Coexistence of Tetranychus urticae (Acarina: Tetranychidae) with different capacities for diapause: comparative life-history traits

Summary Individuals of the two-spotted spider mite, Tetranychus urticae Koch (Acarina: Tetranychidae), with and without a capacity for diapause, coexist in central Japan. Diapause appears to be adaptive because females in diapause suffered less mortality than non-diapausing individuals when frozen at –24°C for more than 4 h. However non-diapausing females showed good survival up to 4 h of freezing. Active non-diapausing mites survived on rose leaves in Kyoto (35°N) throughout the winters of 1988–1989 and 1989–1990. Cultures of mites with low (LD) and high (HD) diapause capacities at 18°C and 9L-15D photoperiod were successfully selected from the rose population and from a population on chrysanthemum in Nara (34.4°N). Their life-history traits at 15, 20, 25 and 30°C were characterized. HD and LD mites from both populations were of similar ages at first reproduction at 15–30° C. However, at temperatures 20° C, HD individuals produced more eggs than LD individuals, resulting in higher fecundity and intrinsic rate of natural increase. These traits allow HD individuals, which stop breeding between October and April, to increase faster in summer than LD individuals. This provides a mechanism, together with climatic fluctuations, in maintaining the coexistence of diapausing and non-diapausing T. urticae in Kyoto where winter conditions are rarely lethal to the non-diapausing individuals.     

Influences of daylength and temperature on the period of diapause and its ending process in dormant larvae of burnet moths (Lepidoptera,Zygaenidae)

The onset of larval diapause in the burnet moth Zygaena trifolii is clearly characterized by the larva molting into a specialized dormant morph. In a potentially bivoltine Mediterranean population (Marseille) two types of diapause can occur within 1 year: firstly, a facultative summer diapause of 3–10 weeks, and secondly, an obligate winter diapause, which can be lengthened by a period of thermal quiescence to several months in temperatures of 5°C. For the first time, three successive physiological periods have been experimentally distinguished within an insect dormancy (between onset of diapause and molting to the next non-diapause stage), using chilling periods of 30–180 days at 5°C, and varying conditions of photoperiod and temperature. These stages are: (1) a continuous Diapause-ending process (DEP); (2) thermal quiescence (Q); and finally, (3) a period of postdiapause development (PDD) before molting to the next larval instar. The result of transferring dormant larvae from chilling at 5°C to 20°C depended on the length of the chilling period. After chilling for 120–180 days, molting to the next instar occurred after 6–10 days, independent of daylength. This period corresponds with the duration of PDD. After shorter chilling periods (90, 60, 30 days and the control, 0 days) the period to eclosion increased exponentially, and included both the latter part of the previous diapause process and the 6–10 day period of PDD. However, photoperiod also influences the time to eclosion after chilling. Short daylength (8 h light / 16 h dark: LD 8/16) lengthened the diapause in comparison to long daylength (16 h light / 8 h dark: LD 16/8). Short daylength had a similar effect during chilling at 5°C, as measured by the longer time to eclosion after transfer. The shorter time to eclosion resulting from longer chilling periods (30–90 days) demonstrates that the state of diapause is continuously shortened at 5°C, and corresponds to the neuroendocrine controlled DEP. Presumably the DEP has already started after the onset of diapause. When chilling was continued after the end of the DEP, which ranged between 90 and 120 days, thermal quiescence (Q) followed (observed maximum 395 days). Different photoperiodic conditions during the pre-diapause inductive period modified diapause intensity (measured as the duration of diapause), in that a photoperiodic signal just below the critical photoperiod for diapause induction (LD 15/9) intensified diapause. Experiments simulating the summer diapause showed that PDD occurred in the range of 10–25°C. Higher temperatures (15 and 20°C) shortened the DEP at LD 16/8, so that at 20°C many individuals had already terminated diapause after 10–40 days and had molted after the 6–10 days of PDD. A temperature of 25°C unexpectedly lengthened the DEP to 110 days in several individuals. The ecological consequences and the adaptive significance of variation in the duration of the diapause are discussed in relation to the persistence of local populations predictably variable and rare climatic extremes throughout the year.     

