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At least 145 records · Page 8Linked to original sources
PubMed2003

Life-cycle experiments of medaka fish aboard the international space station.

Fish are the most likely candidates to be the first vertebrate to live their life cycle aboard the International Space Station (ISS). In the space-shuttle experiment using medaka, the fry born in space had the same number of germ cells as the ground control fish, and these germ cells later developed to produce the offspring on the ground. Fry hatched in space did not exhibit any looping behavior regardless of their strain, visual acuity, etc. The aquatic habitat (AQH) is a space habitat designed for long-term breeding of medaka, zebrafish and Xenopus, and recent advancements in this hardware also support fish life-cycle experiments. From the crosses between two strains, fish having good eyesight and less sensitivity to gravity were obtained, and their tolerance to microgravity was tested by parabolic flight using an airplane. The fish exhibited less looping and no differences in degree of looping between light and dark conditions. These are possible candidates for the first adult medaka (parent fish) to start a life cycle aboard ISS. Embryos were treated with a three-dimensional clinostat. Such simulated microgravity caused no differences in tissue architecture or in gene expression within the retina, nor in formation of cartilage (head skeleton). Otolith formation in embryos and fry was investigated for wild-type and mutant (ha) medaka. The ha embryos could not form utricular otoliths. They formed saccular otoliths but with a delay. Fry of the mutant fish lacking the utricular otoliths are highly light-dependent at the time of hatching, showing a perfect dorsal-light response (DLR). As they grow, they eventually shift from being light dependent to gravity dependent. Continuous treatment of the fry with altered light direction suppressed this shift to gravity dependence. Being less dependent on gravity, these fish can serve as model fish in studying the differences expected for the fish that have experienced a life cycle in microgravity.

Animals↗
PubMed2001

Life-cycle impacts of the use of industrial by-products in road and earth construction.

A two-stage study "Life cycle analysis of road construction and earthworks" was part of a more extensive Finnish research project "Assessment of the applicability of secondary products in earthworks". In the first stage of this work a life-cycle impact assessment procedure for the comparison and evaluation of alternative road and earth constructions was developed. Additionally, a database containing the environmental burdens of the most significant construction materials and unit operations was constructed. In order to evaluate the applicability of the procedure, the use of coal ash, crushed concrete waste and granulated blast-furnace slag in road construction was evaluated in case studies. The use of these secondary products was also compared with the use of natural materials in corresponding applications. The aim of the second stage was to transfer the assembled data for utilisation as a practical model by creating an inventory analysis program to calculate and compare the life cycle impacts of the most common road constructions and foundation engineering methods. The data obtained in the first stage was also augmented to the extent necessary for this purpose. The results of case studies indicate that the production and transport of the materials used in road constructions produce the most significant environmental burdens. Production of the bitumen and cement, crushing of materials and transport of materials are the most energy consuming single life-cycle stages of the construction. A large part of the emissions to atmosphere originates from energy production. In the expert assessment, consumption of natural materials and leaching behaviour were also regarded as being of great significance.

Conservation of Natural Resources↗
PubMed1980

[2 rules on the life cycle of trematodes in the ecosystem].

Rule I: The more advanced in its primary evolution a life cycle is, the greater the participation of the animal component in it is. Parallel to that, most often the direct effect of the non-living component of the ecosystem on the cycle running is decreased. Rule II: In the majority of secondarily evolved life cycles of trematodes the following occurred in comparison with their initial life cycle: a) either a decrease of the direct effect of the non-living component of the ecosystem on the cycle running; b) or a decrease of the participation of the animal component of the ecosystem in the cycle; c) or most often a decrease of both together.

Animals↗
PubMed1979

Population growth, life-cycle saving, and international differences in steady-state optimal saving rates.

Life-cycle savings theories have been a seminal development in analyses of the relationship between rational savings patterns for individuals and the accumulation of wealth or capital at the level of the society as a whole. Applications of the theories in industrialized countries never investigated the significance of large differences in birth and death rates across societies. The strong demographic components of life-cycle saving analysis are here the center of focus. Illustrative general numerical applications of a modified version of the life-cycle approach suggest that mortality differentials comparable to those presently encountered among nations are consistent with very large differentials in steady-state optimal ratios of wealth-to-income. Specific application to Peru of the model estimated by Tobin for the United States indicates that high levels of mortality, current Peruvian birth rates, and Peruvian age-income profiles imply optimal rational savings rates far below those of the United States.

