The role of amino acids in phagostimulation in the shallow-water omnivorous Antarctic sea star Odontaster validus

Experiments were carried out to study the behavioural responses of the omnivorous Antarctic sea star Odontaster validus to natural food odour, several single amino acids and their mixtures. Starved sea stars responded to natural food stimulus by rapid rise of metabolic rate, locomotory activity directed towards signal source, cessation of movement after reaching it and initiation of feeding. All single amino acids that were tested were detected by experimental animals, although there were marked differences in the sea stars reaction to them. Amino acids with narrow and broad scope of influence were distinguished, with glutamic acid being the most potent sea star stimulant. It was also found that the same sea star reaction (e.g. metabolic rate increase or locomotory activity) can be caused by several different amino acids. The effects of amino acid mixtures were significantly stronger than that of single amino acids, with >80% of animals reaching signal source. O. validus seems well adapted to using both single and complicated food signals in its foraging behaviour.     

Feeding repellence of Antarctic and sub-Antarctic benthic invertebrates against the omnivorous sea star Odontaster validus

Antarctic and sub-Antarctic benthic invertebrates are subjected to intense predation by mobile macroinvertebrates. Accordingly, chemical protection as well as other defensive mechanisms are expected to be common in organisms inhabiting these ecosystems. In order to evaluate anti-predation activities and allocation of chemical defenses within the anatomy of marine benthic Antarctic and sub-Antarctic invertebrates, 55 species were tested for feeding repellence against the sea star Odontaster validus, a common eurybathic sympatric predator. The invertebrates tested were collected from the deep waters of two poorly surveyed areas in terms of chemical ecology studies: the eastern Weddell Sea (Antarctica) and the vicinities of Bouvet Island (sub-Antarctica). Experiments were conducted at the Spanish Antarctic Base in Deception Island. In the feeding deterrence experiments, shrimp pieces were treated with crude lipophilic fractions obtained from each species, and were offered to the sea stars. A total of 29 species (53 %) from 7 different phyla (Porifera, Cnidaria, Chordata, Bryozoa, Echinodermata, Mollusca, and Annelida) showed feeding repellence against O. validus, and are therefore chemically protected against this keystone predator. Furthermore, 25 species were dissected into parts to investigate the possible allocation of defensive compounds. Some of the results obtained from these analyses support the prediction that the most exposed/vulnerable tissues concentrate chemical defenses to avoid predation against the sea stars. In summary, the results obtained in our survey support the hypothesis that deep-water Antarctic and sub-Antarctic benthic invertebrates are well protected chemically against sympatric predators, similarly to what has been reported in previous studies investigating shallow-water Antarctic species.     

Behavioural and metabolic responses of the Antarctic sea star Odontaster validus to food stimuli of different concentration

Experiments were carried out to study the behavioural and metabolic responses of the Antarctic sea star, Odontaster validus, to different concentration of food signals (glutamic acid, aspartic acid, glicyne, alanine, tyrosine and a mixture of 11 amino acids). Stimulus concentration increase caused a rise in both the percentage of reacting animals and in the reaction intensity. At low stimulus concentration, O. validus reaction consisted of tube foot waving, and only high concentrations elicited a complicated sequence of several types of behaviour. The metabolic rate of small O. validus was more sensitive to chemical stimuli than of large individuals, with small sea stars reacting even to low signal concentration. It can be speculated that small body size can be a factor restricting sea star capabilities and influencing its reaction to chemical signals.     

First immunocytochemical study of echinoderm smooth muscle: the Antarctic cushionstar Odontaster validus Koehler (Echinodermata,Asteroidea)

Summary.  Our immunocytochemical observations reveal that the muscle present in the tips of the arms of the Antarctic cushionstar Odontaster validus contains caldesmon and calponin but not troponin. Thus, the muscle clearly belongs to the smooth muscle category. Distributions of contractile proteins such as actin, myosin (the latter a typical vertebrate muscle filament protein), paramyosin, and miniparamyosin (the latter two being characteristic of thick invertebrate muscle filaments) were also determined immunocytochemically. The results suggest that the thin filaments of the starfish smooth muscle are similar to those of the vertebrate muscle, but that the thick filaments differ from those of vertebrates and possess traits that are also seen in the muscle organization of invertebrates. The absence from the O. validus muscle of titin and nebulin, proteins so far known almost exclusively from the striated vertebrate muscle, comes as no surprise, but immunoreactivity to mini-titin (a protein of the same family as titin and its replacement in invertebrates) was strong and unambiguously recognizable between filaments. Odontaster validus' histochemical characteristics may be a reflection of the phylogenetic position of the echinoderms as deuterostome invertebrates or they may express an adaptation of the muscle to the harsh environmental conditions under which it has to function in the Antarctic water. Received June 6, 2002; accepted September 17, 2002; published online March 11, 2003     

