Ultrastructure of Bacteriomes and Their Sensitivity to Ambient Temperatures in Prostephanus truncatus (Horn)

In light microscopical sections of Prostephanus truncatus (Horn) (Col.: Bostrychidae) it was shown that both larvae and adults have a pair of bacteriomes dorsally located in the fat body parallel to the midgut. Bacteriome development was shown mainly to occur during larval stages. Bacteriome size was not found to be associated with body size in adults, but in larvae reared at 30°C bacteriome size increased progressively with body length. The shape of the bacteriomes varied from round to conic-oval, but a common feature was that they were larger and rounded in older larvae and females as compared to males, where they usually appeared more shrunken and slightly deformed. Electron microscopy of thin sections showed that the bacteriomes were composed of multinucleate syncytia surrounded by a layer of boundary cells. The syncytia harboured many small coccoid bacteroids. Typical eukaryotic organelles were found in the cytoplasm of the bacteriomes. These and other structural features were outlined. The effect of rearing temperatures at 30, 35 and 37°C on bacteriome development in larvae and adults was examined. The symbiotes could not be eliminated but a significant reduction of bacteriome size was found in females reared at 35°C and 37°C as compared to specimens grown at 30°C. A possible association of bacteriome size and reproduction was evaluated by transferring P. truncatus specimens reared at 35°C and 37°C to 30°C for two months and counting the number of offspring; their reproduction was compared with controls kept at 30°C throughout the experiment. Specimens from 35°C and 37°C had significantly lower reproduction rates than controls. The potential implications of heat sensitivity of bacteriomes of P.truncatus is discussed in an integrated pest management context.     

Fluctuating environments impact thermal tolerance in an invasive insect species Bactrocera dorsalis (Diptera: Tephritidae)

The incidence and severity of environmental stressors associated with global climate change are increasing and insects frequently face variability in temperature and moisture regimes at variable spatio-temporal scales. Coincidental with this, is increased thermal and hydric stress on insects as warming increases vapour pressure deficit (VPD), the drying power of the air. While the effects of mean temperatures on fitness are widely documented, fluctuations in both temperature and relative humidity (RH) are largely unexplored. Here, we investigated the effects of dynamic temperature and RH fluctuations (around the mean [28°C; 65% RH]) on low and high thermal tolerance of laboratory-reared adult invasive Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), measured as critical thermal minima (CT_min), critical thermal maxima (CT_max), chill coma recovery time (CCRT) and heat knockdown time (HKDT). Our results show that increased environmental amplitude significantly influenced low and high temperature responses and varied across traits tested. The highest amplitude (δ12°C; 28% RH) compromised CT_min, CCRT and HKDT traits while enhancing CT_max. Similarly, acclimation to δ3°C; 7% RH compromised both low (CT_min and CCRT) and high (CT_max and HKDT) fitness traits. Variations in fitness reported here indicate significant roles of combined thermal and moisture fluctuations on B. dorsalis fitness suggesting caveats that are worthy considering when predicting species responses to climate change. These results are significant for B. dorsalis population phenology, management, quantifying vulnerability to climate variability and may help modelling future biogeographical patterns.     

To aggregate or not? Capturing the spatio-temporal complexity of the thermal regime

