Ultrastructure and anaerobic metabolism of mitochondria in the marine oligochaete Tubificoides benedii : effects of hypoxia and sulfide

It has often been suggested that ultrastructural properties of mitochondria are correlated with oxygen and sulfide levels from the environment, although careful analyses of this question are rare. In this study the ultrastructure and distribution of mitochondria in Tubificoides benedii, a marine oligochaete from sulfide-rich sediments, were investigated after a series of oxic, hypoxic and hypoxic–sulfidic (200 μM H₂S) incubations up to 24 h. Succinate, one of the key endproducts of an anaerobic metabolism, was used as an indicator of mitochondrial anaerobiosis. Consistent differences in mitochondrial ultrastructure were not observed in any of the incubations, even after 24 h. Stereological parameters of mitochondria (volume density, surface density of the outer mitochondrial membrane, and specific surface) in epidermal and intestinal tissues of T. benedii were not affected by hypoxia or sulfide either. On the other hand, succinate concentrations increased significantly within 24 h under hypoxic and hypoxic–sulfidic conditions. Thus, experimental hypoxia and sulfide clearly caused mitochondrial anaerobiosis without affecting ultrastructure or distribution of mitochondria in T. benedii. Distinct differences in ultrastructural and stereological parameters were common between different tissues and between individuals, showing that different forms of mitochondria can occur within one species. Our results imply that a mitochondrial ultrastructure specific to thiobiotic animals does not appear to exist. Received: 4 August 1996 / Accepted: 20 September 1996     

Association of <Emphasis Type="Italic">Waminoa</Emphasis> sp. (Acoela) with corals in the Wakatobi Marine Park,South-East Sulawesi,Indonesia

This is the first quantitative study on the prevalence of epizoic Waminoa sp. acoel worms and their association with corals in the Wakatobi Marine National Park (WMNP), South-East Sulawesi, Indonesia. Three replicate transects were laid on the reef crest, flat and slope at six sites in 2006 and eight sites in 2007. Four of the sites were common in both years. In total 69 transects were surveyed in 2006, and 87 transects in 2007. A total of 4.8% of all observed hard corals were associated with acoel worms in 2006 and 2.6% of hard and soft corals in 2007. Acoels were present on 16 and 21 of the coral taxa studied in 2006 and 2007 respectively. The worms were strongly associated with the azooxanthellate coral Tubastrea spp. and were rare or absent on the most abundant coral genera Montipora and Porites. The mean number of corals having acoels was highest on reef slopes, whereas acoels were virtually absent on reef flats. Corals that had a high and a medium cover of worms were more common in 2007 than in 2006. No significant trend in the adaptation of the zooxanthellae of Waminoa sp. to different depths at different sites was revealed. The impact of the worm on the coral is unknown, but high numbers may have a shading effect and a negative impact on the coral’s photophysiology. This acoel merits more study of its life cycle, its photophysiology, and its impact on its host corals. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Mitochondrial plasticity in brachiopod (Liothyrella spp.) smooth adductor muscle as a result of season and latitude

Habitat temperature and mitochondrial volume density (Vv_(mt,mf)) are negatively correlated in fishes, while seasonal acclimatization may increase Vv_(mt,mf) or the surface density of the mitochondrial cristae (Sv_(im,mt)). The effect of temperature on invertebrate mitochondria is essentially unknown. A comparison of two articulate brachiopod species, Liothyrella uva collected from Rothera Station, Antarctica in summer 2007, and Liothyrella neozelanica collected from Fiordland, New Zealand in winter 2007 and summer 2008, revealed a higher Vv_(mt,mf) in the Antarctic brachiopod. The Sv_(im,mt) was, however, significantly lower, indicating the Antarctic brachiopods have more, less reactive mitochondria. L. uva, from the colder environment, had larger adductor muscles in both absolute and relative terms than the temperate L. neozelanica. Furthermore, a seasonal comparison (winter vs. summer) in L. neozelanica showed that the absolute and relative size of the adductor increased in winter, Vv_(mt,mf) was unchanged, and Sv_(im,mt) was significantly increased. Thus, seasonal acclimatization to the cold resulted in the same number of more reactive mitochondria. L. neozelanica was clearly able to adapt to seasonal changes using a different mechanism, i.e. primarily through regulation of cristae surface area as opposed to mitochondrial volume density. Furthermore, given the evolutionary age of these living fossils (i.e. approximately 550 million years), this suggests that mitochondrial plasticity has roots extending far back into evolutionary history.     

