Developmental Acclimation Research Articles

Experimental evolution reveals that males evolving within warmer thermal regimes improve reproductive performance under heatwave conditions in a model insect.

Climate change is increasing mean temperatures, and intensifying heatwaves. Natural populations may respond to stress through shorter-term acclimation via plasticity and/or longer-term inter-generational evolution. However, if the pace and/or extent of thermal change is too great, local extinctions occur; one potential cause in ectotherms is identified to be the heat-liability of male reproductive biology. Recent data from several species, including the beetle Tribolium castaneum, confirmed that male reproductive biology is vulnerable to heatwaves, which may constrain populations. However, such reproductive-damage may be overestimated, if there is potential to adapt to elevated mean temperatures associated with climate change via evolution and/or acclimation. Here, we tested this to evaluate whether pre-exposures could improve heatwave tolerance (adaptation or acclimation), by experimentally evolving T. castaneum populations to divergent thermal regimes (30°C versus 38°C). Findings across assays revealed that relative to 30°C-regime males, males from the 38°C regime, maintained constantly at 8°C warmer for 25 generations, displayed an increase; i) in post heatwave (42°C) reproductive fitness by 55%, ii) survival by 33% and iii) 32% larger testes volumes. Unexpectedly, in the acclimation assay, warm-adapted males' post-heatwave survival and reproduction were best if they experienced cool developmental acclimation beforehand, suggesting a cost to adapting to 38°C. These results help progress knowledge of the potential for survival and reproduction to adapt to climate change; trait specific adaptation to divergent thermal regimes can occur over relatively few generations, but this capacity depended on the interaction of evolutionary and thermal acclimatory processes.

Threshold shifts and developmental temperature impact trade-offs between tolerance and plasticity.

Mounting evidence suggests that ectotherms are already living close to their upper physiological thermal limits. Phenotypic plasticity has been proposed to reduce the impact of climate change in the short-term providing time for adaptation, but the tolerance-plasticity trade-off hypothesis predicts organisms with higher tolerance have lower plasticity. Empirical evidence is mixed, which may be driven by methodological issues such as statistical artefacts, nonlinear reaction norms, threshold shifts or selection. Here, we examine whether threshold shifts (organisms with higher tolerance require stronger treatments to induce maximum plastic responses) influence tolerance-plasticity trade-offs in hardening capacity for desiccation tolerance and critical thermal maximum (CTMAX) across Drosophila species with varying distributions/sensitivity to desiccation/heat stress. We found evidence for threshold shifts in both traits; species with higher heat/desiccation tolerance required longer hardening treatments to induce maximum hardening responses. Species with higher heat tolerance also showed reductions in hardening capacity at higher developmental acclimation temperatures. Trade-off patterns differed depending on the hardening treatment used and the developmental temperature flies were exposed to. Based on these findings, studies that do not consider threshold shifts, or that estimate plasticity under a narrow set of environments, will have a limited ability to assess trade-off patterns and differences in plasticity across species/populations more broadly.

Foliar Phenotypic Plasticity Reflects Adaptation to Environmental Variability.

