Timing alters how a heat shock affects a host-parasitoid interaction

Abiotic factors' effects on species are now well-studied, yet they are still often difficult to predict, especially for strongly interacting species. If these altered abiotic factors and species interactions occur as discrete events in time, such complications may occur because of the events’ relative timing. One such discrete abiotic factor is the short-duration, large magnitude increase in temperature called a heat shock. This study investigates how the timing of heat shocks affects the successful attack and reproduction of a parasitoid wasp (Aphidius ervi) attacking its host, the pea aphid (Acyrthosiphon pisum). We tested three relative timings: 1) heat shock before the wasp attacks hosts, 2) heat shock while the wasp is foraging, and 3) heat shock after the wasp has attacked hosts. In each scenario we compared wasp mummy production (pupal stage) with and without a heat shock. Our results showed that a heat shock had the largest effect when it occurred while wasps actively foraged, with fewer mummies produced when exposed to a heat shock compared to the no heat shock control. Follow-up behavioral tests suggest this was caused by wasps becoming inactive during heat shocks. In contrast, when heat shocks were applied three days before or after foraging, we found no difference in mummy production between the heat shock treatment and no heat shock control. These results show the potential importance of timing when considering the ramifications of an altered abiotic factor, especially with relatively discrete abiotic events and interactions.     

Heat shock proteins from the lungless salamanders Eurycea bislineata and Desmognathus ochrophaeus

• 1.1. Exposing adult salamanders, Eurycea bislineata and Desmognathus ochrophaeus, to heat shocks of 1 hr at 2 or 5°C below Critical Thermhal Maximum (CTM) resulted in the induction of two heat shock proteins (hsps) of approx. M_r 70,000 and 30,000.
• 2.2. Induction patterns in response to similar heat shocks generally differed between the two species.
• 3.3. The milder heat shocks (5°C below CTM) caused different induction patterns than those from the more severe heat shocks, on a tissue-dependent basis. These results indicate that induction of the two hsps is probably independent.

     

Effect of sequential heat and cold shocks on nuclear phenotypes of the blood-sucking insect,Panstrongylus megistus (Burmeister) (Hemiptera,Reduviidae)

Thermal shocks induce changes in the nuclear phenotypes that correspond to survival (heterochromatin decondensation, nuclear fusion) or death (apoptosis, necrosis) responses in the Malpighian tubules of Panstrongylus megistus. Since thermal tolerance increased survival and molting rate in this species following sequential shocks, we investigated whether changes in nuclear phenotypes accompanied the insect survival response to sequential thermal shocks. Fifth instar nymphs were subjected to a single heat (35 or 40 degrees C, 1 h) or cold (5 or 0 degrees C, 1 h) shock and then subjected to a second shock for 12 h at 40 or 0 degrees C, respectively, after 8, 18, 24 and 72 h at 28 degrees C (control temperature). As with specimen survival, sequential heat and cold shocks induced changes in frequency of the mentioned nuclear phenotypes although their patterns differed. The heat shock tolerance involved decrease in apoptosis simultaneous to increase in cell survival responses. Sequential cold shocks did not involve cell/nuclear fusion and even elicited increase in necrosis with advancing time after shocks. The temperatures of 40 and 0 degrees C were more effective than the temperatures of 35 and 5 degrees C in eliciting the heat and cold shock tolerances, respectively, as shown by cytological analysis of the nuclear phenotypes. It is concluded that different sequential thermal shocks can trigger different mechanisms of cellular protection against stress in P. megistus, favoring the insect to adapt to various ecotopes.     