Ultrastructure of pedal muscle as a function of temperature in nacellid limpets

Temperature and mitochondrial plasticity are well studied in fishes, but little is known about this relationship in invertebrates. The effects of habitat temperature on mitochondrial ultrastructure were examined in three con-familial limpets from the Antarctic (Nacella concinna), New Zealand (Cellana ornata), and Singapore (Cellana radiata). The effects of seasonal changes in temperature were also examined in winter and summer C. ornata. Stereological methods showed that limpet pedal myocytes were 1–2 orders of magnitude smaller in diameter (≈3.5 μm) than in vertebrates, and that the diameter did not vary as a function of temperature. Mitochondrial volume density (Vv_(mt,f)) was approximately 2–4 times higher in N. concinna (0.024) than in the other species (0.01 and 0.006), which were not significantly different from each other. Mitochondrial cristae surface density (Sv_(im,mt)) was significantly lower in summer C. ornata (24.1 ± 0.50 μm² μm⁻³) than both winter C. ornata (32.3 ± 0.95 μm² μm⁻³) and N. concinna (34.3 ± 4.43 μm² μm⁻³). The surface area of mitochondrial cristae per unit fibre volume was significantly higher in N. concinna, due largely to the greater mitochondrial volume density. These results and previous studies indicate that mitochondrial proliferation in the cold is a common, but not universal response by different species from different thermal habitats. Seasonal temperature decreases on the other hand, leading preferentially to an increase in cristae surface density. Stereological measures also showed that energetic reserves, i.e. lipid droplets and glycogen in the pedal muscle changed greatly with season and species. This was most likely related to gametogenesis and spawning.     

Ultrastructure effects of omethoate and cypermethrin insecticides on maize seedlings

Increasing studies suggest that insecticides are one of the plant stress elements that affect plant growth and productivity by interfering with cell metabolic and biochemical activities. Here, we show that the application of commonly used pesticides omethoate and cypermethrin on maize (Zea mays L. cv. Luyu 9) seedling leaves resulted in adverse effects on leaf ultrastructure changes under laboratory conditions. Electron microscopic studies reveal that the topical application of organophosphorus insecticide omethoate causes direct injury of leaf ultrastructures including cell wall breakdown of abaxial epidermis cells, inner cells, stomata guard cells; degradation of mitochondrial membrane, and chloroplast envelope membrane; and abnormal changes of lamella arrangement of chloroplast. And the topical application of cypermethrin insecticide causes plasmolysis of cells of the adaxial epidermis, mitochondrial cristae are degraded, and loosen arranged lamella of amyloplasts. All these changes indicated that omethoate and cypermethrin are stress factors that caused adverse effects on plant ultrastructures and biochemical molecules.     

Toxicity of 4-methylimidazole on isolated brain mitochondria: using both in vivo and in vitro methods

4-methylimidazole (4MI) is a compound widely used in various industrial and consumer applications. The most important sources of exposure include chemical caramel coloring, ammoniated molasses, dyes and pigments, rube, cleaning and agricultural chemicals. Toxicity attributed to 4MI in foods has recently become a focus of research. Recent studies showed that 4MI induced adverse changes in various target tissues. Brain is known to be a target organ for 4MI-induced toxicity but its cytotoxic mechanisms have not yet been elucidated. In this study, experiments were divided into two parts: (1) using in vivo methodology, doses of 4MI at 100, 200, or 300 mg/kg were administered orally to mice daily for 14 to obtain brain mitochondria; and (2) utilizing in vitro methodology, brain mitochondria were incubated with 4MI at 400, 800, or 1600 μM concentrations. Subsequently, the neurotoxicity of 4MI was assessed using mitochondrial dysfunction tests, including reactive oxygen species (ROS) formation, mitochondrial membrane potential (MMP) collapse, mitochondrial swelling, and cytochrome c release. Our results from both in vivo and in vitro experiments on isolated brain mitochondria showed a significant decrease in complex II activity and also marked elevation in the ROS formation, MMP collapse, mitochondrial swelling, and enhanced release of cytochrome c. Data indicated that 4MI induced neurotoxicity through the impairment of electron transfer chain especially at complex II and elevated ROS formation leading to subsequent oxidative stress events including mitochondrial membrane depolarization, mitochondrial swelling, and release of cytochrome c, which is the starting point of mitochondrial-mediated apoptosis signaling and neurodegeneration.     