Chemical Composition of the Antarctic Starfish Odontaster validus (Koehler 1911) and Its Reactions to Glutamic and Kynurenic Acids

The protein content in the dry body weight of the starfish Odontaster validus is 30%. The composition of amino acids is characterized by a very high level of glycine (27%). Glutamic acid (Glu) in a concentration of 10 mM/liter in seawater causes an increase in the metabolic rate of starved O. validus. As the period of starvation increases, this reaction is enhanced. A two-hour exposure to kynurenic acid (Kyn) in a concentration of 0.1 mM/liter blocks the reaction to glutamic acid.     

Parameter Estimations of Dynamic Energy Budget (DEB) Model over the Life History of a Key Antarctic Species: The Antarctic Sea Star Odontaster validus Koehler, 1906

Marine organisms in Antarctica are adapted to an extreme ecosystem including extremely stable temperatures and strong seasonality due to changes in day length. It is now largely accepted that Southern Ocean organisms are particularly vulnerable to global warming with some regions already being challenged by a rapid increase of temperature. Climate change affects both the physical and biotic components of marine ecosystems and will have an impact on the distribution and population dynamics of Antarctic marine organisms. To predict and assess the effect of climate change on marine ecosystems a more comprehensive knowledge of the life history and physiology of key species is urgently needed. In this study we estimate the Dynamic Energy Budget (DEB) model parameters for key benthic Antarctic species the sea star Odontaster validus using available information from literature and experiments. The DEB theory is unique in capturing the metabolic processes of an organism through its entire life cycle as a function of temperature and food availability. The DEB model allows for the inclusion of the different life history stages, and thus, becomes a tool that can be used to model lifetime feeding, growth, reproduction, and their responses to changes in biotic and abiotic conditions. The DEB model presented here includes the estimation of reproduction handling rules for the development of simultaneous oocyte cohorts within the gonad. Additionally it links the DEB model reserves to the pyloric caeca an organ whose function has long been ascribed to energy storage. Model parameters described a slowed down metabolism of long living animals that mature slowly. O. validus has a large reserve that—matching low maintenance costs- allow withstanding long periods of starvation. Gonad development is continuous and individual cohorts developed within the gonads grow in biomass following a power function of the age of the cohort. The DEB model developed here for O. validus allowed us to increase our knowledge on the ecophysiology of this species, providing new insights on the role of food availability and temperature on its life cycle and reproduction strategy.     

CO2 enrichment and reduced seawater pH had no effect on the embryonic development of Acropora palmata (Anthozoa,Scleractinia).

The effects of decreased pH, caused by carbon dioxide (CO₂) dissolution in seawater (known as ocean acidification (OA)), on the development of newly fertilized eggs of the Caribbean reef-building coral, Acropora palmata, was tested in three experiments conducted during the summers of 2008 and 2009 (two repeats). Three levels of CO₂ enrichment were used: present day conditions (400?µatm, pH 8.1) and two CO₂-enriched conditions (700?µatm, pH 7.9, and 1000?µatm, pH 7.7). No effects on the progression or timing of development, or embryo and larval size, were detected in any of the three experimental runs. The results show that the embryos and larvae of A. palmata are able to develop normally under seawater pH of at least 0.4 pH units lower than the present levels. Acropora palmata larvae do not usually begin to calcify after settlement, so this study only examined the non-calcifying part of the life cycle of this species. Most of the concern about the effects of OA on marine organisms centers on its effect on calcification. Negative effects of OA on the embryonic development of this species were not found and they may not manifest until the newly settled polyps begin to calcify.     