Effect of chilling, heat shock, and vigor on the growth of cucumber (Cucumis sativus) radicles

Chilling at 2.5°C reduced the subsequent growth of cucumber ( Cucumis sativus L.) radicles at 25°C. The reduction in radicle growth was linear for 1–3 days of chilling at ≈10% per day of treatment, but then it increased in a non-linear pattern until subsequent radicle growth was all but eliminated by 6 days of chilling. A heat shock of 40°C for 4–12 min increased chilling tolerance such that 4 days of chilling caused only a 36% decrease in radicle growth, compared to 66% for seedlings not heat shocked. Heat shocks were only able to protect that part of radicle growth that was in excess of the linear decrease in radicle growth projected from 0–3 days. There appear to be two effects of chilling on radicle growth. The first inhibition of subsequent growth was linear and was not affected by heat shocks. The second inhibition was much more severe; it appeared after 3 days of chilling and could be prevented by heat shock. Seeds classified with different levels of vigor (i.e., different initial rates of growth) did not respond significantly different to chilling stresses following heat-shock treatments.     

Triploidy induction in Nile tilapia,Oreochromis niloticus L. using pressure,heat and cold shocks

Summary The results of a study aimed at the identification of treatment optima for triploidy induction in recently fertilised Oreochromis niloticus L. eggs by altering the intensity, duration and timing of application of pressure, heat and cold shocks are reported. Preliminary, but not directly comparable, trials suggested the following treatments to be close to the individual agent optima. Pressure: 8,000 psi 2-min duration applied 9 min after fertilisation (a.f.); heat: 41 °C, 3.5-min duration applied 5 min a.f., cold: 9°C, 30-min duration applied 7 min a.f. In a directly comparable trial in which the eggs of eight different females were separately exposed to the optimum shocks listed above, individual triploid yields were more variable following cold shocks and mean triploid yields were, therefore, higher following pressure and heat shock. These and other results obtained are presented and the light they shed on the timing of the second meiotic division in this species is discussed.     

Effects of heat shock on protein processing and turnover in developing Drosophila wings

Developmental defects called phenocopies can be induced by heating Drosophila melanogaster pupae at specific developmental stages. The induction of the defects is thought to be a result of interference with gene expression at some level (Petersen and Mitchell, Dev Biol 1987; 121:335-341, 1987). Here we look at protein turnover in developing 52-hour wings and at the effect of heat on the proteolytic processing of three proteins that normally turn over rapidly. The effect of the heat treatment itself on the turnover of each protein is different. However, all of the proteins appear to be stabilized at 25 degrees C during recovery from severe heat shocks.     

Survival and molting incidence after heat and cold shocks in Panstrongylus megistus Burmeister

Survival and molting incidence were studied after heat (40 degrees C) and cold (0 degree C) shocks in specimens of Panstrongylus megistus with the aim of establishing its response to temperature stress under laboratory rearing conditions and to understand occasional changes in the biological characteristics of specimens captured in nature. The response to the thermal shocks was found to vary as a function of the temperature and duration of the shock, developmental phase and sex of the specimens, and in certain cases, the insect habit and nourishment conditions. P. megistus specimens were found to be less resistant to the heat shock assay than Triatoma infestans, another reduviid species. The short cold shock affected survival of P. megistus more than did the heat shock, survival of fully-nourished specimens being preferential. The response of adults to the short cold shock was affected by sex, males being generally less resistant. The insect sylvatic habit was found to seldom affect the thermal shock response established for specimens with domestic habit. A decrease in molting frequency and sometimes a slowdown of the molting rate were found after the short heat and cold shocks, possibly promoted by change in hormonal balance, and differing from patterns reported for T. infestans. The results indicate that no generalization should be made for different reduviid species in terms of the effects of temperature shocks.     

Experimental studies on ploidy evolution in yeast

Variation in the prominence of haploidy and diploidy is a striking feature of eukaryote life cycles that has not been explained from an evolutionary point of view. the ease with which ploidy and other variables of population genetics may be manipulated in yeast make Saccharomyces cerevisiae an excellent subject for experiments on the fitness effects of ploidy. Several hypotheses have been advanced to explain the emphasis on diploidy in plants and animals, and yeast experiments have been particularly informative for a few. Evidence suggests that diploids may enjoy an immediate advantage over haploids in masking harmful mutations, avoiding the fitness cost such mutations impose on haploids. A convincing longer-term advantage for diploidy has proven elusive, and different evolutionary explanations for the origin and for the subsequent maintenance of diploidy may be required.     