Comparison of liver mitochondrial membranes from an agnathan (Myxine glutinosa), an elasmobranch (Raja erinacea) and a teleost fish (Pleuronectes americanus)

The membranes of elasmobranch liver mitochondria differ substantially from those of other marine fish. Although the proportions of the major phospholipids in elasmobranch mitochondria are similar to those of other marine fish, there are considerable differences in the fatty acid content of the phospholipids. Specifically, the percentage of saturated fatty acids is much higher, the polyunsaturated fatty acid content is much lower and the chain length is shorter than is typical of other non-urea retaining fishes. The tissues of elasmobranch fishes are unusual in that they contain the chaotropic agent urea at levels that are capable of disrupting the hydrophobic interactions responsible for membrane integrity. The mitochondrial membrane properties of the elasmobranch are consistent with those needed to maintain membrane integrity in the presence of physiological amounts of urea and indicate membrane adaptation to urea. Present address: INRS eau 2800 Rue Einstein, suite 105 Case Postale, 7500, Sainte Foy, Quebec G1V 4C7 Canada     

Diversity of free-living marine nematodes (Enoplida) from Baja California assessed by integrative taxonomy

We used morphological and molecular approaches to evaluate the diversity of free-living marine nematodes (order Enoplida) at four coastal sites in the Gulf of California and three on the Pacific coast of Baja California, Mexico. We identified 22 morphological species belonging to six families, of which Thoracostomopsidae and Oncholaimidae were the most diverse. The genus Mesacanthion (Thoracostomopsidae) was the most widespread and diverse. Five allopatric species, genetically and morphologically differentiated, were found in two localities in the Gulf of California (M. sp1 and M. sp2) and three in the Pacific coast (M. sp3, M. sp4 and M. sp5). Overall, we produced 19 and 20 sequences for the 18S and 28S genes, respectively. Neither gene displayed intraspecific polymorphisms, which allowed us to establish that some morphological variation was likely either ontogenetic or due to phenotypic plasticity. Although 18S and 28S phylogenies were topologically congruent (incongruence length difference test, P > 0.05), divergences between species were much higher in the 28S gene. Moreover, this gene possessed a stronger phylogenetic signal to resolve relationships involving Rhabdodemania and Bathylaimus. On the other hand, the close relationship of Pareurystomina (Enchilidiidae) with oncholaimids warrants further study. The 28S sequences (D2D3 domain) may be better suited for DNA barcoding of marine nematodes than those from the 18S rDNA, particularly for differentiating closely related or cryptic species. Finally, our results underline the relevance of adopting an integrative approach encompassing morphological and molecular analyses to improve the assessment of marine nematode diversity and advance their taxonomy.     

Paralytic shellfish toxins sequestered by bivalves as a defense against siphon-nipping fish

Saxidomus giganteus (butter clams), are known to sequester diet-derived paralytic shellfish toxins (PST), highly potent neurotoxins, in their siphons. Captive staghorn sculpins (Leptocotus armatus), a marine fish species known to crop bivalve siphons, developed a significant aversion to siphons from toxic but not non-toxicS. giganteus following a single conditioning feeding of toxic siphon tissues. Control fish showed no aversive response to siphons from non-toxicS. giganteus during 11 feeding sessions over 56 d. Aversive and non-aversive behavior varied with the toxicity of the siphons, but not with the geographic origin of the clams. Both experimental and control fish ate freely and showed no aversion to siphons from toxic littleneck clams (Protothaca staminea). Littleneck clams, unlikeS. giganteus, retain PST in their visceral mass but not in their siphons. Both toxic and non-toxicS. giganteus extended their siphons significantly more often and higher above the sediment surface during dark hours, but toxicS. giganteus extended their siphons higher than non-toxic individuals. These results support the hypothesis that siphon-nipping by fish may have selected for the retention of PST in butter clam siphons as a chemical defense.     

