also were tolerant to submersion, which could be a key adaptation for overwintering underwater below the ice cover as adults, reducing risk from freezing conditions in the air. The species did not differ significantly in their upper thermal limits, which were similar to those of other dytiscids from lower altitudes. Overall, our results suggest that increasing temperatures is not expected to be the most important threat for the water beetle populations in Sierra Nevada, but rather the colonisation of alpine lakes by lowland dytiscids in a warmer climate scenario.

Feeling the heat: Bumblebee workers show no acclimation capacity of upper thermal tolerance to simulated heatwaves

Climate change is our most significant challenge in the 21st century and among the main drivers of biodiversity loss. Recent distributional shifts and declines in crucial pollinators, such as bumblebees, seem to be associated to this phenomenon. However, despite future climate projections on climate warming, few studies have assessed the ability of temperate bumblebees to acclimate to extreme weather events, such as heatwaves. This study estimates the upper critical thermal limits (Critical Thermal Maximum (CTmax) and Heat Coma Temperature (HCT)), of the bumblebee subspecies Bombus terrestris audax, and assesses whether CTmax increases following exposure to a simulated heatwave. The critical thermal maximum occurred between 48.9 and 52.7 °C, while the heat coma temperature varied between 50.7 and 53.4 °C. After measurement of HCT, around 23% of bees survived 24 h or longer, but coordination was never recovered. There was no significant association between upper critical thermal limits and body mass, which highlights the need to investigate other factors to comprehend the mechanisms behind thermal tolerance limits. Furthermore, the heatwave treatments had no significant effect on the CTmax of bumblebee workers, indicating no acclimation capacity of upper thermal tolerance to simulated heatwaves. Our study provides insights into the upper thermal tolerance limits of Bombus terrestris audax and reveals that exposure to heatwave-like events does not change the upper thermal tolerance of bees, highlighting the need to develop effective strategies that might enable them to cope with extreme weather events.

Acclimation Effects of Natural Daily Temperature Variation on Longevity, Fecundity, and Thermal Tolerance of the Diamondback Moth (Plutella xylostella).

Simple SummaryDiurnal, monthly, or seasonal temperatures can fluctuate substantially. Daily temperature amplitudes (DTAs) can significantly impact the traits of insects but there is limited evidence from the natural environment. Therefore, we studied the acclimation effects of DTA on the longevity, total fecundity, early fecundity, and thermal tolerance of adult diamondback moths (Plutella xylostella) under environmental conditions. The longevity, total fecundity, early fecundity, and heat thermal tolerance of adults significantly changed under different DTAs. These findings highlight the effects of DTA on the acclimation response in the P. xylostella phenotype, and DTA should be incorporated into prediction models for assessing insect populations and the effects of climate change.Daily temperature amplitudes (DTAs) significantly affect the ecological and physiological traits of insects. Most studies in this field are based on laboratory experiments, while there is limited research on the effects of changes in DTA on insect phenotypic plasticity under natural conditions. Therefore, we studied the acclimation effects of DTA on the longevity, total fecundity, early fecundity, and the thermal tolerance of adult diamondback moths (Plutella xylostella L.) under naturally occurring environmental conditions. As DTAs increased, male longevity and total fecundity decreased, and early fecundity increased. An increase in DTA was significantly associated with the increased heat coma temperature (CTmax) of both males and females, but had no significant effect on their cold coma temperature (CTmin). Our findings highlight the effects of DTA on the acclimation response of P. xylostella and emphasize the importance of considering DTA in predicting models for assessing insect populations and the effects of climate change.

Comparison of upper sublethal and lethal temperatures in three species of rice planthoppers

Temperature is an important environmental factor for ectotherms’ fitness and survival. The upper sublethal and lethal temperatures were compared between adults of three closely related destructive planthopper species, the small brown planthopper (Laodelphax striatellus, SBPH), the brown planthopper (Nilaparvata lugens, BPH), and the white-backed planthopper (Sogatella furcifera, WBPH) in the absence and presence of the host plant (Oryza sativa, var. Taichong1). Values of the critical thermal maxima (CTmax) were higher in SBPH than in both BPH and WBPH and higher in BPH than in WBPH, and values of the heat coma temperatures (HCT) were higher in both BPH and SBPH than in WBPH. CTmax and HCT values were higher in the presence than in the absence of plant material. Between sexes, females generally showed higher CTmax and HCT than males. The upper lethal temperatures (ULT50) measured in the absence of plant material were not significantly different among the planthopper species. The planthoppers also exhibited different behaviors in an increasing temperature regime, with fewer insects dropping-off from the plant in SBPH than in BPH and WBPH. These results indicate that SBPH and BPH are more heat tolerant than WBPH. The findings highlight the biological divergence in closely related planthopper species and the importance of performing the heat tolerance measurement in an ecologically relevant setting, which serves to predict seasonal and spatial occurrence patterns of the destructive planthopper species.