Arabidopsis thaliana ecotypes adapted to native habitats with different daylengths, temperatures, and precipitation were grown experimentally under seven combinations of light intensity and leaf temperature to assess their acclimatory phenotypic plasticity in foliar structure and function. There were no differences among ecotypes when plants developed under moderate conditions of 400 µmol photons m-2 s-1 and 25 °C. However, in response to more extreme light or temperature regimes, ecotypes that evolved in habitats with pronounced differences in either the magnitude of changes in daylength or temperature or in precipitation level exhibited pronounced adjustments in photosynthesis and transpiration, as well as anatomical traits supporting these functions. Specifically, when grown under extremes of light intensity (100 versus 1000 µmol photons m-2 s-1) or temperature (8 °C versus 35 °C), ecotypes from sites with the greatest range of daylengths and temperature over the growing season exhibited the greatest differences in functional and structural features related to photosynthesis (light- and CO2-saturated capacity of oxygen evolution, leaf dry mass per area or thickness, phloem cells per minor vein, and water-use efficiency of CO2 uptake). On the other hand, the ecotype from the habitat with the lowest precipitation showed the greatest plasticity in features related to water transport and loss (vein density, ratio of water to sugar conduits in foliar minor veins, and transpiration rate). Despite these differences, common structure-function relationships existed across all ecotypes and growth conditions, with significant positive, linear correlations (i) between photosynthetic capacity (ranging from 10 to 110 µmol O2 m-2 s-1) and leaf dry mass per area (from 10 to 75 g m-2), leaf thickness (from 170 to 500 µm), and carbohydrate-export infrastructure (from 6 to 14 sieve elements per minor vein, from 2.5 to 8 µm2 cross-sectional area per sieve element, and from 16 to 82 µm2 cross-sectional area of sieve elements per minor vein); (ii) between transpiration rate (from 1 to 17 mmol H2O m-2 s-1) and water-transport infrastructure (from 3.5 to 8 tracheary elements per minor vein, from 13.5 to 28 µm2 cross-sectional area per tracheary element, and from 55 to 200 µm2 cross-sectional area of tracheary elements per minor vein); (iii) between the ratio of transpirational water loss to CO2 fixation (from 0.2 to 0.7 mol H2O to mmol-1 CO2) and the ratio of water to sugar conduits in minor veins (from 0.4 to 1.1 tracheary to sieve elements, from 4 to 6 µm2 cross-sectional area of tracheary to sieve elements, and from 2 to 6 µm2 cross-sectional area of tracheary elements to sieve elements per minor vein); (iv) between sugar conduits and sugar-loading cells; and (v) between water conducting and sugar conducting cells. Additionally, the proportion of water conduits to sugar conduits was greater for all ecotypes grown experimentally under warm-to-hot versus cold temperature. Thus, developmental acclimation to the growth environment included ecotype-dependent foliar structural and functional adjustments resulting in multiple common structural and functional relationships.

STN7 is not essential for developmental acclimation of Arabidopsis to light intensity.

Plants respond to changing light intensity in the short term through regulation of light harvesting, electron transfer, and metabolism to mitigate redox stress. A sustained shift in light intensity leads to a long-term acclimation response (LTR). This involves adjustment in the stoichiometry of photosynthetic complexes through de novo synthesis and degradation of specific proteins associated with the thylakoid membrane. The light-harvesting complex II (LHCII) serine/threonine kinase STN7 plays a key role in short-term light harvesting regulation and was also suggested to be crucial to the LTR. Arabidopsis plants lacking STN7 (stn7) shifted to low light experience higher photosystem II (PSII) redox pressure than the wild type or those lacking the cognate phosphatase TAP38 (tap38), while the reverse is true at high light, where tap38 suffers more. In principle, the LTR should allow optimisation of the stoichiometry of photosynthetic complexes to mitigate these effects. We used quantitative label-free proteomics to assess how the relative abundance of photosynthetic proteins varied with growth light intensity in wild-type, stn7, and tap38 plants. All plants were able to adjust photosystem I, LHCII, cytochrome b6 f, and ATP synthase abundance with changing white light intensity, demonstrating neither STN7 nor TAP38 is crucial to the LTR per se. However, stn7 plants grown for several weeks at low light (LL) or moderate light (ML) still showed high PSII redox pressure and correspondingly lower PSII efficiency, CO2 assimilation, and leaf area compared to wild-type and tap38 plants, hence the LTR is unable to fully ameliorate these symptoms. In contrast, under high light growth conditions the mutants and wild type behaved similarly. These data are consistent with the paramount role of STN7-dependent LHCII phosphorylation in tuning PSII redox state for optimal growth in LL and ML conditions.

An exotic allele of barley EARLY FLOWERING 3 contributes to developmental plasticity at elevated temperatures.