Present-day genetic composition suggests contrasting demographic histories of two dominant chaetognaths of the North-East Atlantic, <Emphasis Type="Italic">Sagitta elegans</Emphasis> and <Emphasis Type="Italic">S. setosa</Emphasis>

Sagitta elegans and S. setosa are the two dominant chaetognaths in the North-East (NE) Atlantic. They are closely related and have a similar ecology and life history, but differ in distributional ranges. Sagitta setosa is a typical neritic species occurring exclusively above shelf regions, whereas S. elegans is a more oceanic species with a widespread distribution. We hypothesised that neritic species, because of smaller and more fragmented populations, would have been more vulnerable to population bottlenecks resulting from range contractions during Pleistocene glaciations than oceanic species. To test this hypothesis we compared mitochondrial Cytochrome Oxidase II DNA sequences of S. elegans and S. setosa from sampling locations across the NE Atlantic. Both species displayed very high levels of genetic diversity with unique haplotypes for every sequenced individual and an approximately three times higher level of nucleotide diversity in S. elegans (0.061) compared to S. setosa (0.021). Sagitta setosa mitochondrial DNA (mtDNA) haplotypes produced a star-like phylogeny and a uni-modal mismatch distribution indicative of a bottleneck followed by population expansion. In contrast, S. elegans had a deeper mtDNA phylogeny and a multi-modal mismatch distribution as would be expected from a more stable population. Neutrality tests indicated that assumptions of the standard neutral model were violated for both species and results from the McDonald-Kreitman test suggested that selection played a role in the evolution of their mitochondrial DNA. Congruent with these results, both species had much smaller effective population sizes estimated from genetic data when compared to census population sizes estimated from abundance data, with a factor of ~10⁸–10⁹ difference. Assuming that selective effects are comparable for the two species, we conclude that the difference in genetic signature can only be explained by contrasting demographic histories. Our data are consistent with the hypothesis that in the NE Atlantic, the neritic S. setosa has been more severely affected by population bottlenecks resulting from Pleistocene range shifts than the more oceanic S. elegans.     

Direct toxicity of amyloid beta peptide on rat brain mitochondria: preventive role of Mangifera indica and Juglans regia

Role of mitochondrial dysfunction and oxidative stress has been well documented in various cognitive-related disorders such as Alzheimer's disease (AD). Evidence indicates that Aß formation impairs mitochondrial function and that mitochondrial dysfunction is an early event in the pathogenesis of AD. The present study was, therefore, designed to investigate the direct toxicity of Aß peptide on isolated mitochondria obtained from rat brain. Various mitochondrial toxicity/integrity parameters such as succinate dehydrogenase activity, reactive oxygen species (ROS) formation, mitochondrial membrane potential collapse (MMP), mitochondrial swelling, and cytochrome c release were measured following the addition of Aß peptide on isolated mitochondria and then, mitoprotective effect of aqueous extracts of Mangifera indica and Juglans regia against mitochondrial toxicity endpoints parameters induced by Aß peptide were assessed. Our results showed that exposure to Aß peptide (30 nM) in isolated brain mitochondria induced mitochondrial ROS formation, MMP collapse, mitochondrial swelling, and cytochrome c release which is the starting point of apoptosis signaling. All these mitochondrial toxic endpoints induced by Aß peptide inhibited by aqueous extracts of Mangifera indica (100–400 µg/ml) and Juglans regia (200–400 µg/ml). To our knowledge, this is one of the first apparent studies to claim directly targeting of brain mitochondria and induction of apoptosis by Aß peptide as a new hypothesis for etiology of AD and other related neurodegenerative diseases as well as mitopreventive role of common antioxidant nutritional products including walnut and mango.     

