Prey-Dependent Life Attributes of an Aphidophagous Ladybird Beetle, Propylea dissecta (Coleoptera: Coccinellidae)

Predation potential, development, immature survival and reproduction of an aphidophagous ladybeetle, Propylea dissecta (Mulsant) was studied when fed on seven aphid prey, viz. Aphis gossypii, Aphis craccivora, Lipaphis erysimi, Uroleucon compositae, Brevicoryne brassicae, Rhopalosiphum maidis and Myzus persicae. A. gossypii was most suitable and consumed by the larvae and adults of P. dissecta, while M. persicae, the least. Pre-imaginal development of P. dissecta was fastest (0.080 day^-1) when A. gossypii was used as prey, whilst slowest (0.061 day^-1) on M. persicae. The immature survival, adult emergence, adult male and female longevity of P. dissecta was maximal (i.e., 77.10±0.04 and 93.21±0.79%, 57.10±1.62 and 62.40±1.93 days, respectively) on A. gossypii and minimal (i.e., 63.01±1.87 and 81.73±1.79%, 42.50±1.21 and 49.40±2.32 days, respectively) when M. persicae was provided as prey. Oviposition period, fecundity, percent egg viability and mean reproductive rate was maximum (i.e., 50.30±2.03 days, 856.00±30.00 eggs, 96.40±0.31% and 17.02 eggs per day) on A. gossypii, and minimum (i.e., 18.00±1.40 days, 212.00±18.21 eggs, 72.46±2.81% and 11.78 eggs per day) on M. persicae. Adult weight and developmental rate of P. dissecta have a positive correlation, which suggests that if immature stages of ladybeetle developed faster, they should grow into heavier adults. Female longevity and fecundity also have a positive correlation. The findings also reveal that all seven aphid species tested are essential food. Rank order of prey species was consistent in all experimental parameters.     

The effects of constant and changing tempertures on the development of eggs of the freshwater snail Lymnaea auricularia (L.)

The rate of development of Lymnaea auricularia eggs was studied at various constant temperatures between 10° and 36°C. Development was accelerated as the temperature increased and at 36°C the eggs failed to develop. Spring eggs showed differences in their rate of development when compared with summer eggs when measured at similar tempertures.

Both spring and summer eggs were more than 90% fertile. Hatching success was high at temperatures between 10° and 30° (100%–82/9%); while at 34°C it was reduced to 60.6% for spring eggs. It was above 87% at temperatures between 10° and 34°C but it dropped to 62.3% at 36°C for summer eggs.

In one regularly changing temperature experiment a significant acceleration (P < .05) was found. In two others there was no significant difference beween predicted and observed egg durations. In one suddenly changing temperature regime (1 day at 20°, 1 day at 30° and so on) a huge retardation of development was found. In the other suddenly changing experiment (1 day at 15°, 1 day at 25°) no significant difference was found.

The exposure of eggs to extreme temperature (4°C, freezing and 4°C caused a retardation in the race of subsequent development of eggs at 25°C.     

Effect of thyroxine and noradrenaline on thermoregulation, cardiac rate and oxygen consumption in the monitor lizard Varanus albigularis albigularis

1. 1. At the preferred body temperature (35°C) resting metabolic rate was 0.155 ± 0.015 ml O₂/g·h and heart rate was 54 ± 11 beats/min. Spontaneous activity at this body temperature caused a two-fold increase in heart rate and a six-fold increase in O₂ consumption. Maximum values being 0.86 ml/g·h with an O₂ pulse of 13.6 × 10⁻⁵ ml/g·beat.

2. 2. Pre-treatment for seven days with thyroxine caused a 27% increase in resting metabolic rate and a 63% increase in the thermal gradient between core and ambient temperature at the preferred body temperature.

3. 3. Noradrenaline reduced heart rate but had no effect at the dosage recommended on metabolic rate at body temperatures of either 35 or 15°C, suggesting that non-shivering thermogenesis is absent in lizards. The evolutionary implications of these results have been briefly discussed.

