Further studies on acclimatization to low temperatures in the grain weevils Sitophilus oryzae (L.) and Sitophilus granarius (L.)

The effect of thermal acclimatization on the resting metabolism of adult grain weevils was examined by closely restraining the weevils during respirometry. Sitophilus oryzae (L.) acclimatized to 15°C consumed less oxygen over 11–23°C than 27°C-acclimatized weevils but like amounts over 25–35°C. Similar results were observed with S. granarius (L.). Respiration R–T curves of unrestrained S. oryzae and S. granarius showed no evidence of rotation at temperatures close to their chill-coma thresholds but warm- and cold-acclimatized weevils consumed similar amounts of oxygen when both categories of weevils were in chillcoma. Acclimatizing S. oryzae from 27 to 13.5°C through four, weekly 4.5°C step-transfers lowered the median chill-coma thresholds of the weevils from 8.9 to 6.2°C, increased their life span at 9°C, an unfavourable temperature for this species, from 2 to 8 weeks and lowered their oxygen uptake at 9°C by 19%.     

A comparison of the capacity for increase at a low temperature of foreign and Australian populations of Sitophilus oryzae (L.) and S. granarius (L.)

The capacity for increase (r_c) of three populations of S. oryzae and three populations of S. granarius from Great Britain and Canada was determined over 15 and 24 weeks respectively at 15°C in wheat of 14% moisture content. The fertility of these populations at 27°C, their body weight and chill-coma threshold was also measured. With both S. oryzae and S. granarius, values of r_c for the foreign populations fell within the range previously observed when several Australian populations were reared under the same conditions. The cohort generation times (T_c) of the foreign S. oryzae populations were significantly shorter than those of the Australian populations because of the shorter immature development periods (D) of the former. Two of the foreign S. granarius populations had lower values for D than all but one of their Australian counterparts but their values of T_c were within the range previously observed for Australian weevils. When the Australian and foreign populations were considered together, the value of r_c was more strongly correlated with fertility at 27°, an optimal temperature, than with body weight in both S. oryzae and S. granarius. With S. oryzae, r_c was correlated with the chill-coma threshold of cold-acclimated weevils only. There were no correlations between r_c and chill-coma thresholds in S. granarius. It was concluded that the observed differences in r_c were related to differences in the vigour of the populations rather than to physiological differences in cold-tolerance. The likelihood of grain weevils becoming cold-tolerant as a result of grain aeration is discussed and the practical significance of differences in r_c considered.     

The capacity for increase at a low temperature of some Australian populations of the granary weevil,Sitophilus granarius (L.)

The capacity for increase (r_c) of one laboratory and seven field populations of young adult S. granarius from different sites in Australia was determined over thirty-two weeks at 15°C in wheat of 14% moisture content. The mean value of r_c was 0.0704 ±0.0016 and the populations differed significantly with respect to this parameter. Variation in the net reproductive rate (R₀), which averaged 25.4± 1.29, had a greater effect on the value of I_c than did variation in the cohort generation time (T_c), which averaged 45.7±0.37 weeks. The populations did not differ significantly in terms of adult survivorship and 94% of females were still alive at thirty-two weeks. The maximum rate of oviposition, about ten eggs per female per week, was achieved in the eighteen-twenty week age-interval. About 41% of the immature stages survived to adulthood. Estimates of r_c over a twenty-four week period were only slightly lower than those over thirty-two weeks. The capacity for increase at 15°C of a given population was shown to be correlated with its fertility at 29°C, an optimal temperature, and with its body weight rather than with its cold tolerance, as indicated by its chill-coma temperature, or its previous temperature-history. The temperature experienced by the immature stages had a marked influence on r_c in that weevils reared at 15°C and 27°C had respective values of 0.0654 and 0.0786 when subsequently held at 15°C. The differences in the survivorship and fertility of S. granarius and S. oryzae (L.) when both species were reared at 15°C are considered.     

The capacity for increase at a low temperature of several Australian populations of Sitophilus oryzae (L.)

