Cyst Production Research Articles

Host age and pathogen dosage impact cyst morphogenesis in the invertebrate pathogenic alga Helicosporidium sp. (Chlorophyta: Trebouxiophyceae)

Helicosporidium sp. is a pathogenic alga that replicates in the hemolymph of various invertebrate hosts. Morphogenesis of the infectious life stage, the cyst, occurs in the infected host, but to date cannot be induced in vitro. Using larvae of the heterologous host Helicoverpa zea, we examined potential factors influencing pathogenicity and in vivo cyst production of the alga and the impact of infection on host survival. Factors tested were cyst dosage administered per os (ranging from 10 2 to 10 5 cysts per larva) and host age at exposure (third, fourth, and fifth larval instar). Cyst production occurred between 7 and 13 days after treatment, regardless of host age at treatment. Increasing dosage increased both percent infection and mortality, but cyst production did not track the total infection response. Increasing host age at exposure mitigated dosage effects on infection and mortality and also elevated cyst production in later-treated larvae. Only the highest dosage produced a significant decrease in the overall time to death. Moderate cyst dosages and later host ages were most effective at regenerating Helicosporidium cysts.

Dinoflagellate cyst production on the southern Namaqua shelf of the Benguela upwelling system

To study dinoflagellate cyst production in the southern Benguela, a sediment trap was deployed for a period of 3.5 years at a single station located downstream of the Cape Columbine upwelling cell on the southern Namaqua shelf. The cyst assemblage of surface sediments below the trap was also investigated. Twenty-nine different cyst types were recorded of which 25 were from the sediment trap, and 22 from the surface sediments. The flux of cysts followed a clear seasonal trend with an initial peak in spring followed by a major peak in autumn; with a mean flux for the entire period of deployment of 1.4 × 106 cysts m−2 day−1. Of the cysts recovered from the trap, those of heterotrophic dinoflagellates were six times more abundant than those of autotrophic dinoflagellates. The study also revealed the presence of cysts of species previously unrecorded in the plankton of the southern Benguela, specifically the toxic dinoflagellate Lingulodinium polyedrum.

Species specific encystment patterns in three Baltic cold‐water dinoflagellates: The role of multiple cues in resting cyst formation

The relationships among cellular nutrient status, environmental conditions (temperature and nutrient availability), and cyst production were studied in batch cultures of three cold‐water dinoflagellates (Scrippsiella hangoei, Gymnodinium corollarium, and Woloszynskia halophila) isolated from the Baltic Sea. We tested the effect of increasing temperature while providing nutrient‐replete conditions as well as the effect of ambient nutrient (N, P) deficiency. The results revealed different encystment cues and patterns in the three species. While depletion of ambient nitrogen and subsequent internal N stress were the primary factors behind cyst production of G. corollarium, higher temperature led to substantial encystment of S. hangoei and W. halophila without a direct link to cellular nutrient physiology. In W. halophila, N limitation induced a transition of the population to small cells presumably representing gametes, but this process was not followed by cyst formation. Phosphorus stress was not directly linked to cyst formation in any of the species. Our data indicate that both reliable token cues (such as temperature) and ultimate causes (for example, nutrient depletion) for encystment are likely involved in the cystformation process. Such duality might provide an explanation for multiple triggers inducing encystment in laboratory settings and the lack of evidence for a direct relationship between nutrient depletion and cyst formation in the field.

Environmental factors influencing the variability of Lingulodinium polyedrum and Scrippsiella trochoidea (Dinophyceae) cyst production

