Effect of water temperature on the excystment of the dinoflagellate Ceratium hirundinella (O. F. Müller) Bergh

The effect of water temperature on the excystment of the dinoflagellate Ceratium hirundinella (O. F. Müller) Bergh was studied in the laboratory. Excystment was observed between 15–30 °C and was 2% at an optimum water temperature of 20 °C–25°C. Little excystment occurred between 5 and 10 °C. The results at low temperatures are not in accordance with those obtained in an English lake. This disagreement suggests an adaptability of excystment to the temperature regime of the lake.     

The Excystment Process in the Ciliate Euplotes muscicola: An Integrated Light and Scanning Electron Microscopic Study1

Resting cysts and the excystment process in the freshwater ciliate Euplotes muscicola were studied by both light and scanning electron microscopy. Groups of distinctly crested resting cysts adhere to the substrate. Silver-stained preparations reveal surface conservation of dorsal kinetosomes and dorsal argyrome while ventral organelles are directed inward. Excystment involves the development of an expanding excystment vacuole concurrent with a localized thinning on the dorsal cyst wall surface. Cells exit through the pre-formed ostiole, mid-dorsal region first, initially by the force of cytoplasmic streaming, but later aided by cirral movement. Newly emerged cells retain the excystment vacuole and show no dorsal ridging. As the cell expels its excystment vacuole and partially unfolds, normal trophont morphology is re-established. Both cyst structure and cyst typology have implications for hypotrich taxonomy.     

Temperature effects on survival and excystment of cercariae of Halipegus occidualis (Trematoda)

Survival of the cystophorous cercariae of Halipegus occidualis (Trematoda: Hemiuridae) from naturally infected Helisoma anceps (Gastropoda: Planorbidae) was determined following constant temperature storage at 4, 16, 22, 26 and 30 degrees C. At 4 degrees C, 90% of cercariae survived for 14 weeks and 50% survived for 30 weeks. Survival varied inversely with temperature, and at 30 degrees, 90% survived for 1.5 weeks and 50% survived for 2.5 weeks. At the time of release from snails, cercariae excysted within 0.5 s of stimulation. Excystment times ultimately increased to 1-3 s at all temperatures as length of storage increased, but no connection was detected between excystment time and the activity of the cercaria. Excystment times began increasing while survival was still above 90%. Temperature specific mortality rates of cercariae were estimated, and used to simulate the survival of cercariae released naturally at various times of the year. The results of these simulations suggest that cercariae of H. occidualis are present in the environment at all times of the year, but that cercariae present in late winter (January to mid-March) may have an impaired excystment mechanism that reduces their infectivity.     

Studies on the excystment of trematode metacercariae in vitro.

Excystment of metacercariae of Parorchis acanthus, Posthodiplostomoides leonensis, Posthodiplostomum sp. and Clinostomum tilapiae was found to be an active process initiated by the metacercariae when the correct physico-chemical conditions exist in the environment; but in the excystment of Posthodiplostomum nanum the metacercaria seems not to take part in the process. Temperature, osmotic pressure, pH and eH are factors which influence all the five species studied. Fresh ox bile was found not to be an absolute necessity for the excystment of the five species studied but its presence in the medium increased the rate of excystment of three species.     

Factors regulating excystment of Alexandrium in Puget Sound,WA, USA

Factors regulating excystment of a toxic dinoflagellate in the genus Alexandrium were investigated in cysts from Puget Sound, Washington State, USA. Experiments were carried out in the laboratory using cysts collected from benthic seedbeds to determine if excystment is controlled by internal or environmental factors. The results suggest that the timing of germination is not tightly controlled by an endogenous clock, though there is a suggestion of a cyclical pattern. This was explored using cysts that had been stored under cold (4 °C), anoxic conditions in the dark and then incubated for 6 weeks at constant favorable environmental conditions. Excystment occurred during all months of the year, with variable excystment success ranging from 31–90%. When cysts were isolated directly from freshly collected sediments every month and incubated at the in situ bottom water temperature, a seasonal pattern in excystment was observed that was independent of temperature. This pattern may be consistent with secondary dormancy, an externally modulated pattern that prevents excystment during periods that are not favorable for sustained vegetative growth. However, observation over more annual cycles is required and the duration of the mandatory dormancy period of these cysts must be determined before the seasonality of germination can be fully characterized in Alexandrium from Puget Sound. Both temperature and light were found to be important environmental factors regulating excystment, with the highest rates of excystment observed for the warmest temperature treatment (20 °C) and in the light.     