Increase in ambient temperatures caused by climate change affects various morphological and developmental traits of plants, threatening crop yield stability. In the model plant Arabidopsis thaliana, EARLY FLOWERING 3 (ELF3) plays prominent roles in temperature sensing and thermomorphogenesis signal transduction. However, how crop species respond to elevated temperatures is poorly understood. Here, we show that the barley ortholog of AtELF3 interacts with high temperature to control growth and development. We used heterogeneous inbred family (HIF) pairs generated from a segregating mapping population and systematically studied the role of exotic ELF3 variants in barley temperature responses. An exotic ELF3 allele of Syrian origin promoted elongation growth in barley at elevated temperatures, whereas plant area and estimated biomass were drastically reduced, resulting in an open canopy architecture. The same allele accelerated inflorescence development at high temperature, which correlated with early transcriptional induction of MADS-box floral identity genes BM3 and BM8. Consequently, barley plants carrying the exotic ELF3 allele displayed stable total grain number at elevated temperatures. Our findings therefore demonstrate that exotic ELF3 variants can contribute to phenotypic and developmental acclimation to elevated temperatures, providing a stimulus for breeding of climate-resilient crops.

Thermal fitness costs and benefits of developmental acclimation in fall armyworm

Global increases in mean temperatures and changes in precipitation patterns due to climate change, coupled with anthropogenic pathways, have intensified biological invasions of pest insects. Continuous exposure to bouts of acute and chronic heat and fasting stresses (during e.g., droughts) might improve pest performance under recurring stresses, therefore enhancing/reducing fitness within- or across- life stages (i.e., ‘carry-over’ effects). Here, we examined developmental acclimation effects in the invasive fall army worm Spodoptera frugiperda — a highly invasive economic insect pest of cereal crops, particularly maize — using standardized heat tolerance metrics. Specifically, we assessed the effects of acute (3h) and chronic (3 days) heat treatments (at 32°C, 35°C, 38°C), as well as fasting (48h), on 3rd instar larvae, and tested fitness traits (critical thermal maxima [CTmax] and heat knockdown time [HKDT]) at a later life stage (4th/5th larval instar). Acclimation to heat stress and fasting had significant fitness costs (lower CTmax) across majority of treatments. However, both heat and fasting acclimation improved HKDT (except for 35 and 38°C [acute acclimation] and 35°C [chronic acclimation]). Our results suggest context-specific developmental acclimation costs and benefits in S. frugiperda. In particular, heat and fasting acclimation potentially have fitness costs and benefits for subsequent developmental stages facing high temperature stress. These results are important for estimating the effects of prior stressful events on future survival of invasive insect species and may be significant in predicting pest population dynamics under changing environmental conditions.

Adaptation to Urban Heat Islands Enhances Thermal Performance Following Development under Chronic Thermal Stress but Not Benign Conditions in the Terrestrial Isopod Oniscus asellus.

AbstractThe effects of chronic thermal stress during development on thermal performance traits are not well characterized under urban heat islands, despite these conditions being biologically relevant for how organisms experience the urban environment and the often strong linkages between thermal performance traits and fitness. Here we use the terrestrial isopod Oniscus asellus to examine the effects of chronic thermal stress during development on voluntary running speed of urban and rural isopods. We used a laboratory common-garden experiment design with two developmental acclimation temperature treatments (21°C, a benign treatment, and 29°C, a stressful treatment) and three test temperatures (19°C, 31°C, 40°C); we tested running speed of individuals from urban and rural populations under each of the temperature combinations. We found that for both urban and rural isopods, running speed across three test temperatures was reduced under developmental acclimation conditions of 29°C compared with 21°C. Importantly, however, urban isopods had a running speed advantage over the rural isopods under the 29°C developmental acclimation conditions at the lower two test temperatures. No population differences were detected under benign developmental acclimation conditions of 21°C. The evolution of higher heat tolerance in urban isopods further supported the interpretation of adaptation to heat stress. Convergence of urban and rural isopod running speed at the highest test temperature, however, suggests potential limits or constraints on adaptation. Our results indicate that thermal adaptation to urban heat islands can mitigate negative effects of chronic developmental thermal stress, even when overall performance is reduced compared with benign conditions.