This study analyzes the temporal variability of the abundance of Lingulodinium polyedrum and Scrippsiella trochoidea resting cysts in surface sediments, as well as the temporary cysts and vegetative cells of L. polyedrum in the upper water column of Todos Santos Bay (Baja California, Mexico). Samples were collected monthly from January 2002 to June 2005 at four sites. Multidimensional scaling analysis and analysis of similarities revealed that resting cysts are distributed heterogeneously according to the sedimentary environment. Surface water temperature, inorganic dissolved phosphate, and the abundance of temporary cysts were the main factors influencing the abundance of L. polyedrum resting cysts, while the variability of temporary cysts was explained by the abundance of planktonic cells. Scrippsiella trochoidea resting cysts showed no statistical relationship with the environmental factors considered. Local runoff during the rainy season and sewage from the city of Ensenada contribute to the eutrophication of the bay. This is an important factor for future blooms since inorganic dissolved nitrate + nitrite and daylight hours during the spring-summer season are not limiting factors for dinoflagellate growth. After the dinoflagellate blooms, there was massive cyst production of both species, and the new cysts settled on the surface sediments. Surface water temperatures between 17°C and 22.5°C during spring-summer appear to trigger excystment in these species.

Environmental significance of dinoflagellate cysts from the proximal part of the Po-river discharge plume (off southern Italy, Eastern Mediterranean)

To determine the relationship between region specific dinoflagellate cyst distribution in the Po-river discharge area and oceanic environmental conditions, surface sediments of 48 sites in the middle and distal part of the discharge plume area have been studied. Establishing such a relationship is a prerequisite to create reconstructions of the eutrophication history as well as the palaeoclimatic and palaeoceanography history of the area. Literature based information about the sedimentation rates based on 210Pb dating methods are available for 18 sites. This enables the calculation of cyst accumulation rates of individual cyst species which reflect their cyst production. Correlation of the accumulation rates of individual species with environmental parameters of the upper waters allows us to adapt and refine the ecological characteristics of a selection of cyst species. This latter is trivial since the current concepts on the ecological significance of dinoflagellate cyst have to be revised as a result of the current developments in the dinoflagellate research field. These developments have elucidated that a considerable part of the relative abundance datasets that form the basis for the present day ecological concepts of dinoflagellate cysts might have suffered from so called “closed sum effects” and have been overprinted by early diagenetic processes. The dinoflagellate cyst association reflects both upper and bottom water circulation. Based on the relative abundance data four associations can be distinguished that are characteristic for the major oceanographic settings in the region. (1) River discharge association. This association consists of Echinidinium spp., Lejeunecysta sabrina, Lingulodinium machaerophorum, Polykrikos kofoidii, Polykrikos schwarzii, cysts of Protoperidinium stellatum, Selenopemphix quanta and reworked cysts. These species have high relative abundances in sites where bottom waters are low in oxygen and upper waters are influenced by river discharge waters that are characterized by high productivity and relative low salinity. (2) Warm water association. This association consists of Spiniferites mirabilis, Spiniferites pachydermus, Spiniferites ramosus and Spiniferites spp. which have their highest relative abundances in the sites at the plume margin that are characterized by relative warm upper waters and intermediate chlorophyll- a concentrations. (3) Oxygenated bottom water group. Species of this group; Impagidinium aculeatum, Impagidinium patulum, Impagidinium sphaericum, Operculodinium centrocarpum and Operculodinium israelianum have their highest relative abundances at sites where bottom waters are formed by well ventilated Adriatic Deep Water or Eastern Mediterranean Deep Water. (4) Golfo di Taranto group consisting of round brown cysts produced by Protoperidinium species (grouped as Brigantedinium spp .). The variation in accumulation rates can be related to gradiental changes in the trophic state of the surface waters linked to river outflow. Most species show a positive relationship between cyst production and nutrient/trace element availability in upper waters. No negative correlation between cyst production and nutrient/trace element availability could be documented. Production of Brigantidinium spp., Echinidinium spp., L. sabrina, L. machaerophorum, P. kofoidii/schwarzii, Spiniferites spp., S. mirabilis and S. quanta shows the most pronounced increase with increasing nutrient/trace element availability. These species can be considered as valuable indicators for reconstructing changes in the trophic state of the upper waters within the Po-river area in palaeo-environmental studies.

