Direct Effects Of Elevated Temperature Research Articles

Shading contributes to Sphagnum decline in response to warming.

Experimental warming of an ombrotrophic bog in northern Minnesota has caused a rapid decline in the productivity and areal cover of Sphagnum mosses, affecting whole-ecosystem carbon balance and biogeochemistry. Direct effects of elevated temperature and the attendant drying are most likely the primary cause of the effects on Sphagnum, but there may also be responses to the increased shading from shrubs, which increased with increasing temperature. To evaluate the independent effects of reduction in light availability and deposition of shrub litter on Sphagnum productivity, small plots with shrubs removed were laid out adjacent to the warming experiment on hummocks and hollows in three blocks and with five levels of shading. Four plots were covered with neutral density shade cloth to simulate shading from shrubs of 30%-90% reduction in light; one plot was left open. Growth of Sphagnum angustifolium/fallax and S. divinum declined linearly with increasing shade in hollows, but there was no response to shade on hummocks, where higher irradiance in the open plots may have been inhibitory. Shading caused etiolation of Sphagnum-they were thin and spindly under the deepest shade. A dense mat of shrub litter, corresponding to the amount of shrub litter produced in response to warming, did not inhibit Sphagnum growth or cause increases in potentially toxic base cations. CO2 exchange and chlorophyll-a fluorescence of S. angustifolium/fallax from the 30% and 90% shade cloth plots were measured in the laboratory. Light response curves indicate that maximal light saturated photosynthesis was 42% greater for S. angustifolium/fallax grown under 30% shade cloth relative to plants grown under 90% shade cloth. The response of Sphagnum growth in response to increasing shade is consistent with the hypothesis that increased shade resulting from shrub expansion in response to experimental warming contributed to reduced Sphagnum growth.

375 Importance of cellular resistance to elevated temperature as a determinant of the magnitude of adverse effects of heat stress on farm animals

Abstract Heat stress can compromise most productive functions of mammals and birds raised for agricultural purposes. Many of the deleterious effects of heat stress are a result of physiological adaptations to maintain constant body temperature. These adaptations include reduction in physical activity, reduced feed intake, nutrient repartitioning, redistribution of blood flow from the body core to the periphery, and increased evaporative heat loss. When heat stress becomes greater than can be compensated for physiologically, hyperthermia results and cellular function becomes at risk because of free radical damage, membrane instability, and changes in protein structure. It is well established that effects of heat stress on fertility involve disruption of function of the oocyte and early embryo by direct effects of elevated temperature. It is likely that other physiological systems are also compromised because of cellular damage. There are a variety of molecular systems to limit cellular damage caused by hyperthermia, including antioxidant systems, the endoplasmic reticulum stress response, and heat shock proteins. There has been limited success in mitigating effects of heat stress by manipulating antioxidant status. Cellular resistance to heat stress is subject to genetic variation, and it may be possible to select genetically for cellular resistance to hyperthermia.

Short communication: High incubation temperature in bovine mammary epithelial cells reduced the activity of the mTOR signaling pathway

