Divergence in aerobic scope and thermal tolerance is related to local thermal regime in two populations of introduced Nile perch (Lates niloticus)

We tested whether thermal tolerance and aerobic performance differed between two populations of Nile perch (Lates niloticus) originating from the same source population six decades after their introduction into two lakes in the Lake Victoria basin in East Africa. We used short-term acclimation of juvenile fish to a range of temperatures from ambient to +6°C, and performed critical thermal maximum (CT_max) and respirometry tests to measure upper thermal tolerance, resting and maximum metabolic rates, and aerobic scope (AS). Across acclimation temperatures, Nile perch from the cooler lake (Lake Nabugabo, Uganda) tended to have lower thermal tolerance (i.e., CT_max) and lower aerobic performance (i.e., AS) than Nile perch from the warmer waters of Lake Victoria (Bugonga region, Uganda). Effects of temperature acclimation were more pronounced in the Lake Victoria population, with the Lake Nabugabo fish showing less thermal plasticity in most metabolic traits. Our results suggest phenotypic divergence in thermal tolerance between these two introduced populations in a direction consistent with an adaptive response to local thermal regimes.     

Within‐generation variation of critical thermal limits in adult Mediterranean and Natal fruit flies Ceratitis capitata and Ceratitis rosa: thermal history affects short‐term responses to temperature

Insect thermal tolerance shows a range of responses to thermal history depending on the duration and severity of exposure. However, few studies have investigated these effects under relatively modest temperature variation or the interactions between short‐ and longer‐term exposures. In the present study, using a full‐factorial design, 1 week‐long acclimation responses of critical thermal minimum (CT_min) and critical thermal maximum (CT_max) to temperatures of 20, 25 and 30 °C are investigated, as well as their interactions with short‐term (2 h) sub‐lethal temperature exposures to these same conditions (20, 25 and 30 °C), in two fruit fly species Ceratitis capitata (Wiedemann) and Ceratitis rosa Karsch from South Africa. Flies generally improve heat tolerance with high temperature acclimation and resist low temperatures better after acclimation to cooler conditions. However, in several cases, significant interaction effects are evident for CT_max and CT_min between short‐ and long‐term temperature treatments. Furthermore, to better comprehend the flies' responses to natural microclimate conditions, the effects of variation in heating and cooling rates on CT_max and CT_min are explored. Slower heating rates result in higher CT_max, whereas slower cooling rates elicit lower CT_min, although more variation is detected in CT_min than in CT_max (approximately 1.2 versus 0.5 °C). Critical thermal limits estimated under conditions that most closely approximate natural diurnal temperature fluctuations (rate: 0.06 °C min^?1) indicate a CT_max of approximately 42 °C and a CT_min of approximately 6 °C for these species in the wild, although some variation between these species has been found previously in CT_max. In conclusion, the results suggest critical thermal limits of adult fruit flies are moderated by temperature variation at both short and long time scales and may comprise both reversible and irreversible components.     

Upper thermal tolerance plasticity in tropical amphibian species from contrasting habitats: Implications for warming impact prediction

Tropical ectothermic species are currently depicted as more vulnerable to increasing temperatures because of the proximity between their upper thermal limits and environmental temperatures. Yet, the acclimatory capacity of thermal limits has rarely been measured in tropical species, even though they are generally predicted to be smaller than in temperate species. We compared critical thermal maximum (CT_max) and warming tolerance (WT: the difference between CT_max and maximum temperature, T_max), as well as CT_max acclimatory capacity of toad species from the Atlantic forest (AF) and the Brazilian Caatinga (CAA), a semi-arid habitat with high temperatures. Acclimation temperatures represented the mean temperatures of AF and CAA habitats, making estimates of CT_max and WT more ecologically realistic. CAA species mean CT_max was higher compared to AF species in both acclimation treatments. Clutches within species, as well as between AF and CAA species, differed in CT_max plasticity and we discuss the potential biological meaning of these findings. We did not find a trade-off between absolute CT_max and CT_max plasticity, indicating that species can have both high CT_max and high CT_max plasticity. Although CT_max was highly correlated to T_max, CT_max plasticity was not related to T_max or T_max coefficients of variation. CAA species mean WT was lower than for AF species, but still very high for all species, diverging from other studies with tropical species. This might be partially related to over-estimation of vulnerability due to under-appreciation of realistic acclimation treatments in CT_max estimation. Thus, some tropical species might not be as vulnerable to warming as previously predicted if CT_max is considered as a shifting population parameter.     