PALYNOLOGICAL RECORDS OF CLIMATE AND OCEANIC CONDITIONS IN THE LATE PLEISTOCENE AND HOLOCENE OF THE NILE CONE, SOUTHEASTERN MEDITERRANEAN, EGYPT

Variations in palynomorph concentrations and relative abundances, including pollen and spores, organic-walled dinoflagellate cysts, and amorphous organic matter (AOM), were studied in sediment core NC Core 2 from the upper slope (1,030 m water depth) of the Nile Cone, southeastern Mediterranean, Egypt. Each sample represents palynomorph deposition for intervals of around 500–1,000 years, and this study provides the first detailed palynological record for the Nile Cone. The dinoflagellate cyst assemblages and AOM production reflect changes in surface water temperature and river discharge in response to climate forcing as marked by variations in pollen and spore indicators of semi-desert vegetation and tropical Monsoon intensity. The basal sediments (approximately 14,600–9,500 yr before present [BP]) contain high concentrations and relative abundances of Polysphaeridium zoharyi, Polysphaeridium spp., Spiniferites elongatus, and Spiniferites spp. during the transition from postglacial to interglacial conditions. Variations in these taxa and total Impagidinium spp. suggest a gradual temperature increase, interrupted by a pre-Holocene cool interval around 11,000 yr BP. The high African monsoon index for this preHolocene time corresponds with pollen evidence of relatively high Nile discharge. The organic-rich S1 sapropel sediments, dated as around 9,500–6,270 yr BP, were deposited several thousand years later, during a time of lower Monsoon index, warmer surface water, and increased dinoflagellate cyst production. This was accompanied by moderate Nile flooding and oxygen-deficient or anoxic bottom water on the upper Nile Cone, mainly supporting the increased production and carbon import hypothesis for eastern Mediterranean S1 formation. Dinoflagellate cyst assemblages in the Nile Cone S1 differ from those of the deeper, more northern Levantine and Cretan basins in the near absence of heterotrophic protoperidinioid cysts, despite the uniformly high organic S1 carbon content. The prevailing climate during the formation of sapropelic sediments in the southeastern Mediterranean was tropical to subtropical, but was interrupted by an early cooler interval with reduced humidity, as marked by re-appearance of Spiniferites elongatus and increased Ephedra pollen. The carbonate-rich surface layers were probably deposited under warm dry climatic conditions with minimum Nile input, but evidence of oxidation prevents detailed interpretation.

Artemia parthenogenetica (Branchiopoda: Anostraca) from the Large Aral Sea: Abundance, distribution, population structure and cyst production

The brine shrimp Artemia parthenogenetica appeared in the Large Aral Sea (Central Asia) in 1998 when mineralization reached 63 ppt. Data on Artemia abundance and biomass, along with temperature and salinity measurements were collected in the western basin during 2002–2006, primarily in the autumn. During the study period, population density grew progressively, both in terms of number, from 250 to 1260 individuals per m 3, and in terms of biomass, from 0.3 to 1.3 g per m 3. In 2005, the population density and spatial distribution in the different parts of the sea (western and eastern basins and strait) was assessed. The horizontal distribution of the Artemia population was uniform in the deep central part of the western basin, although the distribution was quite patchy in the shallow coastal zone. Depth habitat of Artemia was restricted to the upper 20–25 m of depth, as the oxygen depletion and formation of anoxic layer prevented distribution of Artemia to the deeper waters. In autumn, all females reproduced oviparously, with an average clutch size of 30–35 eggs per female. The number of eggs in a clutch was positively correlated with female body length ( r 2 = 0.36–0.44).