Shifts in thermoregulatory patterns with pregnancy in the poikilothermic mammal—The naked mole-rat (Heterocephalus glaber)

1. 1. The naked mole-rat (Heterocephalus glaber) is a poikilothermic mammal. During gestation metabolic shifts that differ from both mammalian and reptilian thermoregulatory patterns occurred.

2. 2. Body temperature was directly dependent on ambient temperature. At low ambient temperatures the temperature differential (T_b − T_a) was approximately 3°C, whereas at higher ambient temperatures the temperature differential diminished.

3. 3. In early pregnancy (prior to week 3) oxygen consumption at low ambient temperatures was greater than that of non-reproductive animals. A maximal metabolic rate (3.2 ± 1.0 ml O₂ . g⁻¹ . h⁻¹) occurred at an ambient temperature of 27°C. Thereafter the endothermic pattern of metabolism with increasing ambient temperatures was evident. Oxygen consumption decreased with increasing ambient temperature to minimal rates of 1.2 ± 0.1 ml O₂ . g⁻¹ . h⁻¹ over the ambient temperature range of 31–34°C.

4. 4. Oxygen consumption in late pregnancy (1.8 ± 0.1 ml O₂ . g⁻¹ . h⁻¹) was not correlated with ambient temperature over the entire ambient temperature range measured (24–36°C).

5. 5. Differences in thermoregulation in early and late pregnancy may be attributed to different rates of heat loss as a consequence of (a) changes in surface area and body mass or (b) vascular changes. Furthermore the thermoregulatory changes in late pregnancy may indicate that maximal overall metabolic capacity had been reached, for peak resting metabolism (expressed per animal rather than per gram body mass) in early pregnancy was similar to observed metabolism in late pregnancy.

6. 6. The dissociation of metabolism from both ambient temperature and body temperature in late pregnancy could confer an energetic advantage to this arid dwelling underground inhabitant; for it may enable the breeding female to partition a greater portion of available energy into reproduction.

The respiratory chain of Azotobacter vinelandii II. The effect of cyanide on cytochrome d

1. Cyanide causes a slow disappearance of the oxidized band (648 nm) of cytochrome d in particles of Azotobacter vinelandii and inhibits the appearance of the reduced band (631 nm). No effect of cyanide is found on the reduced band of cytochrome d.

2. The kinetics of the disappearance of the 648-nm band of cytochrome d with excess cyanide deviates from first-order kinetics at lower temperatures (22 °C) indicating that at least two conformations of the enzyme are involved. At higher temperatures (32 °C) the observed kinetics of the cyanide reaction are first order with a k_on = 0.7 M⁻¹·s⁻¹ and with an estimated k_off of approximately 5·10⁻⁵ s⁻¹.

3. The value of the k_off (7·10⁻⁴−14·10⁻⁴ s⁻¹ at 32 °C) determined from the rate of reduction of cyanocytochrome d by Na₂S₂O₄ or NADH is one order of magnitude larger than the k_off value found when the enzyme is in its oxidized state.

4. No effect of cyanide is found on the spectrum of cytochrome a₁.     

Intramuscular temperatures during exercise in the heat following pre-cooling and pre-heating

Pre-cooling improves heat tolerance and time to exhaustion in the heat. We tested the possibility that reduced tissue temperatures may explain this phenomenon, using three whole-body treatments: pre-cooling, thermoneutral (control) and pre-heating. Pre-cooling reduced muscle temperature (T_m) by 6.3 °C while pre-heating increased T_m 3.4 °C, relative to control. Despite this offset, T_m climbed towards a common asymptote, with pre-cooling offering no thermal protection beyond 40 min. Following pre-cooling, exercising oesophageal temperature (T_es) initially increased at 0.09 °C min⁻¹, being significantly faster than control (0.05 °C min⁻¹) and pre-heated conditions (0.03 °C min⁻¹). Pre-cooling lowered the sweat threshold and also resulted in a reduced cardiac frequency across the exercise-heat exposure. Our observations do not support the hypothesis that pre-cooling reduces T_m at the end of an exercise-heat exposure, thereby delaying the development of fatigue.     

