Optimal Thermal Range Research Articles

Reduction of Optimal Thermal Range in Aging Western Cherry Fruit Flies (Diptera: Tephritidae).

The western cherry fruit fly is an economically important pest of sweet cherries in the western United States. The potential of this pest to establish and spread in areas in which it is not currently present has been the focus of recent research. Most published information on the thermal tolerance and optimal thermal range of this pest has focused primarily on the diapausing pupae and predictive phenology models. Microrespirometry and differential calorimetry can be useful tools in describing the thermotolerance and optimal thermal range of insects. This methodology was employed to investigate the effects of western cherry fruit fly adult age on the optimal thermal range. Newly emerged flies exhibited the widest optimal thermal range spanning from 6.6 to 42.2°C for a total range of 35.8°C during heating scans of 0.4°C/min from 2 to 50°C. This range diminished as the flies aged, with the shortest span observed with 28-d-old flies ranging from 10.5 to 37.8°C, a span of 27.2°C. Measurements of heat rate and oxygen consumption at isothermal, or static, temperatures indicated that all flies could survive exposure to 40°C for at least 20 min, and that metabolism was greatly reduced, with a concomitant reduction in oxygen consumption rate at 40 to 42°C. All flies exhibited a heat rate and oxygen consumption rate of zero when exposed to 45 and 50°C. The loss of thermotolerance in adult flies can influence its ability to establish and spread in climates where daily temperatures exceed the optimal thermal range of this species.

Response of Reproductive Traits and Longevity of Beet Webworm to Temperature, and Implications for Migration

Beet webworm, Loxostege sticticalis (L.) is a facultative long-distance migratory insect pest in many regions between 36° and 55° N latitude. The outbreaks of larvae are closely related to temperatures encountered by the immigrant adult. But mechanisms linking population outbreaks and migration are not well understood. We investigated the effect of exposing adults to constant temperatures from 14 to 34°C on mating, oviposition, and longevity. Our results showed that both mating percentage and frequency were highest at 22–26°C and decreased at temperatures outside this optimal range. Time of night when mating began was delayed at higher temperatures, while mating duration progressively decreased with increasing temperature. Both preoviposition period (POP) and oviposition period decreased linearly with increasing temperature. Peak daily and lifetime fecundity were highest at 22–26°C and declined at temperatures outside this range, suggesting that 22–26°C is the optimal thermal range for oviposition. Adult longevity was negatively correlated with temperature. Males lived longer than females at lower temperatures, but females lived longer than males in the 30–34°C treatments. Together, our findings suggest that reproduction occurs when the prevailing temperature is around 22–26°C, and that migratory flight is favored outside this range via increases in POP and proportion of virgins. We predict that larval damage or outbreaks of L. sticticalis will occur only in areas where the prevailing temperature is around 22–26°C, which provides a key basis for the prediction of population outbreaks in areas of immigration.

A thermal window for yawning in humans: Yawning as a brain cooling mechanism

The thermoregulatory theory of yawning posits that yawns function to cool the brain in part due to counter-current heat exchange with the deep inhalation of ambient air. Consequently, yawning should be constrained to an optimal thermal zone or range of temperature, i.e., a thermal window, in which we should expect a lower frequency at extreme temperatures. Previous research shows that yawn frequency diminishes as ambient temperatures rise and approach body temperature, but a lower bound to the thermal window has not been demonstrated. To test this, a total of 120 pedestrians were sampled for susceptibly to self-reported yawn contagion during distinct temperature ranges and seasons (winter: 1.4°C, n=60; summer: 19.4°C, n=60). As predicted, the proportion of pedestrians reporting yawning was significantly lower during winter than in summer (18.3% vs. 41.7%), with temperature being the only significant predictor of these differences across seasons. The underlying mechanism for yawning in humans, both spontaneous and contagious, appears to be involved in brain thermoregulation.

Effect of Temperature on Host Response to Batrachochytrium dendrobatidis Infection in the Mountain Yellow-legged Frog (Rana muscosa)

The pathogenic chytrid fungus Batrachochytrium dendrobatidis, which causes the disease chytridiomycosis, has been implicated in declines of amphibian populations throughout the world, including declines and extinctions of local populations of mountain yellow-legged frogs, Rana muscosa, in the California Sierra Nevada. Previous studies have shown B. dendrobatidis achieves its maximum growth rate in culture in the temperature range of 17-25 C, and exposure to very high temperatures can clear frogs of B. dendrobatidis infection. Here we present the results of a laboratory experiment in which experimentally infected R. muscosa tadpoles were followed through metamorphosis at temperatures of 17 and 22 C. All infected animals developed clinical disease within a similar time frame. However, frogs housed at 22 C exhibited a significantly lower mortality than those housed at 17 C. Within 35 days after metamorphosis, 50% of the frogs housed at 22 C died, while 95% of the frogs housed at 17 C died. Clinical signs subsided in the surviving frogs at 22 C, despite persistent infection. Because both temperatures are within the optimal thermal range for growth of B. dendrobatidis, we propose that the difference in outcome indicates the effect of temperature on the host's resistance to chytridiomycosis, rather than an effect on the fungus alone.

