1,720,998 research outputs found
The effects of daily cyclic hypoxia on the ecophysiology of the Atlantic ditch shrimp, Palaemon varians
No full textOxygen partial pressure (pO2) is not always constant in aquatic environments and can vary on different timescales, from hours to weeks. In many coastal environments, such as estuaries, lagoons or marshes, pO2 level scan vary on a daily base, resulting in daily cyclic hypoxia. By monitoring temperature and pO2 in the Lymington salt marshes (UK), I was able to quantify diel and seasonal pO2 variability in this coastal habitat:diel oscillations in pO2 were measured in winter, spring and summer, and the greatest pO2 oscillations were recorded in summer, when pO2 could fluctuate from ~42 kPa to ~ 1 kPa every 12 hours, causing diel cyclichypoxia. Even if cyclic hypoxia is common in numerous coastal areas around the world and affects many species, this phenomenon is less studied in comparison to acute or chronic hypoxia. The aim of this thesis was to characterize the short-term effects and the long-term consequences of daily cyclic hypoxia on the physiology of an important decapod crustacean, Palaemon varians. This species was found in the Lymington salt marshes (UK) and, in the laboratory, was subjected to a cyclic hypoxic regime that mimicked conditions measured in the field during summer.In the laboratory, a short 8-hour exposure to hypoxia (pO2 < critical oxygen pressure, pcrit) induced behavioural and metabolic changes and suppressed feeding and ammoniacal excretion. Long-term exposure to diel cyclic hypoxia induced changes in the transcriptome of the animals, prompted an acceleration of the moult cycle (validated at transcriptional and phenotypic level) and eventually resulted in morphological changes to the gills, which increased lamellar surface area. Further, long-term exposure to cyclic hypoxia impaired animal’s growth (in terms of body weight and length), reduced ammoniacal excretion and negatively influenced reproduction by reducing egg yolk content. Interestingly, long-term acclimation to cyclic hypoxia increased thermal tolerance and copper tolerance in comparison to control animals, probably as a consequence of the morphological changes to the gills induced by cyclic hypoxia. Overall, results underline that a short hypoxic exposure repeated daily was able to induce in P. varians alterations at multiple levels of biological organisation. In particular, the observed long-term consequences(i.e. growth reduction, reduced ammoniacal excretion and impaired reproduction) might have important ecological implications for the species and for its ecosystem
Acclimation to cyclic hypoxia improves thermal tolerance and copper survival in the caridean shrimp Palaemon varians
No full textIn response to the continuous variation of environmental parameters, species must be able to adjust their physiology to overcome stressful conditions, a process known as acclimatization. Numerous laboratory studies have been conducted to understand and describe the mechanisms of acclimation to one environmental stressor (e.g. cyclic hypoxia), but currently our understanding of how acclimation to one stressor can change tolerance to a subsequent stressor is limited. Here, in two different experiments, we used the shrimp Palaemon varians to test how, following 28-days acclimation to cyclic hypoxia (mimicking a cyclic hypoxic regime currently found in its natural habitat), critical thermal maximum (CT
max) and sensitivity to copper (Cu
2+) exposure (30 mgL
−1) changed in comparison to shrimp acclimated to normoxic conditions and then exposed to thermal stress or Cu
2+. Acclimation to cyclic hypoxia improved both CT
max (~1 °C higher than controls) and survival to acute Cu
2+ exposure (~30% higher than controls) and induced significant gene expression changes (i.e. up-regulation of heat shock protein 70 – HSP70, hypoxia inducible factor – HIF, phosphoenolpyruvate carboxykinase – PEPCK, glucose 6-P transporter – G6Pt, metallothionein – Mt, and down-regulation of hemocyanin – Hem) in animals acclimated to cyclic hypoxia. Our results demonstrate how acclimation to cyclic hypoxia improved tolerance to subsequent stressors, highlighting the complexity of predicting organismal performance in variable (i.e. where multiple parameters can simultaneously change during the day) environments.
