The role of biotic factors in the transmission of free-living endohelminth stages

Parasitology ◽  
2008 ◽  
Vol 135 (4) ◽  
pp. 407-426 ◽  
Author(s):  
D. W. THIELTGES ◽  
K. T. JENSEN ◽  
R. POULIN
Keyword(s):  
Abiotic Factors ◽  
Experimental Studies ◽  
Global Changes ◽  
Parasite Transmission ◽  
Helminth Parasites ◽  
Biotic Factors ◽  
Free Living ◽  
Anthropogenic Pollutants ◽  
Larval Stages

SUMMARYThe transmission success of free-living larval stages of endohelminths is generally modulated by a variety of abiotic and biotic environmental factors. Whereas the role of abiotic factors (including anthropogenic pollutants) has been in focus in numerous studies and summarized in reviews, the role of biotic factors has received much less attention. Here, we review the existing body of literature from the fields of parasitology and ecology and recognize 6 different types of biotic factors with the potential to alter larval transmission processes. We found that experimental studies generally indicate strong effects of biotic factors, and the latter emerge as potentially important, underestimated determinants in the transmission ecology of free-living endohelminth stages. This implies that biodiversity, in general, should have significant effects on parasite transmission and population dynamics. These effects are likely to interact with natural abiotic factors and anthropogenic pollutants. Investigating the interplay of abiotic and biotic factors will not only be crucial for a thorough understanding of parasite transmission processes, but will also be a prerequisite to anticipate the effects of climate and other global changes on helminth parasites and their host communities.

Polychaetes as Intermediate Hosts of Helminth Parasites of Vertebrates: A Review

1971 ◽  
Vol 28 (10) ◽  
pp. 1385-1392 ◽  
Author(s):  
L. Margolis
Keyword(s):  
Helminth Parasites ◽  
Intermediate Hosts ◽  
Larval Stages ◽  
Aquatic Vertebrates

The role of polychaetes as intermediate hosts of helminth parasites of aquatic vertebrates is reviewed. Some 18–20 species of trematodes and three or four each of cestodes and nematodes are known to have larval stages in these annelids. There are no records of acanthocephalan larvae from polychaetes. Trematoda use polychaetes as first (three species) or second intermediate hosts. The polychaete hosts are found among various genera of Errantia, Sedentaria, and Myzostomida. Definitive hosts are mainly fishes, with a few species of trematodes and one of cestodes developing in birds, and apparently one genus of nematodes (two species) maturing in the lungs of seals. A list of polychaetes and their larval helminth parasites is given.

scholarly journals Biogeomorphic feedbacks and the ecosystem engineering of recently deglaciated terrain

2018 ◽  
Vol 43 (1) ◽  
pp. 24-45 ◽  
Author(s):  
Hannah R Miller ◽  
Stuart N Lane
Keyword(s):  
Environmental Stress ◽  
Ecosystem Engineer ◽  
Abiotic Factors ◽  
Ecosystem Engineering ◽  
Soil Development ◽  
Water Dynamics ◽  
Biotic Factors ◽  
Successional Stage ◽  
Abiotic And Biotic Factors

Matthews’ 1992 geoecological model of vegetation succession within glacial forefields describes how following deglaciation the landscape evolves over time as the result of both biotic and abiotic factors, with the importance of each depending on the level of environmental stress within the system. We focus in this paper on how new understandings of abiotic factors and the potential for biogeomorphic feedbacks between abiotic and biotic factors makes further development of this model important. Disturbance and water dynamics are two abiotic factors that have been shown to create stress gradients that can drive early ecosystem succession. The subsequent establishment of microbial communities and vegetation can then result in biogeomorphic feedbacks via ecosystem engineering that influence the role of disturbance and water dynamics within the system. Microbes can act as ecosystem engineers by supplying nutrients (via remineralization of organic matter and nitrogen fixation), enhancing soil development, either decreasing (encouraging weathering) or increasing (binding sediment grains) geomorphic stability, and helping retain soil moisture. Vegetation can act as an ecosystem engineer by fixing nitrogen, enhancing soil development, modifying microbial community structure, creating seed banks, and increasing geomorphic stability. The feedbacks between vegetation and water dynamics in glacial forefields are still poorly studied. We propose a synthesized model of ecosystem succession within glacial forefields that combines Matthews’ initial geoecological model and Corenblit's model to illustrate how gradients in environmental stress combined with successional time drive the balance between abiotic and biotic factors and ultimately determine the successional stage and potential for biogeomorphic feedbacks.

scholarly journals New insights for Drosophila GAGA factor in larvae

2015 ◽  
Vol 2 (3) ◽  
pp. 150011 ◽  
Author(s):  
Marta Blanch ◽  
David Piñeyro ◽  
Jordi Bernués
Keyword(s):  
Abdominal Segment ◽  
Polytene Chromosomes ◽  
Wing Disc ◽  
Global Changes ◽  
Gaga Factor ◽  
Larval Stages ◽  
Maternal Contribution ◽  
Wing Discs ◽  
Abnormal Cell Proliferation

