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

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

Fluctuating environments impact thermal tolerance in an invasive insect species Bactrocera dorsalis (Diptera: Tephritidae)

The incidence and severity of environmental stressors associated with global climate change are increasing and insects frequently face variability in temperature and moisture regimes at variable spatio-temporal scales. Coincidental with this, is increased thermal and hydric stress on insects as warming increases vapour pressure deficit (VPD), the drying power of the air. While the effects of mean temperatures on fitness are widely documented, fluctuations in both temperature and relative humidity (RH) are largely unexplored. Here, we investigated the effects of dynamic temperature and RH fluctuations (around the mean [28°C; 65% RH]) on low and high thermal tolerance of laboratory-reared adult invasive Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), measured as critical thermal minima (CT_min), critical thermal maxima (CT_max), chill coma recovery time (CCRT) and heat knockdown time (HKDT). Our results show that increased environmental amplitude significantly influenced low and high temperature responses and varied across traits tested. The highest amplitude (δ12°C; 28% RH) compromised CT_min, CCRT and HKDT traits while enhancing CT_max. Similarly, acclimation to δ3°C; 7% RH compromised both low (CT_min and CCRT) and high (CT_max and HKDT) fitness traits. Variations in fitness reported here indicate significant roles of combined thermal and moisture fluctuations on B. dorsalis fitness suggesting caveats that are worthy considering when predicting species responses to climate change. These results are significant for B. dorsalis population phenology, management, quantifying vulnerability to climate variability and may help modelling future biogeographical patterns.     

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

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

Thermal stress exposure of pupal oriental fruit fly has strong and trait-specific consequences in adult flies

Global climate change is projected to increase the incidence of heat waves, their magnitude and duration resulting in insects experiencing increasing environmental stress in both natural and managed ecosystems. While studies on insect thermal tolerance are rapidly increasing, variation across developmental or juvenile stress cross-stage effects within and across generations remain largely unexplored. Yet in holometabolous insects, heat stress at an early developmental stage may influence performance and survival during later stages. Here, we investigated the effects of pupal mild heat stress on the performance of laboratory-reared adult Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) measured as longevity, critical thermal maximum (CT_max), critical thermal minima (CT_min), heat knockdown time (HKDT) and chill coma recovery time (CCRT). Pupal heat stress significantly influenced performance of B. dorsalis adults resulting in impaired longevity and heat tolerance (CT_max and HKDT) in both sexes with improved and compromised cold tolerance (CT_min and CCRT) in females and males, respectively. These findings highlight the role of juvenile stages in mediating stress responses at adult stages. For B. dorsalis, pupal heat stress largely compromised thermal tolerance implying that the species has limited potential to shift its geographic range in heat prone areas. Significant benefits in cold tolerance in females following heat stress may help in improving survival in the cold in the short-term despite restricted activity to the same traits in males. This study suggests that basal heat tolerance and not short-term compensatory thermal plasticity following heat stress may have aided the recent invasion of B. dorsalis in African landscapes.     

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

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

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

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

Temperature and photoperiod affect stress resistance traits in Drosophila melanogaster

The long‐term survival of species and populations depends on their ability to adjust phenotypic values to environmental conditions. In particular, the capability of dealing with environmental stress to buffer detrimental effects on fitness is considered to be of pivotal importance. Resistance traits are readily modulated by a wide range of environmental factors. In the present study, Drosophila melanogaster Meigen is used to investigate plastic responses to temperature and photoperiod in stress resistance traits. The results reveal that stress resistance traits (cold, heat, starvation and desiccation resistance) are affected by the factors temperature and sex predominantly. Cooler temperatures compared with warmer temperatures increase cold tolerance, desiccation and starvation resistance, whereas they reduce heat tolerance. Except for heat resistance, females are more stress‐resistant than males. Stress resistance traits are also affected by photoperiod. Shorter photoperiods decrease cold tolerance, whereas longer photoperiods enhance desiccation resistance. Overall, thermal effects are pervasive throughout all measured resistance traits, whereas photoperiodic effects are of limited importance in the directly developing (i.e. nondiapausing) flies used here, suggesting that pronounced photoperiodic effects on stress resistance traits may be largely limited to, and triggered by, diapause‐inducing effects.     

