Growth,stress, and acclimation responses to fluctuating temperatures in field and domesticated populations of Manduca sexta

Diurnal fluctuations in temperature are ubiquitous in terrestrial environments, and insects and other ectotherms have evolved to tolerate or acclimate to such fluctuations. Few studies have examined whether ectotherms acclimate to diurnal temperature fluctuations, or how natural and domesticated populations differ in their responses to diurnal fluctuations. We examine how diurnally fluctuating temperatures during development affect growth, acclimation, and stress responses for two populations of Manduca sexta: a field population that typically experiences wide variation in mean and fluctuations in temperature, and a laboratory population that has been domesticated in nearly constant temperatures for more than 300 generations. Laboratory experiments showed that diurnal fluctuations throughout larval development reduced pupal mass for the laboratory but not the field population. The differing effects of diurnal fluctuations were greatest at higher mean temperature (30°C): Here diurnal fluctuations reduced pupal mass and increased pupal development time for the laboratory population, but had little effect for the field population. We also evaluated how mean and fluctuations in temperature during early larval development affected growth rate during the final larval instar as a function of test temperature. At an intermediate (25°C) mean temperature, both the laboratory and field population showed a positive acclimation response to diurnal fluctuations, in which subsequent growth rate was significantly higher at most test temperatures. In contrast at higher mean temperature (30°C), diurnal fluctuations significantly reduced subsequent growth rate at most test temperatures for the laboratory population, but not for the field population. These results suggest that during domestication in constant temperatures, the laboratory population has lost the capacity to tolerate or acclimate to high and fluctuating temperatures. Population differences in acclimation capacity in response to temperature fluctuations have not been previously demonstrated, but they may be important for understanding the evolution of reaction norms and performance curves.     

Ontogenetic colour change and the evolution of aposematism: a case study in panic moth caterpillars

1. Aposematism is a widely used antipredator strategy in which an organism possesses both warning coloration and unprofitable characters. Theoretical evidence suggests that aposematic colour should develop when high opportunity costs imposed by crypsis force an organism to engage in conspicuous behaviours. Hence, it is expected that ontogenetic colour change (OCC) in larval insects should include aposematism when foraging needs compel behavioural modifications that preclude a continued state of crypsis. 2. To test this idea, I first investigated whether OCC in caterpillars of the panic moth Saucrobotys futilalis was indicative of a switch from cryptic to aposematic coloration. I then examined the context of panic moth OCC as it related to foraging patterns and behavioural conspicuousness. 3. Early Saucrobotys instars are a cryptic green, but later instars become progressively more orange and develop black spots. Early instar larvae forage cryptically on the inner parenchyma of silked-together host plant leaves to avoid predation, but are rapidly forced to engage in conspicuous foraging behaviours as they outgrow the resources afforded by their shelters. Both coloration and behaviour reach maximal conspicuousness in final instar larvae. 4. As predicted, OCC encompassed a change from crypsis to aposematism in Saucrobotys. Aposematic function was demonstrated by changes in both antipredator behaviour patterns and effectiveness of predator deterrence in early and late instars. Moreover, increased opportunity costs of crypsis and behavioural conspicuousness coincided with the onset of aposematic coloration. 5. This pattern of OCC suggests that aposematic coloration in Saucrobotys develops as a response to constraints imposed by crypsis. Moreover, my study illustrates the importance of the study of ontogenetic patterns in determining how behaviour, morphology, and predator responses interact to influence the initial evolution of phenomena such as aposematism.     