Seasonal Change in Distribution and Heat Coma Temperature of Oceanic Skaters, Halobates (Insecta, Heteroptera: Gerridae).

A series of studies were conducted during two cruises between Tokyo and Honolulu in September 2010 and from February to March 2012. The aims of the studies were to (1) compare the distribution of three species of Halobates oceanic skaters, H. germanus, H. micans, and H. sericeus, with respect to their temperature limits; (2) identify the lower temperature limit of H. sericeus, the species that displays the widest distribution range (40°N–35°S) latitude; and (3) test the hypothesis that H. sericeus can change their temperature tolerance to adapt to seasonal changes in sea surface temperatures. The heat coma temperature (HCT) was measured during the two cruises and the values were compared between the two populations of H. sericeus. The species collected in September 2010 were H. germanus, H. micans, and H. sericeus. H. sericeus was dominant, occupying more than 90% of the collecting sites. H. germanus and H. micans were collected in the northern and western part of the cruise track (29–34°N, 141–151°E), and not in the southern and eastern part. The population density of these two species was 9000–150,000/km2 in the first cruise, which took place in summer. On the other hand, H. sericeus was collected throughout the cruise track during that cruise. The population density of H. sericeus was relatively high, at 4000–310,000/km2, in the southern and eastern part of the cruise track (19–29°N, 152°E–165°W). In February and March 2012, only H. sericeus was collected at a density of 17,000–80,000/km2 and only in the eastern and southern part, at 25°–28°N, 169°E–178°W. No Halobates oceanic skaters were found in the western or northern part (30°N and further north, 159°E and further west) during that cruise. The lower limit for the inhabitation of sea surface temperatures appeared to be 27.8 °C or slightly lower for H. germanus and H. micans, but was 22.1 °C or slightly lower for H. sericeus. H. sericeus specimens, mostly adults, that had been collected during the two cruises were used in heat coma experiments. Summer specimens showed significantly higher heat coma temperatures (HCTs) than the winter specimens. This difference in HCTs may be the result of relatively long term temperature acclimation in the summer or winter for the adults that inhabit the temperate and subtropical areas along the cruise tracks between Tokyo and Honolulu in the Pacific Ocean. This temperature plasticity of H. sericeus may be related to the wider latitude area inhabited by this species (main range: 40°N–25°S).

Limited thermal acclimation capacity in cave beetles

Thermal tolerance is a key vulnerability factor for species that cannot cope with changing conditions by behavioural adjustments or dispersal, such as subterranean species. Previous studies of thermal tolerance in cave beetles suggest that these species may have lost some of the thermoregulatory mechanisms common in temperate insects, and appear to have a very limited thermal acclimation ability. However, it might be expected that both thermal tolerance and acclimation ability should be related with the degree of specialization to deep subterranean environments, being more limited in highly specialized species. To test this hypothesis, we use an experimental approach to determine the acclimation capacity of cave beetles within the tribe Leptodirini (family Leiodidae) with different degrees of specialization to the deep subterranean environment. For this, we acclimate groups of individuals at a temperature close to their upper thermal limit (20ºC) or a control temperature (approximately that of the cave in which they were found) for 2 or 10 days (short- vs. long-term acclimation). a temperature close to their upper thermal limit (20ºC) or a control temperature (approximately that of the cave in which they were found) for 2 or 10 days (short- vs. long-term acclimation). Upper thermal limits (heat coma temperature, HC) are then measured for each individual using a ramping protocol (rate of increase of 1ºC/min) combined with infrared thermography and video recording. Preliminary results in a deep subterranean species (Speonomidius crotchi, with an intermediate degree of specialization) showed no significant effect of acclimation temperature in HC at any of the exposure times. Such reduced thermal plasticity could be also expected for other highly specialized subterranean species. The potential implications of these findings for subterranean biodiversity in a climate change context are discussed.