Freshwater stream systems are under immense pressure from various anthropogenic impacts, including climate change. Stream systems are increasingly being altered by changes to the magnitude, timing, frequency, and duration of their thermal regimes, which will have profound impacts on the life-history dynamics of resident biota within their home range. Although temperature regimes have a significant influence on the biology of instream fauna, large spatio-temporal temperature datasets are often reduced to a single metric at discrete locations and used to describe the thermal regime of a system; potentially leading to a significant loss of information crucial to stream management. Models are often used to extrapolate these metrics to unsampled locations, but it is unclear whether predicting actual daily temperatures or an aggregated metric of the temperature regime best describes the complexity of the thermal regime. We fit spatial statistical stream-network models (SSNMs), random forest and non-spatial linear models to stream temperature data from the Upper Condamine River in QLD, Australia and used them to semi-continuously predict metrics describing the magnitude, duration, and frequency of the thermal regime through space and time. We compared both daily and aggregated temperature metrics and found that SSNMs always had more predictive ability than the random forest models, but both models outperformed the non-spatial linear model. For metrics describing thermal magnitude and duration, aggregated predictions were most accurate, while metrics describing the frequency of heating events were better represented by metrics based on daily predictions generated using a SSNM. A more comprehensive representation of the spatio-temporal thermal regime allows researchers to explore new spatio-temporally explicit questions about the thermal regime. It also provides the information needed to generate a suite of ecologically meaningful metrics capturing multiple aspects of the thermal regime, which will increase our scientific understanding of how organisms respond to thermal cues and provide much-needed information for more effective management actions.     

The effect of temperature on bacterial degradation of EDTA in pH-auxostat

The effect of temperature on the maximum specific growth rate and the cell yield was studied during cultivation of two bacterial strains (LPM-4 and Pseudomonas sp. LPM-410) on EDTA under unlimited cell growth conditions in a pH-auxostat. Both strains displayed linear dependence of reciprocal biomass yield against reciprocal specific growth rate, from which the values of rate of substrate expenditure for cell maintenance and the “maximum” yield (i.e., hypothetical yield without cell maintenance processes) were estimated. Analysis of the maximum yield values based on mass–energy balance theory suggested that oxidation of the carboxylic acid side chains of EDTA by a monooxygenase had zero or low energetic efficiency. An Arrhenius equation with different values of Arrhenius parameters within different temperature ranges gave a good fit with the temperature dependence of both growth rate and biomass yield. Specific growth rates of both strains showed a more pronounced temperature dependence than did the cell yields. A possible kinetic mechanism was suggested which might be responsible for the modes of the temperature dependences of specific growth rate and yield that were found. The mechanism is based on a hypothetical key substance governing the metabolic flows, which is formed in a zero-order reaction and destroyed in a first-order reaction, both rate constants depending on temperature according to the Arrhenius law.     

Thermal inhibition of repair of methylmethane sulfonate-damaged DNA in chick embryo fibroblasts

Chick embryo fibroblasts were treated with the monofunctional alkylating agent methylmethane sulfonate at various concentrations for 1 h at 42°C, rinsed and then incubated post-treatment at various temperatures at which the kinetics of alkali-labile bond disappearance was followed. Growth experiments showed that these cells grew similarly at temperatures of either 37°C or 42°C. Repair as assessed by removal of alkali-labile bond was also similar for postincubation in the temperature range 37–42°C for damage due to methylmethane sulfonate treatment at concentrations less than 1.5 mM. When the postincubation temperature was raised higher than 42.5–43°C, this type of repair was stopped. The normal internal body temperature of adult chickens is about 41.6°C. Hence the present finding indicates that chick cells are much more severely restricted in DNA repair at temperatures above normal than are mammalian cells, which can function in this respect for several deg. C above 37°C.     

Hibernation behavior of Rana lessonae and R. esculenta in their natural habitat

We studied the hibernation behavior of the water frog Rana lessonae and its hybridogenetic associate R. esculenta in their natural habitat during three successive winters. Animals caught in pitfall traps at a fenced pond were individually marked with PIT tags and some (n=36) were additionally equipped with radio transmitters. Of the animals caught, 85% left the fenced pond for hibernation. More R. esculenta remained inside the fenced area compared to R. lessonae. R. lessonae emigrated earlier in autumn and came back later in spring than R. esculenta, but the distance to their hibernation sites did not differ. Both species left the fenced pond earlier in the year when ambient temperatures were lower. All radio-tracked animals hibernated in woodland, 3–7 cm below the surface in soil, under moss, fallen leaves or small branches. Soil temperatures at the actual hibernation sites were significantly higher than at randomly chosen control sites. A surprising finding was that most frogs changed their hibernation sites during winter, and often more than once. Movements were more frequent in the warmer first half of the winter than in the cooler second half, but some animals were active even on days with mean temperatures below 1°C. These results show that both species do not spend the whole winter torpid in one particular hibernation site but move around, especially at higher temperatures. Most of the animals lost weight during the winter, and the weight loss was greater in females than in males and higher in warm than in cold winters. To what extent weight loss and survival is influenced by the chosen hibernation sites and the amount of movement during winter, and whether this contributes to the differences in species and sex ratios found in mixed populations, needs more investigation. Received: 4 August 1999 / Accepted: 15 November 1999     