Effects of development, temperature and salinity on metabolism in eggs and yolk-sac larvae of milkfish, Chanos chanos (Forsskål)

Oxygen uptake rates and yolk-inclusive dry weiGhts were measured during the egg and yolk-sac larval stages of milkfish, Chanos chanos (Forsskal). Oxygen uptake by eggs and yolk-sac larvae was measured to assess the effects of four salinities (20,25,30,35 ppt) at 28°C. The effects of three temperatures (23,28,33°C) on oxygen uptake by yolk-sac larvae were determined at a salinity of 35 ppt. Dry weights were measured throughout embryonic development at 28°C and the yolk-sac stage at 23.28 and 33°C.
Oxygen uptake rates of eggs increased more than fivefold during embryogenesis (0.07±0.03 to 0.40 ± 03 μl O₂ egg ⁻¹ h ⁻¹;blastula to prehatch stage). Larval oxygen uptake did not change with age but was affected by rearing temperature (0.33 ± 0.08, 0.44 ± 0.07 and 0.63 ± 0.13 μl O₂ larva ⁻¹ h⁻¹ at 23, 28 and 33°C, respectively; Q₁₀= 1.93). Acute temperature changes from 28 to 33°C caused significant increases in oxygen uptake by embryos (Q ₁₀= 1.69–3.58) and yolk-sac larvae (Q ₁₀=2.55). Salinity did not affect metabolic rates.
Dry weight of eggs incubated at 28°C decreased 13% from fertilization to hatching. Incubation temperatures from 23–33°C did not affect dry weights at hatching. Rearing temperatures significantly affected the rate of larval yolk absorption (Q ₁₀= 2.25).     

Comparative aspects of the thermal biology of the short-tailed gerbil, Desmodillus auricularis, and the bushveld gerbil, Tatera leucogaster

1. 1. The response of oxygen consumption (VO₂), thermal conductance (C_d and C_min, body temperature (T_b), and evaporative water loss (EWL) of Tatera leucogaster and Desmodillus auricularis were measured over the range of ambient temperatures (T_a) from 5–35°C.

2. 2. Basal metabolic rate (BMR) of T. leucogaster was 0.841 ± 0.049 ml O₂ g⁻¹ h⁻¹ and lower than predicted, while that of D. auricularis was similar to the expected value (1.220 ± 0.058 ml O₂ g⁻¹ h⁻¹). D. auricularis had a high, narrow thermoneutral zone (TNZ) typical of nocturnal, xerophilic, burrowing rodents.

3. 3. D. auricularis and T. leucogaster regulated T_b over the range T_a = 5–35°C and kept EWL and dry thermal conductance at a minimum below the TNZ. However, the EWL of T. leucogaster increased rapidly above T_a = 30°C.

4. 4. After comparison with data from other species, it was concluded that there is an optimum size for xeric, nocturnal, burrowing rodents.

Influence of temperature on life-table parameters of Stethorus gilvifrons (Mulsant) (Coleoptera: Coccinellidae) fed on Tetranychus urticae Koch

The influence of temperature on life-table parameters, fecundity and survivorship of the predatory ladybird, Stethorus gilvifrons , fed on Tetranychus urticae was determined at seven constant temperatures of 15°C, 20°C, 25°C, 28°C, 30°C, 35°C and 40°C. No development was observed at 40°C, thus being regarded as the threshold for the development of S. gilvifrons . The results indicate a significant decrease in male and female longevity with increasing temperature from 15°C to 35°C. The longest and shortest longevity were 18.40 and 12.75 days for males and 17.40 and 8.80 days for females, respectively. The intrinsic rate of natural increase ( r _m ) and the net reproductive rate ( R ₀) of S. gilvifrons linearly increased with increasing temperatures from 15°C to 35°C, while the mean generation time ( T ) and doubling time (DT) decreased linearly within this temperature range. The highest values of r _m (0.240 females/female/day) and R ₀ (59.27 females/female) and the lowest mean generation time (17.01 days) and DT (2.88 days) were recorded at 35°C. The maximum (185.50 eggs) and minimum (25.50 eggs) measurement of total fecundity was also recorded at 35°C and 15°C, respectively. The results indicate that temperature greatly affected fecundity, survivorship and life-table parameters of S. gilvifrons , and that 35°C is a suitable temperature for population growth of this predator.     

