"A comparison of thermal stress response between Drosophila melanogaster and Drosophila pseudoobscura reveals differences between species and sexes"

The environment is changing faster than anticipated due to climate change, making species more vulnerable to its impacts. The level of vulnerability of species is influenced by factors such as the degree and duration of exposure, as well as the physiological sensitivity of organisms to changes in their environments, which has been shown to vary among species, populations, and individuals. Here, we compared physiological changes in fecundity, critical thermalmaximum (CTmax), respiratory quotient (RQ), and DNA damage in ovaries in response to temperature stress in two species of fruit fly, Drosophila melanogaster (25 vs. 29.5 °C) and Drosophila pseudoobscura (20.5 vs. 25 °C). The fecundity of D. melanogaster was more affected by high temperatures when exposed during egg through adult development, while D. pseudoobscura was most significantly affected when exposed to high temperatures exclusively during egg through pupal development. Additionally, D. melanogaster males exhibited a decrease of CTmax under high temperatures, while females showed an increase of CTmax when exposed to high temperatures during egg through adult development. while D. pseudoobscura females and males showed an increased CTmax only when reared at high temperatures during egg through pupae development. Moreover, both species showed an acceleration in oogenesis and an increase in apoptosis due to heat stress. These changes can likely be attributed to key differences in the geographic range, thermal range, development time, and other different factors between these two systems. Through this comparison of variation in physiology and developmental response to thermal stress, we found important differences between species and sexes that suggest future work needs to account for these factors separately in understanding the effects of constant increased temperatures.

Protective Effect of Diploschistes ocellatus Against Heat Shock-Mediated Defects on Function of Reproductive Organs in Drosophila melanogaster

Introduction: Repeated heat shock (HS) stresses reduce the reproduction rate of Drosophila flies. Heat shock proteins (HSPs) protect cells against irreversible damages inducing heatinduced.Oxidative stress declines protective function of HSPs. Diploschistes ocellatus lichen aqueous extract possesses a strong antioxidant potential in vitro. Antioxidants can preserve HSPs function. Therefore, the present study for the first time investigated the cytoprotective effects of D. ocellatus aqueous extract against HS-mediated deleterious effects on reproductive function in Drosophila melanogaster. Methods: Three different types of culture media including control, 30% lichen extract, and 60%lichen extract were prepared. Adult D. melanogaster flies were placed on Delcour medium and allowed to lay eggs for 2 hours. Then the eggs were equally distributed between the culture media. After flies completed their life cycle, the adult enclosed flies were exposed to HS. To assess reproductive function, the newly emerged adult flies were transferred to the freshly prepared regular culture medium every three days for 3 times and finally adult offspring born to these flies were enumerated.Results: HS negatively affected the reproduction rate in flies in control group. Quantification of adult enclosed flies born to the D. ocellatus extract treated flies showed that lichen extract could negate the deleterious effects of HS on reproduction function of D. melanogaster in a dose-dependent manner.Conclusion: Diploschistes ocellatus aqueous extract attenuated the harmful effects of HS stress on reproductive function of D. melanogaster. The secondary metabolites present in D. ocellatus can be considered as a bona fide candidate in novel drug development to target reproductive diseases in which oxidative stress is involved. Moreover, it can be concluded that D. melanogaster is an ideal model organism to induce cellular stress in vitro and study therapeutic potential of lichen extracts.

A transcriptional and functional analysis of heat hardening in two invasive fruit fly species, Bactrocera dorsalis and Bactrocera correcta

Many insects have the capacity to increase their resistance to high temperatures by undergoing heat hardening at nonlethal temperatures. Although this response is well established, its molecular underpinnings have only been investigated in a few species where it seems to relate at least partly to the expression of heat shock protein (Hsp) genes. Here, we studied the mechanism of hardening and associated transcription responses in larvae of two invasive fruit fly species in China, Bactrocera dorsalis and Bactrocera correcta. Both species showed hardening which increased resistance to 45°C, although the more widespread B. dorsalis hardened better at higher temperatures compared to B. correcta which hardened better at lower temperatures. Transcriptional analyses highlighted expression changes in a number of genes representing different biochemical pathways, but these changes and pathways were inconsistent between the two species. Overall B. dorsalis showed expression changes in more genes than B. correcta. Hsp genes tended to be upregulated at a hardening temperature of 38°C in both species, while at 35°C many Hsp genes tended to be upregulated in B. correcta but not B. dorsalis. One candidate gene (the small heat shock protein gene, Hsp23) with a particularly high level of upregulation was investigated functionally using RNA interference (RNAi). We found that RNAi may be more efficient in B. dorsalis, in which suppression of the expression of this gene removed the hardening response, whereas in B. correcta RNAi did not decrease the hardening response. The different patterns of gene expression in these two species at the two hardening temperatures highlight the diverse mechanisms underlying hardening even in closely related species. These results may provide target genes for future control efforts against such pest species.