The role of oxygen availability in the embryonation of Heterakis gallinarum eggs.

The importance of oxygen availability in the embryonation of the infective egg stages of the gastrointestinal nematode parasite Heterakis gallinarum was studied in the laboratory. Unembryonated H. gallinarum eggs were kept under either aerobic conditions by gassing with oxygen, or anaerobic conditions by gassing with the inert gas nitrogen, under a range of constant temperatures. Oxygenated eggs embryonated at a rate influenced by temperature. Conversely, eggs treated with nitrogen showed no embryonation although when these eggs were transferred from nitrogen to oxygen gas after 60 days of treatment, embryonation occurred. This demonstrated that oxygen is an essential requirement for H. gallinarum egg development, although undeveloped eggs remain viable, even after 60 days in low oxygen conditions. The effects of climate on the biology of free-living stages studied under constant laboratory conditions cannot be applied directly to the field where climatic factors exhibit daily cycles. The effect of fluctuating temperature on development was investigated by including an additional temperature group in which H. gallinarum eggs were kept under daily temperature cycles between 12 and 22°C. Cycles caused eggs to develop significantly earlier than those in the constant mean cycle temperature, 17°C, but significantly slower than those in constant 22°C suggesting that daily temperature cycles had an accelerating effect on H. gallinarum egg embryonation but did not accelerate to the higher temperature. These results suggest that daily fluctuations in temperature influence development of the free-living stages and so development cannot be accurately predicted on the basis of constant temperature culture.     

Effects of temperature and lipid composition on the serum albumin-induced aggregation and fusion of small unilamellar vesicles

Small unilamellar vesicles of egg phosphatidylcholine (PC) or dimyristoylphosphatidylcholine, mixed with small unilamellar vesicles labelled with 2-(10-(1-pyrene)decanoyl)phosphatidylcholine, exhibit a constant average size and excimer to monomer (E/M) ratio for several hours when incubated at pH 3.6 at a temperature higher than the phase transition temperature (T_c) of the lipids. Addition of bovine serum albumin to this system produces a transient turbidity increase, a fast decrease in the E/M ratio, a partial loss of vesicle-entrapped [¹⁴C]sucrose and a measurable leak-in of externally added sucrose. Sepharose 4B filtration of the system demonstrates that the E/M ratio decrease is strictly paralleled by the formation of liposomes which exhibit a low E/M ratio and a hydrodynamic radius larger than that of small unilamellar vesicles. These data demonstrate that the E/M ratio decrease can be unequivocally ascribed to a vesicle-vesicle fusion process induced by serum albumin. The rate of serum-albumin induced fusion of small unilamellar vesicles is: (a) maximal at a stoichiometric ratio of approx. 2 albumins per vesicle: (b) sensitive to the nature of the lipid and; (c) not altered when human serum albumin replaces bovine serum albumin. The rate of albumin-induced fusion of dimyristoylphosphatidylcholine small unilamellar vesicles is higher below the T_c of the lipid and increases with temperature above the T_c. The formation of protein-bound aggregates with defined stoichiometries and a high local vesicle concentration, as well as changes in the local degree of hydration, are proposed to be the driving forces for the protein-induced vesicle fusion in this system.