The capacity for increase (I_c) of one laboratory and seven field populations of young adult S. oryzae from different sites in Australia was determined over a thirty-week period at 15°C, a supposedly marginal temperature, in wheat of 14% moisture content. The average value of I_c was 0.0838 ± 0.0017 and the populations comprised three significantly different groups. Variations in the net rate of increase per generation (R₀) which averaged 34.7±1.71, had a major effect on the value of r_c whereas variation in the cohort generation time (T_c), which averaged 41.6±.23 weeks had only a minor effect. The survivorship of adults of the populations did not differ significantly and 93% of females were alive after thirty weeks. Estimates of r_c based on a fifteen-week period and on an amended value of Tc differed little from those over thirty weeks. The capacity for increase at 15°C of a given population was found to be correlated with its fertility at 27°C and with its body-weight rather than with its cold-tolerance, as evidenced by chill-coma temperature, or with its previous temperature-history. The temperature experienced by the immature stages of weevils had a profound effect on r_c in that weevils reared at 15 and 27°C had respective values of 0.0350 and 0.0707 when subsequently cultured at 15°C. Because all observed values of r_c were higher than expected, possible errors in method were considered. An alternative estimate of R₀ agreed closely with that observed and indicated that only 17% of the immature stages survived at 15°C. Metabolic heating due to the higher than expected population density shortened the duration of the immature stages by 7% but did not affect their survival.     

Thermal response of juvenile Hawaiian mullet Mugil cephalus (L.) to acclimation time and fluctuating low temperatures*

Rates of acclimation and the response to fluctuating low temperatures of juvenile striped mullet Mugil cephalus (L.) have been described in terms of changes in heat resistance over a period of time. Fish changed from 25.5 to 27 or 29° C were acclimated within seven days. Acclimation to 23 or 15° C required a maximum of 11 days. Thermal responses to fluctuating low temperatures were lower than responses to constant temperature levels. Cyclic variations in heat resistance were present in all experimental and control tests.     

Comparison of the cold hardiness of two larval Lepidoptera (Noctuidae)

Abstract Diapause larvae of the European corn borer (Ostrinia nubilalis (Hubn.)) and the related Mediterranean noctuid Sesamia cretica Led. possess sufficient supercooling ability to avoid freezing over their normal environmental temperature ranges. In progressive chilling experiments (10 days acclimation at each 5° step in the temperature range from 15 to ?5°C), mean supercooling points (measured at a cooling rate of 0.1°C min^?1) were lowered from ?20.4°C at 15°C to ?24.0°C at 5°C (lower lethal temperatures: c.?28°C) in O.nubilalis, compared with ?15.0 to ?17.2°C (lower lethal temperatures: ?15 to ?17°C respectively) in S.cretica. Concentrations of glycerol and trehalose determined by gas chromatography of whole body extracts were consistently higher in the former than in the latter species at both 15 and 5°C, and may be responsible for the deeper supercooling in O.nubilalis larvae. Acclimation to 5°C increased glycerol levels in O. nubilalis extracts compared with 15°C, and this was enhanced in larvae exposed for a further 10 days at each of 0 and ?5°C (glycerol being 438μmol ml^?1 body water). Haemolymph glycerol concentrations showed a similar pattern to whole body extracts in this species. Fat body glycogen was reduced during low temperature acclimation in both species. Body water contents did not change with acclimation in O.nubilalis, whilst S.cretica, containing significantly more water, lost c.7% during acclimation from 15 to 5°C. Haemolymph osmolalities increased during acclimation, especially in Ostrinia larvae, probably as a result of the accumulation of cryoprotectants. The majority of O.nubilalis larvae survived freezing under the conditions of the cooling experiments, whilst larvae of S.cretica did not, thereby confirming an element of freezing tolerance in the former.     

Lack of metabolic temperature compensation in the intertidal gastropods,Littorina saxatilis (Olivi) and L. obtusata (L.)