Trehalase activity in dormant and activated spores of Phycomyces blakesleeanus

Summary Heat treatment of Phycomyces sporangiospores, which breaks dormancy, causes a very rapid 10- to 15fold increase in trehalase activity; soon after the heat shock the enzyme activity decays. This phenomenon can be repeated several times by repeating the heat shocks. Prolonging the heat treatment over the minimum required time delays the decay of enzyme activity. Cycloheximide does not prevent the rise in enzyme activity. It is suggested that heat treatment converts temporarily an inactive form of trehalase into an active one. Optimal enzyme activity is obtained at pH 7.5 and the enzyme requires metal ions for maximal activity. The possible role of trehalase in the spore-activation process is discussed.     

Specific protection from phenocopy induction by heat shock

Mild heat treatments applied to whole animals or cell cultures of Drosophila prior to lethal heat shocks result in increased survival and protection against phenocopy induction. The optimal condition for the preliminary mild heat treatment is that which induces the synthesis of heat-shock proteins but does not turn off the protein synthesis that is in progress. Recovery of protein synthesis but not RNA synthesis following a drastic heat shock is much enhanced by the pretreatments. The results suggest that the protection for survival and against phenocopy induction is due to storage of messenger RNA.     

Non‐additive effects of simulated heat waves and predators on prey phenotype and transgenerational phenotypic plasticity

Understanding the effects of extreme climatic events on species and their interactions is of paramount importance for predicting and mitigating the impacts of climate change on communities and ecosystems. However, the joint effects of extreme climatic events and species interactions on the behaviour and phenotype of organisms remain poorly understood, leaving a substantial gap in our knowledge on the impacts of climatic change on ecological communities. Using an aphid–ladybeetle system, we experimentally investigated the effects of predators and heat shocks on prey body size, microhabitat use, and transgenerational phenotypic plasticity (i.e., the asexual production of winged offspring by unwinged mothers). We found that (i) aphids were smaller in the presence of predators but larger when exposed to frequent heat shocks; (ii) frequent heat shocks shifted aphid distribution towards the plant's apex, but the presence of predators had the opposite effect and dampened the heat‐shock effects; and (iii) aphids responded to predators by producing winged offspring, but heat shocks strongly inhibited this transgenerational response to predation. Overall, our experimental results show that heat shocks inhibit phenotypic and behavioural responses to predation (and vice versa) and that such changes may alter trophic interactions, and have important consequences on the dynamics and stability of ecological communities. We conclude that the effects of extreme climatic events on the phenotype and behaviour of interacting species should be considered to understand the effects of climate change on species interactions and communities.     

Does Diploidy Increase the Rate of Adaptation?

Explanations of the evolution of diploidy have focused on the advantages gained from masking deleterious alleles. Recent theory has shown, however, that masking does not always provide an advantage to diploidy and would never favor diploidy in predominantly asexual organisms. We explore a neglected alternative theory which posits that, by doubling the genome size, diploids double the rate at which favorable mutations arise. Consequently, the rate of adaptation in diploids is presumed to be faster than in haploids. The rate of adaptation, however, depends not only on the rate of appearance of new favorable mutations but also on the rate at which these mutations are incorporated (which depends on the population size and on the dominance of favorable mutations). We show that, in both asexuals and sexuals, doubling the mutation rate via diploidy often does not accelerate the rate of adaptation. Indeed, under many conditions, diploidy slows adaptation.     

Effect of sequential cold shocks on survival and molting incidence in Panstrongylus megistus (Burmeister) (Hemiptera, Reduviidae)

The survival and molting incidence were studied in the insect, Panstrongylus megistus, following sequential cold shocks in which a milder shock at 0 or 5 degrees C for 1 h preceded a more severe shock (0 degrees C, 12 h). The shocks were separated by intervals of 8, 18, 24, and 72 h at 28 degrees C. The survival rate after sequential shocks was identical to that of unshocked controls. Cold-shock tolerance differed from heat-shock tolerance since the latter varied with the time between shocks and was much more transient. Sequential cold shocks produced a higher molting incidence when the first shock was given at 0 compared to 5 degrees C. This response was more rapid than that to sequential heat shocks. Cold-shock tolerance in P. megistus may involve heat-shock proteins, although other protective mechanisms may also occur concurrently. This is the first report of cold-shock tolerance in a blood-sucking hemipteran.     

