Non-stressful Temperature Research Articles

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.

A unified degree day model describes survivorship ofCopitarsia corrudaPogue & Simmons (Lepidoptera: Noctuidae) at different constant temperatures

Predictions of survivorship are critical to quantify the probability of establishment by an alien invasive species, but survival curves rarely distinguish between the effects of temperature on development versus senescence. We report chronological and physiological age-based survival curves for a potentially invasive noctuid, recently described as Copitarsia corruda Pogue & Simmons, collected from Peru and reared on asparagus at six constant temperatures between 9.7 and 34.5 degrees C. Copitarsia spp. are not known to occur in the United States but are routinely intercepted at ports of entry. Chronological age survival curves differ significantly among temperatures. Survivorship at early age after hatch is greatest at lower temperatures and declines as temperature increases. Mean longevity was 220 (+/-13 SEM) days at 9.7 degrees C. Physiological age survival curves constructed with developmental base temperature (7.2 degrees C) did not correspond to those constructed with a senescence base temperature (5.9 degrees C). A single degree day survival curve with an appropriate temperature threshold based on senescence adequately describes survivorship under non-stress temperature conditions (5.9-24.9 degrees C).

Effects of Temperature and UV Radiation Increases on the Photosynthetic Efficiency in Four Scleractinian Coral Species

Experiments were performed on coral species containing clade A (Stylophora pistillata, Montipora aequituberculata) or clade C (Acropora sp., Pavona cactus) zooxanthellae. The photosynthetic efficiency (F(v)/F(m)) of the corals was first assessed during a short-term increase in temperature (from 27 degrees C to 29 degrees C, 32 degrees C, and 34 degrees C) and acute exposure to UV radiation (20.5 W m(-2) UVA and 1.2 W m(-2) UVB) alone or in combination. Increasing temperature to 34 degrees C significantly decreased the F(v)/F(m) in S. pistillata and M. aequituberculata. Increased UV radiation alone significantly decreased the F(v)/F(m) of all coral species, even at 27 degrees C. There was a combined effect of temperature and UV radiation, which reduced F(v)/F(m) in all corals by 25% to 40%. During a long-term exposure to UV radiation (17 days) the F(v)/F(m) was significantly reduced after 3 days' exposure in all species, which did not recover their initial values, even after 17 days. By this time, all corals had synthesized mycosporine-like amino acids (MAAs). The concentration and diversity of MAAs differed among species, being higher for corals containing clade A zooxanthellae. Prolonged exposure to UV radiation at the nonstressful temperature of 27 degrees C conferred protection against independent, thermally induced photoinhibition in all four species.

Altitudinal patterns for longevity, fecundity and senescence in Drosophila buzzatii

We tested for variation in longevity, senescence rate and early fecundity of Drosophila buzzatii along an elevational transect in Argentina, using laboratory-reared flies in laboratory tests performed to avoid extrinsic mortality. At 25 degrees C, females from lowland populations lived longer and had a lower demographic rate of senescence than females from highland populations. Minimal instead of maximal temperature at the sites of origin of population best predicted this cline. A very different pattern was found at higher test temperature. At 29.5 degrees C, longevity of males increased with altitude of origin of population. No clinal trend was apparent for longevity of females at 29.5 degrees C. There was evidence for a trade-off between early fecundity and longevity at non-stressful temperature (25 degrees C) along the altitudinal gradient. This trait association is consistent with evolutionary theories of aging. Population-by-temperature and sex-by-temperature interactions indicate that senescence patterns are expressed in environment specific ways.

Heat-shock protein70 gene expression in four hatchery Pacific Abalone Haliotis discus hannai Ino populations using for marker-assisted selection

Heat shock proteins (Hsps) are molecular chaperones that help organisms cope with stressful conditions. Here, we report on the growth rates and Hsp70 expressions in inbred and hybrid populations of abalone Haliotis discus hannai Ino. In abalone, inbred populations expressed more Hsp70 than hybrid populations at all temperatures, except at very high temperatures close to the physiological limit. At benign temperatures, there was a clear trend towards higher Hsp70 expression in inbred than hybrid populations, whereas at higher temperatures, a trend in the opposite direction was observed. The temperature of maximal Hsp70 expression (Tpeak) varied with the population type. The Tpeak of inbred populations (26°C) was lower than that of the hybrid populations (28°C). The maximal inducible Hsp70 of inbred populations was higher than that of hybrid populations. The results showed a trend towards higher expression in inbred population at a lower temperature. These results provide direct experimental evidence that hybrids can cope with the intrinsic stress even at non-stressful temperatures. The constitutive Hsp70 may therefore be used for marker-assisted selection in a breeding programme.

Heat and cold-induced male sterility in Drosophila buzzatii: genetic variation among populations for the duration of sterility.