Thermal acclimation in a complex life cycle: The effects of larval and adult thermal conditions on metabolic rate and heat resistance in Culex pipiens (Diptera: Culicidae)

It has now been well established that insects can respond to variation in their environment via acclimation, yet the extent of the response varies among populations and environmental characteristics. One under-investigated theme which may contribute to this variation concerns acclimation effects across the life cycle. The present study explores how acclimation in the larval stage of Culex pipiens affects thermal relations in the adult stage. Mosquitoes were reared in a full factorial design at 18 or 26 °C as larvae and adults, then critical thermal maxima (CT_max) and metabolic rate–temperature relationships (MR–T) were determined for all 4 treatments. CT_max was positively affected by both larval and adult acclimation treatments. MR–T slope was significantly affected only by adult treatment: warm acclimated adults had on average shallower slopes and higher y-intercepts than cool acclimated ones. These results demonstrate that larval acclimation effects can alter adult phenotypes in a species whose life cycle includes two drastically different environments, an aquatic and a terrestrial stage. Studying insects with complex life cycles, especially those with aquatic or subterranean larval stages, can provide valuable information on the effects of thermal variability and predictability on phenotypic plasticity.     

Thermal plasticity in the invasive south American tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

South American tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is a devastating invasive global insect pest of tomato, Solanum lycopersicum (Solanaceae). In nature, pests face multiple overlapping environmental stressors, which may significantly influence survival. To cope with rapidly changing environments, insects often employ a suite of mechanisms at both acute and chronic time-scales, thereby improving fitness at sub-optimal thermal environments. For T. absoluta, physiological responses to transient thermal variability remain under explored. Moreso, environmental effects and physiological responses may differ across insect life stages and this can have implications for population dynamics. Against this background, we investigated short and long term plastic responses to temperature of T. absoluta larvae (4th instar) and adults (24–48 h old) from field populations. We measured traits of temperature tolerance vis critical thermal limits [critical thermal minima (CT_min) and maxima (CT_max)], heat knockdown time (HKDT), chill coma recovery time (CCRT) and supercooling points (SCP). Our results showed that at the larval stage, Rapid Cold Hardening (RCH) significantly improved CT_min and HKDT but impaired SCP and CCRT. Heat hardening in larvae impaired CT_min, CCRT, SCP, CT_max but not HKDT. In adults, both heat and cold hardening generally impaired CT_min and CT_max, but had no effects on HKDT, SCP and CCRT. Low temperature acclimation significantly improved CT_min and HKDT while marginally compromising CCRT and CT_max, whereas high temperature acclimation had no significant effects on any traits except for HKDT in larvae. Similarly, low and high temperature acclimation had no effects on CT_min, SCPs and CT_max, while high temperature acclimation significantly compromised adult CCRT. Our results show that larvae are more thermally plastic than adults and can shift their thermal tolerance in short and long timescales. The larval plasticity reported here could be advantageous in new envirnments, suggesting an asymmetrical ecological role of larva relative to adults in facilitating T. absoluta invasion.     

How repeatable is CTmax within individual brook trout over short- and long-time intervals?

As stream temperatures increase due to factors such as heated runoff from impervious surfaces, deforestation, and climate change, fish species adapted to cold water streams are forced to move to more suitable habitat, acclimate or adapt to increased thermal regimes, or die. To estimate the potential for adaptation, a (within individual) repeatable metric of thermal tolerance is imperative. Critical thermal maximum (CT_max) is a dynamic test that is widely used to measure thermal tolerance across many taxa and has been used in fishes for decades, but its repeatability in most species is unknown. CT_max tests increase water temperature steadily over time until loss of equilibrium (LOE) is achieved. To determine if CT_max is a consistent metric within individual fish, we measured CT_max on the same lab-held individually-marked adult brook trout Salvelinus fontinalis at three different times (August & September 2016, September 2017). We found that CT_max is a repeatable trait (Repeatability ± S.E.: 0.48 ± 0.14). CT_max of individuals males was consistent over time, but the CT_max of females increased slightly over time. This result indicates that CT_max is a robust, repeatable estimate of thermal tolerance in a cold-water adapted fish.     