Novel Role of Sphingolipid Synthesis Genes in Regulating Giardial Encystation

Although encystation (cyst formation) is important for the survival of Giardia lamblia outside its human host, the molecular events that prompt encystation have not been fully elucidated. Here, we demonstrate that sphingolipids (SLs), which are important for the growth and differentiation of many eukaryotes, play key roles in giardial encystation. Transcriptional analyses showed that only three genes in the SL biosynthesis pathways are expressed and transcribed differentially in nonencysting and encysting Giardia trophozoites. While the putative homologues of giardial serine palmitoyltransferase (gSPT) subunit genes (gspt-1 and -2) are differentially expressed in nonencysting and encysting trophozoites, the giardial ceramide glucosyltransferase 1 gene (gglct-1) is transcribed only in encysting cells. l-Cycloserine, an inhibitor of gSPT, inhibited the endocytosis and endoplasmic reticulum/perinuclear targeting of bodipy-ceramide in trophozoites, and this could be reversed by 3-ketosphinganine. On the other hand, D-threo-1-phenyl-2-palmitoylamino-3-morpholino-1-propanol (PPMP), an inhibitor of glucosylceramide synthesis, blocked karyokinesis and reduced cyst production in culture. PPMP also altered the expression of cyst wall protein transcripts in encysting cells. Phylogenetic analyses revealed that the gspt genes are paralogs derived from an ancestral spt sequence that underwent gene duplication early in eukaryotic history. This ancestral sequence, in turn, was probably derived from prokaryotic aminoacyl transferases. In contrast, gglct-1 is found in both prokaryotes and eukaryotes without any evidence of gene duplication. These studies indicate that SL synthesis genes are involved in key events in giardial biology and could serve as potential targets for developing new therapies against giardiasis.

Assessing environmental control on dinoflagellate cyst distribution in surface sediments of the Benguela upwelling region (eastern South Atlantic)

Organic‐walled dinoflagellate cyst assemblages in surface sediments of the Benguela Current Upwelling System (eastern South Atlantic) show geographic patterns that cannot entirely originate from cyst production or transport. Aimed at answering how far these variations are due to taphonomic control, this study investigated a possible correlation with the changes in bottom‐water oxygen concentrations typifying this region. Based on 36 samples, multivariate statistics were used to analyze community variability with respect to bottom‐water oxygen concentration, temperature, salinity, nutrient content, chlorophyll a (Chl a) concentration, the organic carbon content of surface sediments, and a measure of water column stratification. Determined relationships to salinity, nutrient supply, nutrition, and environmental steadiness point out the requirements for dinoflagellate cyst production, while cross‐shelf transport processes could have introduced variability prior to burial of cysts in surface sediments. The offshore decrease in the relative abundance of protoperidinacean cyst types was consistent with their lower preservation potential under oxygenated conditions and coincided with a change in assemblage composition toward oxidation resistant species. On elimination of covariation, bottom‐water oxygenation was significantly related to this pattern and determined together with seasonal salinity, Chl a, and annual phosphate concentration, the parameter combination best explaining community variability. These results suggest that postdepositional degradation of peridinioid dinoflagellate cysts would partly explain the onshore‐offshore gradient in species distributions and could be responsible for more variability in assemblage compositions than is presently acknowledged.

Effect of Antimicrobial Compounds on Balamuthia mandrillaris Encystment and Human Brain Microvascular Endothelial Cell Cytopathogenicity

Cycloheximide, ketoconazole, or preexposure of organisms to cytochalasin D prevented Balamuthia mandrillaris-associated cytopathogenicity in human brain microvascular endothelial cells, which constitute the blood-brain barrier. In an assay for inhibition of cyst production, these three agents prevented the production of cysts, suggesting that the biosynthesis of proteins and ergosterol and the polymerization of actin are important in cytopathogenicity and encystment.

Variability in reproductive output across a water quality gradient for a tropical marine sponge

To establish a complete understanding of reproductive variability, larval supply and ultimately population demographics of a species it is important to determine reproduction across a broad spectrum of environmental conditions. This study quantified sexual reproduction of the brooding, gonochoristic sponge Rhopaloeides odorabile from populations across the shelf reefs of the central Great Barrier Reef (GBR). Histological sections of reproductive sponges collected at increasing distances from the coast were used to determine if numbers of reproductive sponges, reproductive output (using a reproductive output index), size at sexual maturity, and sex ratios varied according to their location (distance) from the coastline and therefore from influences of terrigenous/riverine discharge. Significantly higher proportions of reproductive sponges occurred with increasing distance from the coast. The proportion of all reproductive sponges (both male and female) on offshore reefs ranged from 77 to 90%, during November and December, the peak reproductive months of this sponge, compared to 47 to 50% for sponges occurring on coastal reefs. Levels of female reproduction increased with increasing distance from the coastline on two levels. First, oocytes from offshore sponges were significantly larger than oocytes from coastal sponges. Second, sponges from offshore reefs showed a reproductive index (proportions of oocytes, embryos and larvae mm−2) approximately 15 times higher than coastal reef sponges. Therefore, both numbers of oocytes, embryos and larvae in conjunction with larger oocytes contribute to a higher reproductive output index for offshore sponges. The production of spermatic cysts in males was consistent across the GBR. Sex ratios for coastal reef sponges showed a male bias while offshore sponges showed approximate equal sex ratios. The effect of terrigenous riverine input from coastal fluvial plains to the inner GBR is well established and is likely to contribute to the lower levels of reproduction associated with female sponges inhabiting coastal reefs of the central GBR.