Heat tolerance may determine activity time in coprophagic beetle species (Coleoptera: Scarabaeidae)

Although reports have documented loss of species diversity and ecological services caused by stressful temperature changes that result from climate change, some species cope through behavioral compensation. As temperatures and magnitudes of temperature extremes increase, animals should compensate to maintain fitness (such as through temporary behavioral shifts in activity times). Appropriate timing of activity helps avoid competition across species. Although coprophagic dung beetles exhibit species-specific temporal activity times, it is unknown whether temperature drives evolution of these species-specific temporal activity times. Using nine dung beetle species (three each of diurnal, crepuscular, and nocturnal species), we explored differences in heat stress tolerance measured as critical thermal maxima (CT_max; the highest temperature allowing activity) and heat knockdown time (HKDT; survival time under acute heat stress) across these species, and examined the results using a phylogenetically informed approach. Our results showed that day-active species had significantly higher CT_max (diurnal > crepuscular = nocturnal species), whereas crepuscular species had higher HKDT (crepuscular > nocturnal > diurnal species). There was no correlation between heat tolerance and body size across species with distinct temporal activity, and no significant phylogenetic constraint for activity. Species with higher CT_max did not necessarily have higher HKDT, which indicates that species may respond differently to diverse heat tolerance metrics. Acute heat tolerance for diurnal beetles indicates that this trait may constrain activity time and, under high acute temperatures with climate change, species may shift activity times in more benign environments. These results contribute to elucidate the evolution of foraging behavior and management of coprophagic beetle ecosystem services under changing environments.     

Interactive effects of acclimation temperature and short‐term stress exposure on resistance traits in the butterfly Bicyclus anynana

The ability to buffer detrimental effects of environmental stress on fitness is of great ecological importance because, in nature, pronounced environmental variation may regularly induce stress. Furthermore, several stressors may interact in a synergistic manner. In the present study, plastic responses in cold, heat and starvation resistance are investigated in the tropical butterfly Bicyclus anynana Butler, 1879, using a full factorial design with two acclimation temperatures (20 and 27 °C) and four short‐term stress treatments (control, cold, heat, starvation). Warm‐acclimated butterflies are more heat‐ but less cold‐tolerant as expected. Short‐term cold and starvation exposure reduce cold and heat resistance, and short‐term heat exposure decreases cold but increases heat resistance. Starvation resistance is not affected by any of the short‐term treatments. Thus, the effects of short‐term stress exposure are either neutral or negative, except for a positive effect of heat exposure on heat resistance, indicating the negative effects of pre‐exposure to stress. Interestingly, significant interactions between acclimation temperature and short‐term stress exposure for heat and cold resistance are found, demonstrating that larger temperature differences incur more damage. Therefore, animals may not generally be able to benefit from pre‐exposure to stress (through ‘hardening’), depending on their previously experienced conditions. The complex interactions between environmental variation, stress and resistance are highlighted, warranting further investigations.     

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

相似文献   

Heat tolerance in Drosophila subobscura along a latitudinal gradient: Contrasting patterns between plastic and genetic responses

Susceptibility to global warming relies on how thermal tolerances respond to increasing temperatures through plasticity or evolution. Climatic adaptation can be assessed by examining the geographic variation in thermal‐related traits. We studied latitudinal patterns in heat tolerance in Drosophila subobscura reared at two temperatures. We used four static stressful temperatures to estimate the thermal death time (TDT) curves, and two ramping assays with fast and slow heating rates. Thermal death time curves allow estimation of the critical thermal maximum (CT_max), by extrapolating to the temperature that would knock down the flies almost “instantaneously,” and the thermal sensitivity to increasing stressful temperatures. We found a positive latitudinal cline for CT_max, but no clinal pattern for knockdown temperatures estimated from the ramping assays. Although high‐latitude populations were more tolerant to an acute heat stress, they were also more sensitive to prolonged exposure to less stressful temperatures, supporting a trade‐off between acute and chronic heat tolerances. Conversely, developmental plasticity did not affect CT_max but increased the tolerance to chronic heat exposition. The patterns observed from the TDT curves help to understand why the relationship between heat tolerance and latitude depends on the methodology used and, therefore, these curves provide a more complete and reliable measurement of heat tolerance.     