Birth Rate↗
PubMed1997

Seasonal synchronicity and stage-specific life cycles: Topp's beetles revisited.

In his study on Catops nigricans (Coleoptera: Leiodidae), Topp (W. Topp, Selection for an optimal monovoltine life-cycle in an unpredictable environment: Studies on the beetle C. nigricans Spence. Oecologia 84: 134-141 (1990).) observed that the times of eclosion and oviposition of a population of this European beetle are tightly synchronized to the local seasonal environment. Topp proposed that the key mechanism producing such synchrony is the developmental response that individuals exhibit to seasonal fluctuations of temperature and light at discrete stages of their life cycle. Here, an individual-level model of the C. nigricans life cycle is constructed and parameterized with the complete set of Topp's stage-specific development data. Seasonal variations of temperature and light are replicated by sinusoidal functions of time. Simulations are carried out to investigate the temporal behavior of lineages (generated from an arbitrary cohort) exposed to these periodic environmental variations over several generations. Our results support the hypothesis that stage-specific development in a periodic environment produces a powerful mechanism by which life-cycle synchronization can occur.

Animals↗
PubMed1999

Life cycles of species of Proteocephalus, parasites of fishes in the Palearctic region: a review.

The life cycles of species of Proteocephalus Weinland, 1858 (Cestoda: Proteocephalidea) parasitizing fishes in the Palearctic Region are reviewed on the basis of literary data and personal experimental observations, with special attention being paid to the development within the intermediate and definitive hosts. Planktonic crustaceans, diaptomid or cyclopid copepods (Copepoda), serve as the only intermediate hosts of all Proteocephalus species considered. A metacestode, or procercoid, develops in the body cavity of these planktonic crustaceans and the definitive host, a fish, becomes infected directly after consuming them. No previous reports of the parenteral location of metacestodes within the second intermediate host as it is in the Nearctic species P. ambloplitis have been recorded. Thus, the life cycles of Proteocephalus tapeworms resemble in their general patterns those of some pseudophyllidean cestodes such as Eubothrium or Bothriocephalus, differing from the latter in the presence of a floating eggs instead of possessing an operculate egg from which a ciliated, freely swimming larva, a coracidium, is liberated. The scolex of Proteocephalus is already formed at the stage of the procercoid within the copepod intermediate host; in this feature, proteocephalideans resemble caryophyllidean rather than pseudophyllidean cestodes. The morphology of procercoids of individual species is described with respect to the possibility of their differentiation and data on the spectrum of intermediate hosts are summarized. Procercoids of most taxa have a cercomer, which does not contain embryonic hooks in contrast to most pseudophyllidean cestodes. The role of invertebrates (alder-fly larvae-Megaloptera) and small prey fishes feeding upon plankton in the transmission of Proteocephalus tapeworms still remains unclear but these hosts are likely to occur in the life cycle. Data on the establishment of procercoids in definitive hosts, morphogenesis of tapeworms within fish hosts, and the length of the prepatent period are still scarce and new observations are needed. Whereas extensive information exists on the development of P. longicollis (syns. P. exiguus and P. neglectus), almost no data are available on the ontogeny of other taxa, in particular those occurring in brackish waters (P. gobiorum, P. tetrastomus). The morphology of P. cernuae and P. osculatus procercoids from experimentally infected intermediate hosts is described for the first time.

Animals↗
PubMed2005

Population genetics of complex life-cycle parasites: an illustration with trematodes.

Accurate inferences on population genetics data require a sound underlying theoretical null model. Organisms alternating sexual and asexual reproduction during their life-cycle have been largely neglected in theoretical population genetic models, thus limiting the biological interpretation of population genetics parameters measured in natural populations. In this article, we derive the expectations of those parameters for the life-cycle of monoecious trematodes, a group comprising several important human and livestock parasites that obligatorily alternate sexual and asexual reproduction during their life-cycle. We model how migration rates between hosts, sexual and asexual mutation rates, adult selfing rate and the variance in reproductive success of parasites during the clonal phase affect the amount of neutral genetic diversity of the parasite (effective population size) and its apportionment within and between definitive hosts (using F-statistics). We demonstrate, in particular, that variance in reproductive success of clones, a parameter that has been completely overlooked in previous population genetics models, is very important in shaping the distribution of the genetic variability both within and among definitive hosts. Within definitive hosts, the parameter F(IS) (a measure of the deviation from random mating) is decreased by high variance in clonal reproductive success of larvae but increased by high adult self-fertilisation rates. Both clonal multiplication and selfing have similar effects on between-host genetic differentiation (F(ST)). Migration occurring before and after asexual reproduction can have different effects on the patterns of F(IS), depending on values of the other parameters such as the mutation rate. While the model applies to any hermaphroditic organism alternating sexual and clonal reproduction (e.g. many plants), the results are specifically discussed in the light of the limited population genetic data on monoecious trematodes available to date and their previous interpretation. We hope that our model will encourage more empirical population genetics studies on monoecious trematodes and other organisms with similar life-cycles.