Patterns of routine swimming and metabolic rate in juvenile cyyprinids at three temperatures: analysis with a respirometer-activity-monitoring system

Summary The spontaneous swimming activity and oxygen consumption of juvenile roach (Rutilus rutilus (L.)), were monitored for 48–72 h at 8, 15 and 20°C and a photoperiod (L:D) of 11:13. At low levels of activity metabolic cost is constant and thus corresponds to the standard rate of metabolism (low cost activity). At higher levels of activity metabolic cost increases in proportion with the degree of activity. The slope for this high cost activity indicates an expenditure of 0.4–1.3 mol O₂·g^-1·h^-1 per arbitrary activity unit at the three experimental temperatures. Extrapolation of this relationship to zero activity would underestimate the measured standard metabolic rate. High cost activity occurred in only one experiment out of three at 8°C, low cost activity hardly at all at 20°C, whereas at 15°C both forms of activity were present in five of the seven experiments conducted. Thus, not only the intensity but also the pattern of activity is affected by environmental temperature.     

不同温度下黑线仓鼠应对食物短缺的能量学对策

食物资源的不确定性是动物在自然环境中面临的重要挑战之一."代谢率转换"假说认为,动物应对食物短缺的能量学策略在于降低代谢率以减少能量支出.然而在不同环境温度下非冬眠小型哺乳动物应对食物短缺的"代谢率转换"策略,尚不明确.为探究这一问题,将成年雄性黑线仓鼠在低温(5.0℃)、室温(21.0℃)和高温(32.5℃)下断食处...     

The effects of constant and changing temperatures on the period from egg hatching to egg laying in Tanymastix stagnalis

The main duration of time from egg hatching to egg laying (D) in this anostracan crustacean increases at lower constant temperatures. The mean number of eggs per female lay between 25 and 50. In both regularly changing temperature experiments D was significantly increased (P<.05). This may be due to an increase in length of adult life which would also account for the increase in number of eggs per female to about 100. The relation of the results to the life and survival strategy of the animal in Ireland in discussed.     

The effects of acclimation on thermal tolerance, desiccation resistance and metabolic rate in Chirodica chalcoptera (Coleoptera: Chrysomelidae)

Despite much focus on species responses to environmental variation through space and time, many higher taxa and geographic areas remain poorly studied. We report the effects of temperature acclimation on thermal tolerance, desiccation rate and metabolic rate for adult Chirodica chalcoptera (Coleoptera: Chrysomelidae) collected from Protea nerifolia inflorescences in the Fynbos Biome in South Africa. After 7 days of acclimation at 12, 19 and 25 degrees C, critical thermal maxima (mean+/-s.e.: 41.8+/-0.2 degrees C in field-fresh beetles) showed less response (<1 degrees C change) to temperature acclimation than did the onset of the critical thermal minima (0.1+/-0.2, 1.0+/-0.2 and 2.3+/-0.2 degrees C, respectively). Freezing was lethal in C. chalcoptera (field-fresh SCP -14.6 degrees C) and these beetles also showed pre-freeze mortality. Survival of 2 h at -10.1 degrees C increased from 20% to 76% after a 2 h pre-exposure to -2 degrees C, indicating rapid cold hardening. Metabolic rate, measured at 25 degrees C and adjusted by ANCOVA for mass variation, did not differ between males and females (2.772+/-0.471 and 2.517+/-0.560 ml CO2 h(-1), respectively), but was higher in 25 degrees C-acclimated beetles relative to the field-fresh and 12 degrees C-acclimated beetles. Body water content and desiccation rate did not differ between males and females and did not respond significantly to acclimation. We place these data in the context of measured inflorescence and ambient temperatures, and predict that climate change for the region could have effects on this species, in turn possibly affecting local ecosystem functioning.     

Bionomics and population growth statistics of apterous virginoparae of woolly apple aphid, Eriosoma lanigerum, at constant temperatures

