Use of Neurospora spore killer strains to obtain centromere linkage data without dissecting asci

Use of a centromere-linked Spore killer gene Sk reduces manyfold the labor involved in obtaining tetrad data that would otherwise require ordered dissection of intact linear eight-spored asci. Heterozygous crosses are made for Spore killer (SkK X SkS) and for markers to be tested. In such crosses only SkK ascospores survive. The four viable (SkK) and four aborted (SkS) ascospores of each ascus are ejected from the perithecium as a physically disordered group. The four surviving SkK ascospores of individual asci are germinated and scored. SkK segregates from SkS at the first meiotic division. If both marker alleles are represented in the surviving products, they must therefore have segregated from one another at the second division. Four-spore (Fsp) genes have been used to eliminate one postmeiotic nuclear division, so that only two ascospores per ascus need to be scored. The Spore killer method has been useful for mapping closely linked genes in centromere regions, for identifying genes that are far out on chromosome arms, for obtaining information on meiotic crossing-over, and for comparing linkages in different species.     

Expression of Meiotic Drive Elements Spore Killer-2 and Spore Killer-3 in Asci of Neurospora Tetrasperma

It was shown previously that when a chromosomal Spore killer factor is heterozygous in Neurospora species with eight-spored asci, the four sensitive ascospores in each ascus die and the four survivors are all killers. Sk-2K and Sk-3K are nonrecombining haplotypes that segregate with the centromere of linkage group III. No killing occurs when either one of these killers is homozygous, but each is sensitive to killing by the other in crosses of Sk-2K x Sk-3K. In the present study, Sk-2K and Sk-3K were transferred by recurrent backcrosses from the eight-spored species Neurospora crassa into Neurospora tetrasperma, a pseudohomothallic species which normally makes asci with four large spores, each heterokaryotic for mating type and for any other centromere-linked genes that are heterozygous in the cross. The action of Sk-2K and Sk-3K in N. tetrasperma is that predicted from their behavior in eight-spored species. A sensitive nucleus is protected from killing if it is enclosed in the same ascospore with a killer nucleus. Crosses of Sk-2K x Sk-2S, Sk-3K x Sk-3S, and Sk-sK x Sk-3K all produce four-spored asci that are wild type in appearance, with the ascospores heterokaryotic and viable. The Eight-spore gene E, which shows variable penetrance, was used to obtain N. tetrasperma asci in which two to eight spores are small and homokaryotic. When killer and sensitive alleles are segregating in the presence of E, only those ascospores that contain a killer allele survive. Half of the small ascospores are killed. In crosses of Sk-2K x Sk-3K (with E heterozygous), effectively all small ascospores are killed. The ability of N. tetrasperma to carry killer elements in cryptic condition suggests a possible role for Spore killers in the origin of pseudohomothallism, with adoption of the four-spored mode restoring ascospore viability of crosses in which killing would otherwise occur.     

Temperature and pH/CO(2) modulate respiratory activity in the isolated brainstem of the bullfrog (Rana catesbeiana)