Spermatozoan ultrastructure and spermatogenesis in aplousobranch ascidians,with some phylogenetic considerations

Spermatozoa and some stages of spermatogenesis were studied for four species of aplousobranch ascidians. Spermatozoa of Clavelina lepadiformis (Müller) (family Clavelinidae) are plesiomorphous in that they have apical acrosomal vesicles and a moderately elongated, cylindrical nucleus. The elongated mitochondrion is twisted ea. 11/2 times around the nucleus. In their ultrastructural morphology, C. lepadiformis sperm conform in some respects to the least-derived ascidian sperm, those of the phlebobranch ascidian Ciona intestinalis L.; however, the sperm of Clavelina lepadiformis have two apomorphies not shared with those of Ciona sp.: (1) the mitochondrion of Clavelina lepadiformis is long and spiralled along the entire nucleus rather than being comparatively compact and not at all helical; (2) the mitochondrial cristae are elongated parallel to the long axis of the nucleus, whereas in Ciona sp. sperm the cristae are unmodified. In Distaplia sp., Aplidium sp. and Synoicum pulmonaria (Ellis and Solander) the spermatozoa are more derived and consist of a proximal cylindrical and a distal corkscrew-like part. The mitochondrion in Distaplia sp. and Aplidium sp. contains electron-dense material and extends in a long thread around the nucleus. In S. pulmonaria the mitochondrion surrounds the anterior part of the nucleus in mature spermatozoa, and an elongated, dense structure displaying fine striation is enclosed in the mitochondrion in late spermatids. The sperm ultrastructural morphology observed in this study is consistent with the majority view that clavelinids are closest to the ancestral ascidian but is also consistent with other conclusions, particularly that the Cionidae are closest to the stem ascidian.     

Food selectivity of the rotifer Brachionus plicatilis feeding on phytoplankton

Food selectivity was examined in amictic female rotifers, Brachionus plicatilis, fed Chlamydomonas sp. and Olisthodiscus sp. Filtering and ingestion rates of the rotifers in a single food suspension were higher with Chlamydomonas sp. than with Olisthodiscus sp. In every mixture of two food species, the apparent filtering rate on Chlamydomonas sp. was much higher than that on Olisthodiscus sp. Total filtering rate and apparent filtering rate in food suspensions containing Chlamydomonas sp. decreased with increasing cell concentration of Chlamydomonas sp. Total and apparent filtering rates were calculated from the decrease in total food concentration as well as from decreases in concentrations of each of the two food algae, respectively. B. plicatilis ingested Olisthodiscus sp. at an extremely low constant rate in all mixtures. The degree of food selectivity of the rotifers fed Chlamydomonas sp. (i.e., selective filtration) from the mixture of two food algae decreased with increasing cell concentration of Chlamydomonas sp. Filtering and ingestion rates of rotifers fed senescent Chlamydomonas sp. were relatively lower than those fed Chlamydomonas sp. in the exponential phase. This indicates that Brachionus plicatilis displays selectivity in regard to condition of cells as well as type of food.     

Effects of various diets on the nutritional value of Artemia sp. as food for the prawn Penaeus monodon

The nutritional value of Artemia sp. as food for marine fish and crustacean larvae has been linked to the level of its polyunsaturated fatty acid (PUFA) content. Experiments in August 1984 were conducted to determine the effects of various artificial diets and algae on fatty acid composition of PUFA-deficient Artemia sp. (Utah GSL strain) and their resulting value as food for postlarvae of the prawn Penaeus monodon (Fabricius). Nauplii of the brine shrimp were grown on extracts of corn, copra, soybean and rice bran containing precursors (C18) to long-chain PUFA and also on algal species containing different levels of long-chain PUFA (C20). The nauplii were then used as food for P. monodon postlarvae. The results revealed that absence of C20 polyunsaturates from the feeds and their presence in the algae were reflected in the polyunsaturated fatty acid content of the tissues of Artemia sp. When fed with brine shrimp fed on algae, P. monodon displayed better postlarval survival and significantly higher growth; related to the content of polyunsaturated fatty acids in Artemia sp. A practical feeding approach in prawn hatcheries would be to grow Artemia sp. on a cheap diet such as rice bran, and then to enhance its nutritional value with a diet high in PUFA prior to harvesting, in order to improve hatchery production.     