Development, survival, reproduction and population growth statistics of apterous virginoparae of woolly apple aphid, Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae) at constant temperatures of 10, 13, 15, 20, 25, 30 and 32°C are reported. The developmental times of all life stages were inversely related to temperature ranging from 10 to 30°C. Span of total development (time from birth to adulthood) decreased from 57.8 days at 10°C to 11.7 days at 30°C and increased to 16.8 days at 32°C. A good linear model fit (R²>0.96) between developmental rate and temperature in the range 10–25°C was observed for all life stages. The lower developmental threshold was estimated at 5.8°C for instar I, 4.8°C for instar II, 4.9° for instar III and 4.4°C for instar IV. The lower temperature threshold for total development was estimated at 5.2°C. The upper developmental limit was found to be 32°C. Mean degree-day accumulations required for completion of instars I, II, III, IV and total development were: 125.6, 51.0, 47.7, 50.7 and 267.6, respectively. Fecundity, larviposition period and adult longevity were reduced with increasing temperature. Net reproductive rate was greatest at 15°C whereas intrinsic rate of increase peaked at 25°C. Optimal performance, as measured by fecundity, survival and intrinsic rate of increase, ocurred in the range 13–25°C.     

Effects of ambient and preceding temperatures and metabolic genes on flight metabolism in the Glanville fritillary butterfly

Flight is essential for foraging, mate searching and dispersal in many insects, but flight metabolism in ectotherms is strongly constrained by temperature. Thermal conditions vary greatly in natural populations and may hence restrict fitness-related activities. Working on the Glanville fritillary butterfly (Melitaea cinxia), we studied the effects of temperature experienced during the first 2 days of adult life on flight metabolism, genetic associations between flight metabolic rate and variation in candidate metabolic genes, and genotype–temperature interactions. The maximal flight performance was reduced by 17% by 2 days of low ambient temperature (15 °C) prior to the flight trial, mimicking conditions that butterflies commonly encounter in nature. A SNP in phosphoglucose isomerase (Pgi) had a significant association on flight metabolic rate in males and a SNP in triosephosphate isomerase (Tpi) was significantly associated with flight metabolic rate in females. In the Pgi SNP, AC heterozygotes had higher flight metabolic rate than AA homozygotes following low preceding temperature, but the trend was reversed following high preceding temperature, consistent with previous results on genotype–temperature interaction for this SNP. We suggest that these results on 2-day old butterflies reflect thermal effect on the maturation of flight muscles. These results highlight the consequences of variation in thermal conditions on the time scale of days, and they contribute to a better understanding of the complex dynamics of flight metabolism and flight-related activities under conditions that are relevant for natural populations living under variable thermal conditions.     

Strict requirement of fluctuating temperatures as a reliable gap signal in <Emphasis Type="Italic">Picris hieracioides</Emphasis> var. <Emphasis Type="Italic">japonica</Emphasis> seed germination

Picris hieracioides var. japonica (Asteraceae), which grows in occasionally disturbed habitats such as riverbanks, is rarely observed under dense vegetation. We examined the effect of the experience and timing of receiving leaf-transmitted light in gap-detecting seed germination in this plant. Seeds under unfiltered light, which simulated the light conditions of seeds on the soil surface in a canopy gap, germinated at a constant temperature of 20°C. However, most seeds in darkness, which simulated the light conditions of seeds buried in the soil without receiving leaf-transmitted light, germinated under temperature fluctuations of over 4°C. Seeds in darkness after receiving leaf-transmitted light for 1 week, which simulated the light conditions of seeds buried in the soil after receiving leaf-transmitted light, germinated under temperature fluctuations of over 8°C. Finally, seeds under continuous leaf-transmitted light, which simulated the light conditions of seeds on the soil surface below preexisting vegetation, germinated under temperature fluctuations of over 12°C. Seeds that experience unfiltered light, which suggests that they are in a gap, should not delay germination. In contrast, seeds that have received leaf-transmitted light should delay germination until the vegetation above is removed. Seeds exposed to leaf-transmitted light required larger temperature fluctuations in darkness than did untreated seeds, and seeds under continuous leaf-transmitted light required the largest temperature fluctuations. The various germination reactions to each gap signal in P. hieracioides var. japonica seeds allow the more reliable detection of gaps for subsequent seedling establishment. The requirement for gap signals that created high precision of timing in the germination process results in the germination of this species only in gaps. Therefore, P. hieracioides var. japonica is rarely found under dense vegetation.     