Two intertidal snails, Littorina saxatilis (Olivi, 1972) (upper eulittoral fringe/maritime zone) and Littorina obtusata (Linnaeus, 1758) (lower eulittoral) were collected from a boulder shore on Nobska Point, Cape Cod, Massachusetts, in July and acclimated for 15–20 days at 4 ° or 21 °C. Oxygen consumption rate (Vo₂) was determined for 11–15 subsamples of individuals at 4 °, 11 ° and 21 °C with silver/platinum oxygen electrodes. Multiple factor analysis of variance (MFANOVA) of lo₁₀ transformed values of whole animal Vo₂ with log₁₀ dry tissue weight (DTW) as a covariant revealed that increased test temperature induced a significant increase in Vo₂ in both species (P<0.00001). In contrast, MFANOVA revealed that temperature acclimation did not affect Vo₂ in either L. saxatilis (P= 0.35) or L. obtusata (P= 0.095). Thus, neither species displayed a capacity for the typical metabolic temperature compensation marked by an increase in Vo₂ at any one test temperature in individuals acclimated to a lower temperature that is characteristic of most ectothermic animals. Lack of capacity for metabolic temperature acclimation has also been reported in other littorinid snail species, and may be characteristic of the group as a whole. Lack of capacity for respiratory temperature acclimation in these two species and other littorinids may reflect the extensive semi-diurnal temperature variation that they are exposed to in their eulittoral and eulittoral fringe/maritime zone habitats. In these habitats, any metabolic benefits derived from longer-term temperature compensation of metabolic rates are negated by extreme daily temperature fluctuations. Instead, littorinid species appear to have evolved mechanisms for immediate metabolic regulation which, in L. saxatilis and L. obtusata and other littorinids, appear to centre on a unique ability for near instantaneous suppression of metabolic rate and entrance into short-term metabolic diapause at temperatures above 20–35 °C, making typical seasonal respiratory compensation mechanisms characteristic of most ectotherms of little adaptive value to littorinid species.     

General introduction to the lists of threatened biotopes,flora and fauna of the trilateral Wadden Sea Area (red data book)

The effect of the acclimation temperature on the temperature tolerance ofPorphyra leucosticta, and on the temperature requirements for growth and survival ofEnteromorpha linza was determined under laboratory conditions. Thalli ofP. leucosticta (blade or Conchocelis phases), acclimated to twenty-five degrees, survived up to 30°C, i.e. 2°C more than those acclimated to 15°C which survived up to 28°C. Lower temperature tolerance of bothPorphyra phases that were acclimated to 15°C was −1°C after an 8-week exposure time at the experimental temperatures. The upper temperature tolerance ofE. linza also increased by 2°C, i.e. from 31 to 33°C, when it was acclimated to 30°C instead of 15°C. The lower temperature tolerance increased from 1 to −1°C, when it was acclimated to 5°C instead of 15°C.E. linza thalli acclimated for 4 weeks to 5 or 10°C reached their maximum growth at 15°C, i.e. at a 5°C lower temperature than those acclimated to 15 or 30°C. These thalli achieved higher growth rates in percent of maximal growth at low temperatures than those acclimated to 15 or 30°C. Thalli acclimated for 1 week to 5°C reached their maximum growth rate at 20°C and achieved growth rates at low temperatures similar to those recorded for thalli acclimated to 15°C. Thalli ofE. linza acclimated for 4 weeks to 5°C lost this acclimation after being post-cultivated for the same period at 15°C. That was not the case with thalli acclimated for 8 weeks to 5°C and post-acclimated for 4 weeks to 15°C. These thalli displayed similar growth patterns at 10–25°C, while a decline of growth rate was observed at 5 or 30°C. The significance of the acclimation potential ofE. linza with regard to its seasonality in the Gulf of Thessaloniki, and its distribution in the N Atlantic, is also discussed.     

Time-course for attainment and reversal of acclimation to constant temperature in two Ceratitis species

Acclimation in the thermal tolerance range of insects occurs when they are exposed to novel temperatures in the laboratory. In contrast to the large number of studies that have tested for the ability of insects to acclimate, relatively few have sought to determine the time-course for attainment and reversal of thermal acclimation. In this study the time required for the Mediterranean fruit fly, Ceratitis capitata Wiedemann, and the Natal fruit fly, Ceratitis rosa Karsch, to acclimate to a range of constant temperatures was tested by determining the chill-coma recovery time and heat knock-down time of flies that had been exposed to novel benign temperatures for different durations. The time required for reversal of acclimation for both Ceratitis species was also determined after flies had been returned to the control temperature. Acclimation to 31 °C for only one day significantly improved the heat knock-down time of C. capitata, but also led to slower recovery from chill-coma. Heat knock-down time indicated that acclimation was achieved after only one day in C. rosa, but it took three days for C. rosa to exhibit a significant acclimation response to a novel temperature of 33 °C when measured using chill-coma recovery time. Reversal of acclimation after return to initial temperature conditions was achieved after only one day in both C. capitata and C. rosa. Adult C. capitata held at 31.5 °C initially exhibited improved heat knock-down times but after 9 days the heat knock-down time of these flies had declined to levels not significantly different from that of control flies held at the baseline temperature of 24 °C. In both Ceratitis species, heat knock-down time declined with age whereas chill-coma recovery time increased with age, indicating an increased susceptibility to high and low temperatures, respectively.     