Seasonality in the excystment of Alexandrium minutum and Alexandrium tamarense in Irish coastal waters

Excystment experiments were carried out on cysts of Alexandrium minutum and A. tamarense (Group III) taken from Cork Harbour, Ireland. Freshly sampled cysts were isolated into well plates and their excystment was monitored over a 30 day period. A pronounced seasonality was observed in the excystment behaviour in both species when measurements were carried out seasonally. Between 80 and 100% of the isolated cysts excysted within 30 days when samples were taken between March and June. However, between only 0 and 15% excysted in samples taken between August and early February. This seasonal characteristic was observed repeatedly over a 3 year period (2004–2007). The effect was observed in cysts which had been sampled from both inter-tidal and sub-tidal locations. No endogenous clock was evident in the germination of A. tamarense and A. minutum cysts taken from Cork Harbour which had been stored cool and in the dark under anoxic conditions for up to 18 months. The seasonal effect observed was independent of water temperature, although temperature did affect the rate of excystment. Temperature also affected the maturation of cysts which had been freshly formed in the laboratory. The significance of incorporating seasonality in excystment of Alexandrium into models describing its growth is also discussed.     

In vitro excystment of the black spot trematode Uvulifer ambloplitis (Trematoda:Diplostomatidae)

Spellman S. J. and Johnson A. D. 1987. In vitro excystment of the black spot trematode Uvulifer ambloplitis (Trematoda:Diplostomatidae). International Journal for Parasitology17: 897–902. Metacercariae of U. ambloplitis became activated and excysted in both acid pepsin and acidified Locke's balanced salt solution (BSS). The maximum percentage of excystment was 40% in acid pepsin and 4% in Locke's BSS. Acid pretreatment was required for the additional excystment that occurred in the pretreatment reductant sodium dithionite, or in an incubation medium, or in a sodium dithionite-incubation medium sequence. Since larvae excysted during both pretreatments and in incubation media, maximum overall excystment percentages were obtained with three treatments; (1) 0.5% pepsin at pH 2.0 for 30 min, (2) 0.2% sodium dithionite at pH 7.4 for 10 min and (3) an incubation medium of 0.2 or 0.5% ox bile salts a pH 7.4 for 120 min, 66 and 79%, respectively. Excystment occurred in trypsin alone or trypsin containing incubation media following pepsin pretreatment or a pepsin-sodium dithionite sequence, but the larvae were sluggish and died within a few min after excysting. Thus, a synergistic effect between bile salts and trypsin was not found in this study. Excystment was primarily an active process with the larva emerging from the narrow end of the parasite cyst, although a breakdown of the host cyst and some softening of the parasite cyst was observed.     

Excystment of Didinium nasutum

SYNOPSIS. Excystment of Didinium nasutum is solely dependent upon dense bacterial populations and is independent of the type of medium in which the bacteria have been grown. Beers' hypothesis of the need for a factor from proteose-peptone is thereby not confirmed, but the need for living, intact bacteria as postulated by him is fully shown. The process of excystment is initiated by bacteria, but their presence is not required throughout the excystment. Axenically grown paramecia, shown to be adequate as food organisms for didinia, will not induce excystment. Five types of bacteria including Gram-positive, Gram-negative, aerobic and anaerobic all suffice to induce excystment, suggesting that the initiation of this process is caused by some general metabolic process or product of bacteria.     

