Liisa Kivivuori

How to measure the thermal death of Daphnia? A comparison of different heat tests and effects of heat injury

1. 1. The thermal death point of the water flea Daphnia magna (age < 24 h, cultured at 20°C) varied considerably depending on the method used. The median lethal dose (LD50), induced by an acute 24 h heat exposure was 34.8°C. It was 37.8°C following a thermal shock for 15 min, and it was 39.4°C when a continuous temperature increase (0.2°C/min) was used. 2. 2. Heat death temperature of daphnids was related to the acute heating rate. 3. 3. The logarithm of median lethal time (Lt50) of daphnids, kept at a constant high temperature, had a linear relationship to temperature (°C) within the range of 28.0–38.5°C. 4. 4. The mortality after heat exposure increased with recovery time at 20°C for up to 3 days. 5. 5. The animals which survived the heat exposure produced eggs and offspring. Furthermore, no time lag in development between the control and heat exposure group was observed. 6. 6. The comparison of the results made by different heat tests categorized to Methods 1 and 2 by Precht (1973), for use in the determination of lethal limits of ectotherms, has been discussed.

Temperature selection behaviour of cold- and warm-acclimated crayfish [Astacus astacus (L.)]

1. 1.|Using a toroidal gradient apparatus with a thermal water gradient from 4 to 18°C (a cool gradient), the mean temperature on the anterior carapace surface (Ts) of the freely moving crayfish during 1 h period after 3–4 h gradient exposure was 11.9°C in 5°C-acclimated animals and 16.1°C in 20°C-acclimated ones. With a gradient extending from 10 to 25°C (a temperate gradient), the Ts was 15.3 and 18.0°C respectively. 2. 2.|In the cool gradient, 5°C-acclimated crayfish wandered evenly, while 20°C-acclimated ones avoided temperatures below 10.3°C. In the temperate gradient, the means of the upper avoidance temperatures were 20.4 and 23.0°C for the 5°C- and 20°C-acclimated animals respectively. 3. 3.|Temperature acclimation of crayfish Astacus astacus changed their temperature selection and avoidance behaviour.

Effects of temperature and temperature acclimation on the motor and neural functions in the crayfish Astacus astacus L

1. 1. Spring and fall crayfish (Astacus astacus L.) were acclimated for 1–2 weeks at 5°C and 20°C. The effect of temperature on the motor functions of different neural paths as well as on the spontaneous firing of the isolated nerve cord was measured. 2. 2. Both cold and heat resistance increased in the order: righting reflex < walking < scaphognathite beat and escape reflex, and motor functions ≤ spontaneous firing. In many cases temperature acclimation shifted the resistance limits in an adaptive way. 3. 3. Crayfish righted most quickly at temperatures from 15–20°C, cold-acclimated animals using a greater number of escape flips than warm-acclimated ones. The righting reflex time showed no adaptive changes. 4. 4. The rate of scaphognathite beat indicated inverse capacity acclimation in spring and temperature compensation in fall but the steady rate of spontaneous firing indicated opposite changes. 5. 5. Results suggest thermal resistance acclimation of movements which is not solely linked to a high cold and heat sensitivity of receptors and synapses of neural paths. Additionally, neural integration may show adaptive capacity changes using parallel neural paths and changing the driving of motor paths.

Effect of temperature acclimation on thermal dependence and hysteresis of the resting membrane potential of the stretch receptor neurone in crayfish [Astacus astacus (L.)]

Abstract 1. 1.|The resting membrane potential of the slowly adapting stretch receptor neurone of warm-acclimated crayfish depolarized during temperature change from 21 to 5°C with a greater thermal dependence at low than at high temperatures, the inflection was at about 18°C. 2. 2.|Cold acclimation of crayfish changed the thermal dependence of the resting membrane potential to become more independent of temperature. The mean level of the resting membrane potential was not changed by cold acclimation. 3. 3.|Cyclic temperature change induced a hysteresis in the thermal dependence of the resting membrane potential. This means that there were two values in the resting membrane potential, depending on the previous thermal history of the preparation. This gave a hysteresis loop at a temperature range of 7–19°C. The hysteresis loop of the resting membrane potential was observed in both acclimation groups. 4. 4.|The formation of the hysteresis loop during the cyclic temperature change was reversed by temperature acclimation. This indicates that the hysteresis in the temperature dependence of the resting membrane potential of a single sensory neurone was dependent on acclimation temperature of the animal.

Temperature acclimation of walking in the crayfish Astacus astacus L.

Abstract 1. 1. Crayfish (Astacus astacus L.) were acclimated for 3–12 days at 5°C and 20°C. The effect of temperature on the rate of spontaneous walking in intact animals was measured. 2. 2. The spontaneous walking showed a bimodal rate-temperature curve with peaks at 0.5° and 20°C in the cold-acciimated and at 5° and 26°C in the warm-acclimated crayfish. Between the peaks, the rate of spontaneous walking decreased slightly. 3. 3. The time course of the effect of temperature acclimation on spontaneous walking showed a slowly developing and probably permanent decrease of the rate at 5° and 26°C in the cold-acclimated crayfish and a rapid but transient increase of the rate at 26°C in the warm-acclimated crayfish. 4. 4. It is suggested that the decrease of the rate of spontaneous walking during cold acclimation is not a consequence of the lethargic effect of the low temperature, but indicates an adaptive change in the coordination of walking of the crayfish.