Thermal acclimation capacity of Jack Beardsley mealybug (Pseudococcus jackbeardsleyi) to survive in a warming world

Abstract The study of thermal tolerance and acclimation capacity in Jack Beardsley mealybug, Pseudococcus jackbeardsleyi Gimpel and Miller is the crucial step in determining their abilities to cope with climate change. Thus, the aim of this research was to determine the effects of acclimation temperatures on the changes in thermal tolerance of P. jackbeardsleyi. The influences of acclimation temperature at moderate (25 °C) and high (35 °C) temperatures on their lower and upper thermal limits were measured composed of critical thermal minimum (CTmin), maximum (CTmax), chill coma temperature (CCT) and heat coma temperature (HCT) for first instar nymphs and adults. The important information derived from this study revealed that the upper thermal limits of adults are constrained to a relative narrow range that will make them sensitive to relative small changes in temperatures, whilst all mean upper thermal indices at 35 °C were significantly higher than at 25 °C for nymphs. For this highlight notice, nymphs have more potential to change their upper thermal limits which will allow them to withstand high temperatures in the field. These results are a sign to warn us that P. jackbeardsleyi could become highly noxious which cause severe outbreaks damage to the crops in the tropics under global warming.

Heat Coma Temperature and Supercooling Point in Oceanic Sea Skaters (Heteroptera, Gerridae).

Heat coma temperatures (HCTs) and super cooling points (SCPs) were examined for nearly 1000 oceanic sea skaters collected from in the Pacific and Indian Oceans representing four Halobates species; H. germanus, H. micans, H. sericeus, and H. sp. Analysis was conducted using the entire dataset because a negative correlation was seen between the HCTs and SCPs in all four species. A weak negative correlation was seen between HCTs and SCPs with a cross tolerance between warmer HCTs and colder SCPs. The weakness of the correlation may be due to the large size of the dataset and to the variability in ocean surface temperature. The negative correlation does however suggest that oceanic sea skaters may have some form of cross tolerance with a common physiological mechanism for their high and low temperature tolerances.

Relationship between Cool Coma and Heat Coma Temperatures in the Oceanic Sea Skaters Halobates Collected near the Sumatra Island in the Indian Ocean

In the cruise, MR15-04 by R/V MIRAI, the samplings by the neuston net were performed in 23rd November to 14th December 2016 and three species of Halobates (H. germanus, H. micans, H. sp) were used for the temperature tolerance experiments after the collection. The neuston net was towed three times (3 × 15 min) on the starboard side of R/V MIRAI on the water surface with ship speed of 2 knot to water every 3 nights (19:00 - 20:00) at the fixed point in the south-western direction which was located at 50 km from the Sumatra island (4o03'S - 4o05'S, 101o53'E) in the Indonesia. Experiments on cool coma and heat coma were performed on the three species. Seconds for recovery from cool coma and heat coma were also examined on the Halobates in this study. Cool coma temperatures, gap temperature needed (temperature from the adapted temperature) for the cool coma and seconds for the recover from cool coma ranged 13.0oC to 25.0oC, 3.1oC to 16.1oC, 1 second to 4370 seconds, respectively. Heat coma temperature, gap temperature needed for the heat coma, seconds for the recover from heat coma ranged 29.4oC to 43.1oC, 1.9oC to 15.5oC, 2 seconds to 6420 seconds, respectively. The higher temperature of cool coma temperature during the last five days was shown when Madden-Julian Oscillation has passed over the ship, R/V MIRAI than the previous 10 days in the adults of H. germanus collected at the fixed place neat to Sumatra island (One way ANOVA: F-value = 2.314, df = 7, p = 0.028). Adults of un-described species, H. sp collected near to the Sumatra island, showed lower cool coma temperature [Mean ± SD: 15.51 ± 3.76 (9)] than those of H. germanus collected in the same place [16.96 ± 2.57 (191)]. This lower cool coma temperatures shown by this un-described species might be related to that this species should be a “shore” species inhabiting shore water in which many precipitation could cause the decreased surface temperature from 30oC - 31oC into about 25oC. Most of adults which suffered from the cool coma recovered within 20 seconds, whereas adults which suffered heat coma at 38oC and 39oC needed more than 200 seconds for the recovery and many of those which did it at more than 40oC needed more than 1000 second and some ones did not recover at all. All adults who suffered at more than 43oC did not recover at all. There were significant and negative correlation between cool and heat coma temperatures shown by the adults of H. germanus. This correlation might imply a common physiological mechanism for lower and higher temperature tolerances for this species.