Photoperiod acclimation and 24-hour variations in the critical thermal maxima of a tropical and a temperate frog

Summary The effect of photoperiod on the upper thermal tolerance of two species of frogs was studied by using the critical thermal maximum (CTM) as the end point. Both species are heliotropic and from temperate climates, but Hyla labialis lives under a near constant tropical photoperiod while Rana pipiens lives under a varying temperatezone photoperiod. The CTM of both species was studied over a 24-hour period to determine if a rhythm of temperature tolerance exists. In all but one of the acclimatization conditions used, the CTM of R. pipiens was higher than that of H. labialis. This agrees with what is known of their thermal ecology. Photoperiod significantly affects the CTM of both species. For Rana pipiens long (LD 16:8) photoperiods result in significantly higher thermal tolerance than short (LD 8:16) or moderate (LD 12:12) photoperiods at both 15 and 25° C. H. labialis shows a different pattern, having highest CTM at 25°C, LD 12:12 and lowest at 15°C, LD 12:12. When acclimated to a short (LD 8:16) photoperiod certain aspects of the frogs' tolerance of high temperatures are altered. At the same acclimatization the CTM of R. pipiens is higher than that of H. labialis, except under a combination short light regime and low temperature, and H. labialis at LD 8:16 shows no thermal acclimation between 15 and 25°C. Significant variation in the CTM over a 24-hour period occurred in H. labialis acclimatized at 25°C, LD 12:12 and R. pipiens at 25°C, LD 8:16 and 15°C, LD 12:12. For both species the 24-hour rhythm of temperature tolerance, when it occurs at LD 12:12, might be of adaptive value. Times of highest thermal tolerance are in the late morning or early afternoon and lowest tolerance is during the dark period. For R. pipiens under the unnatural combination of 25°C, LD 8:16, the pattern is reversed. When all three significant cycles are phase shifted so that the times of highest tolerance coincide, the pattern of the curves is very similar.     

Influence of salinity and temperature on the germination of Kochia scoparia

Kochia scoparia is one of the most common annual halophytes foundin the Great Basin. Seeds were collected from a population growing in asalt playa at Faust, Utah and were germinated at 5 temperature regimes(12 h night/12 h day, 5–15 ^°C, 10–20 ^°C, 15–25 ^°C,20–30 ^°C and 25–35 ^°C) and 6 salinities (0, 200, 400,600, 800 and 1000 mM NaCl) to determine optimal conditions forgermination and recovery of germination from saline conditions after beingtransferred to distilled water. Maximum germination occurred in distilledwater, and an increase in NaCl concentration progressively inhibited seedgermination. Few seeds germinated at 1000 mM NaCl. A temperatureregime of 25 ^°C night and 35 ^°C day yielded maximumgermination. Cooler temperature 5–15 ^°C significantly inhibited seedgermination. Rate of germination decreased with increase in salinity.Germination rate was highest at 25–35 ^°C and lowest at5–15 ^°C. Seeds were transferred from salt solutions to distilled waterafter 20 days and those from high salinities recovered quickly at warmertemperature regimes. Final recovery germination percentages in high salttreatments were high, indicating that exposure to high concentration ofNaCl did not inhibit germination permanently.     

A laboratory study on the life cycle of Sericostoma personatum (Kirby & Spence), and light dark-dependent food consumption