Fasciola hepatica: Simple,large-scale, in vitro excystment of metacercariae and subsequent isolation of juvenile liver flukes

A simple method has been developed for the in vitro excystment of metacercariae of Fasciola hepatica, and for the isolation of large numbers of juvenile liver flukes free from intact metacercariae and from cyst-wall material. In this method, the outer cyst wall was removed by gently grinding the metacercariae between small glass plates. The metacercariae were activated by incubation for 1 hr under $\text{60\%}\text{CO}{}_2\text{40\%}\text{N}{}_2$ and excysted by the addition of 10% sterilized sheep bile or an equivalent amount of taurocholic acid. Excystment was accomplished in an experimental apparatus allowing the newly excysted juveniles to escape from the bile-containing excystment medium into a medium with low bile content. The yield of isolated liver flukes was 60–80%; their protein content was about 125 ng. Both bile and taurocholic acid, though necessary for excystment, were detrimental to the survival of the juvenile liver flukes. The presence of bile in the host intestine may be a stimulus for juveniles to leave the gut and enter the abdominal cavity.     

Life history,excystment features,and growth characteristics of the Mediterranean harmful dinoflagellate Alexandrium pseudogonyaulax

Studies considering the biology and ecology of the toxic bloom‐forming species, Alexandrium pseudogonyaulax, are rare. Our results highlight five features not described before in A. pseudogonyaulax life cycle: (i) A. pseudogonyaulax gametes showed two modes of conjugation, anisogamy and isogamy, (ii) sexual conjugation occurs either in the dark or in the light phase by engulfment or a fusion process, (iii) the presence of planozygote and newly formed cysts in monoclonal culture suggests homothallism, (iv) newly formed cysts have very dark vesicular content and are mostly unparatabulated when observed under light microscope and (v) natural resting cysts are able to give either a planomeiocyte or two vegetative cells. Cyst viability was enhanced after 5 months of cold storage (4°C), with excystment rate reaching 97% after 3 d of incubation. Excystment rate was highest (43%–79%) in Enriched Natural Sea Water diluted culture medium, whereas few germling cells were able to survive without the culture medium (0%–13%). Salinity‐irradiance experiments revealed that the highest cell concentrations occur at high irradiances for all the tested salinities. Vegetative growth rates generally increased with increasing irradiance, and were less dependent on salinity variations. The relatively low growth rate, low cell densities in the laboratory, and the notable capacity of producing cysts along growth phases of A. pseudogonyaulax could explain the occurrence of high resting cysts densities in the sediment of Bizerte lagoon and the relatively low abundances of vegetative cells in the water column.     

Behavior of Peridinium bipes (Dinophyceae) resting cysts in the Asahi Reservoir

The role of resting cysts includes short- and long-term survival under extreme conditions, bloom initiation, species dispersal, reproduction, and preservation of genetic variation. Accordingly, it is important to understand their behavior in a water environment, especially in lakes and reservoirs where dinoflagellate blooms are observed. In this study, we estimated the behavior of the Peridinium bipes cysts in the Asahi Reservoir using laboratory experiments and field surveys. It was observed that the amount of light strongly influenced excystment, and few cysts germinated under dark conditions in the laboratory experiment. The minimum temperature on excystment was inferred from the laboratory experiment and field surveys to be about 5°C. Although the frequency of excystment did not depend on the water temperature from 10° to 20°C, the average preparation period for excystment decreased with the increase of water temperature. In the Asahi Reservoir, the excystment was estimated to occur during the months of March and April. If excystment did not occur in spring, the dinoflagellate bloom was not be observed until about July, although the bloom often began to appear in about May in the Asahi Reservoir. Consequently, the blooming season in the Asahi Reservoir is affected by the biomass of the germinated cysts in spring. Received: August 31, 2000 / Accepted: March 1, 2001     

UV effects on stoichiometry and PUFAs of Selenastrum capricornutum and their consequences for the grazer Daphnia magna