Oxygen consumption by the bivalve Donax vittatus (da Costa)

The acute oxygen consumption of Donax vittatus (da Costa) freshly collected at different times from a beach at Barrassie, Ayrshire, Scotland, has been measured at different temperatures. The logarithmic relationship between oxygen consumption and body weight showed a significant difference on only one occasion, and a common regression coefficient (b) of 0.865 could be used for regressions of oxygen consumption on weight. Over the temperature range 2.9–20 °C oxygen consumption rose with temperature. There was a linear decline of Q₁₀ with temperature in the range 2.9 –20 °C. Differences in values of the constant (a) in the regression equation suggest that there is some acclimation to temperature, resulting in rotation of the rate/temperature curve counterclockwise for warm-acclimated animals, and a reduction of Q₁₀ in cold-acclimated animals. The differences in oxygen consumption which result are small and appear to have little practical significance. High levels of metabolically-inactive materials such as stored glycogen reserves lead to a reduction in the weight-specific oxygen consumption. Spawning animals show an increased oxygen consumption.     

Effects of ambient temperature and of temperature acclimation on nitrogen excretion and differential catabolism of protein and nonprotein resources in the intertidal snails,Littorina saxatilis (Olivi) and L. obtusata (L.)

Nitrogenous excretion in two snails, Littorina saxatilis (high intertidal) and L. obtusata (low intertidal) was studied in relation to temperature acclimation (at 4° and 21°C), including total N excretion rates, the fraction of urea in N excretion, corresponding O:N ratios and the partitioning of deaminated protein between catabolic and anabolic processes at 4°, 11° and 21°C. Aggregate N excretion rates in both species showed no significant compensatory adjustments following acclimation. Total weight specific N excretion rates at 21°C were higher in standard 3 mg L. saxatilis (739 ng N mg⁻¹ h⁻¹) than standard 5 mg L. obtusata (257 ng N mg⁻¹ h⁻¹) for snails acclimated to 21°C. Comparisons of Q₁₀ values of total weight specific N excretion to Q₁₀ values for weight specific oxygen consumption ({xxV}O₂) between 4° to 11 °C and 11° to 21°C indicated that, while total rates of catabolic metabolism ({xxV}O₂) and protein deamination in L. obtusata were essentially parallel, the relationship between N excretion and {xxV}O₂ in L. saxatilis revealed the partitioning of a larger share of deaminated protein carbon into anabolism at 4° and 21°C than at 11°C. Urea N accounted for a larger share of aggregate N excreted in L. saxatilis than in L. obtusata, but in both species urea N is a greater proportion of total N excreted when acclimated at 4°C (urea N: ammonia N ratio range: 1 to 2.15) than in snails acclimated to 21°C (urea N: ammonia N ratio range: 0.46 to 1.39). Molar O:N ratios indicate that the proportion of metabolism supported by protein catabolism is greater in L. saxatilis (O:N range: 2.5–8.4) than in L. obtusata (O:N range: 7.3–13.0). In both species, regardless of acclimation temperature, the O:N ratios are generally lowest (high protein catabolism) at 4°C and highest at 21°C.     

Impact of different acclimation temperatures and duration on the chill coma temperature and oxygen consumption in the tenebrionid beetle Alphitobius diaperinus

When the ambient temperature is lowered to an insect's lower thermal limit, the insect enters into chill coma. Chill coma temperature and chill coma recovery can vary within species as a result of thermal acclimation, although the physiological basis of the onset of chill coma remains poorly understood. The present study investigates how the temperature of acclimation (0, 5, 10, 15 and 20 °C for 2 or 7 days) affects chill coma temperature and oxygen consumption in adult Alphitobius diaperinus Panzer (Coleoptera: Tenebrionidae). It is hypothesized that the threshold decline in metabolic rate corresponds to the entry into chill coma. Oxygen consumption (as a proxy of metabolism) is measured across the chill coma temperature threshold, and a strong decline in oxygen consumption is expected at entry into chill coma. The acclimation decreases the chill coma temperature significantly from 6.6 ± 1.1 °C in control insects to 3.1 ± 0.7 °C in those acclimated to 10 °C. The change in metabolic rate (Q₁₀) after acclimation to temperatures ranging from 10 to 20 °C is 3.7. Despite acclimation, the metabolic rate of A. diaperinus conforms to Arrhenius kinetics, suggesting that the response of this beetle does not show metabolic compensation. The data suggest the existence of a threshold decline in metabolic rate during cooling that coincides with the temperature at which an insect goes into chill coma.     