The life cycle of Sericostoma personatum (Spence) was studied at 6 °C, 10 °C and 14 °C and at each temperature at 8 and 14 hrs daylength. Embryogenesis was not temperature dependent in the 12°–18°C range. Only 7 of 38 (app. 18%) had a direct development, the rest remained in diapause with partly developed larvae. Hatching success of single egg masses was over 95%. At 6 °C at both LDs, about 452 days are required for larval development. At 10 °C 370 days (LD 8/16), or 320 days (LD 14/10) and at 14° C 319 days (LD 8/16) and 295 days (LD 14/10) were required. Duration of instars III and IV was longer at 6 °C (both LDs), compared with all other groups. Vth instar larvae of the 14 °C (LD 14/10) group grew fastest. Instar VI larvae of the 10 °C short day group developed faster than all others. Instar VII larvae of both 14 °C groups and of the 10 °C long day group develop faster than the rest. Duration of pupal instar is only temperature dependent, regardless of light regime. The field life cycle of S. personatum may require 2–5 years. Larvae are night active. They feed on Coarse Particular Organic Material (CPOM) on the sediment surface at night. They release faeces (Fine Particular Organic Material, FPOM) into the sediment where they rest by day at a few cm depth. Their burrowing behavior thus contributes to the retention of FPOM in the stream channel. Daily food consumption at constant 10 °C is significantly dependent on night length (r ² = 0.979, p < 0.05). Two factors thus may limit food consumption: in winter, low temperatures, and in summer short nights. The species thus avoids competition by day-active shredders and predation by day-active predators.     

Effect of temperature on the ovipositional biology and egg viability of the cattle tickBoophilus annulatus (Acari: Ixodidae)

The effect of temperature on the ovipositional biology ofBoophilus annulatus (Say) was determined under laboratory conditions. Engorged females subjected to constant temperatures of 12 and 45°C died without ovipositing, while females held at 15 and 40°C laid eggs which did not hatch. The preoviposition period at 25–40°C was 2–3 days; however, significant increases occurred at 20°C (5.2 days) and at 15°C (16.3 days). The number of eggs laid per female was ca. 2700 at temperatures of 25–35°C, but decreased significantly at 20°C (ca. 2300 eggs/female), 15°C (ca. 1800 eggs/female), and at 40°C (ca. 300 eggs/female). No differences were observed in the Conversion Efficiency Index (CEI) values at temperatures of 20–30°C (ca. 50%), while temperatures of 15 and 40°C produced the lowest CEI values at 35.6 and 4.9%, respectively. Hatch-ability of eggs was ca. 80% at temperatures of 20–35°C. Incubation period of eggs ranged from 52.2 days at 20°C to 16.2 days at 35°C. The thermal threshold for egg development determined by linear regression was 12.9°C. Females subjected to four fluctuating temperature regimes produced no differences in number of eggs/female (ca. 2400), CEI (ca. 50%), or hatchability of eggs (ca. 75%). Preoviposition period and incubation were significantly affected by a change in the thermoperiod, becoming longer in duration as the temperatures were decreased. From studying females exposed for various intervals from 0 to 105 days at 12°C, indications were that the longer the exposure period the more adverse the effects were on oviposition and egg-hatch. Correspondingly, exposure of eggs to a temperature of 15°C for up to 105 days gave indications that the longer the eggs remained at 15°C, the lower the hatch would be after transfer back to a temperature of 25°C.     

Behaviour of proteolytic Clostridium botulinum types A and B near the lower temperature limits of growth

Summary The behaviour of spores of Clostridium botulinum type A and proteolytic C. botulinum type B has been studied in cooked meat medium at 10°C, 12°C, 15°C, and 20°C, using mixed cultures (9 groups of in total 41 strains) and pure cultures (41 strains).At 10°C a decrease of 1–1.5 log cycles for type B and of 2–4 log cycles for type A Clostridia was observed. Neither growth nor toxin formation could be demonstrated.At 12°C spores of some strains developed and formed toxin with 3–4 weeks, whereas other strains did not develop within 7 weeks.At 15°C growth and toxin formation could be observed within 1 week, whereas at 20°C toxin was formed mostly within 2 or 3 days. Incubation at 10°C prior to incubation at 20°C seemed to have some effect on the lag time.     