1. The effect of ultraviolet (UV) radiation (280–400 nm) on fatty acid composition and elemental ratios of carbon (C), nitrogen (N) and phosphorus (P) of a unialgal culture of the chlorophyte Selenastrum capricornutum was investigated. Algae were cultured in the presence or absence of UV radiation and were subsequently fed to Daphnia magna to assess potential effects of UV on zooplankton fatty acid composition, growth and reproduction. 2. Algal growth rate was substantially reduced by UV radiation, probably because of a severe inhibition of photosynthetic efficiency (measured as optimal quantum yield). 3. Algae exposed to UV radiation had a significantly reduced content of 18 : 1 n‐9, while C18 polyunsaturated fatty acids (PUFAs) were higher under UV radiation. These observations point at an increased demand for and synthesis of PUFAs under UV stress. 4. The C : P and N : P ratios showed a remarkable decrease in UV‐exposed cells primarily owing to an increased uptake of P. The nutritional quality in terms of both fatty acid composition and stoichiometry was therefore higher in the UV treatment relative to the control. 5. Despite the UV‐induced changes in nutritional quality of S. capricornutum, no significant effects on D. magna growth or reproduction were detected. The fatty acid composition of Daphnia fed on UV irradiated algae showed a significantly lower content of 18 : 1 n‐9, but no changes in the essential PUFAs.     

Scanning electron microscopy of pathogenic and non-pathogenic Naegleria cysts

Scanning electron microscopy of pathogenic and non-pathogenic Naegleria cysts. International journal for Parasitology4: 139–142. Cysts of 4 strains of non-pathogenic Naegleria gruberi and 5 strains of pathogenic Naegleria fowleri were examined in the scanning electron microscope. Excystment of the Naegleria gruberi amoebae occurred via preformed exit pores in the cyst wall. Similar structures were not found in the cysts of Naegleria fowleri, and excystment occurred by rupture of the cyst wall. The sequence of cyst wall rupture is illustrated for one of the pathogenic strains.     

Water- and temperature-dependence of DNA damage and repair in the fruticose lichen Cladonia arbuscula ssp. mitis exposed to UV-B radiation

The induction of cyclobutane pyrimidine dimers (CPDs) by ultraviolet‐B radiation (UV‐B, 280–315 nm) and repair mechanisms were studied in the lichen Cladonia arbuscula ssp. mitis exposed to different temperatures and water status conditions. In addition, the development and repair of CPDs were studied in relation to the different developmental stages of the lichen thallus podetial branches. Air‐dried lichen thalli exposed to UV‐B radiation combined with relatively high visible light (HL, 800 μmol m^?2 s^?1; 400–700 nm) for 7 days showed a progressive increase of CPDs with no substantial repair, although HL was present during and after irradiation with UV‐B. Fully hydrated lichen thalli, that had not been previously exposed to UV‐B radiation for 7 days, were given short‐term UV‐B radiation treatment at 25°C, and accumulated DNA lesions in the form of CPDs, with repair occurring when they were exposed to photoreactivating conditions (2 h of 300 μmol m^?2 s^?1, 400–700 nm). A different pattern was observed when fully hydrated thalli were exposed to short‐term UV‐B radiation at 2°C, in comparison with exposure at 25°C. High levels of CPDs were induced at 2°C under UV‐B irradiation, without significant repair under subsequent photoreactivating light. Likewise, when PAR (300 μmol m^?2 s^?1) and UV‐B radiation were given simultaneously, the CPD levels were not lowered. Throughout all experiments the youngest, less differentiated parts of the lichen thallus – namely ‘tips’, according to our arbitrary subdivision – were the parts showing the highest levels of CPD accumulation and the lowest levels of repair in comparison with the older thallus tissue (‘stems’). Thus the experiments showed that Cladonia arbuscula ssp. mitis is sensitive to UV‐B irradiation in the air‐dried state and is not able to completely repair the damage caused by the radiation. Furthermore, temperature plays a role in the DNA damage repairing capacity of this lichen, since even when fully hydrated, C. arbuscula ssp. mitis did not repair DNA damage at the low temperatures.     