The effects of temperature and pH/CO(2) were examined in isolated brainstem preparations from adult North American bullfrogs (Rana catesbeiana). These experiments were undertaken to determine the effects of temperature on fictive breathing, central pH/CO(2) chemoreception, and to examine potential alphastat regulation of respiration in vitro. Adult bullfrog brainstem preparations were isolated, superfused with an artificial cerebrospinal fluid (aCSF) and respiratory-related neural activity was recorded from cranial nerves V, X and XII. In Series I experiments (N=8), brainstem preparations were superfused with aCSF equilibrated with 2% CO(2) at temperatures ranging from 10 to 30 degrees C. Neural activity was present in all preparations in the temperature range of 15-25 degrees C, but was absent in most preparations when aCSF was at 10 or 30 degrees C. The absence of fictive breathing at high (30 degrees C) temperatures was transient since fictive breathing could be restored upon returning the preparation to 20 degrees C. In Series II experiments (N=10), preparations were superfused with aCSF equilibrated with 0%, 2% and 5% CO(2) at temperatures of 15, 20 and 25 degrees C. Fictive breathing frequency (f(R)) was significantly dependent upon aCSF pH at all three temperatures, with slopes ranging from -0.82 min(-1) pH unit(-1) (15 degrees C) to -3.3 min(-1) pH unit(-1) (20 degrees C). There was a significant difference in these slopes (P<0.02), indicating that central chemoreceptor sensitivity increased over this temperature range. Fictive breathing frequency was significantly dependent upon the calculated alpha-imidazole (alpha(Im)) ionization (P<0.05), consistent with the alphastat hypothesis for the effects of temperature on the regulation of ventilation. However, most of the variation in f(R) was not explained by alpha(Im) (R(2)=0.05), suggesting that other factors account for the regulation of fictive breathing in this preparation. The results indicate that the in vitro brainstem preparation of adult bullfrogs has a limited temperature range (15-25 degrees C) over which fictive breathing is consistently active. Although there is a close correspondence of ventilation in vitro and in vivo at low temperatures, these data suggest that, as temperature increases, changes in ventilation in the intact animal are likely to be more dependent upon peripheral feedback which assumes a greater integrative role with respect to chemoreceptor drive, respiratory frequency and tidal volume.     

The action of caffeine on X-irradiated HeLa cells. IX. Hypothermic effects

Hypothermic enhancement of the lethal effect of 3.5 Gy of 220-kV X rays in the absence of caffeine as well as in its presence (4 mM) was examined at temperatures between 10 and 34 degrees C in monolayer cultures in the G1 phase of the cell cycle. Correction has been made for the toxicity of low temperatures, and of caffeine at low temperatures, by concomitantly measuring cell killing in unirradiated cells. In the absence of caffeine, incubation of irradiated cells for up to 34 h at temperatures in the range 15 to 30 degrees C (or possibly 34 degrees C) enhances killing compared to that observed at 38 degrees C; the amount of enhancement is about the same throughout this range, but is nil at 10 degrees C. The enhanced killing induced by caffeine at 38 degrees C decreases as the temperature is lowered to 15 degrees C; there is no enhancement at 10 degrees C. Less killing is manifested in the range 15 to 25 degrees C in the presence of caffeine than in its absence. Recovery (loss of sensitivity to caffeine) and fixation of potentially lethal damage were studied in late-S/G2-phase cells at reduced temperatures by delaying treatment with caffeine for increasing times after irradiation. As the temperature is progressively lowered to 20 degrees C, less recovery is manifested after 5 h of incubation; no recovery is detected in the range 10 to 20 degrees C. Despite extensive recovery at 34 degrees C, no fixation is observed at that (or any lower) temperature in G2-phase cells: the cells are able to recover essentially fully when returned to 38 degrees C. In addition, responses of unirradiated control series to incubation at low temperatures appear to differ from those reported by others for longer treatment times of different cell systems.     

Developmental and reproductive biology of Scirtothrips perseae (Thysanoptera: Thripidae): a new avocado pest in California