Geographic variation in responses of European yellow dung flies to thermal stress

Climatic conditions can be very heterogeneous even over small geographic scales, and are believed to be major determinants of the abundance and distribution of species and populations. Organisms are expected to evolve in response to the frequency and magnitude of local thermal extremes, resulting in local adaptation. Using replicate yellow dung fly (Scathophaga stercoraria; Diptera: Scathophagidae) populations from cold (northern Europe) and warm climates (southern Europe), we compared 1) responses to short-term heat and cold shocks in both sexes, 2) heat shock protein (Hsp70) expression in adults and eggs, and 3) female reproductive traits when facing short-term heat stress during egg maturation. Contrary to expectations, thermal traits showed minor geographic differentiation, with weak evidence for greater heat resistance of southern flies but no differentiation in cold resistance. Hsp70 protein expression was little affected by heat stress, indicating systemic rather than induced regulation of the heat stress response, possibly related to this fly group's preference for cold climes. In contrast, sex differences were pronounced: males (which are larger) endured hot temperatures longer, while females featured higher Hsp70 expression. Heat stress negatively affected various female reproductive traits, reducing first clutch size, overall reproductive investment, egg lipid content, and subsequent larval hatching. These responses varied little across latitude but somewhat among populations in terms of egg size, protein content, and larval hatching success. Several reproductive parameters, but not Hsp70 expression, exhibited heritable variation among full-sib families. Rather than large-scale clinal geographic variation, our study suggests some local geographic population differentiation in the ability of yellow dung flies to buffer the impact of heat stress on reproductive performance.

Genetic variation for resistance to high temperature stress of mature sperm - a study in Drosophila

Genetic variation for resistance to heat stress has been found for a number of life-history components in Drosophila species. For male and female fertility (or sterility), stress resistance of the parents is confounded with stress resistance of the haploid gametes. Many genes are known to influence male fertility in Drosophila melanogaster. Some may carry temperature sensitive alleles that reduce fertility through effects on mature sperm when exposed to heat stress. In this study, sperm from each of 320 males were either not heat shocked (control) or exposed to a heat shock (36.9°C for 2 hours) either in the male testes or in the female reproductive tract. We did not detect any temperature sensitive sterility alleles. These results are relevant in relation to haploid gene expression and the findings of considerable amounts of mRNA in mature sperm, potentially important for sperm function and fertilization.

Evolutionary potential of upper thermal tolerance: biogeographic patterns and expectations under climate change

How will organisms respond to climate change? The rapid changes in global climate are expected to impose strong directional selection on fitness-related traits. A major open question then is the potential for adaptive evolutionary change under these shifting climates. At the most basic level, evolutionary change requires the presence of heritable variation and natural selection. Because organismal tolerances of high temperature place an upper bound on responding to temperature change, there has been a surge of research effort on the evolutionary potential of upper thermal tolerance traits. Here, I review the available evidence on heritable variation in upper thermal tolerance traits, adopting a biogeographic perspective to understand how heritability of tolerance varies across space. Specifically, I use meta-analytical models to explore the relationship between upper thermal tolerance heritability and environmental variability in temperature. I also explore how variation in the methods used to obtain these thermal tolerance heritabilities influences the estimation of heritable variation in tolerance. I conclude by discussing the implications of a positive relationship between thermal tolerance heritability and environmental variability in temperature and how this might influence responses to future changes in climate.