Hyperthermia alters utilization of AA in protein synthesis and cell-signaling activity in bovine mammary cells. Essential AA and insulin regulate translation of proteins by controlling the activity of mammalian target of rapamycin (mTOR) signaling pathway. The objectives of this study were to evaluate (1) the effects of incubation temperature on the mTOR signaling pathway and transcription of AA transporters in a bovine mammary alveolar cell line (MAC-T) and (2) the combined effects of incubation temperature and insulin on the mTOR signaling pathway in this cell line. Cells were cultured in medium with 10% fetal bovine serum at 37°C and 5% CO2. In experiment 1, cells were subjected to 37°C (control) or 41.5°C (high incubation temperature; HT) for 12 h. In experiment 2, cells were assigned to 1 of 4 treatments as a 2 × 2 factorial arrangement, including 2 cell culture temperatures (control and HT) and absence or presence of 1.0 μg/mL of insulin. Proteins were harvested and separated by gel electrophoresis. In experiment 1, gene expression of AA transporters (SLC1A1, SLC1A5, SLC3A2, SLC7A1, SLC7A5, and SLC36A1) were evaluated, and changes of ≥2 fold were deemed significantly different. In experiments 1 and 2, immunoblotting was used to identify total and site-specific phosphorylated forms of protein kinase B (Akt1; Ser473), p70 S6 kinase (S6K1; Thr389), ribosomal protein S6 (rpS6; Ser235/236), and eukaryotic elongation factor 2 (eEF2; Thr56). Phosphorylated and total forms of Akt1, S6K1, rpS6, and eEF2 were quantified and expressed as the ratio of phosphorylated to total protein. In experiment 1, HT resulted in a ≥2-fold increase expression of SLC1A1 and SLC3A2. High incubation temperature reduced the phosphorylated to total ratio of Akt1 and rpS6 and increased the phosphorylated to total ratio of eEF2. In experiment 2, we found no temperature by insulin interactions on phosphorylation state of the protein factors of interest. High incubation temperature reduced the phosphorylated to total ratio of Akt1. The addition of insulin increased the phosphorylated to total ratio of Akt1, S6K1, and rpS6. In summary, HT reduced the activity of the mTOR signaling pathway and increased the expression of AA transporters. High incubation temperature possibly reduced protein translation by reducing the mTOR signaling pathway activity in an effort to adapt to thermal stress. These results may help explain the direct effect of elevated temperature on AA metabolism and protein translation in heat-stressed animals.

Direct effects of elevated temperature on a tri-trophic system: Salix, leaf beetles and predatory bugs

The net effect of climatic change on biotic interactions will depend on how each interacting species is individually affected. Elevated temperatures are predicted to have differential effects on species across trophic levels, due to asymmetric sensitivity to temperature changes. In this study, we examined the direct effects of three temperature regimes (16, 20 and 24 °C) that reflect present and, potentially, future climate conditions on the response of Salix spp. plants, an important bioenergy crop, and its most damaging herbivore (Phratora vulgatissima) and an efficient natural enemy (the omnivorous predator Orthotylus marginalis). We found that plant growth, herbivore oviposition and enemy egg-foraging rate correlated positively with temperature. In the event of elevated temperatures following global climatic changes, these species could potentially respond in tandem. Still, the strength of responses varied among species, with herbivore and natural enemy exhibiting a similar and steeper rate of response relative to plants. Additionally, the herbivore’s response was influenced by plant quality with altered oviposition rates depending on whether it was fed the (previously determined) resistant Salix dasyclados or susceptible S. viminalis. This indicates that host plant chemistry has the potential to mediate differential responses to temperature. Together, our results suggest that indirect effects of elevated temperatures, leading to a disruption of trophic associations, may be less likely or less severe in this tri-trophic system.

Direct effects of elevated temperature, reduced pH, and the presence of macroalgae (<I>Dictyota</I> spp.) on larvae of the Caribbean coral <I>Porites astreoides</I>

Through an aquarium-based study, we provide evidence that exposure to macroalgae (Dictyota spp.), seawater with reduced pH (7.6 vs 8.1), and elevated temperature (31.8 vs 28.8 °C) causes distinct and additive repercussions for larval settlement and condition (photochemical efficiency and oxidative stress). Larvae from the common Caribbean coral Porites astreoides (Lamarck, 1816) were provided settlement substrate and exposed to each factor for 72 hrs in isolation and combination under an orthogonal design. Largely, biotic and abiotic factors did not interact in their impact on coral planulae; instead, stressors independently affected the survival, condition, and settlement of P. astreoides. Dictyota spp. and low pH each individually reduced the survival of coral larvae. Furthermore, the presence of Dictyota spp. and elevated temperature distinctly inhibited larval settlement and photochemical efficiency, respectively. When combined, stressors additively increased cellular oxidative damage (lipid peroxidation) approximately four fold compared to larvae maintained under control conditions. The results indicate that each stressor independently impacts distinct and overlapping facets of coral settlement, and suggest that their combined effects could have severe collective consequences for coral demography.

Genetic variation in resistance of the preimplantation bovine embryo to heat shock.