City limits: Heat tolerance is influenced by body size and hydration state in an urban ant community

Cities are rapidly expanding, and global warming is intensified in urban environments due to the urban heat island effect. Therefore, urban animals may be particularly susceptible to warming associated with ongoing climate change. We used a comparative and manipulative approach to test three related hypotheses about the determinants of heat tolerance or critical thermal maximum (CT_max) in urban ants—specifically, that (a) body size, (b) hydration status, and (c) chosen microenvironments influence CT_max. We further tested a fourth hypothesis that native species are particularly physiologically vulnerable in urban environments. We manipulated water access and determined CT_max for 11 species common to cities in California's Central Valley that exhibit nearly 300‐fold variation in body size. There was a moderate phylogenetic signal influencing CT_max, and inter (but not intra) specific variation in body size influenced CT_max where larger species had higher CT_max. The sensitivity of ants’ CT_max to water availability exhibited species‐specific thresholds where short‐term water limitation (8 hr) reduced CT_max and body water content in some species while longer‐term water limitation (32 hr) was required to reduce these traits in other species. However, CT_max was not related to the temperatures chosen by ants during activity. Further, we found support for our fourth hypothesis because CT_max and estimates of thermal safety margin in native species were more sensitive to water availability relative to non‐native species. In sum, we provide evidence of links between heat tolerance and water availability, which will become critically important in an increasingly warm, dry, and urbanized world that others have shown may be selecting for smaller (not larger) body size.     

Thermal limits to survival and activity in two life stages of false codling moth Thaumatotibia leucotreta (Lepidoptera,Tortricidae)

The present study examines life stage‐related variation in the thermal limits to activity and survival in an African pest, the false codling moth Thaumatotibia leucotreta (Lepidoptera, Tortricidae). Thermal tolerance, including the functional activity limits of critical thermal maxima and minima (CT_max and CT_min respectively), upper and lower lethal temperature, and the effect of heat and cold hardening (short‐term acute plasticity), is measured across a diverse range of low or high temperature stress conditions in both larvae and adults. We also report the sum of inducible and cognate forms of the amounts of heat shock protein 70 (HSP70) as an explanatory variable for changes in thermotolerance. The results show that the larvae have high variability in CT_max and CT_min at different ramping rates and low levels of basal (innate) thermal tolerance. By contrast, the adults show high basal tolerance and overall lower variability in CT_max and CT_min, indicating lower levels of phenotypic plasticity in thermotolerance. HSP70 responses, although variable, do not reflect these tolerance or survival patterns. Larvae survive across a broader range of temperatures, whereas adults remain active across a broader range of temperatures. Life stage‐related variation in thermal tolerance is most pronounced under the slowest (most ecologically‐relevant) ramping rate (0.06 °C min^–1) during lower critical thermal limit experiments and least pronounced during upper thermal limit experiments. Thus, the ramping rate can hinder or enhance the detection of stage‐related variation in thermal limits to activity and survival of insects.     

Desiccation resistance in tropical insects: causes and mechanisms underlying variability in a Panama ant community

Desiccation resistance, the ability of an organism to reduce water loss, is an essential trait in arid habitats. Drought frequency in tropical regions is predicted to increase with climate change, and small ectotherms are often under a strong desiccation risk. We tested hypotheses regarding the underexplored desiccation potential of tropical insects. We measured desiccation resistance in 82 ant species from a Panama rainforest by recording the time ants can survive desiccation stress. Species' desiccation resistance ranged from 0.7 h to 97.9 h. We tested the desiccation adaptation hypothesis, which predicts higher desiccation resistance in habitats with higher vapor pressure deficit (VPD) – the drying power of the air. In a Panama rainforest, canopy microclimates averaged a VPD of 0.43 kPa, compared to a VPD of 0.05 kPa in the understory. Canopy ants averaged desiccation resistances 2.8 times higher than the understory ants. We tested a number of mechanisms to account for desiccation resistance. Smaller insects should desiccate faster given their higher surface area to volume ratio. Desiccation resistance increased with ant mass, and canopy ants averaged 16% heavier than the understory ants. A second way to increase desiccation resistance is to carry more water. Water content was on average 2.5% higher in canopy ants, but total water content was not a good predictor of ant desiccation resistance or critical thermal maximum (CT_max), a measure of an ant's thermal tolerance. In canopy ants, desiccation resistance and CT_max were inversely related, suggesting a tradeoff, while the two were positively correlated in understory ants. This is the first community level test of desiccation adaptation hypothesis in tropical insects. Tropical forests do contain desiccation‐resistant species, and while we cannot predict those simply based on their body size, high levels of desiccation resistance are always associated with the tropical canopy.     

