Ribeiroia marini: pathogenesis and larval trematode antagonism in the snail, Biomphalaria glabrata

Larval trematode antagonism between Ribeiroia marini and Schistosoma mansoni was studied in the snail Biomphalaria glabrata. A laboratory-raised Puerto Rican strain of B. glabrata was exposed to single and double infections with given numbers of: (1) embryonated eggs of R. marini from laboratory rats, and (2) miracidia of S. mansoni from mice. Snails were maintained in outside environmental tanks in San Juan, Puerto Rico and larval trematode interactions were examined in a series of five experiments. Snails of all sizes were highly susceptible to single infections with R. marini. Rediae and cercariae caused extensive damage to the digestive gland and ovotestis resulting in premature death of snails. Heavily infected snails were castrated and stopped laying eggs. Snails infected first with S. mansoni were only partly susceptible to superinfection with R. marini given on Day 23. In a reverse experiment, snails infected first with R. marini were only partly susceptible to a second infection with S. mansoni given on Day 23. In simultaneous exposures, snails developed double infections (22%) with R. marini dominant and S. mansoni sporocyst and cercaria production reduced. While R. marini is not a strong direct antagonist against established S. mansoni infections, it has several attributes as a possible biological control agent: hardy eggs easily produced in rats; high infectivity to snails of all ages; and ability to castrate and prematurely kill B. glabrata. The R. marini-rat system described here provides a convenient laboratory and field model for the study of intrasnail trematode antagonism and biological control.     

苔藓植物对环境变化的响应及适应性研究进展

苔藓植物由于其结构相对简单,对环境变化的反应较为敏感,是一类良好的生物指示植物.本文综述了水分、光照、温度等方面的环境因子变化对苔藓植物的影响以及苔藓植物对环境污染的响应及适应的最近研究进展,以期促进国内深入开展苔藓植物对环境污染和全球变化的响应、适应及其生态指示作用等研究.     

Broad-host-range cloning vectors derived from the W-plasmid Sa

Four nonconjugative broad-host-range cloning vectors were derived from the W-plasmid Sa. They are small (M_r 5.6?7.2 × 10⁶), carry several drug-resistance markers, and allow constructing and screening for recombinant plasmids generated by the restriction enzymes EcoRI, PstI, BglII, HindIII, BamHI and SalI,     

Chronobiology of Coronary Risk Markers in Greenland Eskimos: A Comparative Study with Caucasians Residing in the Same Arctic Area

We report a comparison of fibrinolytic variables between 10 Caucasians on a predominantly European diet and 10 Greenland Eskimos on a traditional Inuit diet containing a substantial amount of fish and sea animals. We studied the diurnal variation in tissue type plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI) antigens and activities during a 24-h period. Blood samples were taken every 4 h. The variations of the sinusoidal curves were evaluated by the Friedman χ² test. t-PA and PAI-1 antigen in plasma fluctuated significantly during the 24 h (Eskimos p < 0.000007 and p < 0.0007; Caucasians p < 0.00003 and p < 0.02), with a peak in the early morning and a nadir in the afternoon. This also held true for PA1 activity (Eskimos p < 0.0008; Caucasians p < O.Ol), whereas t-PA activity showed an inverse but still significant pattern (Eskimos p < 0.006; Caucasians p < 0.0008). Amplitudes, areas underneath, and overall medians of the sinusoidal curves did not deviate between the two groups with respect to t-PA and PAL In contrast to the significant variation of t-PA and PAI, the plasma concentrations of fibrin degradation products (D-Dimer), a measure of effective fibrinolysis, remained constant during the 24 h, and the absolute differences between groups did not reach statistical significance. These findings suggest that circadian variation of fibrinolytic activators and inhibitors is a basic biologic phenomenon, which is not affected by life-style, dietary habits, or ethnic differences. Furthermore, the lack of diurnal variation in D-Dimer raises the question of whether there is a causal relationship between low morning activities of t-PA and the frequent onset of myocardial infarction at that time of day, as suggested by several authors.     