Developmental temperature affects thermal dependence of locomotor activity in Drosophila.

In their natural environments, animals have to cope with fluctuations in numerous abiotic and biotic factors, and phenotypic plasticity can facilitate survival under such variable conditions. However, organisms may differ substantially in the ability to adjust their phenotypes in response to external factors. Here, we investigated how developmental temperature affects the thermal performance curve for locomotor activity in adult fruit flies (Drosophila melanogaster). We examined the thermal dependence of spontaneous activity in individuals originating from two natural populations (from tropical (India) and temperate climate zone (Slovakia)) that developed at three different temperatures (19°C, 25°C, and 29°C). Firstly, we found that developmental temperature has a significant impact on overall activity - flies that developed at high temperature (29°C) were, on average, less active than individuals that developed at lower temperatures. Secondly, developmental acclimation had a population-specific effect on the thermal optimum for activity. Whereas the optimal temperature was not affected by thermal conditions experienced during development in flies from India, developmental temperature shifted thermal optimum in flies from Slovakia. Thirdly, high developmental temperature broadened performance breadth in flies from the Indian population but narrowed it in individuals from the Slovak population. Finally, we did not detect a consistent effect of acclimation temperature on circadian rhythms of spontaneous activity. Altogether, our results demonstrate that developmental temperature can alter different parameters (maximum performance, thermal optimum, performance breadth) of the thermal performance curve for spontaneous activity. Since adult fruit flies are highly vagile, this sensitivity of locomotion to developmental conditions may be an important factor affecting fitness in changing environments.

Additive effects of developmental acclimation and physiological syndromes on lifetime metabolic and water loss rates of a dry‐skinned ectotherm

Abstract Developmental plasticity and thermal acclimation can contribute to adaptive responses to climate change by altering functional traits related to energy and water balance regulation. How plasticity interacts with physiological syndromes through lifetime in long‐lived species is currently unknown. Here, we examined the impacts of long‐term thermal acclimation in a long‐lived temperate ectotherm Vipera aspis and its potential flexibility at adulthood for two related functional traits: standard metabolic rate (SMR) and total evaporative water loss (TEWL). We used climatic chambers to simulate three contrasted daily thermal cycles (warm, medium and cold) differing in mean temperatures (28, 24 and 20℃ respectively) and amplitudes (5, 10 and 13℃ respectively) during immature life (0 to 4 years of age). Individuals were then maintained under common garden conditions (medium cycle) for an additional 3‐year period (4–7 years of age). SMR and TEWL were repeatedly measured in the same individuals throughout life during and after the climate manipulation. Individuals reduced their SMR (negative compensation) when experiencing the warm cycle but flexibly adjusted their SMR to common garden conditions at adulthood. In addition, thermal conditions during the juvenile life stage led to changes in TEWL persisting until adulthood. We further found consistent intra‐individual variation for SMR and TEWL and a positive intra‐individual and inter‐individual covariation between them throughout life. Thus, plastic responses were combined with a physiological syndrome linking SMR and TEWL. Our study demonstrates the capacity of long‐lived organisms to flexibly shift their SMR to reduce daily maintenance costs in warmer and less variable thermal environments, which might be beneficial to low‐energy specialist organisms such as vipers. It further suggests that thermal conditions provide cues for developmental changes in TEWL. Beside plasticity, contrasted individual physiological syndromes could be selected for and contribute to the response to climate change. A free Plain Language Summary can be found within the Supporting Information of this article.

Interactions between developmental and adult acclimation have distinct consequences for heat tolerance and heat stress recovery.