Acclimation responses to short‐term temperature treatments during early life stages causes long lasting changes in spontaneous activity of adult Drosophila melanogaster

Ecotherms adjust their physiology to environmental temperatures. Long‐term exposures to heat or cold typically induce acclimation responses that generate directional, but reversible shifts in thermal tolerance and performance. However, less is known about how short exposure in different life stages will affect the adult phenotype. In the present study, we compared the effects of long‐term temperature exposure to 15, 19 and 31 °C with that of brief (16 h) exposure periods at the same temperatures in Drosophila melanogaster eggs, larvae, pupae, or adults, respectively. The acclimation responses are evaluated using activity measurements at 11, 15, 19, 27, 31 and 33 °C and by measuring upper and lower thermal limits (CT_max and CT_min) in 5‐day‐old adult males. As expected, long‐term cold exposure reduces relative CT_min, whereas long‐term heat exposure increases relative CT_max. By contrast, we find little effect on thermal limits when using short‐term exposures at different life stages. Long‐term exposures to 31 and 15 °C both suppressed activity relative to the 19 °C control, suggesting that development at high and low temperatures may lead to reduced activity later in life. Short‐term cold exposure early in development reduces activity in the adult stage, whereas the effects of short‐term heat exposure on behaviour are dependent on life stage and test temperature. Together, our results highlight how the thermal sensitivity of the trait measured determines the ability to detect acclimation responses.     

Temporal thermal refugia and seasonal variation in upper thermal limits of two species of riverine invertebrates: the amphipod, <Emphasis Type="Italic">Paramelita nigroculus</Emphasis>, and the mayfly, <Emphasis Type="Italic">Lestagella penicillata</Emphasis>

Understanding the response of aquatic organisms to elevated water temperatures offers insight into the ecological consequences of climate change on riverine species. Upper thermal limits were determined for two riverine invertebrates, the amphipod Paramelita nigroculus (Paramelitidae) and the mayfly Lestagella penicillata (Teloganodidae), in two rivers in the south-western Cape, South Africa. Limits were estimated using the critical thermal method (reflected as the critical thermal maxima—CT_max) and the incipient lethal temperature method (reflected as the incipient lethal upper limit—ILUT). Thermal signatures of these rivers were characterized using hourly water temperatures. CT_max for seasonally acclimatized and laboratory-acclimated P. nigroculus varied significantly amongst months and acclimation temperature. CT_max for seasonally acclimatized L. penicillata varied significantly amongst months, but not with acclimation temperature. 96-h ILUT values for seasonally acclimatized individuals varied significantly amongst months for both species. CT_max values, 96-h ILUT and Maximum Weekly Allowable Temperature thresholds were lower for P. nigroculus compared to L. penicillata. Seven-day moving averages of daily mean and maximum water temperatures were significantly correlated with upper thermal limits for seasonally acclimatized L. penicillata but not P. nigroculus. The proportion of time within a 24-h period that chronic thermal stress thresholds are not exceeded provides a measure of monthly or seasonal chronic thermal stress, and reflects the quantity of temporal thermal refugia for vulnerable organisms. Further testing of these relationships for other species, rivers and regions is recommended, to evaluate the potential for stream temperature averaging statistics to serve as proxies for biological thresholds.     

Effects of temperature acclimation on cardiorespiratory performance of the Antarctic notothenioid Trematomus bernacchii

Notothenioid fishes of the Southern Ocean have evolved under cold and stable temperatures for millions of years. Due to rising temperatures in the Southern Ocean, investigating thermal limits and the capacities for inducing a temperature acclimation response in notothenioids has become of increasing interest. Here, we investigated effects of temperature acclimation on cardiorespiratory responses and cardiac and skeletal muscle energy metabolism in a benthic Antarctic notothenioid, Trematomus bernacchii. We acclimated specimens to ?1, 2 and 4.5 °C for 14 days and quantified heart rates and ventilation rates during an acute increase in temperature. Ventilation rates showed an effect of acclimation both at initial steady-state acclimation conditions and during an acute temperature increase, suggesting a partial thermal compensatory response. However, acclimation did not affect heart rates at steady-state acclimation conditions and the temperatures at which onset of cardiac arrhythmia occurred, suggesting lack of inducible thermal tolerance in cardiac performance. Citrate synthase (CS), lactate dehydrogenase (LDH) and 3-hydroxyacyl dehydrogenase activities in skeletal muscle tissues suggested acclimation-induced shifts in metabolic fuel preferences, and a marked increase in LDH activity with acclimation to 4.5 °C showed an increase in anaerobic metabolism. In heart tissue, CS and LDH activities decreased with acclimation to 4.5 °C, suggesting reduced cardiac ATP production. Overall, the data suggest a partial acclimatory response to temperature by T. bernacchii and support the hypothesis that reduced cardiac acclimatory capacity may play a role in limiting the thermal plasticity of T. bernacchii.     