Reproduction is among the physiological functions in mammals most susceptible to disruption by hyperthermia. Many of the effects of heat stress on function of the oocyte and embryo involve direct effects of elevated temperature (i.e. heat shock) on cellular function. Mammals limit the effects of heat shock by tightly regulating body temperature. This ability is genetically controlled: lines of domestic animals have been developed with superior ability to regulate body temperature during heat stress. Through experimentation in cattle, it is also evident that there is genetic variation in the resistance of cells to the deleterious effects of elevated temperature. Several breeds that were developed in hot climates, including Bos indicus (Brahman, Gir, Nelore and Sahiwal) and Bos taurus (Romosinuano and Senepol) are more resistant to the effects of elevated temperature on cellular function than breeds that evolved in cooler climates (Angus, Holstein and Jersey). Genetic differences are expressed in the preimplantation embryo by Day 4-5 of development (after embryonic genome activation). It is not clear whether genetic differences are expressed in cells in which transcription is repressed (oocytes >100 µm in diameter or embryos at stages before embryonic genome activation). The molecular basis for cellular thermotolerance has also not been established, although there is some suggestion for involvement of heat shock protein 90 and the insulin-like growth factor 1 system. Given the availability of genomic tools for genetic selection, identification of genes controlling cellular resistance to elevated temperature could be followed by progress in selection for those genes within the populations in which they exist. It could also be possible to introduce genes from thermotolerant breeds into thermally sensitive breeds. The ability to edit the genome makes it possible to design new genes that confer protection of cells from stresses like heat shock.

Effect of elevated temperatures on bovine corpus luteum function: expression of heat-shock protein 70, cell viability and production of progesterone and prostaglandins by cultured luteal cells

Summer heat stress lowers fertility in cattle in hot environments by influencing oocyte quality, follicular activity and progesterone (P4) level in blood plasma. However, the mechanisms by which elevated temperature influences corpus luteum function remain unclear. Elevated temperature has generally been known to upregulate the gene expression of heat-shock protein (HSP) 70 in a variety of cell types. To clarify the direct effects of elevated temperature on bovine corpus luteum function, we examined the expressions of HSP70, cell viability and the production of P4 and prostaglandins (PGs) in luteal cells cultured at 37.5°C (normal temperature in our culture system), 39.0°C (moderately elevated temperature) or 41.0°C (severely elevated temperature) for 12 or 24 h. HSP70 mRNA expression was increased by incubation at 39.0°C for 12 h and at 41.0°C for 12 and 24 h, whereas HSP70 protein expression was not significantly affected. The viability of luteal cells cultured for 24 h, measured by flow cytometry with propidium iodide staining, was not significantly affected by temperature. Interestingly, the production of P4 by cultured luteal cells was higher at 39.0°C than at 37.5°C after 12 and 24 h of incubation. The production of PGF2α was higher at 39.0°C and 41.0°C than at 37.5°C after 12 and 24 h of incubation. The production of PGE2 was higher at 41.0°C than at 37.5°C after 24 h of incubation. The overall results suggested that elevated temperature does not negatively affect luteal function, and that the low fertility observed during summer is not due to a direct effect of elevated temperature on luteal cells.

Predominant role of water in regulating soil and microbial respiration and their responses to climate change in a semiarid grassland

AbstractClimate change can profoundly impact carbon (C) cycling of terrestrial ecosystems. A field experiment was conducted to examine responses of total soil and microbial respiration, and microbial biomass to experimental warming and increased precipitation in a semiarid temperate steppe in northern China since April 2005. We measured soil respiration twice a month over the growing seasons, soil microbial biomass C (MBC) and N (MBN), microbial respiration (MR) once a year in the middle growing season from 2005 to 2007. The results showed that interannual variations in soil respiration, MR, and microbial biomass were positively related to interannual fluctuations in precipitation. Laboratory incubation with a soil moisture gradient revealed a constraint of the temperature responses of MR by low soil moisture contents. Across the 3 years, experimental warming decreased soil moisture, and consequently caused significant reductions in total and microbial respiration, and microbial biomass, suggesting stronger negatively indirect effects through warming‐induced water stress than the positively direct effects of elevated temperature. Increased evapotranspiration under experimental warming could have reduced soil water availability below a stress threshold, thus leading to suppression of plant growth, root and microbial activities. Increased precipitation significantly stimulated total soil and microbial respiration and all other microbial parameters and the positive precipitation effects increased over time. Our results suggest that soil water availability is more important than temperature in regulating soil and microbial respiratory processes, microbial biomass and their responses to climate change in the semiarid temperate steppe. Experimental warming caused greater reductions in soil respiration than in gross ecosystem productivity (GEP). In contrast, increased precipitation stimulated GEP more than soil respiration. Our observations suggest that climate warming may cause net C losses, whereas increased precipitation may lead to net C gains in the semiarid temperate steppe. Our findings highlight that unless there is concurrent increase in precipitation, the temperate steppe in the arid and semiarid regions of northern China may act as a net C source under climate warming.