The developmental and reproductive biology of a new avocado pest, Scirtothrips perseae Nakahara, was determined in the laboratory at five constant temperatures, 15, 20, 25, 27.5 and 30 degrees C. At 20 degrees C, S. perseae exhibited greatest larval to adult survivorship (41%), and mated females produced a greater proportion of female offspring at this temperature when compared to 15, 25, 27.5 and 30 degrees C. Average lifetime fecundity and preoviposition period was greatest at 15 degrees C at 39.6 eggs per female and 17.6 days, respectively. Jackknifed estimates of net reproduction (Ro), capacity for increase (rc), intrinsic rate of increase (rm), and finite rate of increase (lambda) were all significantly greater at 20 degrees C than corresponding values at 15, 25 and 27.5 degrees C. Population doubling time (Td) was significantly lower at 20 degrees C, indicating S. perseae populations can double 33-71% faster at this temperature in comparison to 15, 25 and 27.5 degrees C. Mean adult longevity decreased with increasing temperature, from a maximum of 52.4 days at 15 degrees C to a minimum of 2.4 days at 30 degrees C. Developmental rates increased linearly with increasing temperatures for eggs and rates were non-linear for development of first and second instar larvae, propupae, pupae, and for egg to adult development. Linear regression and fitting of the modified Logan model to developmental rate data for egg to adult development estimated that 344.8 day degrees were required above a minimum threshold of 6.9 degrees C to complete development. An upper developmental threshold was estimated at 37.6 degrees C with an optimal temperature of 30.5 degrees C for egg to adult development. Unmated females produced only male offspring confirming arrhenotoky in S. perseae.     

Temperature acclimation of photosynthesis and related changes in photosystem II electron transport in winter wheat

Winter wheat (Triticum aestivum L. cv Norin No. 61) was grown at 25 degrees C until the third leaves reached about 10 cm in length and then at 15 degrees C, 25 degrees C, or 35 degrees C until full development of the third leaves (about 1 week at 25 degrees C, but 2-3 weeks at 15 degrees C or 35 degrees C). In the leaves developed at 15 degrees C, 25 degrees C, and 35 degrees C, the optimum temperature for CO(2)-saturated photosynthesis was 15 degrees C to 20 degrees C, 25 degrees C to 30 degrees C, and 35 degrees C, respectively. The photosystem II (PS II) electron transport, determined either polarographically with isolated thylakoids or by measuring the modulated chlorophyll a fluorescence in leaves, also showed the maximum rate near the temperature at which the leaves had developed. Maximum rates of CO(2)-saturated photosynthesis and PS II electron transport determined at respective optimum temperatures were the highest in the leaves developed at 25 degrees C and lowest in the leaves developed at 35 degrees C. So were the levels of chlorophyll, photosystem I and PS II, whereas the level of Rubisco decreased with increasing temperature at which the leaves had developed. Kinetic analyses of chlorophyll a fluorescence changes and P700 reduction showed that the temperature dependence of electron transport at the plastoquinone and water-oxidation sites was modulated by the temperature at which the leaves had developed. These results indicate that the major factor that contributes to thermal acclimation of photosynthesis in winter wheat is the plastic response of PS II electron transport to environmental temperature.     

Development, survivorship, and reproduction of Helicoverpa armigera (Lepidoptera: Noctuidae) under constant and alternating temperatures

Laboratory studies were conducted to assess the effect of temperature on the survival, development, fecundity, and longevity of Helicoverpa armigera (Hübner) at 11 constant temperatures ranging from 12.5 to 40 degrees C, as well as at five alternating temperature regimes (25-10, 30-15, 32.5-17.5, 35-20, and 35-27.5 degrees C) and under a photoperiod of 16:8 (L:D) h. H. armigera reared at constant temperatures did not develop from egg to adult (emergence) outside the temperature range of 17.5-32.5 degrees C. The alternating conditions expanded this range from 10 to 35 degrees C. The lowest developmental thresholds of the immature stages were estimated by a linear model and ranged from 10.17 (pupal stage) to 11.95 degrees C (egg stage) at constant temperature regimes and from 1.1 to 5.5 degrees C, respectively at alternating temperatures. The values of developmental thresholds estimated using the nonlinear (Lactin-2) model were lower than those estimated by the linear model for constant and alternating temperature regimes except for larval and pupal stages at constant temperatures. Mean adult longevity fluctuated from 34.4 d at 15 degrees C to 7.6 d at 35 degrees C. Females reared under all alternating temperature regimes laid more eggs than females reared at any, except the 25 degrees C, constant temperature treatment. The intrinsic rate of increase was highest at 27.5 degrees C, at both the constant and the corresponding alternating temperature regimes (0.147 and 0.139, respectively). Extreme temperatures had a negative effect on life table parameters.     