Hot or not? Comparative behavioral thermoregulation,critical temperature regimes,and thermal tolerances of the invasive lionfish <Emphasis Type="Italic">Pterois</Emphasis> sp. versus native western North Atlantic reef fishes

Temperature influences the geographic range, physiology, and behavior of many ectothermic species, including the invasive lionfish Pterois sp. Thermal parameters were experimentally determined for wild-caught lionfish at different acclimation temperatures (13, 20, 25 and 32 °C). Preferences and avoidance were evaluated using a videographic shuttlebox system, while critical thermal methodology evaluated tolerance. The lionfish thermal niche was compared experimentally to two co-occurring reef fishes (graysby Cephalopholis cruentata and schoolmaster Lutjanus apodus) also acclimated to 25 °C. The physiologically optimal temperature for lionfish is likely 28.7 ± 1 °C. Lionfish behavioral thermoregulation was generally linked to acclimation history; tolerance and avoidance increased significantly at higher acclimation temperatures, but final preference did not. The tolerance polygon of lionfish shows a strong correlation between thermal limits and acclimation temperature, with the highest CT_max at 39.5 °C and the lowest CT_min at 9.5 °C. The tolerance range of invasive lionfish (24.61 °C) is narrower than those of native graysby (25.25 °C) and schoolmaster (26.87 °C), mostly because of lower thermal maxima in the former. Results show that lionfish display “acquired” thermal tolerance at higher and lower acclimation temperatures, but are no more eurythermal than other tropical fishes. Collectively, these results suggest that while lionfish range expansion in the western Atlantic is likely over the next century from rising winter sea temperatures due to climate change, the magnitude of poleward radiation of this invasive species is limited and will likely be equivalent to native tropical and subtropical fishes with similar thermal minima.     

Critical thermal maximum of seven estuarine fishes

Critical thermal maximum (CTM) and loss of righting response (LRR) were determined in seven estuarine fishes. The critical thermal maxima (CTM) ranged from 39.5°C to 44.5°C for fishes acclimated to 28°C. Lates calcarifer and Liza dussumeri had the highest CTM (44.5°C) and Siganus javus had the lowest CTM (39.5°C). The rate of change of CTM due to thermal acclimation was determined for Etroplus suratensis and Therapon jarbua. The CTM for E.suratensis increased from 39.75°C to 43.5°C on a 15°C increase in acclimation temperature and the CTM of T. jarbua shifted from 40.75°C to 43.15°C on a 15°C increase in acclimation. The acclimation response ratio (ARR) as a result of increasing the acclimation temperature was about 0.25 in E. suratensis and 0.2 in T. jarbua.     

CTmax in brook trout (Salvelinus fontinalis) embryos shows an acclimation response to developmental temperatures but is more variable than in later life stages

Critical thermal maximum (CT_max) is widely used to measure upper thermal tolerance in fish but is rarely examined in embryos. Upper thermal limits generally depend on an individual's thermal history, which molds plasticity. We examined how thermal acclimation affects thermal tolerance of brook trout (Salvelinus fontinalis) embryos using a novel method to assess CT_max in embryos incubated under three thermal regimes. Warm acclimation was associated with an increase in embryonic upper thermal tolerance. However, CT_max variability was markedly higher than is typical for juvenile or adult salmonids.     

Intraspecific geographic variation in thermal limits and acclimatory capacity in a wide distributed endemic frog

Intraspecific variation in physiological traits and the standard metabolic rate (SMR) is common in widely distributed ectotherms since populations at contrasting latitudes experiences different thermal conditions. The climatic variability hypothesis (CVH) states that populations at higher latitudes presents higher acclimation capacity than those at lower latitudes, given the wider range of climatic variability they experience. The endemic four-eyed frog, Pleurodema thaul is widely distributed in Chile. We examined the variation in maximum and minimum critical temperatures (CT_max and CT_min), preferred temperature (T_Pref), SMR and their acclimatory capacity in two populations from the northern and center of its distribution. All the traits are higher in the warmer population. The capacity for acclimation varies between traits and, with the exception of CT_max and T_Pref, it is similar between populations. This pattern could be explained by the higher daily thermal variability in desert environments, that increases plasticity to the levels found in the high latitude population. However, we found low acclimatory capacity in all physiological traits, of only about 3% for CT_min, 10% for CT_max and T_Pref, and 1% for SMR. Thus, despite the fact that Pleurodema thaul possess some ability to adjust thermal tolerances in response to changing thermal conditions, this acclimatory capacity seems to be unable to prevent substantial buffering when body temperatures rise. The low acclimatory capacity found for P. thaul suggests that this species use behavioral rather than physiological adjustments to compensate for environmental variation, by exploiting available micro-environments with more stable thermal conditions.     