Modulation of ecdysal cyst and toxin dynamics of two <i>Alexandrium</i> (Dinophyceae) species under small-scale turbulence

Abstract. Some dinoflagellate species have shown different physiological responses to certain turbulent conditions. Here we investigate how two levels of turbulent kinetic energy dissipation rates (ε = 0.4 and 27 cm² s−3) affect the PSP toxins and ecdysal cyst dynamics of two bloom forming species, Alexandrium minutum and A. catenella. The most striking responses were observed at the high ε generated by an orbital shaker. In the cultures of the two species shaken for more than 4 days, the cellular GTX(1+4) toxin contents were significantly lower than in the still control cultures. In A. minutum this trend was also observed in the C(1+2) toxin content. For the two species, inhibition of ecdysal cyst production occurred during the period of exposure of the cultures to stirring (4 or more days) at any time during their growth curve. Recovery of cyst abundances was always observed when turbulence stopped. When shaking persisted for more than 4 days, the net growth rate significantly decreased in A. minutum (from 0.25±0.01 day−1 to 0.19±0.02 day−1) and the final cell numbers were lower (ca. 55.4%) than in the still control cultures. In A. catenella, the net growth rate was not markedly modified by turbulence although under long exposure to shaking, the cultures entered earlier in the stationary phase and the final cell numbers were significantly lower (ca. 23%) than in the control flasks. The described responses were not observed in the experiments performed at the low turbulence intensities with an orbital grid system, where the population development was favoured. In those conditions, cells appeared to escape from the zone of the influence of the grids and concentrated in calmer thin layers either at the top or at the bottom of the containers. This ecophysiological study provides new evidences about the sensitivity to high levels of small-scale turbulence by two life cycle related processes, toxin production and encystment, in dinoflagellates. This can contribute to the understanding of the dynamics of those organisms in nature.

The ingestion rate of Litopenaeus vannamei larvae as a function of Tisbe biminiensis copepod concentration

Artemia nauplius is the food usually used in the culture of Litopenaeus vannamei larvae. However, the production of Artemia cysts does not always meet the increasing demands of aquaculture. Thus, alternative diets need to be tested. The objective of this study was to determine the ingestion rate of the L. vannamei larvae fed on different offspring concentrations of Tisbe biminiensis, composed of nauplii and copepodites, and to estimate the best food concentration. Two types of ingestion rate experiments were made: one using flat bottom flasks without aeration, and another with conic bottom flasks with aeration. In the first type, larvae in the mysis 2 and 3 stages and postlarvae 1, 3, 5 and 7 were stocked individually in vessels containing 50 ml of seawater. In the other type, groups of 6 larvae in the stages mysis 2 and 3 were stocked in vessels containing 300 ml of seawater. In both experiments, the vessels containing seawater of salinity 31–33 were incubated for 24 h, at 25–30 °C and the photoperiod of 13 h light/11 h dark. Four treatments were tested with different copepod offspring concentrations as well as controls without shrimp larvae. In addition, controls using Artemia nauplii as food were also used to verify the physiological condition of tested larvae. In experiments using conic bottom flasks with aeration, the best concentration of copepods was about 5 copepod ml − 1 for mysis 2 and 3, respectively. The mean ingestion rate was 56.7 ± 9 and 188 ± 203 copepod larva − 1 day − 1 for mysis 2 and 3, in that order. In the other type of experiment, mysis 2 did not ingest copepods and mysis 3 ingested only 24.5 ± 10 copepod larva − 1 day − 1 . In postlarval stages, the best concentration of copepod was about 10 copepod ml − 1 for postlarvae 1 to 3 and 20 copepod ml − 1 for postlarvae 5 to 7. The mean ingestion rate was 185 ± 69 copepod larva − 1 day − 1 for postlarva 1, 229 ± 45 copepod larva − 1 day − 1 for postlarva 3, 342.8 ± 98 copepod larva − 1 day − 1 for postlarva 5 and 293 ± 45 copepod larva − 1 day − 1 for postlarva 7. The results indicated some preference for naupliar over copepodite stages. To conclude, the offspring of T. biminiensis copepod were ingested by L. vannamei larvae in the mysis and postlarval stages and the ingestion rate increased with larval development. Thus, the offspring of T. biminiensis copepod are a potential live food to be tested in larviculture of L. vannamei.