Thermal Habitat Use by Lake Trout in Two Contrasting Yukon Territory Lakes

AbstractThermal habitat use by lake trout Salvelinus namaycush in two northern lakes in the southern portion of the Yukon Territory that differ in morphometry and thermal regime was monitored using temperature‐sensitive acoustics and radiotelemetry. We then contrasted in situ temperature selection by lake trout in these lakes with previously published estimates of the species' optimal thermal range of 8–12°C. We found that thermal habitat use by lake trout in the two northern lakes is not consistent with these literature‐derived expectations. In Dezadeash Lake, which is isothermal in summer, temperatures typically exceeded the literature‐derived upper limit of 12°C. Throughout the summer lake trout sought the coldest water in the lake, which was in the form of shallow coldwater plumes derived from alpine ice‐pack meltwater streams. Once lake temperatures declined in the fall, lake trout were distributed throughout the lake. In Kathleen Lake, where water temperatures ranged from approximately 2°C to 12°C in the summer, the majority of lake trout selected habitats throughout the summer and fall that were colder than the 8°C lower limit of their literature‐derived optimal thermal range. Our results highlight the importance of summer thermal refugia for lake trout inhabiting marginal systems and the variation in thermal habitat use among populations inhabiting different thermal environments. Given the established importance of thermal habitat availability to lake trout production, our results suggest the need to better understand optimal thermal habitat characteristics in nature, particularly in light of factors such as climate warming.

Seasonal fluctuations in sand temperature: effects on the incubation period and mortality of loggerhead sea turtle ( Caretta caretta ) pre-emergent hatchlings in Minabe, Japan

Incubation period, hatching success, and emergence percentage in loggerhead (Caretta caretta) nests were quantified during the 1993 and 1995 nesting seasons and following incubation seasons in Minabe, Wakayama, Japan. Sand and nest temperatures were also monitored. Over the seasons, daily mean sand temperature at nest depth fluctuated between 18.0°C and 33.3°C, with a steep increase in the second week of July and a peak in late August. Temperatures inside the nest chambers were a few degrees above those of the surrounding sand at the end of incubation. The incubation period ranged from 46 to 82 days. A significant negative correlation was found between mean sand temperature and incubation period. The relationship conformed to the day-degree concept. There was no significant seasonal trend in hatching success, but many pre-emergent hatchlings were found dead in most of the clutches during the warmest part of the season. Emergence percentage was correlated with mean sand temperature calculated for 4 days before emergence, suggesting that mortality may be due to heat. This heat-related mortality is considered to be a common phenomenon at our study site, because the peak in emergences coincides with the peak in high temperatures. These temperature effects on hatchling mortality must be taken into account in estimates of hatchling sex ratios. Because sand temperatures already exceed the optimal thermal range for incubation, this population is vulnerable to even small temperature increases resulting from global warming.

Thermal Dependence of Glutathione Reductase; Thermal Limitations on Antioxidant Protection in Plants

Though plants have endogenous systems to prevent and/or repair thermal damage, thermal stresses often limit agronomic yields. The enzyme glutathione reductase plays a role in the detoxification of oxidants that often result from exposure of plants to high or low temperatures. Since thermal limitations on the function of glutathione reductase could limit the ability of a plant to withstand thermal stress, it is important to understand its thermal dependence. Previously, the thermal dependence of maximal velocity and apparent KM have been used to describe the thermal dependence of enzymes and define an optimal thermal range for their function. While both maximal velocity and apparent KM are factors in the thermal response of the velocity of an enzyme reaction, they are not necessarily indicative of the thermal dependence of velocity under physiological conditions. In this study, a computer program was used to develop estimates of the thermal dependence of reaction velocity at a given temperature and substrate concentration. Optimal thermal ranges for the glutathione reductascs from spinach (Spinacia oleracea L.), corn (Zea mays L.), and cucumber (Cucurais sativum L. cv. Ashley) were predicted from the thermal dependence of maximal velocity, predicted velocity, Vmax/KM, and apparent KM. These results suggest that the predicted thermal dependence of velocity may be a useful indicator of the optimal thermal range of plant enzymes.

Changes in gross protein and lipid requirements of rainbow trout, Oncorhynchus my kiss (Walbaum), at elevated temperatures

. In southern Africa rainbow trout, Oncorhynchus my kiss (Walbaum), are generally cultured at temperatures between 18 and 22°C, which is higher than the optimal thermal range for maximum growth in this species. Experiments were undertaken on two size classes of fish ( 25g) to determine the gross changes in protein and lipid requirements at these temperatures. The optimal protein and lipid requirements of the smaller fish were found to be 40% and 20–30% of the diet respectively. These levels are significantly different to those under optimal thermal conditions. The protein requirements of the larger fish remained at the ‘threshold level’ of 35% of the diet, although lipid requirements rose lo between 20 and 23% of the diet. The results are discussed in terms of the animal's scope for growth.

Influence of water temperature on behavioural interactions between juvenile brook charr, Salvelinus fontinalis, and rainbow trout, Salmo gairdneri

Interspecific behavioural interactions between paired brook char (Salvelinus fontinalis) and rainbow trout (Salmo gairdneri) were compared at different water temperatures to test the hypothesis that a species realizes a competitive advantage within its optimal thermal range. Three test temperatures were used: 19 °C (optimal temperature for rainbow trout), 13 °C (optimal temperature for brook charr), and 8 °C (below the optima for both species). Brook charr dominated rainbow trout at both 8 and 13 °C. At 19 °C, neither species displayed an obvious competitive advantage. The time (days) to the establishment of a dominance hierarchy reflected specific optimal temperatures; it was shortest for rainbow trout and brook charr at 19 and 13 °C, respectively. The implications of optimal temperatures and competitive ability are discussed in relation to habitat partitioning in the stream environment.