Migration of moth species in a network of small islands

Rapidly increasing fragmentation of natural landscapes decreases the ability of many species to reach the smaller and more isolated patches of habitat in a metapopulation. The densities of local populations of several moth species and the butterfly Hipparchia semele in a network of small islands, and the rates of inter-island movement and movement patterns, were investigated, to determine the factors affecting the rate and pattern of movements. The estimated population densities ranged from 0.001 to 0.2 individuals/m². The observed emigration and immigration rates depended on island isolation and various traits of the species, with great variability in migration rates among species. Thin-bodied, slow-flying species did not move among the islands, whereas many robust, fast-flying species moved among the islands relatively frequently. Migration rate increased significantly with body size and was significantly higher in oligophagous than in polyphagous species, suggesting that these factors are important determinants of the migration rate of the species. Migration rate was low when the surface temperature of the sea was low, and a greater proportion of individuals emigrated from small than large patches of habitat. The migration distances of female noctuids were shorter than those of males and those of both sexes of the butterfly H. semele. The observed movement patterns are consistent with a metapopulation structure in most of the moth species.     

Differences in metabolic rate and evaporative water loss associated with sexual dimorphism in thynnine wasps

Species with sexual dimorphism provide powerful study systems for understanding adaptation to different lifestyles as it removes the potentially confounding effects of phylogeny. Thynnine wasps have a stark sexual dimorphism where males fly patrols in search of the flightless, predominantly fossorial females with which to mate. Using flow-through respirometry, we tested the prediction that the highly active males of the thynnine wasp Zaspilothynnus nigripes would have high metabolic rates (VCO₂) relative to females. Further, the females, which spend more time underground, were predicted to exhibit lower evaporative water loss (EWL) than males. Metabolic rate of both sexes increased exponentially between 12 and 28 °C. As predicted, males had higher mass-corrected VCO₂ at identical temperatures than females. Alternatively, there were no differences in the EWL at identical temperatures between sexes, suggesting that experiencing the same environmental conditions during mating may favour similar EWL. Interestingly, Z. nigripes were estimated to undergo a decrease in metabolism at approximately 30 °C. It is proposed that Z. nigripes persist despite sensitivity to high temperatures using a combination of behavioural strategies and emergence during a period of relatively benign climate that ameliorates the impacts of high temperatures.     

Seasonal trends in body mass, food intake and resting metabolic rate, and induction of metabolic depression in arctic foxes (Alopex lagopus) at Svalbard

 Post-absorptive resting metabolic rates (RMRs), body mass and ad libitum food intake were recorded on an annual cycle in captive arctic foxes (Alopex lagopus) at Svalbard. During the light season in May and in the dark period in November, RMR during starvation and subsequent re-feeding were also measured. In contrast to earlier findings, the present study indicated a seasonal trend in post-absorptive RMR (in W · kg⁻¹ and W · kg^−0.75). The values in the light summer were 15% and 11% higher than the values in the dark winter, suggesting a physiological adaptation aiding energy conservation during winter in arctic foxes. Body mass and ad libitum food intake varied inversely through the year. A significant reduction in RMR (in W and W · kg^−0.75) with starvation (metabolic depression) was recorded both in May and November, indicating an adaptation to starvation in arctic foxes. The lack of metabolic depression during a period of starvation that was concomitant with extremely cold ambient temperatures in November 1994 indicates that metabolic responses to starvation may be masked by thermoregulatory needs. At very low ambient temperatures, arctic foxes may require increased heat production which cannot be achieved via below-average rates of metabolism. Accepted: 7 June 1999     

Effects of constant and fluctuating temperature on time to budburst in Betula pubescens and its relation to bud respiration