Susceptibility of bovine germinal vesicle-stage oocytes from antral follicles to direct effects of heat stress in vitro.

Delineation of maternal versus direct effects of heat stress in reducing development at the germinal vesicle (GV) stage is challenging, because oocytes spontaneously resume meiosis after removal from antral follicles. The use of S-roscovitine (inhibitor of p34(cdc2)/cyclin B kinase) to hold bovine oocytes at the GV stage without compromising early embryo development was previously validated in our laboratory. The objective of the present study was to assess the direct effects of an elevated temperature commonly seen in heat-stressed dairy cows on cumulus-oocyte complexes (COCs) held at the GV stage using 50 microM S-roscovitine. During roscovitine culture, GV-stage COCs (antral follicle diameter, 3-8 mm) were cultured at 38.5 or 41 degrees C. Thereafter, oocytes were removed from roscovitine medium and allowed to undergo in vitro maturation, fertilization, and culture. Zona pellucida hardening (solubility to 0.5% pronase), nuclear stage (Hoechst 33342), cortical granule type (lens culinaris agglutinin-fluorescein isothiocyanate [FITC]), and early embryo development were evaluated. Culture of GV-stage COCs at 41 degrees C increased the proportion that had type III cortical granules and reduced the proportion that progressed to metaphase II after in vitro maturation. Effects of 41 degrees C on zona pellucida hardening, fertilization (penetration, sperm per oocyte, pronuclear formation, and monospermic and putative embryos), and cleavage of putative zygotes were not noted. However, culture of GV-stage COCs at 41 degrees C for 6 h decreased the proportion of 8- to 16-cell embryos, whereas 41 degrees C for 12 h reduced blastocyst development. In summary, antral follicle COCs are susceptible to direct effects of elevated body temperature, which may account in part for reduced fertility in heat-stressed cows.

226HEAT SHOCK OF GERMINAL VESICLE-STAGE BOVINE OOCYTES REDUCES EMBRYO DEVELOPMENT

Culture of germinal vesicle (GV)-stage oocytes at an elevated temperature occurring in heat-stressed dairy cattle reduced ability of oocytes to progress to metaphase II after resumption of meiosis (Payton RR et al., 2003 Biol. Reprod. 68, 343 abst). The objective of this study was to evaluate embryo development of oocytes heat-shocked at GV stage. To prevent cumulus-oocyte complexes from resuming meiosis after removal from follicles, oocytes were cultured in roscovitine (cell cycle inhibitor of p34cdc2/cyclin B kinase;; 50μM) for 24h (McCann LM et al., 2000 Biol. Reprod. 64, 141 abst and Payton RR et al., 2003 Biol. Reprod. 68, 343 abst) showed that roscovitine is effective for maintaining >90% of oocytes at GV-stage in a reversible manner. Germinal vesicle-stage oocytes were cultured at 38.5°C for 24h (experimental control) or 41.0°C as follows: HS 0–6 (41°C for 6h, 38.5°C for 18h), HS 0–12 (41°C for 12h, 38.5°C for 12h), HS 12–24 (38.5°C for 12h, 41°C for 12h), HS 18–24 (38.5°C for 18h, 41°C for 6h), or HS 0–24 (41°C for 24h) in 5.5% CO2 and humidified air. In addition, a group of COC were not cultured in roscovitine but placed in maturation medium (lab control). After a total of 24h, COC were washed extensively of roscovitine and cultured for an additional 24h in maturation medium. Oocytes presumed mature were fertilized with Percoll-prepared frozen-thawed semen. Presumptive zygotes were cultured in KSOM containing 1X nonessential amino acids in 5.5% CO2, 7% O2, and 87.5% N2 at 38.5°C in humidified air. Cleavage and development to blastocyst were recorded on Days 3 and 8 post-insemination, respectively. Data were collected in 7 replicates and analyzed as an incomplete block using mixed models of SAS (2000) after testing for normality. Use of roscovitine for maintaining oocytes at GV-stage for 24h did not alter cleavage (80.5 and 73.4%; SEM=5.8; lab and experimental controls), development to 8–16 cell (50.4 and 52.6%; SEM=4.6; lab and experimental controls), or blastocyst (29.7 and 24.8%; SEM=3.2; lab and experimental controls) stages. Culture of GV-stage oocytes at 41°C for up to 24h did not increase lysis (8.0–11.1%; SEM=2.7). Heat shock of GV-stage oocytes for as few as 6h reduced the proportion developing to 8–16 cell stage after release from inhibitor (Table 1). When experimental control and HS 0–6 were pooled for comparison to HS 0–12, effects of heat shock for reducing development to blastocyst were noted (P<0.005). Moreover, negative effects of heat shock for reducing developmental competence of GV-stage oocytes increased as duration of heat shock increased (linear contrast;; experimental control, HS 0–12, and HS 0–24; P<0.04). Results indicate that a physiologically relevant elevated temperature for as few as 6h compromises continued development of GV-stage oocytes. Seasonal depressions in fertility of heat-stressed cattle may be due in part to direct effects of elevated temperature on GV-stage oocytes. Table 1