A Multigene Analysis of Corallomyxa tenera sp. nov. Suggests its Membership in a Clade that Includes Gromia, Haplosporidia and Foraminifera

We combine a morphological description with a multigene analysis to assess the phylogenetic placement of a poorly known amoeboid taxon Corallomyxa within the eukaryotic tree of life. A detailed morphological analysis including transmission electron microscopy and light microscopy of Corallomyxa sp. ATCC 50975 demonstrates that this isolate is a new species, herein designated, Corallomyxa tenera sp. nov. This species possesses features of the genus, such as a multinucleate, reticulate plasmodium with localized bidirectional streaming and occasional formation of surface buds, but is differentially characterized from other species by its delicate appearance, short duration of the anastomosing reticulate network and production of round smooth-walled cysts. The new species also lacks some features found in some Corallomyxa species, including cytoplasmic condensation and an electron dense "chromocenter". A Bayesian analysis of four concatenated genes (SSU-rDNA, actin, alpha- and beta-tubulin) from a wide diversity of eukaryotes places the new species together with taxa placed in the putative supergroup 'Rhizaria'. All molecular loci refute the traditional placement of Corallomyxa within the supergroup 'Amoebozoa', which includes other Mycetozoidea and Lobosea. Maximum likelihood and Bayesian analyses of the two well-sampled genes, SSU-rDNA and actin, with increased taxon sampling of 'Rhizaria' show a close affinity of Corallomyxa with Foraminifera, Gromia and, for SSU-rDNA, Haplosporidia. We further identify a novel stem, herein designated E23-13-1, in the predicted SSU-rDNA secondary structure that supports this relationship. A hypothesis is presented for the evolution of morphological and molecular synapomorphies in a clade containing Gromia, Corallomyxa, Foraminifera and Haplosporidia.

Sexual reproduction, larval development and release in Spongia officinalis L. (Porifera, Demospongiae) from the Apulian coast

The reproductive cycle of the bath sponge Spongia officinalis L. has been studied over 1 year on 11 tagged specimens of different sizes (from 82 to 886 ml, in volume) from Ionian coasts of Apulia (SE Italy). According to literature data, the sponge is viviparous. All the monitored specimens showed sexual reproduction, even if the process usually involved small portions of the sponge tissue. Ten specimens were gonochoric (sex ratio 1:1), one specimen showed successive hermaphroditism, with alternate production of oocytes and spermatic cysts in the same reproductive season. Young oocytes occur almost all year round, whereas large mature eggs show a peak in October–November, concomitantly with the appearance of spermatic cysts. No relationships were observed between the sponge size and the presence of sexual elements within the range of the sponge size considered in this research. Embryo development occurs in patches of choanosomal tissue, which contain four or more elements. Cleavage is total and equal; it starts in November and in May leads to a solid stereoblastula, which develops into a parenchymella larva, from May to July. The stereoblastula lacks flagella and its surface is delimited by elongated cells well segregated from the internal ones. Parenchymella larvae are released from June to July, asynchronously, either at the individual or population level, with a few days of de-phasing. Up to 523 larval elements/48 h for a sponge specimen were counted. The free-swimming larvae are ovoid and uniformly flagellated. Flagella are longer at the posterior region, than on the rest of the larval body. Flagellated cells form a pseudo-stratified epithelial layer, delimiting the outermost larval surface, and are filled with electron-lucent vesicles showing a homogenous content. No choanocyte chambers, pinacocytes or skeletal elements are present in the newly released larvae.

