K. Bowler

Temperature biology of animals.

This book should be of interest to those interested in the physiology, biochemistry and general biology of animals.

Insect thermal tolerance: what is the role of ontogeny, ageing and senescence?

Temperature has dramatic evolutionary fitness consequences and is therefore a major factor determining the geographic distribution and abundance of ectotherms. However, the role that age might have on insect thermal tolerance is often overlooked in studies of behaviour, ecology, physiology and evolutionary biology. Here, we review the evidence for ontogenetic and ageing effects on traits of high‐ and low‐temperature tolerance in insects and show that these effects are typically pronounced for most taxa in which data are available. We therefore argue that basal thermal tolerance and acclimation responses (i.e. phenotypic plasticity) are strongly influenced by age and/or ontogeny and may confound studies of temperature responses if unaccounted for. We outline three alternative hypotheses which can be distinguished to propose why development affects thermal tolerance in insects. At present no studies have been undertaken to directly address these options. The implications of these age‐related changes in thermal biology are discussed and, most significantly, suggest that the temperature tolerance of insects should be defined within the age‐demographics of a particular population or species. Although we conclude that age is a source of variation that should be carefully controlled for in thermal biology, we also suggest that it can be used as a valuable tool for testing evolutionary theories of ageing and the cellular and genetic basis of thermal tolerance.

THERMAL TOLERANCE OF TWO SPECIES OF MARINE CRAB, CANCER PAGURUS AND CARCINUS MAENAS

The critical thermal maxima of adult Carcinus maenas and Cancer pagurus have been determined. The CTMax for the eurythermal C. maenas were significantly higher than for the stenothermal C. pagurus at each acclimation condition, as would be predicted. Acclimation had a significant effect in both species, with 22°C acclimated crabs having significantly higher CTMax than 8°C acclimated crabs. The acclimation ability (AAR response) was greater in C. pagurus than in C. maenas, suggesting that the ability for acclimation is not directly related to eurythermicity. There was a marked seasonal effect on CTMax in both species. The CTMax of winter caught crabs was significantly lower than in summer or autumn caught animals, a difference that persisted irrespective of laboratory acclimation status.

A near perfect temperature adaptation of bilayer order in vertebrate brain membranes

The bilayer order of a brain synaptic membrane fraction from a number of fish, mammalian and avian species have been compared in relation to their respective body temperatures using steady-state and time-resolved fluorescence anisotropy techniques. Fluorescence anisotropy for both 1,6-diphenyl-1,3,5-hexatriene and trans-parinaric acid increased in the order: antarctic Notothenia, trout, perch, cichlid, rat and starling, this also being the order of increasing body temperature. This suggests that cold-adapted fish species possess more disordered brain membranes than warm-adapted fish species, and mammals and birds membranes were more ordered than fish membranes. Comparison of temperature profiles for both fluorescence probes showed that fish species display similar anisotropies, and by inference bilayer order, to mammals and birds when measured at their respective body temperatures. Time-resolved analysis showed that the interspecific differences in (P2) order parameter was consistently related to body temperature whilst the rotational diffusion coefficient was not. These results suggest that brain membrane order is highly conserved within the vertebrates despite large differences in thermal habits and phylogenetic position. Polar fish species have by far the lowest bilayer order indicating that invasion of extreme cold habitats involved an adaptive decrease in bilayer order and conversely adoption of a high body temperature by mammals involved an adaptive increase in bilayer order. The conservation of membrane static order for these species at their respective body temperatures indicates a regulatory control of this aspect of membrane hydrocarbon structure and the functional importance of this structure.

Temperature dependence of the heart isolated from the cold or warm acclimated perch (Perca fluviatilis)

Abstract 1. 1. Temperature dependence of beating pearch atrium showed an acclimation effect on rate of Precht type 3. Arrhenius plots were non-linear being steepest below 10°C in both 5° and 18–20°C acclimated groups. 2. 2. Temperature dependence of oxygen consumption of non-beating heart also showed the acclimation effect, but the Arrhenius plots were linear over the whole temperature range, 2–25°C. 3. 3. Morphometric analysis showed that the fractional volume of cardiac cells occupied by sarcoplasmic reticulum was greater in cold as compared to warm acclimated fish. No such difference was found for mitochondria.

Heat death in the crayfish Austropotamobius pallipes— Ion movements and their effects on excitable tissues during heat death

1. 1.|Resistance acclimation has been demonstrated in the crayfish Austropotamobius pallipes. 2. 2.|Analysis of muscle, haemolymph and environment showed that dramatic changes occurred in the Na+ and K+ concentrations in all three compartments during exposure to high lethal temperatures. 3. 3.|Ions tended to move along their electrochemical gradients. 4. 4.|Results indicate that death is related to a rise in haemolymph K+ concentration, no relationship between Na+ concentration and heat death was observed. 5. 5.|Exposure to high lethal temperatures cause an increase in sarcolemmal conductivity. Concomitant with this is a fall in resting potential of the muscle fibres, the time-course of which is dependent upon the previous thermal history of the animal. 6. 6.|Muscle fibre resting potential of ‘heat dead’ crayfish was found to be normal when measured in ‘normal’ saline and at room temperature. 7. 7.|Spontaneous activity of the CNS was relatively unaffected by exposure to high lethal temperatures, with a Q10 of 1·3. Raising the extracellular K+ concentrations to levels observed in animals at the time of heat death caused a massive increase in activity. 8. 8.|A sequence of events occurring during heat death is proposed and the implications of this to the possible mechanisms involved in thermal acclimation are discussed.