Developmental and adult thermal acclimation can have distinct, even opposite, effects on adult heat resistance in ectotherms. Yet, their relative contribution to heat-hardiness of ectotherms remains unclear despite the broad ecological implications thereof. Furthermore, the deterministic relationship between heat knockdown and recovery from heat stress is poorly understood but significant for establishing causal links between climate variability and population dynamics. Here, using Drosophila melanogaster in a full-factorial experimental design, we assessed the heat tolerance of flies in static stress assays, and document how developmental and adult acclimation interact with a distinct pattern to promote survival to heat stress in adults. We show that warmer adult acclimation is the initial factor enhancing survival to constant stressful high temperatures in flies, but also that the interaction between adult and developmental acclimation becomes gradually more important to ensure survival as the stress persists. This provides an important framework revealing the dynamic interplay between these two forms of acclimation that ultimately enhance thermal tolerance as a function of stress duration. Furthermore, by investigating recovery rates post-stress, we also show that the process of heat-hardening and recovery post-heat knockdown are likely to be based on set of (at least partially) divergent mechanisms. This could bear ecological significance as a trade-off may exist between increasing thermal tolerance and maximizing recovery rates post-stress, constraining population responses when exposed to variable and stressful climatic conditions.

Acclimation for optimisation: effects of temperature on development, reproduction and size of Trichogramma achaeae

ABSTRACT The performance of biological control agents (BCAs) is strongly regulated by ambient temperature. Understanding the thermal biology of BCAs is a crucial first step for manipulation of their thermal performance, which could be a potential avenue to improve biological control efficacy. In this study, the effects of temperature on several life history parameters (longevity, fecundity, development time, wing size) of the commercialised egg parasitoid Trichogramma achaeae Nagaraja & Nagarkatti (Hymenoptera: Trichogrammatidae) were examined. First, parasitoids were reared at 23°C and tested in the laboratory at four constant temperatures (15, 20, 25 and 30°C) to generate thermal reaction norms. Results demonstrated that temperature significantly affected all investigated parameters. Second, developmental acclimation was applied to investigate the phenotypic plasticity of the same traits. Parasitoids were allowed to develop at either of the above four temperatures and their performances were compared at 23°C. Results showed that developmental acclimation had a significant impact on fecundity, development time and wing size but not on female longevity. Our results have implications for improving the performance of T. achaeae in mass production and potentially for its application for biological control under different thermal conditions.

Plastic changes in cold and drought tolerance of Drosophila nepalensis correlate with sex-specific differences in body melanization, cuticular lipid mass, proline accumulation, and seasonal abundance

Autumn-collected flies of Himalayan Drosophila nepalensis differ in body color phenotypes (males more melanized relative to females) and in their behavior (males abundant in the open sites vs. shelters-seeking females). In contrast, winter-collected flies of both sexes are equally melanized and abundant in the open sites. We tested developmental and adult plasticity changes in cold or drought tolerance in D. nepalensis flies reared under winter or autumn simulated conditions. In D. nepalensis flies reared at 21 °C, male flies were more cold tolerant (as shown by shorter chill-coma recovery time and lower cold-shock mortality). Further, male flies also exhibited greater drought tolerance (increased levels of desiccation resistance, cuticular lipid mass, melanization, hydration level, and dehydration tolerance) as compared to females. We observed sex-specific differences in the adult plasticity responses due to rapid cold or drought hardening (RCH or RDH); and for the persistence of cold acclimation effects. RCH or RDH-induced changes in the level of proline accumulations are negatively correlated with a decrease in the chill-coma recovery time. Therefore, cold or drought hardening treatments are likely to influence cold tolerance through proline accumulation. Developmental acclimation and adult hardening responses revealed significant interaction effects between sexes and thermal treatments. Thus, sex-specific differences in morphological traits (body melanization and cuticular lipid mass) and physiological traits (adult plasticity changes in cold tolerance and proline accumulation) correlate with behavioral divergence (habitat usage) across sexes.

Do aquatic ectotherms perform better under hypoxia after warm acclimation?