<Emphasis Type="Italic">Sympagohydra tuuli</Emphasis> (Cnidaria,Hydrozoa): first report from sea ice of the central Arctic Ocean and insights into histology,reproduction and locomotion

Various cnidarians have adapted their life style to interstitial habitats of marine sediments. Recently, for the first time a hydroid was reported from the interstitial brine channel system of Arctic fast ice. Due to its derived features, the new genus and species Sympagohydra tuuli was introduced. Here we describe findings of S. tuuli in sea ice at several sites within the central Arctic Ocean. In our view the results of this study do not allow assignment of Sympagohydra to any known family and we, therefore, suggest the introduction of a new family Sympagohydridae which is placed within the hydrozoan subclass Hydroidolina, order Anthomedusae, suborder Capitata. A first detailed histological analysis of S. tuuli is presented. In vivo analysis of locomotion and reproduction revealed a remarkable convergent evolution in S. tuuli and distant meiobenthic relatives. Shared traits are a flagellated epidermis enabling the animals to glide within small interstices by means of flagellar beating as well as an internalised embryogenesis. In S. tuuli gametogenesis occurs in the absence of gonophores inbetween gastro- and epidermis clearly separated from the epidermis. Budding was observed as the vegetative mode of reproduction. Documentation of feeding behaviour identified copepod nauplii and rotifers as prey items and demonstrates a high trophical position of the hydroids within the sympagic food web. Occurrence of reproducing individuals and pronounced tolerances towards changing temperatures and salinities indicate S. tuuli as a truly sympagic species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>–ATPase activity and gill ultrastructure in the hyper-hypo-regulating crab<Emphasis Type="Italic"> Chasmagnathus granulatus</Emphasis> acclimated to dilute,normal, and concentrated seawater

We studied Na⁺/K⁺ –ATPase activity and ultrastructure in gills of the hyper-hypo-regulating crab Chasmagnathus granulatus Dana, 1851 acclimated to different salinities: 10, 30 and 45, known to be hypo-, iso-, and hyper-osmotic to the hemolymph, respectively. After centrifugation of homogenates at 11,000 g, Na⁺/K⁺–ATPase activity was almost entirely found in the pellets from the posterior (6–8) and anterior (3–5) gills, whereas very little was detected in the supernatant liquid. Specific activity of gill 6 was 41.3, 30.2, and 28.2 µmol Pi h^–1 mg prot^–1 for crabs acclimated to 10, 30, and 45, respectively, the result for 10 being significantly higher than those at 30 and 45. Although the concentration of sodium at which the reaction rate is half-maximal (K _M) was similar in the three acclimation salinities, only the enzyme from crabs acclimated to 10 was inhibited by high sodium concentration. Specific activity of gill 5 increased with the increment in external salinity (10.1, 15, and 18.1 µmol Pi h^–1 mg prot^–1 for 10, 30, and 45, respectively), the only significant difference being that between the extreme salinities. The epithelium thickness of the dorsal portion of gill 6 showed a variation among salinities: 21.7, 15.8 and 17.2 µm for 10, 30 and 45, respectively. There were significant differences in epithelium thickness between the 10 and the other salinities. In all three salinities, the ultrastructure of gill 6 epithelium showed a high density of mitochondria, estimated by their volume fraction (Vv _m=0.307–0.355). These mitochondria were packed between extensive basolateral membrane interdigitations in ionocytes and pillar cells. Gill 5 showed three cell types: pillars which possess mitochondria packed between membrane folds only in their interdigitations with neighbouring cells; type-I cells 8.0 µm thick with low density of mitochondria (Vv _m=0.088), and type-II cells, 9.9 µm thick and rich in mitochondria (Vv _m=0.423), but lacking basolateral interdigitations. Vv _m of type-I cells of gill 5 was significantly lower than those of type-II cells of the same gill and the ionocytes of gill 6. No significant difference in Vv _m was detected between the latter cell types.Communicated by P.W. Sammarco, Chauvin     

Phylogenetic relationships of the intercellular fish pathogenIchthyophonus hoferi and fungi,choanoflagellates and the rosette agent