Growth and behavioral responses to elevated temperatures by juvenile sablefish Anoplopoma fimbria and the interactive role of food availability

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 217:121-134 (2001) - doi:10.3354/meps217121 Growth and behavioral responses to elevated temperatures by juvenile sablefish Anoplopoma fimbria and the interactive role of food availability Susan M. Sogard*, Bori L. Olla Alaska Fisheries Science Center, National Marine Fisheries Service, Hatfield Marine Science Center, Newport, Oregon 97365, USA *E-mail: susan.sogard@noaa.gov ABSTRACT: Larval and age-0 sablefish Anoplopoma fimbria reside in neustonic waters of the North Pacific during spring and summer. We estimated the potential impacts of elevated surface temperatures on ecological processes of growth, conversion efficiency, and behavior in early juvenile sablefish. Growth experiments tested a wide range of temperatures from 6 to 24°C, with fish receiving ad libitum or low (3% body weight d-1) rations. With unlimited food, growth increased rapidly as temperature increased to 14°C, then displayed a more gradual rise to 22°C. Growth rates at the warmer temperatures were among the highest recorded for teleosts, attaining a maximum of 3.3 mm d-1 in length and a specific growth in weight of 11.8%. A similar response to temperature was observed at low rations, although at lower overall growth rates. At 24°C, there was a severe decline in growth for both ration levels, and few fish survived the 3 wk experiments. Gross growth efficiency, measured at temperatures of 6 to 22°C, displayed an interactive effect of temperature with ration level consistent with bioenergetic relationship. Conversion peaked at 16 to 20°C for fish receiving ad libitum rations, and at 10°C for fish on restricted rations. Conversion rates of sablefish were comparable to those calculated for a diverse array of fish species, suggesting that the rapid growth rates are driven by high consumption rather than unusually efficient energy transfer. Experiments analyzing sablefish behavior in thermally stratified water columns demonstrated increasing movement into colder water as ration level decreased, in agreement with an energy conserving strategy. Average monthly temperatures within the major nursery areas of neustonic juveniles (north of 40°N) did not exceed 19°C during the last 19 yr. These results suggest that juvenile sablefish are capable of tolerating and thriving at increased temperatures, with the critical caveat that sufficient food resources must be available. Thus, impacts on early life stages exerted by El Niño conditions, oceanographic regime shifts, or climate changes induced by current global warming scenarios are likely to be a consequence of indirect effects on circulation and productivity patterns rather than direct effects of warmer temperatures. However, because the upper thermal limit for growth nearly coincides with the upper limit for survival, exhibiting a sharp demarcation between favorable growth conditions and intolerable temperatures, juvenile sablefish at the southern limit of their distribution may suffer the direct effects of elevated temperature; recruitment of juveniles to southern populations may become more sporadic if the frequency of warming events increases with climate change. KEY WORDS: Growth efficiency · Temperature selection · Ration · Activity Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 217. Online publication date: July 31, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Below-Ground Microbial Community Development in a High Temperature World