Indonesia

Artemia is one of live feed needed in aquaculture as fishes and crustacean. Commercially, Artemia usually sold in dry cysts which can kept for years. The aim of this research were to know increasing quantity and quality A. franciscana cysts after exposing various concentration of fish silage as artificial food and to know optimal concentration of fish silage that can increase quantity and quality A. franciscana cysts. This research was done in Laboratory of Live Feed BBPBAP Jepara Central Java. This research was conducted by 5 treatments. Treatments were grouped based on amount of concentration given, i.e: control (coconut cake) with concentrate 10 g/m3, fish silage concentrate 10, 20, 30, and 40 g/m3. Parameter investigated were number of cysts produced by individual female A. franciscana, diameter of A. franciscana cysts, hatching percentage, and hatching rate of A. franciscana cysts. Data were analyzed using ANOVA and continued using Tukeys test at significant level 5%. The result of this research showed that exposing fish silage can increase quantity and quality A. franciscana cysts. They were increase number of cysts production by individual females, decrease cysts diameter, increase hatching percentage and hatching rate. Optimal concentration of fish silage on increase quantity and quality of A. franciscana cysts was 20 g/m3.

Effects of temperature, light and salinity on cyst production and morphology of Tuberculodinium vancampoae (the resting cyst of Pyrophacus steinii)

Cyst forming dinoflagellates are useful in reconstructing past environments. For accuracy it is essential to know how environmental parameters such as salinity, temperature and light influence dinoflagellate cyst production and morphology. Here the effect of variation in these parameters on production and morphology of Tuberculodinium vancampoae (the resting stage of Pyrophacus steinii) is detailed. Encystment of T. vancampoae has been observed in all studied culture-experiments although only a few cysts are being formed at the limits of the temperature and salinity ranges (16.5°C, 34.8 °C and 20, 45 psu) with highest cyst production at 27 °C and 35 psu. Temperature clearly affects cyst morphology; cysts formed in cultures grown at 16.5 °C and 34.8 °C possess small, flattened processes. These cysts are not completely absent in cultures grown at intermediate temperatures but form only a minor part of the association. In previous studies, salinity has been found to influence the cyst morphology of several dinoflagellate species but this seems not to be the case for T. vancampoae. In this study there was no morphological variation related to salinity. High cyst production was observed in cultures grown under moderate to strong illumination but variation in illumination did not lead to morphological change. Our findings correspond to field observations where T. vancampoae has been observed in surface sediments of the sub-tropical to tropical regions characterised by mean sea surface temperatures between 12.7 °C and 29.5 °C, and sea surface salinities between 16.9 and 36.6 psu. In contrast to previous suggestions, T. vancampoae appears to be heterothallic rather than homothallic.

Vertical distribution and cyst production of Peridiniella catenata (Dinophyceae) during a spring bloom in the Baltic Sea

Vertical distribution and cyst production of the chain-forming, spring dinoflagellate Peridiniella catenata were studied throughout the spring season of 2000 in the coastal Gulf of Finland. Numbers of cells were monitored in the water column, and cyst sedimentation was recorded using multiple sediment traps moored at three discrete depths. At the onset of the spring bloom, most of the population was situated in the euphotic zone. When the bloom progressed, the population was more evenly dispersed throughout the water column. Coinciding with the decline of the spring bloom, after nitrogen depletion, a general reduction of cell size of P. catenata and a break-up of chains were observed. Resting cysts started to appear shortly after the peak of the bloom, in sedimentation traps moored at 30 and 40 m depth. Cysts were only retrieved from the uppermost sediment trap on three of the six sampling occasions, constituting only a small proportion of all cysts produced by P. catenata during spring. Our results suggest that cyst production of this vertically migrating organism takes place to a large extent in deep water layers and emphasizes the necessity of whole water column monitoring in studies aiming to understand in situ life-cycle transformations of vertically migrating dinoflagellates.