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

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

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

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

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

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

Maximum thermal tolerance trades off with chronic tolerance of high temperature in contrasting thermal populations of Radix balthica

Thermal adaptation theory predicts that thermal specialists evolve in environments with low temporal and high spatial thermal variation, whereas thermal generalists are favored in environments with high temporal and low spatial variation. The thermal environment of many organisms is predicted to change with globally increasing temperatures and thermal specialists are presumably at higher risk than thermal generalists. Here we investigated critical thermal maximum (CT_max) and preferred temperature (T_p) in populations of the common pond snail (Radix balthica) originating from a small‐scale system of geothermal springs in northern Iceland, where stable cold (ca. 7°C) and warm (ca. 23°C) habitats are connected with habitats following the seasonal thermal variation. Irrespective of thermal origin, we found a common T_p for all populations, corresponding to the common temperature optimum (T_opt) for fitness‐related traits in these populations. Warm‐origin snails had lowest CT_max. As our previous studies have found higher chronic temperature tolerance in the warm populations, we suggest that there is a trade‐off between high temperature tolerance and performance in other fitness components, including tolerance to chronic thermal stress. T_p and CT_max were positively correlated in warm‐origin snails, suggesting a need to maintain a minimum “warming tolerance” (difference in CT_max and habitat temperature) in warm environments. Our results highlight the importance of high mean temperature in shaping thermal performance curves.     

Resistance to environmental stress in Drosophila ananassae: latitudinal variation and adaptation among populations

Geographical variation in traits related to fitness is often the result of adaptive evolution. Stress resistance traits in Drosophila often show clinal variation, suggesting that selection affects resistance traits either directly or indirectly. Multiple stress resistance traits were investigated in 45 natural populations of Drosophila ananassae collected from all over India. There was significant positive correlation between starvation resistance and lipid content. Significant negative correlations between desiccation and lipid content and between desiccation and heat resistance were also found. Flies from lower latitudes had higher starvation resistance, heat resistance and lipid content but the pattern was reversed for desiccation resistance. These results suggest that flies from different localities varied in their susceptibility to starvation because of difference in their propensity to store body lipid. Multiple regression analysis provided evidence of climatic selection driven by latitudinal variation in the seasonal amplitude of temperature and humidity changes within the Indian. Finally, our results suggest a high degree of variation in stress resistance at the population level in D. ananassae.     

Developmental acclimation affects clinal variation in stress resistance traits in Drosophila buzzatii

Patterns of clinal genetic variation in Drosophila are often characterized after rearing at constant temperatures. However, clinal patterns might change after acclimation if populations differ in their plastic response to fluctuating environments. We studied longevity, starvation and heat knock‐down resistance after development at either constant or fluctuating temperatures in nine Drosophila buzzatii populations collected along an altitudinal gradient in Tenerife, Spain. Flies that developed at fluctuating temperatures had higher stress resistance despite experiencing a slightly lower average temperature than those at constant temperatures. Genetic variation along the gradient was found in both stress‐resistance traits. Because Q_ST values greatly exceeded F_ST values, genetic drift could not explain this diversification. In general, differences among populations were larger after rearing at fluctuating temperatures, especially in heat knock‐down, for which clinal patterns disappeared when flies were reared at constant temperatures. This result emphasizes the importance of determining whether populations originating from different environments differ in their plastic responses to stress.