Exposure to solar radiation drives organismal vulnerability to climate: Evidence from an intertidal limpet

Understanding the physiological abilities of organisms to cope with heat stress is critical for predictions of species’ distributions in response to climate change. We investigated physiological responses (respiration and heart beat rate) of the ectotherm limpet Patella vulgata to heat stress events during emersion and the role of seasonal and microclimatic acclimatization for individual thermal tolerance limits. Individuals were collected from 5 microhabitats characterized by different exposure to solar radiation in the high intertidal zone of a semi-exposed rocky shore in winter and summer of 2014. Upper thermal tolerance limits (heat coma temperatures – HCTs, and heart rate Arrhenius break temperatures - ABTs) were determined for individuals from each microhabitat in both seasons under laboratory conditions. While we found a clear seasonal acclimatization, i.e., higher HCTs and ABTs in summer than in winter, we did not find evidence for microhabitat-specific responses that would suggest microclimatic acclimatization. However, operative limpet temperatures derived from in-situ temperature measurements suggest that individuals from sun exposed microhabitats have a much narrower thermal safety margins than those from less exposed surfaces or within crevices. Microhabitat specific thermal safety margins caused by high thermal heterogeneity at small spatial scales and the lack of short term acclimatization will likely shape small scale distribution patterns of intertidal species in response to the predicted increase in the frequency and intensity of heat waves.

Thermal tolerance and climate warming sensitivity in tropical snails

Tropical ectotherms are predicted to be especially vulnerable to climate change because their thermal tolerance limits generally lie close to current maximum air temperatures. This prediction derives primarily from studies on insects and lizards and remains untested for other taxa with contrasting ecologies. We studied the HCT (heat coma temperatures) and ULT (upper lethal temperatures) of 40 species of tropical eulittoral snails (Littorinidae and Neritidae) inhabiting exposed rocky shores and shaded mangrove forests in Oceania, Africa, Asia and North America. We also estimated extremes in animal body temperature at each site using a simple heat budget model and historical (20years) air temperature and solar radiation data. Phylogenetic analyses suggest that HCT and ULT exhibit limited adaptive variation across habitats (mangroves vs. rocky shores) or geographic locations despite their contrasting thermal regimes. Instead, the elevated heat tolerance of these species (HCT=44.5±1.8°C and ULT=52.1±2.2°C) seems to reflect the extreme temperature variability of intertidal systems. Sensitivity to climate warming, which was quantified as the difference between HCT or ULT and maximum body temperature, differed greatly between snails from sunny (rocky shore; Thermal Safety Margin, TSM=-14.8±3.3°C and -6.2±4.4°C for HCT and ULT, respectively) and shaded (mangrove) habitats (TSM=5.1±3.6°C and 12.5±3.6°C). Negative TSMs in rocky shore animals suggest that mortality is likely ameliorated during extreme climatic events by behavioral thermoregulation. Given the low variability in heat tolerance across species, habitat and geographic location account for most of the variation in TSM and may adequately predict the vulnerability to climate change. These findings caution against generalizations on the impact of global warming across ectothermic taxa and highlight how the consideration of nonmodel animals, ecological transitions, and behavioral responses may alter predictions of studies that ignore these biological details.

Heat coma temperature, relative contents of saturated/unsaturated fatty acids and reproductive maturation in the oceanic sea skaters Halobates micans

This study was performed to clarify how the relative volume of saturated/unsaturated lipid and reproductive maturation relate to resistance to high temperature in the oceanic sea skaters, Halobates micans. Heat coma temperature (HCT) was measured in H. micans adults collected from a fixed sampling location (12°00′N, 135°00′E) in the western tropical Pacific Ocean. After measuring HCT, the specimen were dissected to measure the testes size and to determine the presence and number of oocytes in females. Bodies of the specimen were assessed by lipid analysis to evaluate saturated and unsaturated lipid content. A negative trend was seen between heat coma temperature and percentage of a saturated fatty acid, myristic acid (ratio of carbon number to number of double bonds=14:0) (Pearson's correlation test: r=−0.520, p=0.101). In contrast, a positive trend was detected between heat coma temperature and percentage of an unsaturated fatty acid, palmitoleic acid (16:1) (r=478, p=0.137). Young males with small testes showed lower heat coma temperatures, whereas females that showed relatively high heat coma temperatures of 36–40°C tended to have fewer mature oocytes in their ovaries than those that showed low heat coma temperatures of 30–34°C. As Halobates appears to exhibit embryonic diapause rather than adult diapause, males of H. micans may develop both testes and resistance to high temperature in the parallel as they grow. In females, a trade-off may occur between heat tolerance function and oogenesis in the oceanic sea skaters.