Identification, genomic organization and expression profiles of four heat shock protein genes in the western flower thrips, Frankliniella occidentalis

The western flower thrips, Frankliniella occidentalis, is an important invasive pest with a strong tolerance for extreme temperatures; however, the molecular mechanisms that regulate thermotolerance in this insect remain unclear. In this study, four heat shock protein genes were cloned from F. occidentalis and named Fohsp90, Fohsc701, Fohsc702 and Fohsp60. These four Hsps exhibited typical characteristics of heat shock proteins. Subcellular localization signals and phylogenetic analysis indicated that FoHsp90 and FoHsc701 localize to the cytosol, whereas FoHsc702 and FoHsp60 were located in the endoplasmic reticulum and mitochondria, respectively. Analysis of genomic sequences revealed the presence of introns in the four genes (three, four, seven, and five introns for Fohsp90, Fohsc701, Fohsc702 and Fohsp60, respectively). Both the number and position of introns in these four genes were quite different from analogous genes in other species. qRT-PCR indicated that the four Fohsps were detected in second-stage larvae, one-day-old pupae, and one-day-old adults, and mRNA expression levels were lowest in larvae and highest in pupae. Fohsc701 and Fohsc702 possessed similar expression patterns and were not induced by cold or heat stress. Expression of Fohsp60 was significantly elevated by heat, and Fohsp90 was rapidly up-regulated after exposure to both cold and heat stress. Exposure to -8°C had no effect on expression of the four Fohsps; however, expression of Fohsp90 and Fohsp60 was highest after a 2-h incubation at 39°C. Furthermore, cold and heat hardening led to significant up-regulation of the four Fohsps compared to their respective controls. Collectively, our results indicate that the four FoHsps contribute to insect development and also function in rapid cold or heat hardening; furthermore, FoHsp90 and FoHsp60 contribute to thermotolerance in F. occidentalis.

Status of research on Drosophila ananassae at global level

Drosophila, a dipteran insect, has been found to be the best biological model for different kinds of studies. D melanogaster was first described by Meigen in 1830 , is most extensively studied species of the genus Drosophila and a number of investigations employing this species have been documented in areas such as genetics, behaviour, evolution, development, molecular biology, ecology, population biology, etc. Besides D. melanogaster, a number of other species of the genus Drosophila have also been used for different kinds of investigations. Among these, D. ananassae, a cosmopolitan and domestic species endowed with several unusual genetic features, is noteworthy. Described for the first time from Indonesia (Doleschall 1858), this species is commonly distributed in India. Extensive research work on D. ananassae has been done by numerous researchers pertaining to cytology, genetics, mutagenesis, gene mapping, crossing-over in both sexes, population and evolutionary genetics,behaviour genetics, ecological genetics, sexual isolation, fluctuating asymmetry, trade-offs etc. Genome of D. ananassae has also been sequenced. The status of research on D. ananassae at global level is briefly described in this review. Bibliography on this species from different countries worldwide reveals that maximum contribution is from India.

Effects of heat stress on the quality of Trichogrammatoidea bactrae Nagaraja (Hymenoptera: Trichogrammatidae)

Trichogrammatoidea bactrae Nagaraja (Hymenoptera: Trichogrammatidae) is an important natural enemy of many species of lepidopterous pests. The effects of heat stress temperature (33, 36, and 39 °C), duration of exposure (2, 4, 6, and 8 h), and developmental stage during exposure (embryo-first instar larvae, second instar larvae, prepupae, and pupae) on the development and reproduction of parasitoid T. bactrae were investigated in the laboratory. When exposed to 39 °C for 8 h during pupal stage, only 19.90% adults emerged from host eggs, and more than 14% were deformed (wings were folded or incomplete). Parasitoid females exposed to 39 °C for 8 h as prepupae only lived for 1.45 days and parasitized about 23.5 host eggs. Moreover, life-table parameters of T. bactrae were also influenced by exposure to heat stress temperatures during each preimaginal developmental stage. Based on these results, we propose that T. bactrae is susceptible to high temperatures, especially at 39 °C. Thus, this parasitoid may be more effectively controlling lepidopterous pests during cooler weather conditions.

How does heat shock affect the life history traits of adults and progeny of the aphid parasitoid Aphidius avenae (Hymenoptera: Aphidiidae)?

Because insects are ectotherms, their physiology, behaviour and fitness are influenced by the ambient temperature. Any changes in environmental temperatures may impact the fitness and life history traits of insects and, thus, affect population dynamics. Here, we experimentally tested the impact of heat shock on the fitness and life history traits of adults of the aphid parasitoid Aphidius avenae and on the later repercussions for their progeny. Our results show that short exposure (1 h) to an elevated temperature (36 degrees C), which is frequently experienced by parasitoids during the summer, resulted in high mortality rates in a parasitoid population and strongly affected the fitness of survivors by drastically reducing reproductive output and triggering a sex-dependent effect on lifespan. Heat stress resulted in greater longevity in surviving females and in shorter longevity in surviving males in comparison with untreated individuals. Viability and the developmental rates of progeny were also affected in a sex-dependent manner. These results underline the ecological importance of the thermal stress response of parasitoid species, not only for survival, but also for maintaining reproductive activities.

