David Hyde

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.

STRUCTURES, ASSAYS AND RECEPTORS FOR LOCUST ADIPOKINETIC HORMONES

This review is concerned mainly with the adipokinetic hormones (AKHs) of locusts: their molecular conformations, actions and functions and the development of microfiltration assays in vitro. The physiological significance of having multiple hormones with overlapping actions whose efficacy changes during development is discussed in relation to the possibility that these reflect variations in populations of receptors and/or the pharmacokinetics of the peptides. The involvement of second messengers in the transduction mechanism of AKHs is reviewed, and we describe hormone-induced changes of intracellular calcium in single dispersed fat body cells. The structure activity relationships of the three locust AKHs and a number of analogues with variations at the N- and C-termini are discussed. A number of areas are identified where there are gaps in our understanding of these hormones, and some of these will be the focus of our future research.

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.

Heterologous acclimation: a novel approach to the study of thermal acclimation in the crab Cancer pagurus

The control of the attainment of acclimation in Cancer pagurus has been studied. Homologous (8 or 22°C) and heterologous acclimation [central nervous system (CNS) and periphery of crabs simultaneously held at 8 or 22°C] were used. The dependence of electrophysiological parameters of dactylopodite closer muscles of walking legs on nerve stimulation was determined between 6 and 26°C. Muscle resting potential (RP) hyperpolarized linearly with increasing measurement temperatures and showed a 69% compensation between 8 and 22°C on homologous acclimation. With the CNS temperature constant at 8°C, the leg muscle RP showed a 72% compensation on heterologous acclimation to 8 and 22°C; when CNS temperature was constant at 22°C, leg muscle RP showed a 48% compensation on heterologous acclimation to 8 and 22°C. In homologous acclimation, the shape of the excitatory junction potential vs. temperature relationship was characteristic of acclimation temperature. In heterologous acclimation, the shape of this plot was related to the temperature experienced by the leg and not by the CNS. Thus acclimation was principally dependent on local tissue temperature and was relatively independent of CNS or hormonal influences.The control of the attainment of acclimation in Cancer pagurus has been studied. Homologous (8 or 22 degrees C) and heterologous acclimation [central nervous system (CNS) and periphery of crabs simultaneously held at 8 or 22 degrees C] were used. The dependence of electrophysiological parameters of dactylopodite closer muscles of walking legs on nerve stimulation was determined between 6 and 26 degrees C. Muscle resting potential (RP) hyperpolarized linearly with increasing measurement temperatures and showed a 69% compensation between 8 and 22 degrees C on homologous acclimation. With the CNS temperature constant at 8 degrees C, the leg muscle RP showed a 72% compensation on heterologous acclimation to 8 and 22 degrees C; when CNS temperature was constant at 22 degrees C, leg muscle RP showed a 48% compensation on heterologous acclimation to 8 and 22 degrees C. In homologous acclimation, the shape of the excitatory junction potential vs. temperature relationship was characteristic of acclimation temperature. In heterologous acclimation, the shape of this plot was related to the temperature experienced by the leg and not by the CNS. Thus acclimation was principally dependent on local tissue temperature and was relatively independent of CNS or hormonal influences.

THE SHORT AND LONG-TERM EFFECTS OF TEMPERATURE ON THE DYNAMIC RANGE OF SIGNALLING IN HORIZONTAL CELLS OF CARP RETINA

Abstract 1. 1. Intracellular recordings of luminosity horizontal cell responses were made from retinas isolated from carp ( Cyprinus carpio ) acclimated for at least three weeks to temperatures of 8, 16 and 26°C. 2. 2. Changing the temperature of the isolated retina resulted in an increase in the rate of rise and fall phases of horizontal responses and a reduction of response latency as temperature increased. 3. 3. The maximum amplitudes ( V max ) of horizontal cell responses were reduced for low and high temperatures with a small, intermediate range over which the largest values of V max were recorded. 4. 4. The range of temperatures for which V max was maximum was found to be dependent on the temperature of acclimation in an adaptive manner.

Temperature sensitivity of the photoreceptor dark current in the teleost retina

Abstract The dark voltage profile across the teleost photoreceptor layer was measured using a two-electrode technique. At 10°C the measured voltage gradient indicates two current components across the photoreceptor membrane, an inward current located at the photoreceptor outer segment, and an outward current located at the photoreceptor inner segment. The peak outward current was found to be temperature dependent, Q 10 2·4. This corresponds to an Ahrrenius μ, between 5 and 25°C of 15 Kcal mole −1 . At 25–30°C the Ahrrenius μ was found to be 11· Kcal mole −1 although the poor survival of the preparation at these temperatures renders this value unreliable.