Effects of acclimation on the thermal tolerance of the brown planthopper Nilaparvata lugens (Stål)

Abstract The influence of acclimation on the cold and heat tolerance of Nilaparvata lugens was determined by measurements of the critical thermal minimum and maximum (CTmin and CTmax), chill and heat coma temperature (CCT and HCT) and lower and upper lethal temperature (LLT50 and ULT50). First‐instar nymphs were acclimated for 5 days at 15 °C and for 2 days at 30 °C and compared with a population maintained at 23 °C; for the adult comparisons, first‐instar nymphs were reared at 15, 23 and 30 °C until adult emergence, requiring development periods of 50–55, 30–35 and 18–20 days, respectively. The thermal tolerance limits of both age groups changed significantly with acclimation and were correlated with rearing temperature. Across the 48 separate measurements of thermal tolerance (CTmin, CCT, CTmax, HCT, LLT50 and ULT50 of nymphs and adult males and females), the temperature differential across the three indices of cold tolerance after acclimation at 15 °C compared with a population maintained at 23 °C were between 0.5–2.8 and 2.9–5.0 °C for nymphs and adults, respectively. By comparison, acclimation at 30 °C increased heat tolerance in terms of changes in the CTmax, HCT and ULT50, and the temperature differentials compared with the 23 °C population were between 1.1–3.3 °C for nymphs and 0.3–1.6 °C for adults. These data indicate that, under the acclimation regimes applied to N. lugens, increases in cold tolerance were greater than heat tolerance.

Supercooling points and heat coma temperatures in four species of oceanic sea skaters of the genus Halobates (Heteroptera: Gerridae: Halobatinae)

The only insects known to live in the open ocean are several species of sea skaters of the genus Halobates (Heteroptera: Gerridae). We have collected four species in the tropical western Pacific Ocean and measured heat coma temperature (HCT) and supercooling point (SCP) in 132 specimens. The SCPs were relatively low (ranging between −18°C and −19°C) and similar in all species. Significant inter-species differences were found in the level of HCT. The lowest HCT 32.9°C was found in Halobates micans Eschscholtz, 1822, which is distributed in thermally stable tropical waters. The highest HCT levels of 36.6°C and 36.0°C were observed in Halobates sericeus Eschscholtz and Halobates germanus White, 1883, respectively, mostly occurring in thermally more fluctuating habitats (subtropical and warm temperate waters, and coastal waters, respectively). A new species, H. sp. (under process of description) showed an intermediate HCT of 34.8°C. In addition, we found significant negative statistical correlation between HCT and SCP values at the species and individual levels. We discuss our results in the light of putative relationship between thermal physiology of sea skaters and their distribution.

Can tropical insects stand the heat? A case study with the brown planthopper Nilaparvata lugens (Stål).

The brown planthopper Nilaparvata lugens (Stål) is the most serious pest of rice across the world, especially in tropical climates. N. lugens nymphs and adults were exposed to high temperatures to determine their critical thermal maximum (CTmax), heat coma temperature (HCT) and upper lethal temperature (ULT). Thermal tolerance values differed between developmental stages: nymphs were consistently less heat tolerant than adults. The mean (± SE) CTmax of nymphs and adult females and males were 34.9±0.3, 37.0±0.2 and 37.4±0.2°C respectively, and for the HCT were 37.7±0.3, 43.5±0.4 and 42.0±0.4°C. The ULT50 values (± SE) for nymphs and adults were 41.8±0.1 and 42.5±0.1°C respectively. The results indicate that nymphs of N. lugens are currently living at temperatures close to their upper thermal limits. Climate warming in tropical regions and occasional extreme high temperature events are likely to become important limiting factors affecting the survival and distribution of N. lugens.

