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Different Life Stages (different + life_stage)
Selected AbstractsOcean transport paths for the early life history stages of offshore-spawning flatfishes: a case study in the Gulf of AlaskaFISH AND FISHERIES, Issue 1 2008Kevin M Bailey Abstract Offshore- and deepwater-spawning flatfish species face the problem of transport of their planktonic stages to shallow juvenile nursery grounds that are often far shoreward in bays or estuaries. We compare life history attributes of four offshore-spawning flatfish species in the Gulf of Alaska: Pacific halibut (Hippoglossus stenolepis), arrowtooth flounder (Atheresthes stomias), rex sole (Glyptocephalus zachirus) and Dover sole (Microstomus pacificus) to examine how their larvae get from a spawning location at the edge or beyond the continental shelf to specific inshore nursery zones. We utilize historical records of survey catches of different life stages to characterize the stage-specific changes in distribution of spawning, planktonic stages and juvenile nursery areas. We infer transport mechanisms based on the shifts in distribution of the life stages and in comparison with local physical oceanography. This comparison provides insight into the different mechanisms marine species may use to solve the common ,problem' of planktonic drift and juvenile settlement. [source] A NEW CELL STAGE IN THE HAPLOID-DIPLOID LIFE CYCLE OF THE COLONY-FORMING HAPTOPHYTE PHAEOCYSTIS ANTARCTICA AND ITS ECOLOGICAL IMPLICATIONS,JOURNAL OF PHYCOLOGY, Issue 5 2010Steffi Gaebler-Schwarz Few members of the well-studied marine phytoplankton taxa have such a complex and polymorphic life cycle as the genus Phaeocystis. However, despite the ecological and biogeochemical importance of Phaeocystis blooms, the life cycle of the major bloom-forming species of this genus remains illusive and poorly resolved. At least six different life stages and up to 15 different functional components of the life cycle have been proposed. Our culture and field observations indicate that there is a previously unrecognized stage in the life cycle of P. antarctica G. Karst. This stage comprises nonmotile cells that range in size from ,4.2 to 9.8 ,m in diameter and form aggregates in which interstitial spaces between cells are small or absent. The aggregates (hereafter called attached aggregates, AAs) adhere to available surfaces. In field samples, small AAs, surrounded by a colony skin, adopt an epiphytic lifestyle and adhere in most cases to setae or spines of diatoms. These AAs, either directly or via other life stages, produce the colonial life stage. Culture studies indicate that bloom-forming, colonial stages release flagellates (microzoospores) that fuse and form AAs, which can proliferate on the bottom of culture vessels and can eventually reform free-floating colonies. We propose that these AAs are a new stage in the life cycle of P. antarctica, which we believe to be the zygote, thus documenting sexual reproduction in this species for the first time. [source] What determines emergence and net recruitment in an early succession plant community?JOURNAL OF VEGETATION SCIENCE, Issue 4 2008Disentangling biotic, abiotic effects Abstract Question: How do different regeneration scenarios shape species composition at two stages of plant community establishment (emergence and net recruitment) in an early succession? Location: Northern Spain. Methods: In a recently ploughed field, we created eight regeneration scenarios with light, water and nitrogen availability (five replicates each). Seedlings of all species were monitored from emergence to death during one year. Abiotic and biotic variables were measured per quadrat, i.e. soil texture, nutrient contents, seed bank densities and composition, neighbour plant species densitiy and cover. We used partial ordination methods in order to separate the effect of each environmental variable on species composition during emergence and adult net recruitment. Results: Light treatment determined annual plant density at time of emergence and recruitment, while water addition controlled the recruitment of perennials. Resource levels explained the emerged species composition; this effect was not translated into the recruited species composition. N-addition and N + water addition were strongly associated to species abundances at the time of emergence. Seedling composition in summer was correlated with seed abundance of Cerastium spp. Neighbour species density and cover (mainly Arrhenatherum bulbosum, Agropyron repens and Picris echioides) explained significant fractions of species composition in the emergence and recruitment of the different cohorts. Interactions between species seem to vary in intensity among cohorts and in the key plant species that determined species abundance along succession. Conclusions: Our scenarios exerted contrasting and multilevel effects on the development of our early succession community. Resource availability differently affected plant density and species composition at different life stages. It is relevant to consider different life stages in plant community