Effects of reduced salinities on development and bioenergetics of early larval shore crab, Carcinus maenas

The shore crab, Carcinus maenas L. (Portunidae), is a coastal and estuarine species, which can live and reproduce under brackish water conditions; freshly hatched larvae have been observed in the field at salinities below 15‰. In the present laboratory study, the tolerance of hypo-osmotic stress was experimentally investigated in early larvae of a marine (North Sea) population of C. maenas reared at four different salinities (15, 20, 25, 32‰). Two and 4 days after hatching, the Zoea I larvae were moult-staged microscopically, and their rates of respiration and growth (changes in dry weight, W, carbon, C, nitrogen, N, and hydrogen, H) were measured. Survival and development were monitored until the megalopa was reached: 15‰ did not allow for development beyond the first zoeal stage, while metamorphosis to the megalopa was reached at salinities ≥20‰. At 20‰, development was significantly delayed and mortality enhanced as compared with 25 and 32‰. Rates of growth and respiration decreased during exposure to reduced salinities ≤25‰. Hence, the suppression of growth could not be explained as a consequence of enhanced metabolic losses per larva. Instead, a partial C budget indicates that the Zoea I larvae suffered from decreased capabilities of assimilating ingested and subsequently converting assimilated matter to tissue growth. Net growth efficiency (K₂, C-based) was at 25 and 32‰ initially high (>60% during the postmoult and intermoult stages of the Zoea I moult cycle), but decreased during the later stages (down to ≤30% in premoult). An inverse pattern of C partitioning was observed at ≤20‰, with initially low K₂ values (≤21% during the first 2 days of the moult cycle), and a later increase (up to ≥46% in premoult). Thus, larval growth was initially suppressed under conditions of reduced salinity, but this was later (during premoult) partially compensated for by an increase in C assimilation and K₂. Our observations indicate that Zoea I shore crab larvae react during the late stages of their moulting cycle less sensitively against reduced salinities than during postmoult and intermoult. This suggests that the transition between moult cycle stages C and D₀ may be a critical point for effects of hypo-osmotic stress, similarly as already known in relation to effects of nutritional stress. Negative effects were found also when freshly hatched Zoea I shore crab larvae were exposed only transitorily (for 24–72 h) to 20‰, with significantly lower rates of survival, development, growth, respiration, and K₂. These effects increased with increasing duration of initial exposure to reduced salinity.     

Embryonic and larval development of a cold adapted Antarctic ascidian

Ova of the Antarctic ascidian Cnemidocarpa verrucosa were mature at 240–245 μm. At 0 to −1.5°C, embryos hatched as swimming tadpoles at 8 days from fertilization, which is close to the ages at which some Antarctic echinoderm and nemertean embryos hatch as blastulae. Comparisons of Antarctic and temperate ascidian larvae suggest that the ascidian’s development rate is affected by low environmental temperatures to about the same extent as embryos and larvae of an echinoid, nemertean, and calanoid copepods. The ascidian’s tadpoles were bright orange and large, >2 mm in length including tunic and >1.5 mm in length without tunic. The large and brightly colored tadpoles were conspicuous when swimming, which supports the hypothesis that larvae of C. verrucosa are chemically defended against predators. Metamorphosed juveniles were found in cultures within 16 days from fertilization, when some unsettled tadpoles still moved but were less active. The potential pelagic period may therefore be 16 or more days with 8 days as an unhatched embryo and up to 8 or more days as a tadpole. The resting metabolic rate of tadpole larvae was 15 pmol O₂ h⁻¹ individual⁻¹ which is equivalent to larval respiration rates in Antarctic echinoderms. A low resting metabolic rate suggests a potential mechanism for the extended larval lifespan in C. verrucosa.     

Comparative study of in vivo and in vitro phagocytosis including germicidal capacity in Odontaster validus (Koehler, 1906) at 0 degree C

The phagocytosis and germicidal capacity of Saccharomyces cerevisiae by phagocytic amoebocytes (PA) of the Antarctic starfish Odontaster validus were studied in vivo (after incubation periods of 1, 2, and 4 h) and in vitro (after incubation periods of 1, 2, 4, 8, and 12 h) at 0 degree C. The total number of PA and the phagocytic capacity (PC), phagocytic index (PI), and germicidal capacity (GC) of the PA were calculated. Results showed significant variability of the total PA number in different animals. There was a significant increase in PC and no significant differences in PI and GC for different in vitro incubation times. In vivo, experiments showed no significant difference of PC and PI, but there was a significant increase in GC as incubation periods increased. Comparison between in vitro and in vivo results revealed that PI and PC were significantly higher in vitro and that GC was significantly higher in vivo. The present study shows for the first time the phagocytosis and GC of an Antarctic invertebrate in vivo at low temperature (0 degree C), and the results are comparing with the available literature for echinoderms.     