Avian embryonic thermoregulation: role of Q10 in interpretation of endothermic reactions

1. Incubated chicken eggs (D14 to D21) were placed separately in transparent acrylic glass chambers which were immersed in a 37.5°C water bath for 3 h. The chambers were then moved for 3 h to another water bath controlled at 34.5°C. Oxygen consumption and temperature of the allantoic fluid (T_af) were measured at 5-min intervals for the whole experiment using an oxygen analyzer and CrNi–Ni-thermocouples, respectively. Heat production (HP) was calculated, using an assumed RQ of 0.72.

2. At 37.5°C the relationship between HP and embryonic age follows a sigmoid curve. Between D18 (HP 7.25 J g⁻¹ h; 2.01 W kg⁻¹) and D19 (HP 7.21 J g⁻¹ h⁻¹; 2.00 W kg⁻¹) this function had a plateau phase with a duration of about 24 h.

3. During the cooling process, HP decreased continuously and the relationship between T_a and HP could be described by an exponential function. From the results, it was possible to calculate the relationships between T_af, as a measure of body core temperature, and Q₁₀; the lower the T_af the higher the Q₁₀.

4. Because the actual measured HP is the result of the negative effect of Q₁₀ on HP and the stimulating influence of the CNS-generated HP, a Q₁₀ of more than 2.0 demonstrates the absence of endothermy. Chicken embryos aged between 14 and 21 d have a Q₁₀ of less than 2.0 at body temperatures (T_af) between 34 and 30°C. It is postulated that in chicken embryos of this age endothermic reactions may occur.

5. The Q₁₀-method is suitable for investigating the prenatal development of endothermic reactions in avian embryos.     

Continuous-flow complete-mixing system for assessing the effects of environmental factors on colony-level coral metabolism

A small-scale chamber experimental system was designed to study the effects of temperature on colony-level coral metabolism. The system continuously supplies fresh seawater to the chamber, where it is mixed immediately and completely with the seawater already present. This continuous-flow complete-mixing system (CFCM system), in conjunction with theoretical equations, allows quantitative determination of chemical uptake and release rates by coral under controlled environmental conditions. We used the massive hermatypic coral Goniastrea aspera to examine variations in pH, total alkalinity, and total inorganic carbon for 16 days at 27 °C under controlled light intensities (300 and 0 µmol m^− 2 s^− 1). We confirmed the stability of the CFCM system with respect to coral photosynthetic and calcification fluxes. In addition, we obtained daily photosynthetic and calcification rates at different temperatures (27 °C, 29 °C, 31 °C, and 33 °C). When seawater temperature was raised from 31 °C to 33 °C, the gross primary production rate (P_gross) decreased 29.5%, and the calcification rate (G) decreased 85.7% within 2 days. The CFCM system allows quantitative evaluation of coral colony chemical release and uptake rates, and metabolism.     

Influence of phosphorus concentration on the growth kinetics and stoichiometry of the microalga Scenedesmus obliquus

The growth of the freshwater microalga Scenedesmus obliquus was studied at 30°C in a mineral culture medium with phosphorus concentrations of between 0 and 372 μ . The values for the specific growth rates, between and , fitted a semistructured substrate-limitation model with μ_m1 = 0·0466 h⁻¹, μ_m2 = 0·0256 h⁻¹ and . The specific uptake rate of phosphorus reached a maximum value of q_Sm1 = 658·01 × 10⁻⁴ μmol P mg⁻¹ biomass h⁻¹.     