Animals↗
PubMed2000

Ribonucleotide reductase is regulated via the R2 subunit during the life cycle of Trypanosoma brucei.

We have examined the occurrence of the R1 and R2 subunits of ribonucleotide reductase during the life cycle of Trypanosoma brucei. Whereas the R1 protein is present throughout the life cycle, the R2 protein is not found in cell cycle-arrested short stumpy trypanosomes. RT-PCR/hybridization analysis revealed almost equal amounts of the R1 and R2 mRNAs in all life cycle stages of the parasite. The data indicate that ribonucleotide reductase of African trypanosomes is developmentally controlled by post-transcriptional regulation of the R2 subunit.

Animals↗
PubMed1999

[Current views on the life cycle of cyst-forming Coccidia (Eucoccidia, Sporozoa, Apicomplexa)].

The life cycles of cyst-forming coccidia of the genera Sarcocystis and Toxoplasma have been first analysed in terms of generally recognized biological phenomena, such as proliferation, differentiation, dedifferentiation, programmed cell death. The differences, existing between the respective obligatory heteroxenous (Sarcocystis) and facultatively heteroxenous (Toxoplasma) life cycles, have been found to involve the obvious differences in the degree of a zoite's differentiation, occurring in the course of asexual development in the intermediate host. In Sarcocystis spp., the degree of differentiation in merozoites, throughout their development, is much higher than in those of T. gondii. This level of merozoite differentiation in Sarcocystis is thought to determine the irreversible, one-directional way of both pre-cystic and cystic development of the pathogen, starting from the sporozoite stage and terminating in gamont formation within the tissue cyst. Unlike, in T. gondii, the level of merozoite differentiation is not so strong as in Sarcocystis spp., which may account for the reversible merozoite development in the former, which is clearly demonstrated by a ready conversion of pre-cystic tachyzoites into cystic bradyzoites, and the other way round. In the course of endogenous development, the pathogens adversely affect their environment (the infected cells and tissues), which, in its turn, may exert its influence on the particular parasites. Thus, both the parasite and the host represent a unique feed-bach regulatory system.

Animals↗
PubMedDate not supplied

Identification of amoebae implicated in the life cycle of Pfiesteria and Pfiesteria-like dinoflagellates.

This study was undertaken to assess whether amoebae commonly found in mesohaline environments are in fact stages in the life cycles of Pfiesteria and Pfiesteria-like dinoflagellates. Primary isolations of amoebae and dinoflagellates were made from water and sediment samples from five tributaries of the Chesapeake Bay. Additional amoebae were also cloned from bioassay aquaria where fish mortality was attributed to Pfiesteria. Electron microscopy and small subunit (SSU) rRNA gene sequence analysis of these isolates clearly demonstrated that the commonly depicted amoeboid form of Pfiisteria is very likely a species of Korotnevella and is unrelated to Pfiesteria or Pfiesteria-like dinoflagellates. We have determined that the Pfiesteria and Pfiesteria-like dinoflagellates examined in this study undergo a typical homothallic life cycle without amoeboid stages. Furthermore, we have demonstrated that cloned amoebae sharing morphological characteristics described for stages in the life cycle of Pfiesteria do not transform into dinozoites. The strict clonal isolation and cultivation techniques used in this study substantially support the conclusion that the amoebae and some of the flagellates depicted in the life cycle of Pfiesteria are environmental contaminants of the Pfiesteria culture system and that the Ambush Predator Hypothesis needs to be rigorously reevaluated.

Animals↗
PubMedDate not supplied

Alternation of actinosporean and myxosporean phases in the life cycle of Zschokkella nova (Myxozoa).