Association between milk production and treatment response of ovarian cysts in lactating dairy cows using the Ovsynch protocol

The objective of this study was to evaluate the association between the level of milk production on the day of diagnosis of ovarian cysts and treatment response using the Ovsynch protocol. On the day of cyst diagnosis (Day 0), 260 lactating dairy cows with ovarian cysts were treated with gonadotropin-releasing hormone (GnRH), PGF2α on Day 7, GnRH on Day 9, and timed inseminated 16–20 h later (Ovsynch protocol). Pregnancy was determined (by transrectal palpation) between 42 and 49 days after insemination. On Day 0, data for milk production (kg/day), parity, days in milk (DIM), and body condition score (BCS) were recorded. Using the median value for milk production on the day of diagnosis, cows were classified as high producers (>28.5 kg) and low producers (≤28.5 kg). Cows were classified as primiparous (first lactation) or multiparous (second or more lactations). Data for conception rate (CR) were analyzed using logistic regression accounting for milk production on the day of diagnosis, parity, DIM, and BCS. The CR for low and high producers was 6 and 16%, respectively. There was no association between DIM and BCS with the other variables ( P ≥ 0.05). Primiparous cows were more likely (adjusted odds ratio: AOR = 3.63; 95% CI: 95% confidence intervals = 1.28–10.30; P ≤ 0.01) to become pregnant than multiparous cows, and low producers were less likely (AOR = 0.31; 95% CI = 0.11–0.85; P ≤ 0.02) to become pregnant than high producers. It was concluded that cows with high milk production on the day of cyst diagnosis were more likely to become pregnant following treatment than cows with low milk production. It appears paradoxical that high milk production predisposes to the occurrence of ovarian cysts, but that high-producing cows respond better to treatment compared to low-producing cows. It is hypothesized that the level of milk production on the day of cyst diagnosis could be an additional potential predictor of success to treatment of lactating cows with ovarian cysts using the Ovsynch protocol.

EFFECTS OF PARENTAL FACTORS AND MEIOSIS ON SEXUAL OFFSPRING OF GYMNODINIUM NOLLERI (DINOPHYCEAE)1

Clonal strains of the dinoflagellate Gymnodinium nolleri Ellegaard and Moestrup were intercrossed to determine if cyst‐related traits are genetically regulated and to clarify unknown aspects in the sexuality of this species. The objectives were to determine whether the parental identity influenced the physiological and morphological aspects of the cyst offspring, and to describe and compare nuclear development and cell division of encysting and non‐encysting zygotes. Variables characteristic of each parental cross (difference in growth rates among parents, cyst production (CP), and genetic distance (GD) among parents assessed via an amplified fragment length analysis analysis) were studied to seek for possible relationships of the parental crosses with some characteristics of the cyst offspring (cyst size, length of dormancy period, germination success, and germling viability (V)). A principal component analysis using these variables showed three main results: (1) the dormancy period of cysts responded to a simple pattern of inheritance, (2) the larger the GD between parents, the smaller the CP, and progeny V, and (3) the size of cysts was influenced by both CP and the parental strain identity. A stable inheritance of the short dormancy period (14.6±5.5 days), dominant over medium (31.0±8.5 days) and long periods (52.7±9.2 days), was confirmed through two subsequent generations of cysts. The regulation of the sexual processes by a multiple loci system is discussed based on the pattern of inheritance of the dormancy period and the number of sexual recombination events recorded within cultures with self‐CP capability. Fusion of the gamete nuclei happened 0–48 h after the total cytoplasmic fusion. The nucleus of the zygote was bilobed and had thick and distinct chromosomes. Similar processes of nuclear and cell division occurred in the non‐encysting or encysting planozygote, and were characterized by the loss of the chromosomal structure, an apparent increase of the DNA content, and the formation of thinner chromosomes.