Oxygen consumption of engorged nymphs and unfed adults of Hyalomma asiaticum ticks (Acari: Ixodidae) exposed to various photoperiods

The oxygen consumption of engorged nymphs of Hyalomma asiaticum was measured at various intervals after drop-off from mice hosts. Duration of nymphal development to the emergence of adults was 25–32 days at 25°C. The oxygen consumption was high immediately after completing the blood meal (193–248 mm³ g^-1 h^-1 but decreased significantly 18 days later (at 25°C) to 45–65 mm³ g^-1 h^-1. It increased again before ecdysis (81–102 mm³ g^-1 h^-1, and also after ecdysis in freshly moulted adults (177–220 mm³ g^-1 h^-1. The oxygen consumption in 8-month-old adult ticks was very variable ranging from 40–42 to 172 mm³ g^-1 h^-1. Neither engorged nymphs nor unfed adult ticks showed any dependence of their respiratory metabolism on the photoperiodic regimes tested (LD 20:4 and LD 12:12, with or without transfer to an alternative photoperiod after engorgement of nymphs).     

Heat production in cold and long scotophase acclimated and winter acclimatized rodents

Heat production by means of oxygen consumptionVo₂ (at T_a = 6° C, 25° C, 30° C, and 32° C) and non-shivering thermogenesis (NST) were studied in individuals of a diurnal rodent (Rhabdomys pumilio) and a nocturnal rodent (Praomys natalensis). The studied mice were acclimated to cold at T_a=8°C with a photoperiod of LD 12:12. On the otherhand specimens of these two species were acclimated at T_a=25°C with a long scotophase LD8:16. The results were compared with a control group (T_a=25° C, LD 12:12) and winter acclimatized individuals of both species.Vo₂ in cold acclimated mice of both species was significantly increased when compared to the control group and was even higher than the winter acclimatized group when measured below the lower critical temperature. Long scotophase acclimated mice of both species also increased their oxygen consumption significantly when compared to the control group. NST was significantly increased in long scotophase acclimated mice from both species when compared to the control group. The results of this study indicate that the effects of acclimation to long scotophase are similar to those of cold acclimation. As changes in photoperiod are regular, it may be assumed that heat production mechanisms in acclimatization to winter will respond to changes in photoperiodicity.Present address: University of Haifa, Oranim, P.O. Kiryat Tivon, Israel.Presented at the Eighth International Congress of Biometeorology, 9–14 September 1979, Shefayim, Israel.     

Life history and growth in culture of the endemic New Zealand kelp <Emphasis Type="Italic">Lessonia variegata</Emphasis> J. Agardh in response to differing regimes of temperature,photoperiod and light

Lessonia variegata J. Agardh (Laminariales, Phaeophyta) is endemic to New Zealand, where it occurs in subtidal kelp forests on wave exposed coasts in the North, South and Stewart Islands. This is the first account of the growth in culture and life history of L. variegata. Microscopic gametophytes alternate with macroscopic sporophytes, characteristic of members of the order Laminariales. The life history was completed in culture within 14 days under growth conditions of 12 °C, 12:12 (L:D) and 15 °C, 15:9 (L:D). Maximum growth of sporophytes occurred at 15 °C, 15:9, and slowest growth at 10 °C, 9:15. Under low light conditions (8–9 μmol photon m⁻² s⁻¹) filamentous growth of gametophytes predominated, and both the proportion of gametogenesis and the growth of sporophytes after 30 days was much reduced from equivalent cultures grown under conditions of higher light (16–17.5 μmol photon m⁻² s⁻¹). Interest in this species relates both to its potential for commercial utilisation as well as in the role it plays in coastal rocky reef ecosystems.     

Energy budgets for Stentor coeruleus Ehrenberg (Ciliophora)

Summary Growth and feeding rates in Stentor coeruleus fed on Tetrahymena are described in relation to prey concentrations ranging from 10:1–50:1 at 15°C and 20°C. Feeding rate was independent of temperature, but governed by prey concentration. Stentor decreased in size where less than 1,000 J were consumed in 24 hrs. A maximum level of growth was attained at 15°C, but not at 20°C within the range of prey concentration offered. Energy budgets, constructed using respiratory data published elsewhere (Laybourn, 1975), are presented. Assimilation efficiencies ranged from 74.4–76.4% at 20°C and 65.1–83.2% at 15°C. Gross growth efficiencies were between 70.9–73.6% at 20°C and 63.7–81.6% at 15°C. Net growth efficiencies were very high, 95.6–96.3% at 20°C and 97.5–97.9% at 15°C. The results are explained and discussed in relation to other Protozoa.     