studies. However, regeneration conditions and other abiotic factors are not enough to explain how community composition varies. [source] Toxicity of plant essential oils to different life stages of the poultry red mite, Dermanyssus gallinae, and non-target invertebratesMEDICAL AND VETERINARY ENTOMOLOGY, Issue 1 2010D. R. GEORGE Seven essential oils with potential as acaricides for use against the poultry red mite, Dermanyssus gallinae (De Geer) (Acari: Dermanyssidae), were selected for study. These products (essential oils of manuka, cade, pennyroyal, thyme, garlic, clove bud and cinnamon bark) were deployed against different life stages of D. gallinae in laboratory tests at the (lethal concentration) LC50 level for adult mites. For all essential oils tested, toxicity to D. gallinae juveniles was as high as toxicity to adults, if not higher. However, at the LC50 level determined for adults, some oils were ineffective in preventing hatching of D. gallinae eggs. The essential oils were also tested under laboratory conditions at their LC90 levels for D. gallinae adults on two model non-target species, the brine shrimp, Artemia salina (L.), and the mealworm beetle, Tenebrio molitor (L.). Results showed that not all essential oils were as toxic to A. salina and T. molitor as they were to D. gallinae, suggesting that it may be possible to select certain oils for development as acaricides against D. gallinae that would have minimal impact on non-target organisms. However, the level of toxicity to A. salina and T. molitor was not consistent across the selected essential oils. [source] A combined proteomic and transcriptomic approach to the study of stage differentiation in Leishmania infantumPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 12 2006François McNicoll Abstract Protozoan parasites of the genus Leishmania are found as promastigotes in the sandfly vector and as amastigotes in mammalian macrophages. Mechanisms controlling stage-regulated gene expression in these organisms are poorly understood. Here, we applied a comprehensive approach consisting of protein prefractionation, global proteomics and targeted DNA microarray analysis to the study of stage differentiation in Leishmania. By excluding some abundant structural proteins and reducing complexity, we detected and identified numerous novel differentially expressed protein isoforms in L.,infantum. Using 2-D gels, over 2200,protein isoforms were visualized in each developmental stage. Of these, 6.1% were strongly increased or appeared unique in the promastigote stage, while the relative amounts of 12.4% were increased in amastigotes. Amastigote-specific protein isoform and mRNA expression trends correlated modestly (53%), while no correlation was found for promastigote-specific spots. Even where direction of regulation was similar, fold-changes were more modest at the RNA than protein level. Many proteins were present in multiple spots, suggesting that PTM is extensive in this organism. In several cases, different isoforms appeared to be specific to different life stages. Our results suggest that post-transcriptional controls at translational and post-translational levels could play major roles in differentiation in Leishmania parasites. [source] Development of the Insect Pathogenic Alga HelicosporidiumTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 3 2006VERENA-ULRIKE BLÄSKE-LIETZE ABSTRACT. This study examined the morphogenesis and replication dynamics of the different life stages (cysts, filamentous cells, vegetative cells) of Helicosporidium sp., a non-photosynthetic, entomopathogenic alga. The isolate (SjHe) used originated from an infected black fly larva. Filamentous cell transformation into vegetative cells and autosporulation during vegetative cell replication were observed under controlled in vitro conditions. The transformation process was initiated by a partial swelling of the filamentous cell along with the reorganization of the nuclear material. Two subsequent nuclear and cell divisions resulted in the release of 4 rod-shaped daughter cells, which divided into oval to spherical vegetative cells. These underwent several cycles of autosporogenic cell division. Multiple-passaged vegetative cell cultures formed non-motile, adherent cell clusters (palmelloid colonies). Vegetative replication dynamics were also observed in 2 experimental noctuid hosts, Spodoptera exigua and Helicoverpa zea. The average density of helicosporidial cells produced per microliter hemolymph exceeded cell concentrations obtained in vitro by 15- and 46-fold in S. exigua and H. zea, respectively. Cyst morphogenesis was only observed in the hemolymph, whereas no cysts differentiated at various in vitro conditions. [source] Assessment of demographic risk factors and management priorities: impacts on juveniles substantially affect population viability of a long-lived seabirdANIMAL CONSERVATION, Issue 2 2010M. E. Finkelstein Abstract Predicting population-level effects from changes in demographic rates of different life stages is critical to prioritize conservation efforts. Demographic modeling and sensitivity analysis in