Exposure of eggs to solar UV‐B leads to reduced hatching rates in two sparid fishes,red sea bream Pagrus major and black sea bream Acanthopagrus schlegeli

Hatching success was examined under exposure to solar ultraviolet radiation (UVR) using filters to give three different light conditions [C1: UV‐B, UV‐A and photosynthetically active radiation (PAR), C2: UV‐A and PAR, C3: PAR] in red Pagrus major and black Acanthopagrus schlegeli sea bream. Hatching rate of both species was reduced by an exposure over a 2 day period to UVR and was not significantly different between two species under the three light conditions.     

Functional acclimation to solar UV-B radiation in Gunnera magellanica, a native plant species of southernmost Patagonia

The ecosystems of Tierra del Fuego (in southern Patagonia, Argentina) are seasonally exposed to elevated levels of ultraviolet‐B radiation (UV‐B: 280–315 nm), due to the passage of the ‘ozone hole’ over this region. In the experiments reported in this article the effects of solar UV‐B and UV‐A (315–400 nm) on two UV‐B defence‐related processes: the accumulation of protective UV‐absorbing compounds and DNA repair, were tested. It was found that the accumulation of UV‐absorbing sunscreens in Gunnera magellanica leaves was not affected by plant exposure to ambient UV radiation. Photorepair was the predominant mechanism of cyclobutane‐pyrimidine dimer (CPD) removal in G. magellanica. Plants exposed to solar UV had higher CPD repair capacity under optimal conditions of temperature (25 °C) than plants grown under attenuated UV. There was no measurable repair at 8 °C. The rates of CPD repair in G. magellanica plants were modest in comparison with other species and, under equivalent conditions, were about 50% lower than the repair rates of Arabidopsis thaliana (Ler ecotype). Collectively our results suggest that the susceptibility of G. magellanica plants to current ambient levels of solar UV‐B in southern Patagonia may be related to a low DNA repair capacity.     

A new species in the genus Cyrtostrombidium (Ciliophora,Oligotrichia, Oligotrichida): its morphology,seasonal cycle and resting stage

Cysts of an oligotrich ciliate were collected from natural sediment samples in Onagawa Bay, northeastern coast of Japan, and examined for their excystment capability. A high excystment ratio was obtained at lower temperatures of 10 or 15 degrees C; no excystment occurred at 20 degrees C. Excysted vegetative cells were observed after protargol staining and were identified as a new species, Cyrtostrombidium boreale n. sp. The seasonal changes in the vegetative population and sedimentation of newly formed cysts were also investigated in situ. Planktonic vegetative cells were abundant during the cold season from February to May, when the water temperature was lower than 10 degrees C. Mass encystment occurred abruptly just after the seasonal peak of the vegetative population in April. These results indicate that C. boreale is a cold-water species and aestivates during the longer, warm period from late spring to fall.     

The effect of nutritional state on photoreversal of ultraviolet injuries in Didinium nasutum

1. The effect of the nutritional state of Didinium nasutum on its resistance to short ultraviolet (UV) radiation (2654 A) and its recovery from the injury following illumination with visible light (4350 A, blue) was studied. 2. The resistance of a didinium to UV is considerably increased by feeding it a paramecium 15 to 60 minutes before exposure to UV. If fed just before exposure to UV, the resistance is less than that of an unfed control. 3. Photoreversal is only slightly greater in didinia fed after irradiation with UV but before exposure to visible light as compared to those fed after exposure to visible light. 4. Irradiated paramecia are eaten by didinia, provided they have not started to cytolyze. Didinia fed on irradiated paramecia divide at about the same rate as controls or slightly faster. 5. The available stock of Didinium declines in vigor with lapse of time after excystment, as measured by the time required for division. The sensitivity of Didinium to UV did not change essentially during the 5 month period over which tests were made. 6. The theoretical implications of the results are considered.