Thermal tolerance and acclimation response of larvae of the sub-Antarctic beetle Hydromedion sparsutum (Coleoptera: Perimylopidae)

Hydromedion sparsutum is a locally abundant herbivorous beetle on the sub-Antarctic island of South Georgia, often living in close association with the tussock grass Parodiochloa flabellata. Over a 4-day period in mid-summer when the air temperature varied from 0 to 20°C, the temperature in the leaf litter 5–10 cm deep at the base of tussock plants (the microhabitat of H. sparsutum) was consistently within the range of 5–7.5°C. Experiments were carried out to assess the ability of H. sparsutum larvae collected from this thermally stable environment to acclimate when maintained at lower (0°C) and higher (15°C) temperatures. The mean supercooling points (freezing temperature) of larvae collected in January and acclimated at 0°C for 3 and 6 weeks and 15°C for 3 weeks were all within the range of −2.6 to −4.6°C. Larvae in all treatment groups were freeze tolerant. Acclimation at 0°C significantly increased survival in a 15-min exposure at −8°C (from 27 to 96%) and −10°C (from 0 to 63%) compared with the field-fresh and 15°C-treated larvae. Similarly, survival of 0°C-acclimated larvae in a 72-h exposure at −6°C increased from 20 to 83%. Extending the acclimation period at 0°C to 6 weeks did not produce any further increase in cold tolerance. The concentrations of glucose and trehalose in larval body fluids increased significantly with low temperature acclimation. Larvae maintained at 15°C for 3 weeks (none survived for 6 weeks) were less able to survive 1-h exposures between 30 and 35°C than the 0°C-treated samples. Whilst vegetation and snow cover are an effective buffer against low winter temperatures in many polar insects, the inability of H. sparsutum larvae to acclimate or survive at 15°C suggests that protection against high summer temperatures is equally important for this species. Accepted: 2 August 1999     

The effect of acute warming and thermal acclimation on maximum heart rate of the common killifish Fundulus heteroclitus

Common killifish Fundulus heteroclitus were acclimated to ecologically relevant temperatures (5, 15 and 33°C) and their maximum heart rate (f_Hmax) was measured at each acclimation temperature during an acute warming protocol. Acclimation to 33°C increased peak f_Hmax by up to 32% and allowed the heart to beat rhythmically at a temperature 10°C higher when compared with acclimation to 5°C. Independent of acclimation temperature, peak f_Hmax occurred about 3°C cooler than the temperature that first produced cardiac arrhythmias. Thus, when compared with previously published values for the critical thermal maximum of F. heteroclitus, the temperature for peak f_Hmax was cooler and the temperature that first produced cardiac arrhythmias was similar to these critical thermal maxima. The considerable thermal plasticity of f_Hmax demonstrated in the present study is entirely consistent with eurythermal ecology of killifish, as shown previously for another eurythermal fish Gillichthys mirabilis.     