Pyrolysis of safflower (Charthamus tinctorius L.) seed press cake: part 1. The effects of pyrolysis parameters on the product yields

Safflower (Charthamus tinctorius L.) seed press cake was pyrolysed in a fixed-bed reactor. The effects of pyrolysis temperature, heating rate and sweep gas flow rates on the yields of the products were investigated. Pyrolysis runs were performed using pyrolysis temperatures between 400 and 600 °C with heating rates of 10, 30 and 50 °C min⁻¹. The obtained bio-char, gas and bio-oil yields ranged between 25 and 34 wt%, 19 and 25 wt%, and 28 and 36 wt%, respectively, at different pyrolysis conditions. The highest liquid yield was obtained at 500 °C pyrolysis temperature with a heating rate of 50 °C min⁻¹ under the sweep gas of N₂ with a flow rate of 100 cm³ min⁻¹. Employing the higher heating rate of 50 °C min⁻¹ results in maximum bio-oil yield, probably due to the decrease in mass transfer limitations. According to the results obtained under the conditions of this study, the effects of pyrolysis temperature and sweep gas flow rate are more significant than the effect of heating rate on the yields.     

Some aspects of the biology of a cyprinid, Aspius vorax Heckel

Scales were used for the determination of age with back-calculation of length. The oldest fish was VII + years old. Back-calculation did not exhibit Lee's phenomenon. The most rapid growth occurred in summer at water temperatures over 25°C. The growth in weight was c . 331 g year^-1 after IV vears of life. Growth was well described by von Bertalanffy equation : l_l - 91·0 [ l= ^{0·122(l0·25)}] The length-weight relationship followed the cube law (b = 3·0601) K_n ranged from 0·74 to 1·18 with a mean value of 1·0. Spawning occurred in January, fecundity was 74 509 with a mean of 1157 eggs -¹ body weight. Mean diameter of eggs was 1071 (pm). A developed ovary had ova of two sizes, immature oocytes and mature ova. The fish is a carnivorous feeder.     

The effect of temperature on the egg incubation period of Capnia bifrons (Plecoptera: Capniidae) from Windermere (English Lake District)

Gravid females of Capnia bifrons (Newman) from Windermere (English Lake District) were almost completely ovoviviparous, the eggs hatching within 15 min after oviposition in the water. When kept in the laboratory at constant temperatures between 3.8 and 19.8°C, few females survived to lay eggs at temperatures above 12.1°C. The relationship between air temperature (T°C) and the egg incubation period (Y days between fertilisation and oviposition) was given by the regression equation: Y = 316.4 T^−0.9996 (r²= 0.957, p < 0.001). This equation successfully predicted egg incubation periods for gravid females kept in cages in the field.
Comparisons with similar studies on four non-ovoviviparous species of Plecoptera showed that egg development was rarely more rapid in C. bifrons . It was also shown that the hypothesis of ovoviviparity being an adaptation to combat low water temperatures could be rejected for C. bifrons from Windermere.     

Characterization of functional VIP/PACAP receptors in the human erythroleukemic HEL cell line