 Effects of fluctuating and constant temperatures on budburst time, and respiration in winter buds were studied in Betula pubescens Ehrh. Dormant seedlings were chilled at 0°C for 4 months and then allowed to sprout in long days (LD, 24 h) at constant temperatures of 6, 9, 12, 15, 18 and 21°C, and at diurnally fluctuating temperatures (12/12 h, LD 24 h) with means of 9, 12, 15 and 18°C. No difference in thermal time requirements for budburst was found between plants receiving constant and fluctuating temperatures. The base temperature for thermal time accumulation was estimated to 1°C. Respiration in post-dormant (dormancy fully released) excised winter buds from an adult tree increased exponentially with temperature and was 20 times as high at 30°C than at 0°C. However, respiration in buds without scales was 30% higher at 0°C, and it was 2.7 times higher at 24°C than in intact buds. Thus, the tight bud scales probably constrain respiration and growth and are likely to delay budburst in spring. Arrhenius plots of the respiration data were biphasic with breaks at 13–15°C. However, this phase transition is unlikely to be associated with chilling sensitivity since the present species is hardy and adapted to a boreal climate. Received: 10 January 1997 / Accepted: 23 June 1997     

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.     

Life history and reproductive capacity of Gammarus fossarum and G. roeseli (Crustacea: Amphipoda) under naturally fluctuating water temperatures: a simulation study

SUMMARY 1. Mathematical functions developed in long‐term laboratory experiments at different constant temperatures were combined with daily water temperatures for 1991–93 in eight Austrian streams and rivers to simulate the complex life histories and reproductive capacities of two freshwater amphipods: Gammarus fossarum and G. roeseli. The functions describe brood development times, hatching success, times taken to reach sexual maturity, growth, and fecundity. The sex ratio was assumed to be 0.5 and an autumn–winter reproductive resting period was based on observations of six river populations. Simulations included summer‐cold mountain streams, summer‐warm lowland rivers, watercourses fed by groundwater or influenced by heated effluents, and varying amplitudes of change within each year. 2. A fortran 77 computer program calculated growth from birth to sexual maturity of first‐generation females born on the first day of each calendar month in 1991, and the numbers of offspring successfully released from the maternal broodpouch in successive broods. At the 1991–93 regimes of temperature, individual G. fossarum released 127–208 offspring and G. roeseli released 120–169 in seven or eight successive broods during life spans of less than 2 years in six rivers. Life spans extended into a third year in the relatively cool River Salzach (mean temperature 7.5 °C). They were not completed in the very cold River Steyr (mean 5.6, range 2.5–7.9 °C), where G. fossarum produced five broods (totalling 120 offspring) and G. roeseli only two broods (totalling 28 offspring) in the 3‐year period. Except in the Steyr, some offspring grew rapidly to maturity and produced several second‐generation broods during the simulation period; in the warmest rivers some third‐generation broods were also produced. Birth dates, early or late in the year, influenced the subsequent production of broods and young, depending on temperature regimes in particular rivers. Total numbers of offspring produced by the second and third generations represent the theoretical reproductive capacities of G. fossarum and G. roeseli. Minimum and maximum estimates mostly ranged from 100 to 17 300, were larger for G. fossarum except in the warmest river (March), where temperatures rose above 20 °C for 56–78 days in summer, and largest (maximum 37 600) in the River Voeckla heated by discharge from a power‐station (mean 11.5 °C). Results from the simulations agree with preliminary assessments of relative abundances for G. fossarum and G. roeseli in several of the study rivers, but in some one or both species appear to be absent. On a wider scale, the present study confirms that G. fossarum is potentially more successful than G. roeseli in cool rivers but indicates that neither species is likely to maintain viable populations in cold rivers strongly influenced by snow and ice‐melt. 3. The potential impacts of future river warming by increases of 1, 2 and 3 °C, due to climate change, vary according to river site, date of fertilisation, the extent of temperature increase, and the species of Gammarus. For Austrian rivers with mean temperatures in the range c. 7–10 °C, future warming would result in modest changes in the life histories and reproductive capacities of both G. fossarum and G. roeseli; the former would find improved temperature conditions in watercourses that are currently very cold throughout the year, and both would find warm rivers less tolerable. 4. The high potential reproductive capacity of gammarids, with rapid production of numerous successive broods when sexual maturity is finally achieved, indicates adaptation to high mortality during the relatively long period of growth to sexual maturity, and provides scope for an opportunistic strategy of emigration from centres of population abundance to colonise new territory when conditions are favourable. Rapid expansion of populations is desirable to combat the effects of environmental catastrophes, both frequent and short‐term floods and droughts, and more long‐term climatic changes that have occurred several times in glacial–interglacial periods during the current Ice Age.     