Food Vacuoles During Heat-Shock-Induced Transformation from the Microstomal to the Macrostomal Cell Type of Tetrahymena vorax1

ABSTRACT. The heat-shock method for induction of the macrostomal form of Tetrahymena vorax involves the transfer of cells to reduced nutrient medium and the application of a series of elevated temperature shocks followed by washing the protozoa into inorganic medium. The component of the procedure that had the greatest effect on food vacuoles was the heat shocks. At the end of the heat shocks, cells formed vacuoles at a lower rate than non-heat-shocked cells, but the size of the vacuoles formed was larger and the protozoa contained an increased number of vacuoles and total vacuolar membrane. The rate was further reduced by washing cells into nonnutrient medium. In the absence of the heat shocks, the medium had little effect on the capacity of the cells to form vacuoles although after 7.5 h in inorganic medium, the vacuoles formed were smaller and the protozoa possessed fewer vacuoles and therefore less vacuolar membrane. The amount of membrane required to form the cytopharyngeal pouch of the macrostomal cell type was equivalent to the surface area of food vacuoles present in cells prior to the onset of the heat shocks, but the number and surface area of vacuoles decline between the time of oral resorption and pouch development.     

Heat shock protein (hsp70) expression and thermal tolerance in sublethally heat-shocked eastern oysters Crassostrea virginica infected with the parasite Perkinsus marinus

To investigate whether sublethal heat shock protects Perkinsus marinus (Dermo)-infected oysters Crassostrea virginica from lethal heat stress, and the effects of P. marinus infection on sublethal heat shock response, oysters were first experimentally challenged with P. marinus. Then, when infections in oysters progressed to moderate levels (parasite burden = 10(4) to 10(5) cells g(-1) wet tissue weight), oysters were treated with a sublethal heat shock at 40 degrees C for 1 h (heat shock + Dermo challenge). Other treatment groups included heat-shocked, unchallenged (non-P. marinus challenged) oysters and non-heat-shocked, P. marinus-challenged and -unchallenged oysters. Thermal tolerance was compared among these treatments by administering a lethal heat treatment at 44 degrees C for 1 h, 7 d after sublethal heat shock. Sublethal heat shock enhanced survival to lethal heat treatment in both P. marinus-challenged and -unchallenged oysters. Although levels of hsp70 isoforms (hsp69 and hsp72) did not vary significantly by heat shock or infection with P. marinus, responses due to these treatments were apparent when comparing hsp70 levels within infected and uninfected oysters. Infection enhanced expression of hsp69, regardless of whether oysters were heat shocked or not. In uninfected oysters, hsp72 increased due to heat shock 2 and 7 d post heat shock. Overall, this study demonstrates that heat shock can improve survival in oysters, even in oysters infected with P. marinus. Expression of hsp70 varied among isoforms after sublethal and lethal heat shocks and in infected and uninfected oysters. The heat shock response was not negatively affected by P. marinus infection.     

Somatic Mutation Favors the Evolution of Diploidy

Explanations of diploidy have focused on advantages gained from masking deleterious mutations that are inherited. Recent theory has shown that these explanations are flawed. Indeed, we still lack any satisfactory explanation of diploidy in species that are asexual or that recombine only rarely. Here I consider a possibility first suggested by EFROIMSON in 1932, by MULLER in 1964 and by CROW and KIMURA in 1965: diploidy may provide protection against somatic, not inherited, mutations. I both compare the mean fitness of haploid and diploid populations that are asexual and investigate the invasion of ``diploidy' alleles in sexual populations. When deleterious mutations are partially recessive and somatic mutation is sufficiently common, somatic mutation provides a clear advantage to diploidy in both asexual and sexual species.