Aquatic animals increasingly encounter environmental hypoxia due to climate-related warming and/or eutrophication. Although acute warming typically reduces performance under hypoxia, the ability of organisms to modulate hypoxic performance via thermal acclimation is less understood. Here, we review the literature and ask whether hypoxic performance of aquatic ectotherms improves following warm acclimation. Interpretation of thermal acclimation effects is limited by reliance on data from experiments that are not designed to directly test for beneficial or detrimental effects on hypoxic performance. Most studies have tested hypoxic responses exclusively at test temperatures matching organisms' acclimation temperatures, precluding the possibility of distinguishing between acclimation and acute thermal effects. Only a few studies have applied appropriate methodology to identify beneficial thermal acclimation effects on hypoxic performance, i.e. acclimation to different temperatures prior to determining hypoxic responses at standardised test temperatures. These studies reveal that acute warming predominantly impairs hypoxic performance, whereas warm acclimation tends to be either beneficial or have no effect. If this generalises, we predict that warm-acclimated individuals in some species should outperform non-acclimated individuals under hypoxia. However, acclimation seems to only partially offset acute warming effects; therefore, aquatic ectotherms will probably display overall reduced hypoxic performance in the long term. Drawing on the appropriate methodology, future studies can quantify the ability of organisms to modulate hypoxic performance via (reversible) thermal acclimation and unravel the underlying mechanisms. Testing whether developmental acclimation and multigenerational effects allow for a more complete compensation is essential to allow us to predict species' resilience to chronically warmer, hypoxic environments.

Diminished warming tolerance and plasticity in low-latitude populations of a marine gastropod.

Models of species response to climate change often assume that physiological traits are invariant across populations. Neglecting potential intraspecific variation may overlook the possibility that some populations are more resilient or susceptible than others, creating inaccurate predictions of climate impacts. In addition, phenotypic plasticity can contribute to trait variation and may mediate sensitivity to climate. Quantifying such forms of intraspecific variation can improve our understanding of how climate can affect ecologically important species, such as invasive predators. Here, we quantified thermal performance (tolerance, acclimation capacity, developmental traits) across seven populations of the predatory marine snail (Urosalpinx cinerea) from native Atlantic and non-native Pacific coast populations in the USA. Using common garden experiments, we assessed the effects of source population and developmental acclimation on thermal tolerance and developmental traits of F1 snails. We then estimated climate sensitivity by calculating warming tolerance (thermal tolerance - habitat temperature), using field environmental data. We report that low-latitude populations had greater thermal tolerance than their high latitude counterparts. However, these same low-latitude populations exhibited decreased thermal tolerance when exposed to environmentally realistic higher acclimation temperatures. Low-latitude native populations had the greatest climate sensitivity (habitat temperatures near thermal limits). In contrast, invasive Pacific snails had the lowest climate sensitivity, suggesting that these populations are likely to persist and drive negative impacts on native biodiversity. Developmental rate significantly increased in embryos sourced from populations with greater habitat temperature but had variable effects on clutch size and hatching success. Thus, warming can produce widely divergent responses within the same species, resulting in enhanced impacts in the non-native range and extirpation in the native range. Broadly, our results highlight how intraspecific variation can alter management decisions, as this may clarify whether management efforts should be focused on many or only a few populations.

Developmental acclimation of the thylakoid proteome to light intensity in Arabidopsis.

Photosynthetic acclimation, the ability to adjust the composition of the thylakoid membrane to optimise the efficiency of electron transfer to the prevailing light conditions, is crucial to plant fitness in the field. While much is known about photosynthetic acclimation in Arabidopsis, to date there has been no study that combines both quantitative label-free proteomics and photosynthetic analysis by gas exchange, chlorophyll fluorescence and P700 absorption spectroscopy. Using these methods we investigated how the levels of 402 thylakoid proteins, including many regulatory proteins not previously quantified, varied upon long-term (weeks) acclimation of Arabidopsis to low (LL), moderate (ML) and high (HL) growth light intensity and correlated these with key photosynthetic parameters. We show that changes in the relative abundance of cytb6 f, ATP synthase, FNR2, TIC62 and PGR6 positively correlate with changes in estimated PSII electron transfer rate and CO2 assimilation. Improved photosynthetic capacity in HL grown plants is paralleled by increased cyclic electron transport, which positively correlated with NDH, PGRL1, FNR1, FNR2 and TIC62, although not PGR5 abundance. The photoprotective acclimation strategy was also contrasting, with LL plants favouring slowly reversible non-photochemical quenching (qI), which positively correlated with LCNP, while HL plants favoured rapidly reversible quenching (qE), which positively correlated with PSBS. The long-term adjustment of thylakoid membrane grana diameter positively correlated with LHCII levels, while grana stacking negatively correlated with CURT1 and RIQ protein abundance. The data provide insights into how Arabidopsis tunes photosynthetic electron transfer and its regulation during developmental acclimation to light intensity.