Effects of crop rotation and reduced nitrogen fertilisation on Apera spica-venti populations in a long-term experiment

Apera spica-venti is one of the most serious annual grass weeds in Germany and may cause considerably yield losses in untreated fields. A long-term field experiment was conducted investigating the effects of crop rotation and nitrogen fertiliser use on A. spica-venti populations. A six-field cash-crop rotation with 67% winter cereals and a six-field fodder crop rotation with 50% winter cereals were studied. The rate of tillering was in the fodder crop rotation significantly higher than in the cash crop rotation. The halving of nitrogen fertilizer dose caused a significant increase in the tillering rate. Most plants of A. spica-venti emerged in winter wheat. There was an increase of emerged A. spica-venti in winter wheat from year to year.     

amontillado,the Drosophila homolog of the prohormone processing protease PC2, is required during embryogenesis and early larval development

Biosynthesis of most peptide hormones and neuropeptides requires proteolytic excision of the active peptide from inactive proprotein precursors, an activity carried out by subtilisin-like proprotein convertases (SPCs) in constitutive or regulated secretory pathways. The Drosophila amontillado (amon) gene encodes a homolog of the mammalian PC2 protein, an SPC that functions in the regulated secretory pathway in neuroendocrine tissues. We have identified amon mutants by isolating ethylmethanesulfonate (EMS)-induced lethal and visible mutations that define two complementation groups in the amon interval at 97D1 of the third chromosome. DNA sequencing identified the amon complementation group and the DNA sequence change for each of the nine amon alleles isolated. amon mutants display partial embryonic lethality, are defective in larval growth, and arrest during the first to second instar larval molt. Mutant larvae can be rescued by heat-shock-induced expression of the amon protein. Rescued larvae arrest at the subsequent larval molt, suggesting that amon is also required for the second to third instar larval molt. Our data indicate that the amon proprotein convertase is required during embryogenesis and larval development in Drosophila and support the hypothesis that AMON acts to proteolytically process peptide hormones that regulate hatching, larval growth, and larval ecdysis.     

Necator americanus: temperature, pH, light, and larval development, longevity, and desiccation tolerance

The effect of incubation temperature and pH on the hatch rate of eggs of Necator americanus, and the desiccation tolerance of the resulting infective stage-3 larvae were investigated in the laboratory under controlled conditions. Hatching did not occur below 15 C and above 35 C. A 21% hatch rate was obtained at 15 C while a 10.6% hatch rate was obtained at 35 C. The highest hatch rate (93.7%) was obtained at 30 C. The optimum pH for hatching was 6.0, but the larvae did not reach the infective stage. Incubation temperature of the eggs affected the longevity and desiccation tolerance of resultant infective larvae. Larvae hatched at 30 C and maintained at 26 C under bright fluorescent light had a 50% survival time (S50) of 4 days. In the dark or shade, the S50 for larvae raised at 30 C was 5 weeks, while that of larvae hatched at 20 C was 7 weeks. Incubation temperature also affected the desiccation tolerance of larvae. Larvae developed at 20 C were more resistant to desiccation at various relative humidity values than larvae hatched at 30 C.     