Conditionality of circadian rhythmicity: Synergistic action of light and temperature

Summary With cells which have been grown at 20°C, the circadian rhythm of bioluminescence inGonyaulax polyedra disappears at a critical temperature, which is about 12°C. The transition from the rhythmic to the arrhythmic state is very sharp with temperature: the two states are separated by only 1–2°C. Following a return to a higher temperature (20°C) under otherwise constant conditions, the rhythm resumes with its new phase defined by the time of the cool to warm transition. Loss of rhythmicity also occurs in constant bright light, with a similar resumption and phase determination upon transfer to darkness. The experiments described here show that the effects of light and low temperature are additive: rhythmicity is lost under combined low temperature and light intensity treatments which are ineffective individually.Abbreviations CT circadian time - ft-c footcandle - LD 12:12 12 h light/12 h dark cycle NIH Predoctoral Trainee in Biophysics, 2 T01 GM00782-16.     

Circadian and circannual variations in growth and cold resistance of warm acclimated rats and their relationship with the geomagnetic activity

In winter, summer, spring and fall, groups of 200 g Sprague Dawley male rats were kept for 14 days at constant Ta 28°C±°C and LD 12:12(07:00–19:00 h). They were fed a laboratory chow (P) or a semi-purified diet (H). They were weighed at 0, 7 and 14 days. Cold resistance was determined by the fall in rectal temperature during 4 hours of restrained exposure to +1°C either in the morning (09:00 – 13:00 h) or in the afternoon (14:00 – 18:00 h). Rats fed the H diet could better tolerate cold exposure in the morning than in the afternoon, whereas the chow-fed rats were more vulnerable and became severely hypothermic both in morning and afternoon. The greater morning resistance provided by the H diet was evident in summer and winter but not in spring or fall. With both diets, cold resistance as well as growth decreased during spring and fall. Frozen storage of the diets and the water for use during other seasons showed that the nutrients per se were not a factor in the observed seasonal cycle. Although humidity in the 28°C room varied between a minimum of 26.5% in April to a maximum of 44.3% in August, it was not a statistically significant factor in the growth cycle. Arguments are presented to rule out relative humidity as a significant factor in the seasonal variation in the degree of cold resistance. A significant correlation was found for growth and cold resistance with geomagnetic activity.NRCC # 17310     

Effects of ambient Lake Mohave temperatures on development,oxygen consumption,and hatching success of the razorback sucker

Synopsis Spawning of razorback suckers,Xyrauchen texanus, in Lake Mohave occurred from 10–22°C and larvae were collected at water temperatures from 10–15°C in 1982 and 1983. In the laboratory, hatching success was similar from 12–20°C, but reduced hatching success was found at 10°C while none hatched a 8°C. Development rate and oxygen consumption were positively related to incubation temperature. Direct effects of ambient Lake Mohave water temperatures on hatching success of razorback sucker embryos are considered minimal. Historical spawning temperatures for the species are hypothesized based upon successful incubation temperatures and comparison to the white sucker,Catostomus commersoni.     