Dormancy release during hydrated storage in Lolium rigidum seeds is dependent on temperature, light quality, and hydration status

The influence of temperature, light environment, and seed hydration on the rate of dormancy release in Lolium rigidum (annual ryegrass) seeds during hydrated storage (stratification) was investigated. In a series of experiments, seeds were subjected to a range of temperatures (nine between 5 degrees C and 37 degrees C), light (white, red, far-red, and dark), and hydration (4-70 g H(2)O 100 g(-1) FW) during stratification for up to 80 d. Samples were germinated periodically at 25/15 degrees C or constant 15, 20, or 25 degrees C with a 12 h photoperiod to determine dormancy status. Dark-stratification was an alternative, but not equivalent dormancy release mechanism to dry after-ripening in annual ryegrass seeds. Dormancy release during dark-stratification caused a gradual increase in sensitivity to light, but germination in darkness remained negligible. Germination, but not dormancy release, was greater under fluctuating diurnal temperatures than the respective mean temperatures delivered constantly. Dormancy release rate was a positive linear function of dark-stratification temperature above a base temperature for dormancy release of 6.9 degrees C. Dormancy release at temperatures up to 30 degrees C could be described in terms of thermal dark-stratification time, but the rate of dormancy release was slower at < or =15 degrees C (244 degrees Cd/probit increase in germination) than > or =20 degrees C (208 degrees Cd/probit). Stratification in red or white, but not far-red light, inhibited dormancy release, as did insufficient (<40 g H(2)O 100 g(-1) FW) seed hydration. The influence of dark-stratification on dormancy status in annual ryegrass seeds is discussed in terms of a hypothetical increase in available membrane-bound phytochrome receptors.     

Effects of temperature, incubation period and substrate on production of fusaproliferin by Fusarium subglutinans ITEM 2404

The kinetics of the production of fusaproliferin by Fusarium subglutinans ITEM 2404 in maize and rice cultures was investigated at various incubation temperatures. The growth rate of F. subglutinans was highest at 20 degrees C and 25 degrees C in maize cultures and at 15 degrees C in rice cultures. Although the growth rate was higher in rice than in maize, the maximal production of fusaproliferin was obtained in maize cultures, with a maximum yield (4309 microg g(-1)) at 20 degrees C for 6 weeks. In rice cultures the optimal incubation regimen was at 15 degrees C for 6 weeks, with a fusaproliferin level of 1557 microg g(-1). The production of fusaproliferin at 25 degrees C and 30 degrees C in both substrates was very low, with maximal yield at 25 degrees C of 979 microg g(-1) after 2 weeks and 143 microg g(-1) after 3 weeks in maize and rice cultures, respectively.     

Lateral diffusion of gramicidin C in phospholipid multibilayers. Effects of cholesterol and high gramicidin concentration

We have measured the lateral diffusion coefficient (D), of active dansyl-labeled gramicidin C (DGC), using the technique of fluorescence photobleaching recovery, under conditions in which the cylindrical dimer channel of DGC predominates. In pure, hydrated, dimyristoylphosphatidylcholine (DMPC) multibilayers (MBL), D decreases from 6 X 10(-8) cm2/s at 40 degrees C to 3 X 10(-8) cm2/s at 25 degrees C, and drops 100-fold at 23 degrees C, the phase transition temperature (Tm) of DMPC. Above Tm, addition of cholesterol decreases D; a threefold stepwise drop occurs between 10 and 20 mol %. Below Tm, increasing cholesterol increases D; a 10-fold increase occurs between 10 and 20 mol % at 21 degrees C, between 20 and 25 mol % at 15 degrees C, and between 25 and 30 mol % at 5 degrees C. In egg phosphatidylcholine (EPC) MBL, D decreases linearly from 5 X 10(-8) cm2/s at 35 degrees C to 2 X 10(-8) cm2/s at 5 degrees C; addition of equimolar cholesterol reduces D by a factor of 2. Thus this transmembrane polypeptide at low membrane concentrations diffuses quite like a lipid molecule. Its diffusivity in lipid mixtures appears to reflect predicted changes of lateral composition. Increasing gramicidin C (GC) in DMPC/GC MBL broadened the phase transition, and the diffusion coefficient of the lipid probe N-4-nitrobenzo-2-diazole phosphatidylethanolamine (NBD-PE) at 30 degrees C decreases from 8 X 10(-8) cm2/s below 5 mol % GC to 2 X 10(-8) cm2/s at 14 mol % GC; D for DGC similarly decreases from 4 X 10(-8) cm2/s at 2 mol % GC to 1.4 X 10(-8) cm2/s at 14 mol % GC. Hence, above Tm, high concentrations of this polypeptide restrict the lateral mobility of membrane components.     