particular, has become a standard tool to evaluate how management actions influence species' survival. Demographic analyses have resulted in the robust generalization that, for long-lived species with delayed reproduction, population growth rates will be most sensitive to changes in survivorship of older-aged individuals. Although useful in guiding management, this simple maxim may limit options for conservation by causing managers to overlook actions that, although possibly not the most effective in terms of increasing a population's growth rate in an ideal world, can nonetheless more feasibly and rapidly slow a population's decline. We examine the population-level benefits of increasing chick survival in a long-lived seabird, the Laysan albatross Phoebastria immutabilis. Specifically, we use a simple deterministic modeling approach to evaluate the impact of chick mortality (from ingestion of lead-based paint) on the population growth rate (,) for Laysan albatross that breed on Sand Island, Midway Atoll (part of the Hawaiian Archipelago). We estimate that up to 7% of chicks on Sand Island fail to fledge as a result of lead poisoning, which will create a 16% reduction in the Laysan albatross population size (,190 000 less birds) at 50 years into the future. We demonstrate how straightforward management actions that increase juvenile survivorship (e.g. removal of lead-based paint) can help slow population declines while efforts are underway to reduce politically and logistically challenging threats to adult survivorship (e.g. mortality from international fisheries bycatch). Our work exemplifies a situation where overgeneralizations about demography can stifle useful conservation actions and highlights the need to consider the population-level benefits from multiple management strategies. [source] Fatty acid profiles of spiny lobster (Panulirus homarus) phyllosoma fed enriched ArtemiaAQUACULTURE RESEARCH, Issue 10 2010Kajal Chakraborty Abstract Three different life stages of spiny lobster larvae (phyllosoma) of Panulirus homarus were fed A1-Selco-enriched Artemia in two culture treatments, one with the microalgae Nannochloropsis salina (green water) and the other without the microalgae (clear water) to assess the ability to manipulate their fatty acid composition. Phyllosoma fed with 3-h A1-Selco-enriched Artemia salina attained Stage VIII (5.3 mm) and Stage V (3.4 mm) in 42 days in the green and clear water treatments respectively. The higher content of the essential fatty acids in N. salina (eicosapentaenoic acid, 25.8%; arachidonic acid, 9.5%; and docosahexaenoic acid, 4.2%) in the green water system increased the fatty acid content of the live food Artemia, and ultimately the phyllosoma. In spite of phyllosoma being fed with enriched Artemia in the clear water system, the total polyunsaturated fatty acid content of the early (Stages I,III) and mid stage (Stages IV,V) phyllosoma were significantly smaller (18.8% and 14.6% respectively) (P<0.05) than in the green water system (25.3% and 21.2% respectively). These results indicate the positive role of the microalgae in boosting the essential fatty acid content of lobster larvae. [source] Shade facilitates an invasive stem succulent in a chenopod shrubland in South AustraliaAUSTRAL ECOLOGY, Issue 5 2003TANJA I. LENZ Abstract The invasive stem succulent Orbea variegata (L) Haw. (Asclepiadaceae) tends to be more abundant underneath shrubs than in open areas in chenopod shrublands near Whyalla, South Australia. To assess the role of facilitation in the life cycle of O. variegata, we investigated the effect of chenopod shrubs on different life stages of the species by experimentally manipulating temperature, light, soil moisture and nutrient levels. Experimental results suggest that the reduction in light and temperature under shrubs, but not increased nutrient levels, are the main facilitative mechanisms for O. variegata. Temperatures above 30°C, which are more likely to occur on the soil surface of open areas than under shrubs, inhibited seed germination. Seedling survival at low watering frequency and the growth of established ramets were increased by 75,80% shade cloth. Ramets growing in full light contained a high concentration of anthocyanin pigments. One of the functions of these pigments is to absorb excess radiation, suggesting that O. variegata experiences radiation stress in full light. In the field O. variegata performed considerably better under Atriplex vesicaria Heward ex Benth. (Chenopodiaceae) or under 75,80% shade cloth than in full light. Monthly irrigation of 20 mm did not reduce this positive effect of the A. vesicaria canopy on O. variegata, suggesting that O. variegata is inhibited by high light intensities or temperatures, independent of water availability. In conclusion, whereas shrub canopies do not seem to be required for the establishment or survival of O. variegata, shrubs improve adult growth and can improve establishment. The possibility of exotic plants being facilitated by other plants has to be taken into account when assessing the probability and rate of invasion. [source] | |||||||||||||