GAGA factor plays important roles during Drosophila embryogenesis and its maternal contribution is essential for early development. Here, the role of GAGA factor was studied in 3rd instar larvae using depletion and overexpression conditions in wing disc and transcriptome analysis. We found that genes changing expression were different to those previously described using GAGA mutants in embryos. No apparent phenotypes on GAGA depletion could usually be observed at larval stages in imaginal discs but a strong effect on salivary gland polytene chromosomes was observed. In the adult, GAGA depletion produced many defects like abnormal cell proliferation in the wing, impaired dorsal closure and resulted in homeotic transformation of abdominal segment A5. Unexpectedly, no effects on Ultrabithorax expression were observed. Short overexpression of GAGA factor in 3rd instar larvae also resulted in activation of a set of genes not previously described to be under GAGA regulation, and in lethality at pupa. Our results suggest a little contribution of GAGA factor on gene transcription in wing discs and a change of the genes regulated in comparison with embryo. GAGA factor activity thus correlates with the global changes in gene expression that take place at the embryo-to-larva and, later, at the larva-to-pupa transitions.

Surface carbohydrates of Eudiplozoon nipponicum pre- and post-fusion

2004 ◽  
Vol 78 (1) ◽  
pp. 63-68 ◽  
Author(s):  
I. Schabussova ◽  
B. Koubková ◽  
M. Gelnar ◽  
M. Schabuss ◽  
P. Horák
Keyword(s):  
Developmental Stages ◽  
Parasite Development ◽  
Helminth Parasites ◽  
Surface Binding ◽  
Larval Stages ◽  
Pattern Distribution ◽  
Quantitative Changes ◽  
Surface Carbohydrates ◽  
Eudiplozoon Nipponicum

AbstractThe development of the monogenean Diplozoon (Nordmann, 1832) (Diplozoidae) necessitates fusion of two larval stages (diporpae) into one double organism. How diporpae find, distinguish and contact each other is unclear, nor is the nature of the stimuli responsible for the dedifferentiation of cells and the formation of new tissues at the site of somatic fusion. Previous studies have implied a role for carbohydrates and glycoproteins in the interactions between helminth parasites and their hosts. Hypothetically, glycoconjugates may also be involved in the establishment of parasite–parasite associations. Changes in the surface saccharide residues during the development of Eudiplozoon nipponicum, a gill ectoparasite of carp (Cyprinus carpio) are described. Flat-fixed specimens and sections of diporpae, juveniles (just-fused) and adult worms were examined following exposure to a panel of 12 FITC-conjugated lectins. All developmental stages exhibited a specific surface binding pattern with ten lectins, indicating that Man/Glc, GlcNAc, Gal and GalNAc are probably present on their surfaces. No reaction was observed with Fuc-specific lectins (UEA-I and LTA). There is evidence that parasite development is accompanied by both qualitative and quantitative changes in the saccharide pattern distribution. The diporpa sucker reacted with nine lectins, excluding BS-II. A very strong binding of PNA, LCA and ConA (Gal and Man/Glc-specific lectins) was observed with the papilla glands of juvenile worms. The role of glandular secretions in this unique fusion process is discussed.

scholarly journals Trematode cercariae as prey for zooplankton: effect on fitness traits of predators

Parasitology ◽  
2018 ◽  
Vol 146 (1) ◽  
pp. 105-111 ◽  
Author(s):  
Ekaterina Mironova ◽  
Mikhail Gopko ◽  
Anna Pasternak ◽  
Viktor Mikheev ◽  
Jouni Taskinen
Keyword(s):  
Experimental Studies ◽  
Parasite Transmission ◽  
Feeding Rates ◽  
Free Living ◽  
Diplostomum Pseudospathaceum ◽  
Trophic Links ◽  
Fitness Traits ◽  
Filtration Apparatus ◽  
Sida Crystallina

AbstractRemoval of parasite free-living stages by predators has previously been suggested an important factor controlling parasite transmission in aquatic habitats. Experimental studies of zooplankton predation on macroparasite larvae are, however, scarce. We tested whether trematode cercariae, which are often numerous in shallow waters, are suitable prey for syntopic zooplankters. Feeding rates and survival of freshwater cyclopoids (Megacyclops viridis, Macrocyclops distinctus), calanoids (Arctodiaptomus paulseni), cladocerans (Sida crystallina) and rotifers Asplanchna spp., fed with cercariae of Diplostomum pseudospathaceum, a common fish trematode, were studied. In additional long-term experiments, we studied reproduction of cyclopoids fed with cercariae. All tested zooplankton species consumed cercariae. The highest feeding rates were observed for cyclopoids (33 ± 12 cercariae ind−1 h−1), which actively reproduced (up to one egg clutch day−1) when fed ad libitum with cercariae. Their reproductive characteristics did not change significantly with time, indicating that cercariae supported cyclopoids’ dietary needs. Mortality of rotifers and cladocerans was high (25–28% individuals) when exposed to cercariae in contrast to cyclopoids and calanoids (<2%). Cercariae clogged the filtration apparatus of cladocerans and caused internal injuries in predatory rotifers, which ingested cercariae. Observed trophic links between common freshwater zooplankters and cercariae may significantly influence food webs and parasite transmission in lentic ecosystems.