Influence of temperature on survival, growth and fecundity of the freshwater snail Indoplanorbis exustus (Deshayes).

To note the effect of temperature on survival, growth and fecundity, newly hatched (zero day old) snails Indoplanorbis exustus were cultured at 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees and 35 degrees C constant temperatures and room temperature (17.5 degrees-32.5 degrees C). Individuals exposed to 10 degrees C died within 3 days while those reared at 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees C and room temperature survived for a period of 6, 27, 18, 16, 12 and 17 weeks respectively. An individual added on an average 0.21 mm and 0.45 mg, 0.35 mm and 7.94 mg, 0.63 mm and 15.5 mg, 0.81 mm and 27.18 mg, 1.07 mm and 41.48 mg and 0.78 mm and 31.2 mg to the shell diameter and body weight respectively at those temperatures per week. The snails cultured at 15 degrees C died prior to attainment of sexual maturity. On an average, an individual produced 31.9 and 582.77, 54.86 and 902.18, 56.01 and 968.45, 49.32 and 798.68 and 62.34 and 1143.97 capsules and eggs respectively at 20 degrees, 25 degrees, 30 degrees, 35 degrees C and room temperature (17.5 degrees-32.5 degrees C).     

Leaf respiration of snow gum in the light and dark. Interactions between temperature and irradiance

We investigated the effect of temperature and irradiance on leaf respiration (R, non-photorespiratory mitochondrial CO(2) release) of snow gum (Eucalyptus pauciflora Sieb. ex Spreng). Seedlings were hydroponically grown under constant 20 degrees C, controlled-environment conditions. Measurements of R (using the Laisk method) and photosynthesis (at 37 Pa CO(2)) were made at several irradiances (0-2,000 micromol photons m(-2) s(-1)) and temperatures (6 degrees C-30 degrees C). At 15 degrees C to 30 degrees C, substantial inhibition of R occurred at 12 micromol photons m(-2) s(-1), with maximum inhibition occurring at 100 to 200 micromol photons m(-2) s(-1). Higher irradiance had little additional effect on R at these moderate temperatures. The irradiance necessary to maximally inhibit R at 6 degrees C to 10 degrees C was lower than that at 15 degrees C to 30 degrees C. Moreover, although R was inhibited by low irradiance at 6 degrees C to 10 degrees C, it recovered with progressive increases in irradiance. The temperature sensitivity of R was greater in darkness than under bright light. At 30 degrees C and high irradiance, light-inhibited rates of R represented 2% of gross CO(2) uptake (v(c)), whereas photorespiratory CO(2) release was approximately 20% of v(c). If light had not inhibited leaf respiration at 30 degrees C and high irradiance, R would have represented 11% of v(c). Variations in light inhibition of R can therefore have a substantial impact on the proportion of photosynthesis that is respired. We conclude that the rate of R in the light is highly variable, being dependent on irradiance and temperature.     