Fluidity of Neuronal Membranes of Crayfish (Astacus astacus L.) Acclimated to 5°C and 20°C

Abstract The fluidity of microsomal membranes from nerve cords of eurythermal freshwater crayfish Astacus astacus acclimated to 5°C or to 20°C was measured by steady-state fluorescence polarization. Membrane fluidity was measured at 4–24°C during a cyclic temperature change (0.2°C/min) using 1,6-diphenyl-1,3,5-hexatriene (DPH) or 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) molecule as probes. The fluidity of neuronal membranes depended on temperature but not on the direction of temperature change. Thermal dependence of fluidity was higher with DPH than with TMA-DPH. Neuronal microsomal membranes of cold-acclimated crayfish were more fluid than those of warm-acclimated animals. Except at the lowest experimental temperatures, in both microsomal and plasma membranes, the TMA-DPH polarization values were higher than the DPH polarization values, indicating the anchorage of TMA-DPH to the more rigid hydrophilic surface of the bilayer at these temperatures in both membranes. Neuronal plasma membranes were more rigid than microsomal membranes measured with DPH. With TMA-DPH plasma membranes were more fluid than microsomal membranes.

Effect of temperature acclimation in the crayfish Astacus astacus L. on the locomotor activity during a cyclic temperature change

Abstract 1. 1.|The thermal dependence of the locomotor activity of 5°C- and 20°C-acclimated crayfish (Astacus astacus L.) was studied using a cyclic temperature change (0.3°C/min) at 4-23-4°C. 2. 2.|The thermal dependence of the locomotor activity rate of the 5°C-acclimated crayfish showed hysteresis between 5 and 14°C; activity being higher during cooling than during warming. In the 20°C-acclimated animals, no hysteresis in the thermal dependence of locomotor activity was observed. 3. 3.|In both acclimation groups the locomotor activity rate was inversely related to temperature between 7 and 23°C, irrespective of the direction of the temperature change. 4. 4.|During warming from 9 to 19°C, the 20°C-acclimated crayfish were more active than the 5°C-acclimated ones. 5. 5.|At the lowest temperatures (4–6°C), inactivity related to chill coma was observed in the warm-acclimated crayfish.

Temperature acclimation of axonal functions in the crayfish Astacus astacus L.

Abstract 1. 1.|Crayfish ( Astacus astacus L.) were acclimated for 1–3 weeks at 5 and 20°C. The effects of temperature on the functions of the unicellular medial giant axon were studied. 2. 2.|The resting membrane potential of the giant axon increased slightly with the experimental temperature from 2 to 32°C. The temperature dependence of the resting membrane potential could be described by two lines, which intersected at about 12°C in cold-acclimated crayfish and at about 16°C in the warm-acclimated. 3. 3.|The amplitude of the action potential was stable at temperatures from 4 to 26°C. It decreased at temperatures above 26°C in both acclimation groups. 4. 4.|The duration of the falling phase of action potential was highly temperature dependent at low temperatures. A break in the slope of the dependence was found at about 14°C in cold-acclimated crayfish and at about 17°C in the warm-acclimated.

The rate and retention of the habituation of the shadow reflex in Balanus improvisus (Cirripedia)

Abstract 1. 1. There is large variation in the rate of habituation of the shadow reflex in the barnacle Balanus improvisus . This variation cannot be accounted for by the variation in the body size or in the activity of the animals. 2. 2. When only a short recovery time is allowed, the rate of the recovery of the habituated response is correlated with the rate of the preceding habituation. The same result is obtained when the habituation rate is varied using different animals or different temperatures. 3. 3. Habituation is more rapid at 12 °C than at 22 °C. 4. 4. Acetylcholine chloride (1·67 × 10 −5 g per ml) enhances the recovery of the habituated response. 5. 5. The results are in agreement with the transmitter depletion hypothesis of habituation.

Temperature acclimation of the caudal photoreceptor response in the crayfish Astacus astacus L

Abstract 1. 1, Crayfish ( Astacus astacus L.) were acclimated for 1–2 weeks at 5 C and 20 C. The effect of temperature on the latency and on the axonal maximum frequency of the caudal photoreceptor response (CPR) as well as on the spontaneous spike activity (SSA) of the isolated abdominal nerve cord was measured. 2. 2. CPR was less heat and cold resistant than SSA. CPR showed thermal resistance acclimation. 3. 3. The latency of CPR was highly dependent on temperature below 15 C, but in the upper temperatures, the latency was almost independent of temperature. A change of the latency caused by temperature acclimation was observed at 31 C. 4. 4. Temperature for the thermal maximum of the maximum frequency shifted by temperature acclimation in an adaptive way. The maximum frequency showed inverse acclimation above 26 C. 5. 5. Inverse acclimation of SSA of the nerve cord was observed at 31 C. 6. 6. The results suggest that acclimatory changes in the receptor function may have a role in thermal acclimation mechanisms of the nervous system.