R. LEMA-KISOKA, N. HAYEZ, I. LANGER, P. ROBBERECHT, E. SARIBAN AND C. DELPORTE. Characterization of functional VIP/PACAP receptors in the human erythroleukemic HEL cell line. PEPTIDES. The presence of VIP/PACAP receptors was investigated on the human erythroleukemic cell line HEL. Specific binding of [¹²⁵I]-PACAP or [¹²⁵I]-VIP on HEL cells or membranes was very low and did not allow to perform competition curves. At 37°C PACAP transiently increased cAMP levels in the presence of the non-specific phosphodiesterase inhibitor IBMX, suggesting rapid desensitization. Kinetic studies revealed that optimal conditions to measure the EC₅₀ of PACAP(1–27) were 10 min at 20°C. Under those conditions, PACAP-related peptides increased cAMP levels with EC₅₀ in agreement with the pharmacological profile of the VPAC₁ receptor subtype: PACAP = VIP > [K¹⁵, R^16, L²⁷]VIP(1–7)/GRF(8–27) = [R¹⁶]ChSn (two VPAC₁ agonists) HELODERMIN = secretin. RO 25–1553, a selective activator of VPAC₂ receptor was inactive at 1 μM. Dose-response curves of VPAC₁ agonist molecules (PACAP, VIP, [K¹⁵, R¹⁶, L²⁷]VIP(1–7)/GRF(8–27), [R¹⁶]ChSn) were shifted to the right by the VPAC₁ receptor antagonist [AcHis¹, D-Phe², Lys¹⁵, Leu¹⁷]VIP(3–7)/GRF(8–27), with a K_i of 3 ± 1 nM (n = 3). The presence of VPAC₁ receptor mRNA was confirmed by RT-PCR. Preincubation with PACAP or PMA showed that VPAC₁ receptors underwent homologous and heterologous desensitization.

This study provides the first evidence for the expression of functional VPAC₁ receptors undergoing rapid desensitization in HEL cells.     

Kinetics and equilibria of Ga(III)---thiocyanate complex formation. Mechanism of ligand substitution reactions of Ga(III) in aqueous solution

The kinetics and equilibria of complex formation by Ga(III) with NCS⁻ in aqueous solution have been measured over a range of acidities and temperatures, the contributing paths to the reaction resolved, and their rate constants and activation parameters determined. The hydrolysis equilibria required to carry out this resolution of kinetic behaviour have also been measured.

Unlike the other reported complexation reactions of Ga(III) in aqueous solution, the separate reaction pathways can be assigned with no ambiguity. At 25 °C and ionic strength 0.5 M, the observed forward rate constant for the complex formation is described by {k₁ + k₂K_1h/[H⁺] + k₃K_1hK_2h/[H⁺]²} M⁻¹ s⁻¹. For these conditions, the first and second successive hydrolysis constants of Ga(H₂O)₆³⁺ are given by pK_1h = 3.69 ± 0.01 and pK_2h = 3.74 ± 0.04. The rate constants corresponding to the reactions of the species Ga(H₂O)₆³⁺, Ga(H₂O)₅(OH)²⁺ and Ga(H₂O)₄(OH)₂⁺ with NCS⁻ are k₁ = 57 ± 4 M^{−1 −1}, k₂ = (1.08 ± 0.01) × 10⁵ M⁻¹ s⁻¹ and k₃ = 3 × 10⁶ M⁻¹ s⁻¹ respectively. The complexation equilibrium quotient [GaNCS²⁺]/([Ga³⁺][NCS⁻]) has been independently determined by spectrophotometric titration to be 20.8 ± 0.3 M⁻¹ at 25 °C and ionic strength 0.5 M.

These kinetic results lead to an interpretation of the data, and a reinterpretation of other data for aquo-Ga(III) complex formation kinetics from the literature which support the assignment of a dissociative interchange mechanism for these reactions rather than the associative activation mode sometimes proposed.     

Study of the thermal stability of D-amino acid oxidase from Trigonopsis variabilis reveals enzyme inactivation via multiple steps