Ichthyophonus hoferi Plehn and Mulsow, 1911 is thought to be one of the few pathogenic fungal infections of marine fish. The result of an attack is severe epizootics in herring stocks with drastic reduction in the population as a consequence. The exact phylogenetic position of the genusIchthyophonus is not known. In the present study, a combination of molecular data, ultrastructure and biochemical characters were utilized to investigate the phylogeny ofI.hoferi. The genomic DNA encoding the small subunit ribosomal RNA (18S rRNA) was amplified and sequenced. Comparisons with other eukaryotic 18S rRNA sequences indicate thatI. hoferi is not a member of the Fungi. In both the parsimony and the neighborjoining trees,I. hoferi is the sister taxon to the rosette agent. The clade encompassingI.hoferi and the rosette organism is the sister group to the chanoflagellate clade in the neighbor-joining tree, while in the parsimony tree theI. hoferi/rosette clade is equally distant to both the choanoflagellate and animal clades. Transmission electron microscopy showed thatI. hoferi has a defined cell wall, an endoplasm that consists of a fine granulated matrix with numerous ribosomes, several nuclei, vacuoles of varying density distributed throughout the cell, and mitochondria with tubular cristae. The cell wall ofI. hoferi contains chitin.     

Why do female Belding's ground squirrels disperse away from food resources?

We examined the effects of food provisioning on the natal dispersal behavior of Belding's ground squirrels (Spermophilus beldingi). We provided extra food to adult and yearling females in their maternal territories during pregnancy and lactation, and to offspring of these females in their natal areas for 6 weeks after weaning. We used unprovisioned young of unprovisioned mothers as controls. Provisioning influenced the probability of dispersal from the natal area by female but not male S. beldingi. All surviving male S.␣beldingi dispersed by 55 weeks of age, regardless of whether they and their mothers received extra food. By contrast, we observed a significant trend, beginning 3 weeks after weaning and continuing through the yearling year, for a greater proportion of provisioned than control female S. beldingi to emigrate from the natal area. Competition for food did not appear to influence natal dispersal of females. However, overall population density, density of females weaning litters, and rates of aggression and vigilance among these females, were higher in provisioned than control areas, suggesting that competition for non-food resources was unusually intense in provisioned areas. We propose that juvenile female, but not juvenile male, S. beldingi may emigrate from the natal site to increase access to areas with low densities of conspecifics. Together with findings of earlier workers, our results suggest that spatial and temporal distributions of environmental resources are important influences on the dispersal behavior of female ground squirrels. Received: 28 February 1996 / Accepted after revision: 16 October 1996     

Interactions during feeding among certain coral reef fishes in Elat

From July 1983 to March 1984 coral reef fishes in Elat (Red Sea) were fed in novel feeding situations. Thalassoma rüppelli had the shortest latency to first feed, Chaetodon paucifasciatus had the longest latency, while Sufflamen albicaudatus, Coris aygula and Lethrinus sp. had intermediate latencies. The mean number of T. rüppelli feeding at the beginning of experiments was higher than that of the other species. The difference decreased rapidly and disappeared within 90 s of the beginning. Latencies to first feed, and the number of fish feeding, were not correlated with the number of fish of each species in the study area. Aggression was directed predominantly by S. albicaudatus and by C. aygula towards Lethrinus sp. and T. rüppelli. It is suggested that these species which suffer more disturbances during their feeding and which receive more aggression are more likely to approach and feed more quickly in novel feeding situations.     

A mechanism of “red-tide” formation

Three semi-continuous culture experiments were conducted by using natural algal populations [dominants: Skeletonema costatum, Thalassiosira sp., Gymnodinium sp., Heterosigma sp. (formerly called Olisthodiscus luteus) and Eutreptiella sp.] collected from Tanigawa Harbor, Japan, where red-tides occurred occasionally. The effects of macro- and micro-nutrients onto the growth of different species of algae were specifically evaluated by a dialysis bag culture technique. Two types of responses for nutrients were clearly observed; macro- and micro-nutrient dependency. The former group includes S. costatum, Thalassiosira sp. and Eutreptiella sp. which mainly stimulated their growth by macro-nutrients. Heterosigma sp. was in the latter group which was stimulated by micronutrients. Gymnodinium sp. showed an intermediate type. A red-tide of Heterosigma sp. formed during the experiment in the harbor and is discussed with the results of the present culture experiments and some field observations.