Environmentally-induced parental or developmental conditioning influences coral offspring ecological performance

The persistence of reef building corals is threatened by human-induced environmental change. Maintaining coral reefs into the future requires not only the survival of adults, but also the influx of recruits to promote genetic diversity and retain cover following adult mortality. Few studies examine the linkages among multiple life stages of corals, despite a growing knowledge of carryover effects in other systems. We provide a novel test of coral parental conditioning to ocean acidification (OA) and tracking of offspring for 6 months post-release to better understand parental or developmental priming impacts on the processes of offspring recruitment and growth. Coral planulation was tracked for 3 months following adult exposure to high pCO2 and offspring from the second month were reciprocally exposed to ambient and high pCO2 for an additional 6 months. Offspring of parents exposed to high pCO2 had greater settlement and survivorship immediately following release, retained survivorship benefits during 1 and 6 months of continued exposure, and further displayed growth benefits to at least 1 month post release. Enhanced performance of offspring from parents exposed to high conditions was maintained despite the survivorship in both treatments declining in continued exposure to OA. Conditioning of the adults while they brood their larvae, or developmental acclimation of the larvae inside the adult polyps, may provide a form of hormetic conditioning, or environmental priming that elicits stimulatory effects. Defining mechanisms of positive acclimatization, with potential implications for carry over effects, cross-generational plasticity, and multi-generational plasticity, is critical to better understanding ecological and evolutionary dynamics of corals under regimes of increasing environmental disturbance. Considering environmentally-induced parental or developmental legacies in ecological and evolutionary projections may better account for coral reef response to the chronic stress regimes characteristic of climate change.

Rejection of the beneficial acclimation hypothesis (BAH) for short term heat acclimation in Drosophila nepalensis.

Beneficial acclimation hypothesis (BAH) is the phenotypic plasticity in response to changing environments which enables organisms to enhance their fitness. In recent years, however, BAH has received vigorous criticism and is still debatable. In this study, we tested thermal hardiness phenotypes (melanization, chill coma recovery, heat knockdown and percentage survival) on adult and pre-adult stages of Drosophila nepalensis, reared in different thermal environments (14, 17, 21 and 25°C) to check whether increasing natural surrounding temperature and acclimation limit towards environmental change is detrimental or beneficial. Results showed that rearing D. nepalensis at higher temperatures (21 and 25°C) reduces its melanization and cold hardiness but improves heat knockdown times. When temperature was raised to 26.2°C (0.6°C above the upper thermal maxima), to determine the short-term acclimation effects, survival and fitness of adults diminished approximately 1.5 to 2 folds. These results suggest that D. nepalensis has long-term developmental acclimation to both heat and cold which would be extremely beneficial as temperatures and climates alter in the region due to global warming. However, a lack of short-term heat acclimation suggests that rapid shifts in thermal extreme could be detrimental to D. nepalensis.

Beneficial developmental acclimation in reproductive performance under cold but not heat stress.