Here we studied three phenotypic traits in Drosophila buzzatii that are strongly effected by temperature, and are expected to be closely associated with fitness in nature. The traits measured were thermal threshold of male sterility, time for males to gain fertility when reared at a sterility-inducing temperature and transferred to 25 degrees C on eclosion and survival after development. The last two traits were measured under four temperature regimes, constant 12 degrees C, 25 degrees C, 31 degrees C, and fluctuating 25 degrees C (18 h) and 38 degrees C (6 h). We looked for genetic variation in these traits and relations among them in four lines of D. buzzatii originating from Argentina and Tenerife. The thermal threshold of heat-induced male sterility was found to lie within the range of 30.0-31.0 degrees C. When measuring the time for males to gain fertility, males reared at a nonstressful temperature (25 degrees C) were fertile 58-67 h after emergence with only minor differences among lines. When reared constant 31 degrees C, males were fertile 174-225 h after hatching. The Argentinean lines were significantly faster in recovering from sterility than were the lines from Tenerife. When reared in a fluctuating temperature regime, differences among lines increased, dividing the lines into three significantly different groups, with a sterility period of 135-215 h. When reared at 12 degrees C from the pupal stage, males were fertile after 106-130 h with significant difference in the variance but not in the mean duration of sterility. Significant differences in viability were found among development temperatures, but not among lines, and viability and the duration of sterility seem to be genetically independent.

Developmental upregulation of inducible hsp70 transcripts, but not the cognate form, during pupal diapause in the flesh fly, Sarcophaga crassipalpis

Partial clones of the Sarcophaga crassipalpis heat shock protein 70 (hsp70) and of heat shock cognate 70 (hsc70) were developed by RT-PCR and library screening respectively. These clones were used to probe total RNA northern blots for the expression of transcripts in response to high and low temperature stress and in conjunction with the entry into an overwintering pupal diapause. In nondiapausing individuals, hsp70 was highly expressed in response to a 40°C heat shock, while hsc70 was unaffected by the heat stress. In contrast, both hsp70 and hsc70 were upregulated in nondiapausing flies following a −10°C cold shock. In diapausing pupae, hsp70 was highly upregulated during diapause, even at a non-stress temperature of 20°C. Upregulation was initiated at the onset of diapause and persisted throughout diapause. During diapause, heat shock did not further elevate the level of hsp70 expression. Within 12 h after diapause was terminated, hsp70 ceased to be expressed. The expression of hsc70 was unaltered by diapause. The developmental regulation of hsp70 in relation to diapause suggests a critical role for this stress protein during insect dormancy.

Measurement of heat injury in plant tissue by using electrical impedance analysis

Electrical impedance spectra (100 Hz to 800 kHz) were measured in pieces of potato (Solanum tuberosum L.) tuber tissue that had been heat stressed. Analysis of the impedance data based on equivalent circuits showed that tissue injury was revealed as decreases in membrane capacitance and extracellular resistance. By using a single piece of tissue, membrane thermostability (in relation to heat stress temperature or time of heat stress) was measured. Nonstressful temperature changes produced changes in tissue parameters that were fully reversible when the direction of temperature change was reversed. Stressful temperature changes produced irreversible changes in parameters. During heat injury, decrease in extracellular resistance always preceded a decrease in tonoplast capacitance. It is suggested that two stages may be involved in heat injury to membranes: functional injury leading to electrolyte leakage to extracellular space, and structural damage leading to membrane disintegration. It is concluded that electrical impedance analysis is useful in plant heat stress physiology. Key words: potato (Solanum tuberosum L.) tuber, electrical impedance, membrane capacitance, heat injury, membrane thermostability.

Acute carbofuran exposure and cold stress: Interactive effects in mallard ducklings

Interactive effects of carbofuran and cold exposure on thermoregulatory ability, cholinesterase inhibition, and mortality were studied in 2-day old mallard ( Anas platyrhynchos) ducklings. An initial experiment indicated that brain and plasma cholinesterase activity of ducklings receiving a sublethal dose (0.22 mg/kg wt) of carbofuran at a nonstressful temperature reached a maximum inhibition of 75–78% of controls by 30 min postdose. Plasma cholinesterase activity had completely recovered to control levels by 4 hr postdose; brain ChE activity still tended to be lower at 4 hr ( P = 0.057) but had recovered fully by 8 hr postdose. In a second experiment, ducklings dosed with 0.22 mg carbofuran/kg wt underwent hypothermia after 30 and 60 min of exposure to ambient temperatures of 10 and 20°C, while those at 36°C maintained homeothermy. Internal temperatures of ducklings dosed with 0.11 mg/kg declined slightly at 10 and 20°C, but never differed significantly from those of controls. Cholinesterase activity was equally depressed at both levels of dosage, but was not affected by ambient temperature. In a final experiment, mortality of ducklings at three dosage levels (0.3, 0.4, and 0.5 mg/kg) was greater at an ambient temperature of 10°C than at 36°C ( P = 0.01); there was no mortality in control birds at either temperature. All mortalities had brain and plasma ChE activities depressed to <20 and <31% of controls, respectively, but there was no effect of ambient temperature or dose on depression. All ducklings that succumbed at 10°C exhibited severe hypothermia prior to death, but this was not apparent in mortalities at 36°C. The findings of these experiments indicate that sublethal doses of carbofuran at temperatures within the thermoneutral zone of ducklings can impair thermoregulatory ability and increase mortality at low ambient temperatures, suggesting that wild ducklings exposed to carbofuran under inclement weather conditions are at greater risk of dying than may be indicated from standard laboratory LD 50 testing.