Effects of maternal identity and incubation temperature on snapping turtle (Chelydra serpentina) metabolism

Individual variation in physiological traits may have important consequences for offspring survivorship and adult fitness. Variance in offspring phenotypes is due to interindividual differences in genotype, environment, and/or maternal effects. This study examined the contributions of incubation environment, maternal effects, and clutch identity to individual variation in metabolic rates in the common snapping turtle, Chelydra serpentina. We measured standard metabolic rate, as determined by oxygen consumption, for 246 individuals representing 24 clutches at 15 degrees and 25 degrees C, and we measured standard metabolic rates additionally for 34 individuals at 20 degrees and 30 degrees C. Standard metabolic rate for 34 snapping turtles measured at 15 degrees, 20 degrees, 25 degrees, and 30 degrees C increased with increasing temperature. Mean standard metabolic rate for 246 individuals was 0.247 microL O(2) min(-1) g(-1) at 15 degrees C and 0.919 microL O(2) min(-1) g(-1) at 25 degrees C. At 15 degrees C, mass at hatching, individual mass, and egg mass had no significant effects on metabolic rate, but at 25 degrees C, mass at hatching, individual mass, and egg mass did have significant effects on metabolic rate. Incubation temperature had no significant effect on metabolic rate at 15 degrees, but it did have a significant effect at 25 degrees C. Clutch identity had a significant effect on metabolic rate at both 15 degrees and 25 degrees C. Interindividual variation in standard metabolic rate due to incubation temperature, and especially clutch identity, could have large effects on energy budgets. Results suggest that there were both environmental and genetic effects on standard metabolic rate.     

Low temperature requirement for embryonic development of Itasenpara bitterling Acheilognathus longipinnis

The Itasenpara bitterling has an embryonic period up to 7 months, when the embryo experiences large seasonal temperature changes. We examined the temperature requisites for normal development during the embryonic stage. Fertilized eggs reared under any of the constant temperatures ranging from 5 degrees C to 30 degrees C did not achieve complete embryogenesis, and none reached the swim-up stage. The optimum temperature for normal embryonic development was found to be stage-dependent: 10-30 degrees C for fertilization, 15-25 degrees C for hatching, 5 degrees C for the requisite low temperature, 10-15 degrees C for eye pigmentation, and 20-30 degrees C for swim-up. These temperatures correlated well with the embryo's natural environmental conditions. Embryos raised at these temperatures sequentially grew normally, with 70% of the fertilized eggs achieving complete embryogenesis and, for the first time, developed to the swim-up stage. These results indicate that the low temperature, as required by the bitterling embryo, is an essential factor and correlates well with the embryo's natural ambient temperatures. Since the populations of Itasenpara bitterlings have been declining in Japan, this study is the first to provide additional information for successful artificial breeding of this endangered species.     

Interaction of local and reflex thermal effects in control of forearm blood flow

We measured forearm blood flow (ABF) bilaterally on six subjects during 15-min periods of leg exercise and the first 10 min of recovery. One forearm (control) was kept at about 33 degrees C skin temperature in all experiments. In experiments at ambient temperature (Ta) of 15 degrees C, the other arm (experimental) was kept at about 26, 33, and 40 degrees C, respectively, during three successive cycles of exercise and recovery. ABF in the 26 degrees C forearm was linearly related to and averaged 42% of control. The relation of ABF in the 40 degrees C forearm to control ABF showed a bend at control ABF of 4-5 ml X 100 ml-1 X min-1. Below the bend, experimental ABF average 213% of control. Above the bend, experimental ABF averaged 5.09 ml X 100 ml-1 X min-1 above control. In four subjects, after heating the experimental forearm to 40 degrees C, we measured ABF for 25-30 min at rest in Ta of both 15 and 25 degrees C. At 25 degrees C Ta, ABF in the heated forearms rose gradually, but control ABF showed little change. At 15 degrees C Ta, the effect on ABF of local heating to 40 degrees C was much reduced, apparently due to reflex vasoconstrictor signals.     