The thermal stability of a highly purified preparation of D-amino acid oxidase from Trigonopsis variabilis (TvDAO), which does not show microheterogeneity due to the partial oxidation of Cys-108, was studied based on dependence of temperature (20-60°C) and protein concentration (5-100 µmol L^-1). The time courses of loss of enzyme activity in 100 mmol L^-1 potassium phosphate buffer, pH 8.0, are well described by a formal kinetic mechanism in which two parallel denaturation processes, partial thermal unfolding and dissociation of the FAD cofactor, combine to yield the overall inactivation rate. Estimates from global fitting of the data revealed that the first-order rate constant of the unfolding reaction (k _a) increased 10⁴-fold in response to an increase in temperature from 20 to 60°C. The rate constants of FAD release (k _b) and binding (k _-b) as well as the irreversible aggregation of the apo-enzyme (k _agg) were less sensitive to changes in temperature, their activation energy (E _a) being about 52 kJ mol^-1 in comparison with an E _a value of 185 kJ mol^-1 for k _a. The rate-determining step of TvDAO inactivation switched from FAD dissociation to unfolding at high temperatures. The model adequately described the effect of protein concentration on inactivation kinetics. Its predictions regarding the extent of FAD release and aggregation during thermal denaturation were confirmed by experiments. TvDAO is shown to contain two highly reactive cysteines per protein subunit whose modification with 5,5'-dithio-bis (2-nitrobenzoic acid) was accompanied by inactivation. Dithiothreitol (1 mmol L^-1) enhanced up to 10-fold the recovery of enzyme activity during ion exchange chromatography of technical-grade TvDAO. However, it did not stabilize TvDAO at all temperatures and protein concentrations, suggesting that deactivation of cysteines was not responsible for thermal denaturation.     

Environmental influences on fecundity, egg viability and egg cannibalism in the scale insect predator, Chilocorus nigritus

The effects of temperature on age-specific fecundity, egg viability and egg cannibalism were examined in the coccidophagous coccinellid, Chilocorus nigritus being fed on the cyanophyllum scale, Abgrallaspis cyanophylli. There were no significant differences in lifetime fecundity or oviposition rate at constant temperatures in the range of 20 to 30°C although there was a trend for both parameters to increase with increasing temperatures. Total fecundity ranged from five to 1890 eggs per female whilst the oviposition rate varied from 0.2–12.1 eggs day^-1. Egg viability was significantly greater at 26 and 30°C (63 and 74%, respectively) than at lower temperatures (18 to 30%) whilst egg cannibalism was highest at 24 and 26°C (being the mid range of the temperatures tested). Mean pre-oviposition periods varied from 54 days at 20°C to 8.2 days at 30°C. The effect of relative humidities in the range of 33% to 75% on oviposition rate, egg viability and egg cannibalism was measured and found to have no significant effect on either parameter.     

Effects of temperature, irradiance, and daylength on the marine diatom Leptocylindrus danicus Cleve. IV. Growth

Growth and dark respiration rates of the marine diatom Leptocylindrus danicus Cleve were measured in axenic batch culture under 49 combinations of temperature (5, 10, 15, 20°C), daylength(15:9, 12:12, 9:15 LD), and irradiance (at least four irradiances per daylength). Cell division rates exhibited a temperature-dependent daylength effect. Optimal temperatures occurred between 15 and 20°C. Both the initial slope () and the growth rate at light saturation (μ_max) were strongly influenced by temperature; increased five-fold and μ_max by an order of magnitude between 5 and 20°C. The compensation irradiance (I_c) was independent of temperature. μ_max was 2.7 div day⁻¹ at 20°C, 2.6 at 15°C, 1.1 at 10°C, and 0.3 at 5 °C. Cells grown under 15:9 and 12:12 LD exhibited similar growth-light curves at 20°C and at 15°C. μ_max of cells grown under 9:15 LD at these temperatures were substantially lower than μ_max under longer daylengths. Growth at 10 and 5°C was independent of daylength.

Dark respiration rates were a linear function of cell division rates at 10, 15, and 20°C, and support the concept that growth rate is dependent on dark respiration rate. These relationships were not influenced by daylength. A detectable relationship between dark respiration and growth at 5°C was not observed.

Photosynthesis and excretion showed temperature-dependent curvilinear relationships with growth rate, reflecting the lower saturation irradiance for growth compared to light saturation of photosynthesis and excretion. The relationship between Chl a-specific photosynthesis and growth was controlled by the C:Chl a ratio, which showed a positive correlation with cell division rate. At 15 and 20°C, light saturation of growth was associated with C:Chl a ratios of 40 to 60; at 5 and 10°C, cells growing at μ_max contained C:Chl a in ratios of 80 to 110.