Experimental evidence has been gathered to show that the life cycle of the myxozoan gallbladder parasite Zschokkella nova Klokacewa, 1914, which infects the fish Carassius carassius, has a complex life cycle with alternation of two hosts (fish and Oligochaeta) and two developmental phases (myxosporean and actinosporean). The gut epithelium of the oligochaete, Tubifex tubifex, exposed experimentally to Z. nova, obtained from C. carassius, became infected with organisms resembling Actinosporea. The spore structure and cube-like network of the interconnected spores is reminiscent of Siedleckiella silesica Janiszewska, 1952, although the spores are very different in size and number of sporoplasm nuclei. The life cycle of Z. nova resembles that of the whirling disease agent Myxosoma cerebralis described by Wolf and Markiw, which also alternates between fish and oligochaete hosts.

Animals↗
PubMed2002

Life cycle of Trichostrongylus retortaeformis in its natural host, the rabbit (Oryctolagus cuniculus).

The chronology of the life cycle of Trichostrongylus retortaeformis (Zeder, 1800) (Nematoda, Trichostrongyloidea) is studied in its natural host Oryctolagus cuniculus. The free living period lasted 5 days at 24 degrees C. Worm-free rabbits were each infected per os with T. retortaeformis larvae. Rabbits were killed at 12 h post-infection (p.i.) and every day from one day to 13 days p.i. By 12 h p.i., all the larvae were exsheathed and in the small intestine. The third moult occurred between 3 and 5 days p.i. and the last moult between 4 and 7 days p.i. The prepatent period lasted 12 to 13 days. The patent period lasted five and a half months. The four known life cycles of species of Trichostrongylus in ruminants were compared with that of T. retortaeformis. No significant difference was found except in the duration of the prepatent period. These similarities in the life cycles confirm the previously formulated hypotheses on the relationship between the parasites of the two host groups (Durette-Desset, 1985).

Animals↗
PubMed2006

Analysis of the roles of E6 binding to E6TP1 and nuclear localization in the human papillomavirus type 31 life cycle.

The E6 oncoproteins of high-risk human papillomaviruses provide important functions not only for malignant transformation but also in the productive viral life cycle. E6 proteins have been shown to bind to a number of cellular factors, but only a limited number of analyses have investigated the effects of these interactions on the viral life cycle. In this study, we investigated the consequences of HPV 31 E6 binding to E6TP1, a putative Rap1 GAP protein. HPV 16 E6 has been shown to bind as well as induce the rapid turnover of E6TP1, and similar effects were observed with HPV 31 E6. Mutation of amino acid 128 in HPV 31 E6 was found to abrogate the ability to bind and degrade E6TP1 but did not alter binding to another alpha-helical domain protein, E6AP. When HPV 31 genomes containing mutations at amino acid 128 were transfected into human keratinocytes, the viral DNAs were not stably maintained as episomes indicating the importance of this residue for pathogenesis. Many E6 binding partners including E6TP1 are cytoplasmic proteins, but E6 has been also reported to be localized to the nucleus. We therefore investigated the importance of E6 localization to the nucleus in the viral life cycle. Using a fusion of E6 to Green Fluorescent Protein, we mapped one component of the nuclear localization sequences to residues 121 to 124 of HPV 31 E6. Mutation of these residues in the context of the HPV 31 genome abrogated the ability for episomes to be stably maintained and impaired the ability to extend the life span of cells. These studies identify two activities of HPV 31 E6 that are important for its function in the viral life cycle and for extension of cell life span.

Alphapapillomavirus↗
PubMed2001

A life cycle model of public policy issues in health care: the importance of strategic issues management.

Public policy affects health and social services organizations. Senior management has a responsibility to prevent inappropriate demands of stakeholders from predominating and to influence the outcome of public policy to the benefit of their organization through the strategic issues management process. This article presents a public policy issue life cycle model, life-cycle stages and suggested strategies, paths issues can take in the life cycle, and factors that affect issue paths. An understanding of these dynamics can aid senior managers in shaping and changing public policy issues and lessening external environment threats to their organization.

Decision Making, Organizational↗
PubMed2005

Life cycle assessment of switchgrass- and corn stover-derived ethanol-fueled automobiles.