Effect of thermoperiod on diapause intensity in Pyrrhocoris apterus (Heteroptera Pyrrhocoridae)

The intensity of adult diapause in Pyrrhocoris apterus was measured in two series of experiments as the duration of pre-oviposition period at a constant temperature of 25 degrees C after transfer from short (12L:12D) to long day conditions (18L:6D). Higher diapause intensity was induced with a thermoperiod than at constant temperatures. After the induction throughout larval instars 3-5 and during 4 weeks of adult life at short days and a thermoperiod of 25/15 degrees C the pre-oviposition period was 30+/-4 and 26+/-3 days. After induction at constant 25 degrees C the pre-oviposition period was 22+/-3 and 23+/-4 days, while after induction at constant 20 degrees C it was 17+/-4 and 19+/-4 days. Induction at a lower constant temperature of 20 degrees C was thus followed by a less intense diapause than the induction at a higher constant temperature of 25 degrees C. These counterintuitive results are discussed. The oxygen consumption rate measured at experimental temperatures prior to transfer from short to long days was higher at thermoperiodic conditions than at constant temperatures and it was similar at constant 20 and 25 degrees C. Thus, the oxygen consumption rate measured prior to the transfer was highest (indication of the least intense diapause) in the insects that showed later, after the transfer to long days, the longest pre-oviposition period (indication of the most intense diapause). Within the first two days after transfer to constant 25 degrees C, oxygen consumption rate measured at 25 degrees C decreased in the thermoperiodic insects, while it transiently increased in insects from constant 20 degrees C. Two days and later after the transfer, oxygen consumption rate was similar in all groups. Cold hardiness was not correlated with diapause intensity. The low lethal temperature in diapausing insects was correlated with the night temperature during diapause induction.     

Strongyloides ratti: thermokinetic behavior of third-stage larvae on a temperature gradient

We examined the thermokinetic behaviors of infective third-stage larvae (L3) of the rodent parasitic nematode Strongyloides ratti on temperature gradients using an in vitro agarose tracking assay method. Observed behaviors included both negative and positive thermokineses, the direction of movement depending both on the gradient temperature at which larvae were initially placed and on prior experience of culture temperature. Larvae isolated from rat feces cultured at 25 degrees C and placed on a gradient at temperatures between 22 degrees and 29 degrees C tended to move toward higher temperatures. At higher placement temperatures, most larvae moved little and showed no directional response, whereas at lower placement temperatures, many migrated toward cooler temperatures. At placement temperatures of 20 degrees C or below, few or no larvae moved toward the zone of higher temperature. Larvae isolated from rat feces cultured at 20 degrees C tended to migrate to a high temperature area regardless of placed temperature. Those cultured at 30 degrees C did not respond to the temperature gradient. L3 cultured at 30 degrees C were significantly less infective to rats than those cultured at 25 degrees or 20 degrees C. Additional experiments were designed to demonstrate thermokinetic behaviors during the period after reaching the L3 stage. Larvae incubated in double distilled water (DDW) for 24 h at 37 degrees C lost their ability to respond to lower temperatures, while in those incubated in DDW at 15 degrees and 25 degrees C, responses were still apparent. The thermokinetic behavior of S. ratti L3 is affected by surrounding environmental temperatures and this may have an important role in host finding.     

Direct effects of temperature on phospholipid and polyunsaturated fatty acid metabolism in isolated brain cells from rainbow trout, Oncorhynchus mykiss.