Factors affecting oviposition and fecundity in the grain miteAcarus siro L. (Acarina:Acaridae), especially temperature and relative humidity

Oviposition and fecundity in the grain miteAcarus siro were studied at 5–30°C and 62.5–90% RH. At and above 20°C, 80% RH, mating and oviposition occurred soon after emergence, but at lower temperatures and humidities egg laying was progressively delayed from one to several days. Females needed to mate repeatedly in order to achieve maximum egg production, optimum conditions for which were 15°C, 90% RH, where total output per female averaged 435 with a maximum of 858. Oviposition rates were highest at higher temperatures, the mean daily rate at 20 and 25°C, 90% RH, rising to maximum levels of 28/29 eggs per female per day on day six.Oviposition followed clearly defined patterns, favourable conditions producing rapid increases in the mean daily oviposition rate to high peak levels reached at an early stage in the oviposition period. Less favourable conditions resulted in reduced outputs and lower, more uniform rates of egg laying. The mean oviposition period, varying with humidity, fell from 72–122 days at 5°C to 9–13 days at 30°C and the mean incubation period from 42–70 days at 5°C to 3–4 days at 30°C. Egg viability increased with increasing humidity but was little affected by temperature and unaffected by age of the female at time of oviposition.Males tended to live longer than females at most conditions; longevity—depending on humidity—averaging 13–15 days at 30°C and 129–175 days at 5°C. Adult life for females averaged 12–19 days at 30°C and 88–169 days at 5°C. An index of suitability, calculated from egg number, viability and duration of the egg stage and oviposition period, indicated that the most favourable conditions for oviposition and hatching were 20–25°C and 80–90% RH.     

In vitro pollen embryogenesis in Nicotiana tabacum L. and its relation to pollen sterility,sex balance,and floral induction of the pollen donor plants

Pollen sterility, sex balance, and floral induction of the pollen donor plants were tested for a possible relation to embryogenesis from in vitro cultured tobacco pollen (Nicotiana tabacum L. var. Badischer Burley). The pollen grains destined to become embryos in culture (P-grains) were sterile for the donor plants as judged by their staining reaction with acetocarmine and fluorescin-diacetate, and by an in vitro germination test. They were produced in high frequency in flowers which exhibited a shift in sex balance towards femaleness. Sex balance could be measured by the relative length of pistil to stamens. High P-grain frequency, high pollen sterility, and a shift in sex balance towards femaleness could be induced by raising the donor plants under short days and/or low temperature (18–15° C) as compared to long days at 24° C. Short days and/or low temperature also reinforced floral induction, revealing that the tobacco variety Badischer Burley is a quantitative short day and low temperature plant and that the variety follows the rule that conditions of strong floral induction shift sex balance towards femaleness. At 12° C and short days, contabescent flowers were formed with completely sterile anthers containing a few and mostly collapsed P-grains. Based on these results, it is now possible to predict conditions by which haploids via pollen embryogenesis might be produced in high frequency from low-yielding and recalcitrant species.Abbreviations DPF dead pollen grain frequency - LD24 long days at 24° C - PD pollen dimorphism - P:S ratio of pistil to stamen length - SD15 short days at 15° C     

Diapause Induction and Termination in Eggs of the Fruit Tree Red Spider Mite Panonychus Ulmi in Northern Greece

In apple orchards in northern Greece, females of Panonychus ulmi Koch were found to lay diapause eggs from late August to the beginning of October. The course of diapause termination in the field was determined by transferring diapause eggs during winter and early spring from apple orchards with the varieties Starkinson and Firiki to short days (LD 8:16) (1992–1996), and long days (LD 16:8) (1994–1995), both at 20 °C. Percentages of diapause termination were very low to zero from October to the beginning of January, then progressively increased throughout January and February. Diapause termination in 50% of the eggs occurred in the first half of February in lowland mite populations irrespective of the year and location from which the eggs originated, and about one month earlier in a population originating from an altitude of 300 m. For each sampling date throughout the winter, the mean number of days required for 50% egg hatch at 20 °C (T_50%) was similar under either a long (LD 16:8) or a short (LD 8:16) photoperiod. Diapause eggs collected in October 1995 from two orchards and maintained at 0, 5, 10 and 15 °C for various periods were subsequently transferred to 20 °C and LD 8:16, where TP_50% was determined. It was shown that temperature, duration of maintenance at the different temperatures and the orchard from which the eggs originated had a significant effect on T_50% and therefore on diapause development. Additionally, in our strains diapause intensity was much weaker than in strains from more northern latitudes and was terminated even without any cold exposure. The variation in diapause intensity in different strains of P. ulmi may have an adaptive significance for this widespread species.     