Thermal plasticity can help organisms coping with climate change. In this study, we analyse how laboratory populations of the ectotherm species Drosophila subobscura, originally from two distinct latitudes and evolving for several generations in a stable thermal environment (18°C), respond plastically to new thermal challenges. We measured adult performance (fecundity traits as a fitness proxy) of the experimental populations when exposed to five thermal regimes, three with the same temperature during development and adulthood (15-15°C, 18-18°C, 25-25°C), and two where flies developed at 18°C and were exposed, during adulthood, to either 15°C or 25°C. Here, we test whether (1) flies undergo stress at the two more extreme temperatures; (2) development at a given temperature enhances adult performance at such temperature (i.e. acclimation), and (3) populations with different biogeographical history show plasticity differences. Our findings show (1) an optimal performance at 18°C only if flies were subjected to the same temperature as juveniles and adults; (2) the occurrence of developmental acclimation at lower temperatures; (3) detrimental effects of higher developmental temperature on adult performance; and (4) a minor impact of historical background on thermal response. Our study indicates that thermal plasticity during development may have a limited role in helping adults cope with warmer - though not colder - temperatures, with a potential negative impact on population persistence under climate change. It also emphasizes the importance of analysing the impact of temperature on all stages of the life cycle to better characterize the thermal limits.

Critical thermal maxima of early life stages of three tropical fishes: Effects of rearing temperature and experimental heating rate

Marine ectotherms are often sensitive to thermal stress, and certain life stages can be particularly vulnerable (e.g., larvae or spawners). In this study, we investigated the critical thermal maxima (CTmax) of larval and early juvenile life stages of three tropical marine fishes (Acanthochromis polyacanthus, Amphiprion melanopus, and Lates calcarifer). We tested for potential effects of developmental acclimation, life stage, and experimental heating rates, and we measured metabolic enzyme activities from aerobic (citrate synthase, CS) and anaerobic pathways (lactate dehydrogenase, LDH). A slightly elevated rearing temperature neither influenced CTmax nor CS activity, which otherwise could have indicated thermal acclimation. However, we found CTmax to either remain stable (Acanthrochromis polyacanthus) or increase with body mass during early ontogeny (Amphiprion melanopus and Lates calcarifer). In all three species, faster heating rates lead to higher CTmax. Acute temperature stress did not change CS or LDH activities, suggesting that overall aerobic and anaerobic metabolism remained stable. Lates calcarifer, a catadromous species that migrates from oceanic to riverine habitats upon metamorphosis, had higher CTmax than the two coral reef fish species. We highlight that, for obtaining conservative estimates of a fish species' upper thermal limits, several developmental stages and body mass ranges should be examined. Moreover, upper thermal limits should be assessed using standardized heating rates. This will not only benefit comparative approaches but also aid in assessing geographic (re-) distributions and climate change sensitivity of marine fishes.

Respiration rates of herring larvae at different salinities, and effects of previous environmental history

Metabolic rates of early life history stages of marine fishes show considerable inter-individual differences, and are highly influenced by extrinsic factors like temperature or food availability. Measuring oxygen uptake rates is a proxy for estimating metabolic rates. Still, the relationship between respiration rates and ambient or previous salinity conditions as well as parental and developmental acclimation to changes in salinity remains largely unexplored. In the present study, we conducted experiments to investigate the effects of salinity on the routine metabolic rates (RMR) of euryhaline Atlantic herringClupea harenguslarvae at 3 levels of salinity: low (6 psu), intermediate (16 psu) and high (35 psu), reflecting ecologically relevant conditions for herring populations in the Atlantic Ocean and Baltic Sea. The larvae originated from different genetic backgrounds and salinity adaptations to account for cross-generation effects on metabolic rates. Closed respirometry carried out over 24 h on individual fish larvae generally confirmed near isometric respiration rates at all salinity regimes, with rates being 15.4% higher at 6 psu and 7.5% higher at 35 psu compared to 16 psu conditions. However, transgenerational acclimation to different salinity regimes of the parents had no effect on the salinity-specific metabolic rates of their offspring. Our study demonstrates the ability of herring to cope with a wide range of salinity conditions, irrespective of parental environmental history and genetic origin. This phenotypic plasticity is considered to be one of the main contributing factors to the success of herring as a widely distributed fish species in the North Atlantic and adjacent waters.