Utilizing domestically produced cellulose-derived ethanol for the light-duty vehicle fleet can potentially improve the environmental performance and sustainability of the transport and energy sectors of the economy. A life cycle assessment model was developed to examine environmental implications of the production and use of ethanol in automobiles in Ontario, Canada. The results were compared to those of low-sulfur reformulated gasoline (RFG) in a functionally equivalent automobile. Two time frames were evaluated, one near-term (2010), which examines converting a dedicated energy crop (switchgrass) and an agricultural residue (corn stover) to ethanol; and one midterm (2020), which assumes technological improvements in the switchgrass-derived ethanol life cycle. Near-term results show that, compared to a RFG automobile, life cycle greenhouse gas (GHG) emissions are 57% lower for an E85-fueled automobile derived from switchgrass and 65% lower for ethanol from corn stover, on a grams of CO2 equivalent per kilometer basis. Corn stover ethanol exhibits slightly lower life cycle GHG emissions, primarily due to sharing emissions with grain production. Through projected improvements in crop and ethanol yields, results for the mid-term scenario show that GHG emissions could be 25-35% lower than those in 2010 and that, even with anticipated improvements in RFG automobiles, E85 automobiles could still achieve up to 70% lower GHG emissions across the life cycle.

Air Pollution↗
PubMed2000

Observations on the morphology and life-cycle of Procerovum varium (Onji & Nishio, 1916) (Trematoda: Heterophyidae).

The life-cycle of Procerovum varium (Digenea: Haplorchiinae) was studied experimentally and the morphology of stages in the life-cycle has been described and illustrated. Infections with adult flukes were found in the pond heron Ardeola grayii and heavy infections with metacercariae were found, attached to the liver of the fish Oryzias melastigma (Oryziatidae) occurring in a freshwater stream situated in Visakhapatnam, India. The cercariae developing in the snail Thiara tuberculata possessed typical haplorchiine features and were characterised by the presence of numerous cystogenous glands. Early stages of metacercarial development occurred free in the muscles of the fish intermediate host. The larvae reached the liver at 5 days post-infection, encystment commenced 2 days later and 15-day-old metacercariae were found to be infective to chicks, ducks and mice that served as suitable experimental hosts. The adult flukes obtained from natural and experimental infections showed many intraspecific variations, especially in the size and shape of the expulsor which depend on the quantity of sperm it contains. The validity of various species described in the genus and differentiated on the basis of differences in the size of the expulsor has been examined. It is concluded that only three species of the genus, namely P. varium, P. cheni and P. calderoni, are valid. "P. sisonli" of Chen (1949) is confirmed as a synonym of P. varium. P. varium is reported for the first time from India.

Animals↗
PubMed1994

Characterization of a high molecular weight antigen of Cryptosporidium parvum micronemes possessing epitopes that are cross-reactive with all parasitic life cycle stages.

Crossreacting antigens between life cycle stages of Cryptosporidium parvum (Protozoa, Apicomplexa) were detected using monoclonal antibodies (mAbs). Shared epitopes were demonstrated by immunoelectron microscopy, at the level of micronemes of the sporozoite and merozoite stages; some dense granules were also labelled but not so intensively. The parasitophorous vacuole membranes of all intracellular stages, the wall-forming bodies of macrogametes and the outer oocyst walls all shared these epitopes. The antigens that bear these epitopes were characterized using the whole oocyst and sporozoite stages as sources of antigenic material. Complex labelling patterns were observed on Western blots. However, all the mAbs used in this study recognized an antigen of more than 500 kDa. The glycoproteinic nature of this antigen was demonstrated by its sensitivity to pronase and periodate treatments. The expression of this high molecular weight immunoreactive antigen in the intracellular stages of C parvum was not investigated and remains to be found.

Animals↗
PubMed2004

Using artificial streams to assess the effects of metal-mining effluent on the life cycle of the freshwater midge (Chironomus tentans) in situ.

In 2002, we developed an in situ life-cycle bioassay with Chironomus tentans in artificial streams to evaluate the effects of a complex metal mine effluent under ambient environmental conditions. The bioassay was tested in the field using effluent from the Copper Cliff Waste Water Treatment Plant at INCO (Sudbury, ON, Canada). Chironomus tentans were exposed throughout the life cycle to 45% Copper Cliff effluent, which is the average effluent concentration measured in Junction Creek (ON, Canada), the natural receiving environment. Chironomus tentans in the effluent treatment exhibited reduced survival (p = 0.001), reduced total emergence (p = 0.001), increased time-to-emergence (p = 0.001), and reduced hatching success (p = 0.001) relative to animals in the reference water treatment. Chironomus tentans in the effluent treatment were not significantly different from the reference in terms of growth, sex ratio, number of egg cases/female, and number of eggs/egg case. This research showed how a life-cycle bioassay could be used in situ to assess metal mine effluent effects on a benthic invertebrate.

Animals↗