Superior basal and plastic thermal responses to environmental heterogeneity in invasive exotic stemborer Chilo partellus Swinhoe over indigenous Busseola fusca (Fuller) and Sesamia calamistis Hampson

Lepidopteran stemborers are the most destructive insect pests of cereal crops in sub‐Saharan Africa. In nature, these insects are often exposed to multiple environmental stressors, resulting in potent impact on their thermal tolerance. Such environmental stressors may influence their activity, survival, abundance and biogeography. In the present study, we investigate the effects of acclimation to temperature, starvation and desiccation on thermal tolerance, measured as critical thermal limits [critical thermal minima (CT_min) and maxima (CT_max)] on laboratory‐reared economic pest species Chilo partellus Swinhoe (Lepidoptera: Crambidae), Busseola fusca (Fuller) and Sesamia calamistis Hampson (Lepidoptera: Noctuidae) using established protocols. Low temperature acclimation results in improved CT_min for B. fusca and C. partellus, whereas high temperature acclimation enhances the same trait for B. fusca and S. calamistis. Similarly, high temperature and starvation pretreatment improve CT_max for C. partellus relative to S. calamistis and B. fusca. In addition, starvation and desiccation pretreatments improve CT_min for all stemborer species. Furthermore, rapid cold‐hardening (RCH) enhancs CT_min for B. fusca and C. partellus, whereas rapid heat‐hardening (RHH) improves the same trait for C. partellus. However, RCH and RHH impair CT_max for all stemborer species. These findings show differential thermal tolerances after exposure to heterogeneous environmental stress habitats. Chilo partellus, of exotic origin, shows a higher magnitude of basal thermal tolerance plasticity relative to the indigenous African species S. calamistis and B. fusca. This indicates that C. partellus may have a fitness and survival advantage under climate‐induced heterogeneous environments, and also have a greater chance for geographical range expansion and invasion success compared with the indigenous B. fusca and S. calamistis.     

Hydric effects on thermal tolerances influence climate vulnerability in a high-latitude beetle

Species' thermal tolerances are used to estimate climate vulnerability, but few studies consider the role of the hydric environment in shaping thermal tolerances. As environments become hotter and drier, organisms often respond by limiting water loss to lower the risk of desiccation; however, reducing water loss may produce trade-offs that lower thermal tolerances if respiration becomes inhibited. Here, we measured the sensitivity of water loss rate and critical thermal maximum (CT_max) to precipitation in nature and laboratory experiments that exposed click beetles (Coleoptera: Elateridae) to acute- and long-term humidity treatments. We also took advantage of their unique clicking behavior to characterize subcritical thermal tolerances. We found higher water loss rates in the dry acclimation treatment compared to the humid, and water loss rates were 3.2-fold higher for individuals that had experienced a recent precipitation event compared to individuals that had not. Acute humidity treatments did not affect CT_max, but precipitation indirectly affected CT_max through its effect on water loss rates. Contrary to our prediction, we found that CT_max was negatively associated with water loss rate, such that individuals with high water loss rate exhibited a lower CT_max. We then incorporated the observed variation of CT_max into a mechanistic niche model that coupled leaf and click beetle temperatures to predict climate vulnerability. The simulations indicated that indices of climate vulnerability can be sensitive to the effects of water loss physiology on thermal tolerances; moreover, exposure to temperatures above subcritical thermal thresholds is expected to increase by as much as 3.3-fold under future warming scenarios. The correlation between water loss rate and CT_max identifies the need to study thermal tolerances from a “whole-organism” perspective that considers relationships between physiological traits, and the population-level variation in CT_max driven by water loss rate complicates using this metric as a straightforward proxy of climate vulnerability.     