The response of above-ground plant and ecosystem processes to climate change are likely to be influenced by both direct and indirect effects of elevated temperature on soil biota and their activities. This study examined the effects of elevated atmospheric temperature on the development of the soil microbial community in a model terrestrial ecosystem facility. The model system was characterized by a soil of low nutrient availability, a condition that simulates most native terrestrial plant communities. The experiment was run over three plant generations, broadly mimicking the early stages of a plant succession, and showed that microbial biomass, measured using phospholipid fatty acid (PLFA) analysis, increased significantly in response to elevated temperature during the first generation only. This increase was unrelated to changes in plant productivity or soil C-availability, and was largely due to a direct effect of elevated temperature on fast-growing Gram-positive bacteria. Slow growing soil micoorganisms such as fungi and actinomycetes were unaffected by elevated temperature throughout the experimental period. Measures of microbial biomass, microbial respiration and N-mineralization were also unaffected by elevated atmospheric temperature over the three generations. The lack of effects on the soil microbial community is thought to be due to the fact that elevated temperature did not influence root biomass or soil C-availability. We suggest that the observed reductions in above-ground plant productivity, in response to elevated temperature, will become apparent in the longer term when litter decomposition pathways are more established. The temporal measures of PLFA and microbial biomass indicated that over the experimental period rapid initial changes occurred in most soil biological characteristics, followed by periods of stabilization during later plant succession. These changes were associated with increases in above-ground plant productivity and amounts of available C in the soil. In contrast, total microbial biomass declined during the last plant generation. Reductions in the diversity of PLFAs in later plant generations appeared to be associated with an increase in the proportion of fatty acids associated with fungi, relative to those from bacteria. These changes are likely to be related to increased competition for resources within the soil, and an associated reduction in N- and C-availability. These changes appear to be broadly consistent with those reported for other studies on the successional development of soil microbial and plant communities. Overall, our data suggest that elevated atmospheric temperature has little effect on the development of below-ground microbial communities and their activities in soils of low nutrient status.

The effects of water table manipulation and elevated temperature on the net CO2 flux of wet sedge tundra ecosystems

Abstract In situ manipulations were conducted in a naturally drained lake on the arctic coastal plain near Prudhoe Bay, Alaska (70 °21.98′ N, 148 °33.72′ W) to assess the potential short‐term effects of decreased water table and elevated temperature on net ecosystem CO2 flux. The experiments were conducted over a 2‐year period, and during that time, water table depth of drained plots was maintained on average 7 cm lower than the ambient water table, and surface temperatures of plots exposed to elevated temperature were increased on average 0.5 °C. Water table drainage, and to a lesser extent elevated temperature, resulted in significant increases in ecosystem respiration (ER) rates, and only small and variable changes in gross ecosystem productivity (GEP). As a result, drained plots were net sources of ≈ 40 gC m–2 season–1 over both years of manipulation, while control plots were net sinks of atmospheric CO2 of about 10 gC m–2 season–1 (growing season length was an estimated 125 days). Control plots exposed to elevated temperatures accumulated slightly more carbon than control plots exposed to ambient temperatures. The direct effects of elevated temperature on net CO2 flux, ER, and GEP were small, however, elevated temperature appeared to interact with drainage to exacerbate the amount of net carbon loss. These data suggest that many currently saturated or nearly saturated wet sedge ecosystems of the north slope of Alaska may become significant sources of CO2 to the atmosphere if climate change predictions of increased evapotranspiration and reduced soil water status are realized. There is ample evidence that this may be already occurring in arctic Alaska, as a change in net carbon balance has been observed for both tussock and wet‐sedge tundra ecosystems over the last 2–3 decades, which coincides with a recent increase in surface temperature and an associated decrease in soil water content. In contrast, if precipitation increases relatively more than evapotranspiration, then increases in soil moisture content will likely result in greater carbon accumulation.