Effects of seawater ozonation on biofilm development in aquaculture tanks

Microbial biofilms developing in aquaculture tanks represent a reservoir for opportunistic bacterial pathogens, and procedures to control formation and bacterial composition of biofilms are important for the development of commercially viable aquaculture industries. This study investigated the effects of seawater ozonation on biofilm development on microscope glass slides placed in small-scale aquaculture tanks containing the live feed organism Artemia. Fluorescence in situ hybridization (FISH) demonstrated that ozonation accelerated the biofilm formation cycle, while it delayed the establishment of filamentous bacteria. Gammaproteobacteria and Alphaproteobacteria were the most abundant bacterial groups in the biofilm for both water types, but ozonation influenced their dynamics. With ozonation, the bacterial community structure was relatively stable and dominated by Gammaproteobacteria throughout the experiment (21–66% of total bacteria). Without ozonation, the community showed larger fluctuations, and Alphaproteobacteria emerged as dominant after 18 days (up to 54% of total bacteria). Ozonation of seawater also affected the dynamics of less abundant populations in the biofilm such as Betaproteobacteria, Planctomycetales and the Cytophaga/Flavobacterium branch of phylum Bacteroidetes. The abundance of Thiothrix, a bacterial genus capable of filamentous growth and fouling of larvae, increased with time for both water types, while no temporal trend could be detected for the genus Vibrio. Denaturing gradient gel electrophoresis (DGGE) demonstrated temporal changes in the dominant bacterial populations for both water types. Sequencing of DGGE bands confirmed the FISH data, and sequences were related to bacterial groups commonly found in biofilms of aquaculture systems. Several populations were closely related to organisms involved in sulfur cycling. Improved Artemia survival rates in tanks receiving ozonated water suggested a positive effect of ozonation on animal health. Although the used ozonation protocol did not hinder biofilm formation, the results suggest ozonation as a promising approach for manipulation of bacterial populations in aquaculture systems, which can prove beneficial for cultured animals.     

Effects of Pluronic F-68 on larval development of the hookworm,Necator americanus

Summary Eggs of the nematode,Necator americanus, were incubated at 28°C for up to 120h in medium (prepared from mouse faeces) supplemented with 0.4% (w/v) or 5% of either commercial grade or a silica-Amberlite purified fraction of the non-ionic surfactant, Pluronic F-68. Exposure to commercial grade or purified Pluronic at both concentrations delayed egg hatching. However, subsequent larval growth, as assessed by length of larva, buccal capsule, oesophagus and tail, was significantly (P<0.05) increased (maximally following exposure to 5.0% of the purified fraction). No further development occurred in larvae exposed to other Pluronic fractions tested after 48h, irrespective of concentration. These results suggest that Pluronic may be a valuable supplement in media used for the axenic culture of nematode larvae.     

幼虫密度对二点委夜蛾生长发育及繁殖的影响

【目的】在不同幼虫密度饲养条件下,研究二点委夜蛾Athetis lepigone生长发育及繁殖的情况,明确幼虫密度对该害虫的室内种群增长的影响。【方法】本实验设置5个幼虫饲养密度即1,5,10,20和30头/瓶(750 mL),分别观察5个饲养密度下该虫的各个龄期及整个幼虫发育历期及存活率、蛹重、蛹期以及成虫生殖情况。【结果】幼虫密度对该虫幼虫各龄期及整个幼虫发育历期及存活率、蛹重、蛹期以及成虫生殖情况均有显著性影响。整个幼虫发育历期随着密度的增加而缩短,10头/瓶达到最短(18.27 d),之后随着幼虫密度的增加而显著延长;幼虫至蛹的存活率随着密度增高而显著下降,30头/瓶最低(39.37%)。蛹期随着密度的增加而延长(10头/瓶除外)。蛹重和每雌产卵量均以1头/瓶最高,随着幼虫密度的增加而显著下降。雌雄蛾寿命均以10头/瓶最长,与1和5头/瓶没有显著性差异。生命表分析显示:二点委夜蛾的种群增长指数以5头/瓶最高,幼虫密度过低或者过高均不利于种群增长。【结论】幼虫密度是影响二点委夜蛾种群增长的重要因子之一。     

温度对中华虎凤蝶幼虫生存与生长发育的影响

本文就温度对中华虎凤蝶幼虫的生存与生长发育进行了研究。结果表明,１龄幼虫１６～３２℃范围内的死亡率无显著差异;２龄幼虫死亡率在３２℃下达３０．９２％,显著高于其它温度;３～５龄幼虫３２℃下全部死亡,其它温度下多以２８℃为高。１～２龄幼虫在１６～３２℃和３～５龄幼虫在１６～２８℃范围内的发育历期随温度升高而显著缩短,而平均发育速率则反之。用Ｗｅｉｂｕｌｌ分布函数能较好地拟合各龄幼虫的存活率曲线,并由此判断出各存活率曲线类型。此外,还测定了各龄幼虫的发育起点温度和有效积温。最后建议中华虎凤蝶１～２龄和３～５龄幼虫饲养适宜温度分别为２８℃和２０～２４℃。