Effects of acclimation and latitude on the activity thresholds of the aphid Myzus persicae in Europe

AbstractActivity thresholds were measured in nine anholocyclic clones of the peach‐potato aphid Myzus persicae collected along a latitudinal cline of its European distribution from Sweden to Spain. The effects of collection origin and intra‐ and intergenerational acclimation on these thresholds were investigated. Low‐temperature (10°C) acclimation for one generation depressed the movement threshold and chill coma temperatures, with the largest reduction in movement threshold recorded for clone UK 1 (8.8–2.5°C) and in chill coma for UK 2 (4.8–2.0°C). High‐temperature (25°C) acclimation for one generation increased the heat movement threshold and heat coma temperature with the largest increase in the movement threshold (40.1–41.1°C) and heat coma (41.4–42.3°C) recorded for clone Swed 1. There was no further intergenerational acclimation over three generations. High‐temperature activity thresholds were less plastic than low‐temperature thresholds, and, consequently, thermal activity ranges were expanded following low‐temperature acclimation. No constant affect of acclimation was observed on chill coma recovery, although clonal differences were observed with Swed 1 and 3 requiring some of the longest complete recovery times. There was no relationship between latitude and activity thresholds with the exception of heat coma data where Scandinavian clones Swed 2 and 3 consistently displayed some of the lowest heat coma temperatures (e.g. 41.3°C for both clones at 20°C) and Mediterranean clones Span 1, 2 and 3 displayed some of the highest (e.g. 42.1, 41.9 and 42.5°C, respectively, at 20°C). These data suggest that clonal mixing could occur over a large scale across Europe, limiting local adaptation to areas where conditions enable long‐term persistence of populations, e.g. adaptation to higher temperatures in the Mediterranean region. It is suggested that aphid thermal tolerance could be governed more by clonal type than the latitudinal origin.

Heat coma and its relationship to ocean dynamics in the oceanic sea skaters of Halobates (Heteroptera: Gerridae) inhabiting Indian and Pacific Oceans

This study was performed to clarify how weather and current dynamics affect the resistance to temperature change in the oceanic sea skaters, Halobates. Heat coma temperature (HCT) was measured for the adults and 5th instar larvae of four Halobates species collected from a fixed sampling location (12°00′N, 135°00′E ) in western tropical Pacific Ocean and from 13 locations in the eastern area of the India Ocean ranging from 08°00′N–06°00′S and 86°00–76°00′E. Both the gap temperature for heat coma (GTHC, mean±SD: 7.83±1.86 °C, n=32) and the heat coma temperature (HCP, 35.03±1.80 °C, n=32) of individuals collected from the Pacific Ocean, during the first half (10 days) of the sampling period at the fixed sampling point, were significantly higher than those during the second half (GTHC: 5.10±2.05 °C, n=63; HCP: 34.03±2.02 °C, n=63). The reduction in heat tolerance shown in the second half of the 20 day period may have been caused by a decrease in air temperature due to rainfall that occurred around the sampling point accompanied with the arrival of Typhoon No. 6. In the study of individuals collected from the Indian Ocean, significantly higher average GTHCs of >8 °C were recorded for the adult H. micans collected at 02°00′S and 06°00′S (89°00′E) than those at 0°00–8°00′N in the eastern Indian Ocean. Dynamic mixture of water from northern and southern currents occurs at 02°00–6°00′S of the Indian Ocean and might relate to such high heat tolerance. Temperature dynamics in the ocean habitat might directly affect the temperature resistance of the oceanic sea skaters.

Hyperthermic aphids: Insights into behaviour and mortality

Although the impact of warming on winter limitation of aphid populations is reasonably well understood, the impacts of hot summers and heat wave events are less clear. In this study, we address this question through a detailed analysis of the thermal ecology of three closely related aphid species: Myzus persicae, a widespread, polyphagous temperate zone pest, Myzus polaris, an arctic aphid potentially threatened by climate warming, and, Myzus ornatus, a glasshouse pest that may benefit from warming. The upper lethal limits (ULT 50) and heat coma temperatures of the aphid species reared at both 15 and 20 °C did not differ significantly, suggesting that heat coma is a reliable indicator of fatal heat stress. Heat coma and CT max were also measured after aphids were reared at 10 and 25 °C for one and three generations. The extent of the acclimation response was not influenced by the number of generations. Acclimation increased CT max with rearing temperature for all species. The acclimation temperature also influenced heat coma; this relationship was linear for M. ornatus and M. polaris but non-linear for M. persicae (increased tolerance at 10 and 25 °C). Bacteria known generically as secondary symbionts can promote thermal tolerance of aphids, but they were not detected in the aphids studied here. Assays of optimum development temperature were also performed for each species. All data indicate that M. persicae has the greatest tolerance of high temperatures.