Standardized ethograms and a device for assessing amphibian thermal responses in a warming world

Most predictions of how populations and species of ectotherms will respond to global warming are based on estimates of the temperature at which organisms lose motor control (i.e., CT_max - the Critical Thermal Maximum). Here, we describe a non-lethal protocol and ethograms to estimate the relative tolerance of amphibians to increasing temperatures. These methods—suitable for field or laboratory conditions—are replicable, inexpensive and applicable to both post-metamorphic stages and organisms with direct development. We illustrate the use of this standardized protocol for four amphibians from a tropical cloud forest in Veracruz, Mexico with contrasting life histories: a lungless salamander (Aquiloeurycea cafetalera: Plethodontidae), a leaf-litter frog (Craugastor rhodopis: Craugastoridae), a semiaquatic frog (Lithobates berlandieri: Ranidae), and a tree frog (Rheohyla miotympanum: Hylidae). We identified four behavioral responses preceding CT_max for all amphibians included in this study: 1) Optimal Activity Range, 2) Supra-optimal Activity Range, 3) Heat Stress Range, and 4) Involuntary Movements Range. Additionally, we identified a fifth parameter associated with resilience to heat shock: 5) Recovery Stage after reaching CT_max. We conclude that the behavioral responses preceding the Critical Thermal Maximum are as informative as CT_max. Using behavioral responses to estimate thermal tolerance has the additional advantage of reducing the risk of injury or death of amphibians during physiological experiments.     

Thermoregulatory behaviour explains countergradient variation in the upper thermal limit of a rainforest skink

The vulnerability of a terrestrial ectotherm to high environmental temperatures depends on the animal's thermal physiology and thermoregulatory behaviour. These variables – environment, physiology, and behaviour – interact with each other, complicating assessment of species vulnerability to global warming. We previously uncovered a counterintuitive pattern in rainforest sunskinks Lampropholis coggeri: a negative relationship between their critical thermal maximum (CT_max) and the temperature of their environment. Could this result be explained by a three‐way interaction between environment, physiology, and behaviour? Here we find that sunskink thermal preference is correlated positively with CT_max, but, importantly, skinks from hotter environments prefer lower temperatures than conspecifics from cooler environments. In an acclimation experiment, we find that CT_max is plastic and shifts in alignment with acclimation temperature. We also found heritable variation in this trait in a common garden study, but this variation was small relative to the plastic shifts observed in CT_max. Thus, our previous observation of a negative correlation between field CT_max and temperature is explained, at least in part, by the lizard's thermoregulatory behaviour: lizards from hot environments preferentially choose cool microenvironments, and their physiology acclimates to these cooler experienced temperatures. Our results suggest that behavioural adjustments to the environment can produce countergradient variation in physiological traits. More broadly, our work underscores the importance of interactions between environment, behaviour, and physiology in ectotherms. Understanding these interactions will be crucial in assessing vulnerability to climate change.     

Sub-lethal temperature thresholds indicate acclimation and physiological limits in brook trout Salvelinus fontinalis

The upper thermal tolerance of brook trout Salvelinus fontinalis was estimated using critical thermal maxima (CT_max) experiments on fish acclimated to temperatures that span the species' thermal range (5–25°C). The CT_max increased with acclimation temperature but plateaued in fish acclimated to 20, 23 and 25°C. Plasma lactate was highest, and the hepato-somatic index (I_H) was lowest at 23 and 25°C, which suggests additional metabolic costs at those acclimation temperatures. The results suggest that there is a sub-lethal threshold between 20 and 23°C, beyond which the fish experience reduced physiological performance.     

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 (ULT₅₀) 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.     

Kin recognition in embryonic damselfishes

Predator‐induced mortality rates are highest in early life stages; therefore, early recognition of threats can greatly increase survival chances. Some species of coral reef fishes have been frequently found to recruit back to their natal reefs; in this instance, there is a high chance of juveniles encountering their siblings, among other kin, after hatching. Kin recognition plays an important ecological role in that it allows individuals to protect genetically similar relatives, and hence increase their inclusive fitness. By observing changes in heart rates, we demonstrated that embryos of two damselfish species, Acanthochromis polyacanthus and Amphiprion melanopus, not only possess recognition of kin and damage‐released alarm odours, but also react to them in a graded manner. Such refined olfactory capabilities in embryonic stage organisms (seven and eleven days after fertilisation) suggest identification of threats may provide survival advantages post‐hatching, such as the informed choice of low risk habitats at settlement. To our knowledge this is the first time that kin recognition has been identified in embryos of any species.