Host activity and wasp experience affect parasitoid wasp foraging behaviour and oviposition on nematode‐infected larvae of the forestry pest Hylobius abietis

1. Entomopathogenic nematodes (EPN) are currently being used as introduced biological control agents against the larvae of the native European forestry pest Hylobius abietis L. which develop under the bark of stumps and roots of newly dead conifer trees. 2. The potential for resource competition between gregarious ectoparasitoid Bracon hylobii Ratz and EPN by recording oviposition and related behaviours of B. hylobii females on EPN‐infected H. abietis larvae was investigated. Wasps did not parasitise EPN‐infected host larvae that were dead when presented, but naÏve and experienced wasps parasitised live EPN‐infected hosts. NaÏve wasps parasitised live EPN‐infected hosts significantly less frequently than healthy hosts only when the infected larvae were close to death (i.e. died during 24‐h trial). Parasitism by experienced wasps was unaffected by host infection. 3. Wasp probing and oviposition were positively associated with the amount of host movement. Preventing H. abietis larvae from chewing on bark significantly reduced parasitism by naÏve, but not experienced wasps. 4. The number of eggs per clutch was not affected by bark chewing or EPN‐infection of H. abietis larvae. 5. NaÏve and experienced B. hylobii parasitised two abnormal hosts (larvae of coleopteran Rhagium bifasciatum Fabricius and lepidopteran Galleria mellonella L.), both of which moved and chewed on bark during trials. 6. It was concluded that B. hylobii can use vibrational cues generated by host movement and feeding to locate hosts at short range and accepts unsuitable (EPN‐infected or abnormal) hosts as long as these create such cues. The implications for competition between B. hylobii and EPN and possible ways of minimising it when applying EPN are discussed.     

Inheritance of antagonistic properties and lytic enzyme activities in sexual crosses of Talaromyces flavus

Two wild-type strains and three benomyl-resistant mutants of the antagonistic ascomycete Talaromyces flavus were crossed in six combinations, two of which yielded hybrid cleistothecia. Parental strains and their ascospore progenies varied in several traits considered to play an important role in the capacity to control soilborne fungal pathogens: extracellular activities of glucose oxidase and cell-wall degrading enzymes, antibiosis towards Verticillium dahliae, and parasitism and biocontrol of Sclerotium rolfsii. A non-Mendelian quantitative mode of inheritance was found for β-1, 3-glucanase and chitinase activities but only the latter exhibited a normal frequency distribution. Some of the progenies exhibited higher glucanase and chitinase activities than those found in the parental strains. Progeny analysis for chitinase, glucanase, cellulase, and glucose oxidase activities revealed no genetic association between any two of these enzymes. Antibiosis was correlated with glucose-oxidase activity in one cross, but not in the other. The ability to reduce bean root rot caused by S. rolfsii was correlated with mycoparasitic activity against S. rolfsii sclerotia in one cross, but not in the other. One out of the 20 progenies tested was able to reduce bean root rot more effectively than its parent strains, thus demonstrating the feasibility of improving a biocontrol agent by conventional breeding.     

Urinary 6-Sulfatoxymelatonin Cycle-To-Cycle Variability

For either clinical or research purposes, the timing of the nocturnal onset in production of the urinary melatonin metabolite 6-sulfatoxymelatonin (UaMT6s-onset), has been proposed as a reliable and robust marker of circa-dian phase. However, given that most circadian rhythms show cycle-to-cycle variability, the statistical reliability of phase estimates obtained from a single study using UaMT6s-onset remains to be determined. Following 2 weeks of sleep diary and wrist actigraphy, 15 young, healthy good sleepers participated in four UaMT6s sampling sessions spaced 1 day apart. During the sampling sessions subjects remained indoors under low light conditions and hourly urine samples were collected from 19:00 to 02:00 h. Samples were subsequently assayed for UaMT6s using standard radioimmunographic techniques. UaMT6s-onset was determined by the time at which melatonin production exceeded the average of three proceeding trials by 100%. Sleep onset times were derived from sleep diary and actigraphic measures taken before the melatonin collection nights. We found that there was no significant variation between nights in group mean UaMT6s-onset times, and intraindividual variability was small. In addition, UaMT6s-onset times were highly and significantly correlated between nights (grand mean r = 0.804). Our results suggest that within 95% confidence interval limits, individual UaMT6s-onset estimates obtained from a single night UaMT6s-onset study can be used to predict subsequent UaMT6s-onset times within ±97 min. A close temporal relationship was also found between the timing of UaMT6s-onset and sleep onset. Overall, our results suggest that under entrained conditions single-session UaMT6s-onset studies can provide reliable individual UaMT6s-onset phase estimates and that the protocol described in this study is a practical and noninvasive methodology. (Chronobiology International, 13(6), 411-421, 1996)     