scholarly journals Environmental abiotic and biotic factors affecting the distribution and abundance of Naegleria fowleri

2020 ◽  
Vol 97 (1) ◽  
Author(s):  
Leigha M Stahl ◽  
Julie B Olson
Keyword(s):  
Current Knowledge ◽  
Abiotic Factors ◽  
Dust Particles ◽  
Biotic Factors ◽  
Naegleria Fowleri ◽  
Free Living ◽  
Factors Affecting ◽  
Wide Ph Range ◽  
Abiotic And Biotic Factors ◽  
Nægleria Fowleri

ABSTRACT Naegleria fowleri is a free-living protozoan that resides in soil and freshwater. Human intranasal amoebae exposure through water or potentially dust particles can culminate in primary amoebic meningoencephalitis, which generally causes death. While many questions remain regarding pathogenesis, the microbial ecology of N. fowleri is even less understood. This review outlines current knowledge of the environmental abiotic and biotic factors that affect the distribution and abundance of N. fowleri. Although the impacts of some abiotic factors remain poorly investigated or inconclusive, N. fowleri appears to have a wide pH range, low salinity tolerance and thermophilic preference. From what is known about biotic factors, the amoebae preferentially feed upon bacteria and are preyed upon by other free-living amoebae. Additional laboratory and environmental studies are needed to fill in knowledge gaps, which are crucial for surveillance and management of N. fowleri in freshwaters. As surface water temperatures increase with climate change, it is likely that this amoeba will pose a greater threat to human health, suggesting that identifying its abiotic and biotic preferences is critical to mitigating this risk.

Calculation-and-experimental estimation of the role of the frequency ratio in changing the endurance at two-frequency deformation modes

2019 ◽  
Vol 85 (1(I)) ◽  
pp. 64-71 ◽  
Author(s):  
M. M. Gadenin
Keyword(s):  
High Frequency ◽  
Experimental Studies ◽  
Low Frequency ◽  
Reduction Factor ◽  
Single Frequency ◽  
Cyclic Loads ◽  
Small Ratio ◽  
Harmonic Components ◽  
Deformation Modes

The cycle configuration at two-frequency loading regimes depends on the number of parameters including the absolute values of the frequencies and amplitudes of the low-frequency and high-frequency loads added during this mode, the ratio of their frequencies and amplitudes, as well as the phase shift between these harmonic components, the latter having a significant effect only with a small ratio of frequencies. Presence of such two-frequency regimes or service loading conditions for parts of machines and structures schematized by them can significantly reduce their endurance. Using the results of experimental studies of changes in the endurance of a two-frequency loading of specimens of cyclically stable, cyclically softened and cyclically hardened steels under rigid conditions we have shown that decrease in the endurance under the aforementioned conditions depends on the ratio of frequencies and amplitudes of operation low-frequency low-cycle and high-frequency vibration stresses, and, moreover, the higher the level of the ratios of amplitudes and frequencies of those stacked harmonic processes of loading the greater the effect. It is shown that estimation of such a decrease in the endurance compared to a single frequency loading equal in the total stress (strains) amplitudes can be carried out using an exponential expression coupling those endurances through a parameter (reduction factor) containing the ratio of frequencies and amplitudes of operation cyclic loads and characteristic of the material. The reduction is illustrated by a set of calculation-experimental curves on the corresponding diagrams for each of the considered types of materials and compared with the experimental data.

Helping when desire is low: The role of Expectancy in helping

2020 ◽  
Author(s):  
Małgorzata Kossowska
Keyword(s):  
Experimental Studies ◽  
Helping Behavior ◽  
Perceived Effectiveness ◽  
Do So

One might assume that the desire to help (here described as Want) is the essential driver of helping declarations and/or behaviors. However, even if desire to help is low, helping behavior may still occur if the expectancy regarding the perceived effectiveness of helping is high. We tested these predictions in a set of three experimental studies. In all three, we measured the desire to help (Want) and the Expectancy that the aid would be impactful for the victim; in addition, we manipulated Expectancy in Study 3. In Studies 1 and 3, we measured the participants’ declaration to help while in Study 2, their helping behavior was examined. In all three studies, we used variations of the same story about a victim. The results supported our hypothesis. Thus, the studies help to tease apart the determinants of helping behavior under conditions of lowered desire to do so, an issue of great importance in public policymaking.

The capacity of short term memory from an evolutionary perspective

2019 ◽  
Author(s):  
Majid Manoochehri
Keyword(s):  
Short Term Memory ◽  
Memory Span ◽  
Critical Role ◽  
Experimental Studies ◽  
Cognitive System ◽  
Evolutionary Approach ◽  
Evolutionary Perspective ◽  
Short Term ◽  
Term Memory

Memory span in humans has been intensely studied for more than a century. In spite of the critical role of memory span in our cognitive system, which intensifies the importance of fundamental determinants of its evolution, few studies have investigated it by taking an evolutionary approach. Overall, we know hardly anything about the evolution of memory components. In the present study, I briefly review the experimental studies of memory span in humans and non-human animals and shortly discuss some of the relevant evolutionary hypotheses.

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