Variations in feed intake and growth of Baltic salmon and brown trout exposed to continuous light at constant low temperatures

Interindividual variations in feed intake and growth were studied in Baltic salmon Salmo salar and brown trout S. trutta , held under constant low temperatures of 2, 4 or 6° C and continuous light for 2 months. Rates of feed intake and growth were dependent upon rearing temperature, being lowest at 2° C and highest at 6° C. Further, feed intake and growth were initially low, but increased during the course of the experiment in both species and at all temperatures. These results suggest that acclimatization to the rearing conditions may have required several weeks. The increase in group mean feed intake with time was the result of both an increase in the proportions of fish that fed and an increase in feed intake amongst feeding fish. At the same time as feeding and growth rates increased, interindividual variations in feed intake and growth tended to decrease, suggesting that individual fish were acclimatizing to the new rearing conditions at different rates. Thus, the differences in group mean feed intake and growth rates observed at a given temperature reflected interindividual variations among fish making up the groups. This suggests that group rates of feed intake and growth are not only temperature- dependent, but that they are also highly influenced by variability among fish making up the group.     

Effects of light and temperature on the circadian system controlling sperm release in moth Spodoptera littoralis

Reproductive physiology of male moths is regulated by a peripheral circadian system, which controls the timing of sperm release from the testis into the upper vas deferens (UVD) and timing of sperm transfer from the UVD to the seminal vesicles. We investigated various effects of light and temperature on sperm release and transfer rhythms in the moth Spodoptera littoralis. We report that both rhythms persist for up to 1 week in constant darkness without significant dampening and are also temperature compensated in the range from 20°C to 30°C. However, the duration of sperm retention in the UVD is temperature-dependent; consequently, temperature exerts a masking effect on the rhythm of sperm transfer. Experimental manipulations of light and temperature regime demonstrated that light dominates over temperature in entraining the timing of sperm release and transfer. Nevertheless, temperature plays a critical role in the absence of light Zeitgeber. Sperm release and transfer are arrhythmic in constant light (LL); however, both rhythms are restored by temperature cycles.     

Seasonal variation in metabolic rate of a medium-sized frugivore, the Knysna Turaco (Tauraco corythaix)

Many seasonal thermoregulation studies have been conducted on Holarctic birds that live in predictable, highly seasonal climates with severe winters. However, relatively few studies have been conducted on their southern hemisphere Afrotropical counterparts that encounter less predictable climates with milder winters. These latter birds are expected to conserve energy in winter by downregulating their metabolic rates. Therefore in this study, metabolic rate was measured during summer and winter in Knysna Turaco, Tauraco corythaix (Musophagiformes, Musophagidae) (c. 310 g), a non-passerine, in order to test whether there is energy conservation in winter. No overall significant differences in resting metabolic rates over a range of ambient temperatures were observed between winter and summer. However, whole-organism basal metabolic rates were 18.5% higher (p=0.005) in winter than in summer (210.83±15.97 vs. 186.70±10.52 O₂ h⁻¹). Knysna Turacos had broad thermoneutral zones ranging from 20 to 28 °C in winter and 10 to 30 °C in summer. These results suggest that Knysna Turacos show seasonal thermoregulatory responses that represent cold defense rather than energy conservation, which is contrary to what was expected.