TEMPERATURE ACCLIMATION OF MARINE CRABS: CHANGES IN PLASMA MEMBRANE FLUIDITY AND LIPID COMPOSITION

Abstract 1. 1. Crabs were acclimated for 3 weeks to cold and warm temperatures. Plasma membranes prepared from leg muscle were analysed for fluidity and lipid composition. 2. 2. Plasma membranes from cold-acclimated crabs were more fluid and had lower cholesterol to phospholipid ratios than those from warm-acclimated crabs. The ratio saturated/unsaturated fatty acids was little altered by temperature acclimation. 3. 3. Plasma membranes from the stenothermal species ( Cancer pagurus ) were slightly more fluid (at DPH probe level) and had lower cholesterol/phospholipid ratios than those from the eurythermal species ( Carcinus maenas ). 4. 4. Plasma membranes from crabs acclimated in spring had more saturated and less polyunsaturated fatty acids than those from crabs acclimated in autumn.

The resting potential of cockroach muscle membrane

1. 1. Evidence is presented that Em of cockroach muscle has two components, an active component generating about 18 mV and an ionic electrode, dominated by K+, which is responsible for about 42 mV. 2. 2. Equilibration between the saline and extracellular fluid is probably complete within 60 min. 3. 3. Em vs. log [K+]o produces a linear plot with a slope of 43 mV for a 10-fold change in [K+]o. 4. 4. Em>EK. 5. 5. The active, electrogenic component is inhibited by metabolic inhibitors, low temperature, anoxia, ouabain, absence of [HCO3−]o and omission of [Cl−]o. The nature of this component is discussed and it is believed that one of its functions is the outward transport of K+. 6. 6. The role of [Cl−]o is discussed. 7. 7. When metabolism is inhibited the membrane depolarizes and Em becomes insensitive to reductions in [K+]o, an effect which disappears in the absence of [Na+]o. Under these conditions, PK outwards is believed to be very low. 8. 8. Comparisons are made with results obtained with other insects and similarities with mammalian smooth muscle are emphasized.

Homeoviscous adaptation and its effect upon membrane-bound proteins

Abstract Synaptic membranes of goldfish showed compensatory adjustments in fluidity when the fish were acclimated to high or low temperature. This was associated with changes in the thermal stability of the synaptic (Na + +K + ) ATPase at high inactivating temperatures. The importance of membrane fluidity to the structural stability of membrane-bound enzymes was supported by the labilising effects of the fluidising anaesthetic, n-hexanol, upon the (Na + +K + ) ATPase. These results indicate that homeoviscous adaptation elicits adaptive changes in the (Na + +K + ) ATPase.

Studies on ouabain-binding to (Na+ + K+)-ATPase from Malpighian tubules of the locust, Locusta migratoria L.

Abstract A study has been made on the binding of [ 3 H]ouabain to (Na + + K + )-ATPase in microsomal preparations from Malpighian tubules of Locusta migratoria . The rate constants at 30°C were 1.5 · 10 3 ± 3.5 · 10 2 M −1 · s −1 and 3.7 · 10 −3 ± 0.6 · 10 −1 for the association and dissociation of the ouabian and the receptor, respectively. This yielded a dissociation constant of 2.5 · 10 −6 M. Scatchard plots indicate heterogeneity of ouabain binding. These have been analysed on the basis that binding occurrd at two classes of independent sites. High-affinity sites were characterized by a dissociation constant of 0.2 ± 0.1 μ M and low capacity ( B max = 11.0 ± 1.2 pmol/mg protein). Low-affinity sites were characterized by a dissociation constant of 4.2 ± 1.3 μ M and B max equal to 25.9 ± 2.5 pmol/mg protein. K d for the low-affinity site was not significantly different from the I 50 value of 1.12 μM, suggesting that this class of site may be associated with inhibition of (Na + + K + )-ATPase activity. Comparison of (Na + + K + )-ATPase activity and amount of ouabain bound indicate a turnover of 2645 ATP hydrolysed/site per min. It is estimated that there are in excess of 3.4 · 10 6 high-affinity sites and 8.1 · 10 6 low-affinity sites per cell (i.e., a total of 1.15 · 10 7 sites/cell). This total site density value, taken in conjunction with the turnover number, predicts rates of metabolic demand and cation translocation which are consistent with observed values.