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.

Variations in morphological and life-history traits under extreme temperatures in Drosophila ananassae

Using half-sib analysis, we analysed the consequences of extreme rearing temperatures on genetic and phenotypic variations in the morphological and life-history traits of Drosophila ananassae. Paternal half-sib covariance contains a relatively small proportion of the epistatic variance and lacks the dominance variance and variance due to maternal effect, which provides more reliable estimates of additive genetic variance. Experiments were performed on a mass culture population of D. ananassae collected from Kanniyakumari (India). Two extremely stressful temperatures (18 degree C and 32 degree C) and one standard temperature (25 degree C) were used to examine the effect of stressful and non-stressful environments on the morphological and life-history traits in males and females. Mean values of various morphological traits differed signifi cantly among different temperature regimens in both males and females. Rearing at 18 degree C and 32 degree C resulted in decreased thorax length, wing-to-thorax (w/t) ratio, sternopleural bristle number, ovariole number, sex comb-tooth number and testis length. Phenotypic variances increased under stressful temperatures in comparison with non-stressful temperatures. Heritability and evolvability based on among-sires (males), among-dams (females), and the sum of the two components (sire + dam) showed higher values at both the stressful temperatures than at the non-stressful temperature. These differences reflect changes in additive genetic variance. Viability was greater at the high than the low extreme temperature. As viability is an indicator of stress, we can assume that stress was greater at 18 degree C than at 32 degree C in D. ananassae. The genetic variations for all the quantitative and life-history traits were higher at low temperature. Variation in sexual traits was more pronounced as compared with other morphometric traits, which shows that sexual traits are more prone to thermal stress. Our results agree with the hypothesis that genetic variation is increased in stressful environments.

Effect of environmental stress on fluctuating asymmetry in certain morphological traits in Drosophila ananassae: nutrition and larval crowding

The association of fluctuating asymmetry and phenotypic and genetic variability with environmental stress was investigated using poor nutrition and larval density as stresses on 10 recently collected isofemale lines of Drosophila ananassae Doleschall, 1858. Trait means for different morphological traits were reduced by stress, whereas phenotypic and genetic variability increased. The levels of fluctuating asymmetry and positional fluctuating asymmetry were similar in flies reared on poor and standard media. In constrast, there is a significant difference in both asymmetry measures in the flies reared at different larval densities for all traits. However, when asymmetry values across all traits were combined into a single index, composite fluctuating asymmetry, significant differences were found in males and females reared at different larval densities but not under nutritional stress. Moreover, composite fluctuating asymmetry is higher in males than in females, suggesting that males are more vulnerable to developmental stress. The results suggest that trait means are more sensitive to stress than fluctuating-symmetry measures and that the effect of stress is trait- and sex-specific. Generalizations based on the use of fluctuating asymmetry as an indicator of environmental stress in D. ananassae should therefore be used with caution.

Life history consequences of temperature transients in Drosophila melanogaster

The physiological and life history consequences of chronic temperatures are well studied in ectotherms. However, little is known about the consequences of short-term exposure to unusually high or low temperatures, as would occur during a weather front. What are the immediate life-history effects of such thermal transients? Can ectotherms recover quickly or do they suffer carry-over effects that persist after weather returns to normal? We measured the impact of thermal transients on egg and progeny production of Drosophila melanogaster Meigen from Washington State. We reared flies at 25°C and then transferred 3- to 5-day old adults to one of three transient treatments (1 or 3 days at 18°C, 1 day at 29°C) before returning them to 25°C. We monitored daily egg production and egg-to-adult viability before (as a control), during, and after the transient as well as fecundity and viability of flies held at constant 18°, 25° and 29°C. This population appears particularly heat tolerant as neither constant nor transient exposure to 29°C (usually a stressful temperature for this species) affected female fecundity or the viability of her progeny. However, a 1- or 3-day exposure to 18°C reduced female fecundity by 75–90% relative to controls, and eggs laid during the 3-day exposure had greatly reduced viability. When returned to 25°C after transient exposure to 18°C, females immediately matched the fecundity and viability of females maintained constantly at 25°C. Therefore, these flies do not suffer negative carry-over effects from these moderate thermal transients. Surprisingly, fitness (intrinsic rate of population growth) was not depressed by transient temperature exposure. However, the severity and especially the timing of the transient will probably determine the likelihood of carry-over effects as well as its effect on fitness.