A genetic map of tetraploid <Emphasis Type="Italic">Paspalum notatum</Emphasis> Flügge (bahiagrass) based on single-dose molecular markers

Paspalum notatum Flügge is a warm-season forage grass with mainly diploid (2n = 20) and autotetraploid (2n = 40) representatives. Diploid races reproduce sexually and require crosspollination due to a self-incompatible mating system, while autotetraploids reproduce by aposporous apomixis. The objectives of this work were to develop a genetic linkage map of Paspalum notatum Flügge at the tetraploid level, identify the linkage/s group/s associated with apomixis and carry out a general characterization of its mode of inheritance. A pseudo test-cross F₁ family of 113 individuals segregating for the mode of reproduction was obtained by crossing a synthetic completely sexual tetraploid plant (Q4188) as female parent with a natural aposporous individual (Q4117) as pollen donor. Map construction was based on single-dose markers (SDAFs) segregating from both parents. Two linkage maps (female and male) were constructed. Within each map, homologous groups were assembled by detecting repulsion-phase linked SDAFs. Putative Q4188 and Q4117 homolog groups were identified by mapping shared single dose markers (BSDF). The Q4188 map consisted of 263 markers distributed on 26 co-segregation groups over a total genetic distance of 1.590.6 cM, while the Q4117 map contained 216 loci dispersed on 39 co-segregation groups along 2.265.7 cM, giving an estimated genome coverage of 88% and 83%, respectively. Seven and 12 putative homologous chromosomes were detected within Q4188 and Q4117 maps, respectively. Afterward, ten female and male homologous chromosomes were identified by mapping BSDFs. In the Q4117 map, a single linkage group was associated with apospory. It was characterized by restriction in recombination and preferential chromosome pairing. A BPSD marker mapping within this group allowed the detection of the female homolog and the putative four male groups of the set carrying apospory.     

Alginate embedding and subsequent sporulation of in vitro-produced Conidiobolus thromboides hyphae using a pressurised air-extrusion method

Conidiobolus thromboides is an entomophthoralean fungus with potential as a biological control agent of aphids. However, its application in biological control is limited due to its formulation requirements. The objective of this study was to develop and optimise a novel air-extrusion method to embed C. thromboides hyphae at high density in alginate pellets. An orthogonal experimental design was used to investigate selected combinations of parameters known to affect hyphal density within pellets. The diameter of pellets produced, and the calculated density of hyphae within them, ranged from 0.18 ± 0.09 to 3.17 ± 0.06 mm and from 0.02 to 350.56 mg/mm³ respectively. These data were used to predict the optimal parameter combination to deliver the greatest density of hyphae of C. thromboides per pellet: 1% sodium alginate, a 1:2 ratio of hyphae to sodium alginate, an orifice diameter of 0.232 mm and an air pressure of 0.05 MPa. Pellets made under the optimal conditions predicted produced a mean total of 4.3 ± 0.6 × 10⁵ conidia per pellet at 100% relative humidity which was significantly greater than the mean total number of conidia produced from infected aphid cadavers of comparable size (9.35 ± 0.85 × 10⁴) (p < 0.001). In conclusion, air-extrusion embedding appears to be a promising method for formulating in vitro-produced hyphae of C. thromboides for use in biological control.