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Silencing two main isoforms of crustacean hyperglycemic hormone (CHH) induces compensatory expression of two CHH-like transcripts in the red swamp crayfish Procambarus clarkii
Full text linkRNA interference has frequently been applied to modulate gene function in organisms. With the aim of creating new autocidal methods based on neuro-endocrine disruptors for invasive populations of Procambarus clarkii, we silenced the Crustacean Hyperglycemic Hormone (CHH) by injecting the corresponding dsRNA. CHH is a pleiotropic hormone that primarily regulates the mobilization of energy reserves and plays a pivotal role in stress responses. Here, we describe two experiments aimed at testing whether CHH silencing significantly alters important physiological aspects. The first experiment investigates the effects of CHH silencing at the glycemic and transcriptomic level in the eyestalk. The second experiment explores the long-term effects of CHH silencing and the effects on mortality and moulting rates. Osmotic deficits and mortality were recorded in specimens injected with
CHH dsRNA, whilst controls were injected with GFP dsRNA. After 20 days, despite still silenced for CHH, individuals that survived recovered a strong hyperglycemic response after serotonin injection due to the compensatory effect of two peptides belonging to the crustacean neurohormone CHH protein family
Reproductive plasticity of a Procambarus clarkii population living 10°C below its thermal optimum
Full text linkIn this study the annual reproductive biology of a Procambarus clarkii (Girard, 1852) population living in an atypical habitat with cold
spring waters is investigated by monitoring Gonado-Somatic and Hepato-Somatic Indexes (GSI and HSI) and by performing cytology on
ovaries. Despite its known preference for habitats with water temperature from 21 to 30 °C, our results clearly confirm the adaptation of this
population to the atypical thermal habitat, characterised by an annual mean water temperature value of 13.32 ±0.08 °C. Maximum gonadal
development was reached in August, with maximum GSI median value of 0.64 (instead of reported values even 10 times higher for other
populations), and ovigerous females were found in autumn, with mean realized fecundity of 35 ±7 compared to 285–995 reported from other
habitats. Histological analysis was consistent with other studies and allowed us to follow ovarian development at cytological level. The
importance of all these results is not to be underestimated: to our knowledge these findings are the first report of the coolest habitat
successfully colonized by this species at the present time and so they have to be taken as a warning about the possible range expansion of P.
clarkii also to northern and colder habitats that have few things in common with the native habitat of the species and, up to now, were
considered “safe” from the invasion of the red swamp crayfish
The consequences of daily cyclic hypoxia on a European grass shrimp: from short-term responses to long-term effects
No full text1.Salt marshes are a key coastal environment for their important role as nursery habitats for marine and estuarine fish and crustaceans. Salt marshes are variable environments where species can experience daily cyclic hypoxic stress, characterized by profound variations in oxygen partial pressure (pO2) from supersaturated conditions (~42kPa) to extremely hypoxic conditions (~3kPa) in ~12‐hours.
2.Here, under laboratory conditions, we assessed the physiological consequences of exposing the shrimp Palaemon varians, a species commonly found in the salt marshes of northern Europe, to the daily cyclic hypoxic regime currently experienced in its habitat in August (7.1±1.8 hours day−1 below 4.0kPa). In the laboratory adults were kept at water pO2 <4.5kPa for 7‐hours each night and in normoxic conditions for the rest of the time.
3.We recorded an acceleration of P. varians’ moult cycle, which was 15% shorter in animals kept in cyclic hypoxia compared to animals in normoxia. Similarly, the pattern of expression of two cuticular proteins over an entire moult cycle indicated an effect of cyclic hypoxia on moult stage‐related genes. After 16 days, morphological changes to the gills were detected, with shrimps in cyclic hypoxia having a 13.6% larger lamellar surface area (measured in μm2/mg animal) than normoxic animals, which could improve gas exchange capacity. Overall, phenotypic and morphological data indicate that faster moulting is triggered in response to cyclic hypoxia, with the benefit that gill modifications can be prompted more rapidly in order to meet oxygen requirements of the body.