EVOLUTIONARY ADAPTATION TO TEMPERATURE. VI. PHENOTYPIC ACCLIMATION AND ITS EVOLUTION IN ESCHERICHIA COLI

Acclimation refers to reversible, nongenetic changes in phenotype that are induced by specific environmental conditions. Acclimation is generally assumed to improve function in the environment that induces it (the beneficial acclimation hypothesis). In this study, we experimentally tested this assumption by measuring relative fitness of the bacterium Escherichia coli acclimated to different thermal environments. The beneficial acclimation hypothesis predicts that bacteria acclimated to the temperature of competition should have greater fitness than do bacteria acclimated to any other temperature. The benefit predicted by the hypothesis was found in only seven of 12 comparisons; in the other comparisons, either no statistically demonstrable benefit was observed or a detrimental effect of acclimation was demonstrated. For example, in a lineage evolutionarily adapted to 37°C, bacteria acclimated to 37°C have a higher fitness at 32°C than do bacteria acclimated to 32°C, a result exactly contrary to prediction; acclimation to 27°C or 40°C prior to competition at those temperatures confers no benefit over 37°C acclimated forms. Consequently, the beneficial acclimation hypothesis must be rejected as a general prediction of the inevitable result of phenotypic adjustments associated with new environments. However, the hypothesis is supported in many instances when the acclimation and competition temperatures coincide with the historical temperature at which the bacterial populations have evolved. For example, when the evolutionary temperature of the population was 37°C, bacteria acclimated to 37°C had superior fitness at 37°C to those acclimated to 32°C; similarly, bacteria evolutionarily adapted to 32°C had a higher fitness during competition at 32°C than they did when acclimated to 37°C. The more surprising results are that when the bacteria are acclimated to their historical evolutionary temperature, they are frequently competitively superior even at other temperatures. For example, bacteria that have evolved at either 20°C or 32°C and are acclimated to their respective evolutionary temperatures have a greater fitness at 37°C than when they are acclimated to 37°C. Thus, acclimation to evolutionary temperature may, as a correlated consequence, enhance performance not only in the evolutionary environment, but also in a variety of other thermal environments.     

Antarctic fish can survive prolonged exposure to elevated temperatures

The Antarctic notothenioid Pagothenia borchgrevinki was collected from the stenothermal waters of McMurdo Sound in the summers of 2004, 2005 and 2006. Acclimation ability at 4° C was tested in healthy P. borchgrevinki and in individuals infected with x‐cell gill disease. All healthy fish successfully acclimated to 4° C, establishing compensatory changes in resting oxygen consumption rate (R_rest) and critical swimming speed (U_crit) during a 1 month acclimation period, which were maintained during a longer, 6 month acclimation period. In contrast, individuals infected with x‐cell disease were unable to acclimate to 4° C, demonstrating significantly reduced survival rates compared with healthy individuals at 4° C. Measurements of R_rest suggest that limitations in the ability of x‐cell fish to uptake oxygen from the external milieu may have a negative effect on their survival at 4° C.     

A laboratory investigation of temperature and salinity tolerances of juvenile Metapenaeus bennettae Racek and Dall (Crustacea: Penaeidae)

Temperature and salinity tolerances of juvenile Metapenaeus bennetlae Racek and Dall were estimated by abrupt exposure to critically high or low levels of each factor following acclimation to 12 combinations of temperature (17, 22, 27 and 32°C) with salinity (5, 20 and 35‰.). No significant differences were found between tolerances of males and females. Acclimation temperature influenced both temperature and salinity tolerances, while acclimation salinity affected only the salinity tolerance. Irrespective of temperature and salinity acclimation levels, juvenile M. bennettae were able to tolerate temperatures from 8.1 to 32.9°C and salinities from 1.0 to 62.0‰ These findings are discussed in relation to similar published studies.     

Acclimation of isoprene emission and photosynthesis to growth temperature in hybrid aspen: resolving structural and physiological controls

Acclimation of foliage to growth temperature involves both structural and physiological modifications, but the relative importance of these two mechanisms of acclimation is poorly known, especially for isoprene emission responses. We grew hybrid aspen (Populus tremula x P. tremuloides) under control (day/night temperature of 25/20 °C) and high temperature conditions (35/27 °C) to gain insight into the structural and physiological acclimation controls. Growth at high temperature resulted in larger and thinner leaves with smaller and more densely packed chloroplasts and with lower leaf dry mass per area (M_A). High growth temperature also led to lower photosynthetic and respiration rates, isoprene emission rate and leaf pigment content and isoprene substrate dimethylallyl diphosphate pool size per unit area, but to greater stomatal conductance. However, all physiological characteristics were similar when expressed per unit dry mass, indicating that the area‐based differences were primarily driven by M_A. Acclimation to high temperature further increased heat stability of photosynthesis and increased activation energies for isoprene emission and isoprene synthase rate constant. This study demonstrates that temperature acclimation of photosynthetic and isoprene emission characteristics per unit leaf area were primarily driven by structural modifications, and we argue that future studies investigating acclimation to growth temperature must consider structural modifications.