1. The direct effects of temperature on the metabolism of [1-14C]18:2(n-6), [1-14C]18:3(n-3), [1-14C]20:4(n-6) and [1-14C]20:5(n-3) were studied in isolated brain cells from rainbow trout, Oncorhynchus mykiss. 2. Recovery of radioactivity from all the polyunsaturated fatty acids (PUFA) in total lipid was significantly greater at 5 and 15 degrees C than at 25 degrees C. 3. The lower incubation temperatures decreased the relative net incorporation of all the 14C-labelled PUFA into phosphatidylcholine (PC) and increased the relative incorporation of the PUFA into the other phosphoglycerides, especially phosphatidylethanolamine (PE). 4. The effects on PC were generally more significant between 25 and 15 degrees C, whereas the effects on PE were generally significant both between 25 and 15 degrees C and between 15 and 5 degrees C. 5. This suggests that the lysophospholipid acyltransferases responsible for the incorporation of PUFA into different phosphoglycerides may have differential sensitivities to temperature. 6. In contrast, the acyltransferase activities showed fatty acyl preferences that were independent of temperature. 7. Although a trend towards decreased activity at 5 degrees C was apparent, temperature generally had little significant effect on the relative percentages of the PUFA metabolized via the desaturase pathways.     

Inverted hexagonal and cubic phases induced by alpha-tocopherol in fully hydrated dispersions of dilauroylphosphatidylethanolamine

The effect of alpha-tocopherol on the thermotropic phase behaviour and structure of aqueous dispersions of 1,2-di-lauryl-sn-glycero-3-phosphoethanolamine was examined by synchrotron X-ray diffraction. The pure phospholipid exhibited a lamellar gel to liquid-crystal phase transition at 30 degrees C on heating at 3 degrees C min(-1) between 10 degrees C and 90 degrees C. The transition was reversible with a temperature hysteresis of 0.3 degrees C on cooling. At temperatures less than 10 degrees C only lamellar gel phase of the pure phospholipid was seen in co-dispersions of up to 20 mol % alpha-tocopherol. The presence of 2.5 mol % alpha-tocopherol caused the appearance of inverted hexagonal phase at temperatures just below the main phase transition temperature that co-existed with the lamellar gel phase. The intensity of scattering from the hexagonal-II phase increased with increasing proportion of alpha-tocopherol in the mixture and in proportions greater than 10 mol % it persisted at temperatures above the main transition and co-existed with the lamellar liquid-crystal phase of the pure phospholipid. At higher temperatures all co-dispersions containing up to 15 mol % alpha-tocopherol showed the presence of cubic phases. These phases indexed a Pn3m or Pn3 space grouping. When the proportion of alpha-tocopherol was increased to 20 mol % the only non-lamellar phase observed was inverted hexagonal phase. This phase co-existed with lamellar gel and liquid-crystal phases of the pure phospholipid, but was the only phase present at temperatures >60 degrees C. The X-ray diffraction data were used to construct a partial phase diagram of the lipid mixture in excess water between 10 degrees and 90 degrees C and up to 20 mol % alpha-tocopherol in phospholipid.     

Discontinuous gas exchange in the fire ant,Solenopsos invicta Buren: Caste differences and temperature effects

The discontinuous gas exchange cycle (DGC), the cyclic release of CO(2) and uptake of O(2), were investigated in workers and female and male alates of the red imported fire ant, Solenopsis invicta Buren, using real-time CO(2) emission measurement by flow-through respirometry. All S. invicta castes displayed discontinuous emission of CO(2) in the temperature range of 15-25 degrees C, but only male alates and workers exhibited a DGC at 30 degrees C. The closed (C) and flutter (F) periods of the DGC were distinguishable in alates of both sexes at the lowest temperature, but not clearly differentiated in females at temperatures above 15 degrees C, in males above 20 degrees C, or workers at any temperature. DGC frequency increased for all castes as temperature increased, ranging from a low of 0.9+/-0.05 mHz (male alates at 15 degrees C) to 18+/-0.79 mHz (workers at 30 degrees C). O period (or burst) volumes of all castes decreased as temperature increased, and increased with body mass - this mass effect was most pronounced at lower temperatures. Q(10) values for DGC frequency (4.27, 5.81, and 5.62 for workers, female and male alates, respectively) were high compared with Q(10)'s for standard Vdot;(CO(2)). Differences in the salient characteristics of the DGC between castes are presented and discussed, and S. invicta DGC patterns are compared to known values for some other ant species.