4.On the first experimental day, in cyclic hypoxic exposed animals, we recorded a 50% decrease in feeding rates (during hypoxic conditions) in comparison to normoxic animals. Similarly, ammonium excretion was reduced by 66‐75% during the 1st and 21st experimental day. Body size was reduced by ~4% after 28 days. Females that reproduced in cyclic hypoxic conditions reduced the amount of yolk in each egg by ~24%. Overall, results underline how, in a decapod shrimp living in a key coastal environment, many physiological parameters are impaired by a cyclic hypoxic regime that is currently found in its natural habitat
Reproductive plasticity of a Procambarus clarkii population living 10°C below its thermal optimum
No full textIn this study the annual reproductive biology of a Procambarus clarkii (Girard, 1852) population living in an atypical habitat with cold spring waters is investigated by monitoring Gonado-Somatic and Hepato-Somatic Indexes (GSI and HSI) and by performing cytology on ovaries. Despite its known preference for habitats with water temperature from 21 to 30 °C, our results clearly confirm the adaptation of this population to the atypical thermal habitat, characterised by an annual mean water temperature value of 13.32 ±0.08 °C. Maximum gonadal development was reached in August, with maximum GSI median value of 0.64 (instead of reported values even 10 times higher for otherpopulations), and ovigerous females were found in autumn, with mean realized fecundity of 35 ±7 compared to 285–995 reported from other habitats. Histological analysis was consistent with other studies and allowed us to follow ovarian development at cytological level. The importance of all these results is not to be underestimated: to our knowledge these findings are the first report of the coolest habitat successfully colonized by this species at the present time and so they have to be taken as a warning about the possible range expansion of P.clarkii also to northern and colder habitats that have few things in common with the native habitat of the species and, up to now, were considered “safe” from the invasion of the red swamp crayfish
Data from: The consequences of daily cyclic hypoxia on a European grass shrimp: from short-term responses to long-term effects
No full text1. Salt marshes are a key coastal environment for their important role as nursery habitats for marine and estuarine fish and crustaceans. Salt marshes are variable environments where species can experience daily cyclic hypoxic stress, characterized by profound variations in oxygen partial pressure (pO2) from supersaturated conditions (~42kPa) to extremely hypoxic conditions (~3kPa) in ~12-hours. 2. Here, under laboratory conditions, we assessed the physiological consequences of exposing the shrimp Palaemon varians, a species commonly found in the salt marshes of northern Europe, to the daily cyclic hypoxic regime currently experienced in its habitat in August (7.1±1.8 hours day-1 below 4.0kPa). In the laboratory adults were kept at water pO2 <4.5kPa for 7-hours each night and in normoxic conditions for the rest of the time. 3. We recorded an acceleration of P. varians’ moult cycle, which was 15% shorter in animals kept in cyclic hypoxia compared to animals in normoxia. Similarly, the pattern of expression of two cuticular proteins over an entire moult cycle indicated an effect of cyclic hypoxia on moult stage-related genes. After 16 days, morphological changes to the gills were detected, with shrimps in cyclic hypoxia having a 13.6% larger lamellar surface area (measured in µm2/mg animal) than normoxic animals, which could improve gas exchange capacity. Overall, phenotypic and morphological data indicate that faster moulting is triggered in response to cyclic hypoxia, with the benefit that gill modifications can be prompted more rapidly in order to meet oxygen requirements of the body. 4. On the first experimental day, in cyclic hypoxic exposed animals, we recorded a 50% decrease in feeding rates (during hypoxic conditions) in comparison to normoxic animals. Similarly, ammonium excretion was reduced by 66-75% during the 1st and 21st experimental day. Body size was reduced by ~4% after 28 days. Females that reproduced in cyclic hypoxic conditions reduced the amount of yolk in each egg by ~24%. Overall, results underline how, in a decapod shrimp living in a key coastal environment, many physiological parameters are impaired by a cyclic hypoxic regime that is currently found in its natural habitat. </span
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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