Reproductive biology of Stictosiphonia hookeri (Rhodomelaceae,Rhodophyta) from Argentina,Chile, South Africa and Australia in laboratory culture

The red alga Stictosiphonia hookeri is epilithic in shaded habitats of the upper intertidal zone from 30 to 55° S. Thalli of this species from Argentina, Chile, South Africa and Australia, usually without reproductive structures when collected, all developed tetrasporangia in culture. Although good vegetative growth occurred in all nine isolates at 20–25 °C, 12:12 light: dark cycle, 10–30 µmol photons m^–2 s^–1, none reproduced in these conditions except one isolate from Australia. At 15 °C the four South African (34 °S) isolates developed tetrasporangial stichidia, and three completed a Polysiphonia-type life history. Gametophytes were unisexual or bisexual. At 15 °C one isolate from Chile (36 °S) formed tetrasporangia, but sporelings were not viable. At 10 °C isolates from Argentina and Chile (53 °S and 54 °S) formed tetrasporangia; however, only the Chile isolate completed a Polysiphonia-type life history with unisexual gametophytes. The temperature required to induce sporogenesis correlates with the range of water and air temperatures in the natural habitats of each isolate. In irradiances >50 µmol m^–2 s^–1 the thalli became yellow- brown within two weeks because of phycobiliprotein loss, but this did not impair growth or reproduction. The Argentina and Chile isolates were resistant to freezing in seawater for at least two days, showing no cell damage. The protein cuticle of the outer cell wall is repeatedly shed in culture. This may serve to minimize the attachment of epiphytes in the field.     

Enzymatic activity of rodents acclimated to cold and long scotophase

Rodents representative of a diurnal species (Rhabdomys pumilio) as well as a nocturnal species (Praomys natalensis) were acclimated to cold (T_a = 8°C) at a photoperiod of LD 12:12 and a long scotophase (LD 8; 16) at a temperature of 25° C(T_a). Control groups were kept for both species at T_a = 25° C and LD 12:12 and winter acclimated individuals were obtained during July and August to serve as further reference. Blood samples obtained from the tail were analysed for enzymes representative of three major biochemical pathways. The enzymatic activity of LDH (glycolytic pathway), MDH (Krebs cycle) and G6PDH (hexose monophosphate shunt, as an indicator of gonadal activity) were monitored to represent metabolic activity of the respective cycles. Cold acclimated as well as winter acclimatized mice revealed similar enzymatic patterns for both species and significant increases in LDH and MDH were recorded with a concurrent decrease in G6PDH activity. Specimens exposed to long scotophase exhibited similar enzymatic patterns for both species studied, but enzymatic activity was higher than those of cold acclimated individuals. From these results it is concluded that cold as well as long scotophase induce metabolic adaptations through biochemical activity in the experimental animals. The effect of long scotophase is assumed to be an important factor in the induction of winter acclimatization.Present address: University of Haifa, Oramin, P.O. Kiryat Tivon, Israel.Presented at the Eighth International Congress of Biometeorology, 9–14 September 1979, Shefayim, Israel.     

The effects of temperature on the respiration and production of the freshwater nematode Anonchus sp.

Summary Growth and respiration were measured in a species of Anonchus (Nematoda: Plectidae) at 5°C, 10°C, 15°C, 20°C and 25°C. At 5°C no growth was measurable but the organisms remained active. Maximum production occurred at 15°C, but the highest rate of growth occurred at 20°C. Thus, adult size attained is dependent on the temperature of growth. Respiratory energy losses derived from Cartesian diver microrespirometry, increased with temperature up to 25°C. Regression coefficients (b values) derived from a log log linear regression of weight against oxygen consumption varied between 0.574–1.793, the lowest value being attained at 5°C, the highest at 20°C. Based on Q₁₀, production and respiratory energy losses the optimum temperatures for Anonchus appears to lie between 10°C–15°C.