J. Strickler - Academia.edu (original) (raw)
Papers by J. Strickler
Journal of Marine Systems, 2010
The calanoid Clausocalanus furcatus and the cyclopoid Oithona plumifera are species dominating th... more The calanoid Clausocalanus furcatus and the cyclopoid Oithona plumifera are species dominating the copepod assemblage in oligotrophic environments but displaying contrasting swimming behaviour. C. furcatus moves almost continuously along very convoluted trajectories, while O. plumifera sinks slowly with occasional brief relocating jumps. To evaluate the efficiency of such opposing behaviour in encountering potential prey, the swimming performances of both species are here simulated with a Lagrangian, individual-based approach, implemented to simulate the realistic motion and perceptive fields of the two species. For each modelled swimming trajectory, we calculate the number of realised encounters and the associated search efficiency in uniform and patchy distributions of virtual prey. C. furcatus will perform better than O. plumifera in terms of realised encounters, but its search efficiency will be lower owing to the peculiar motion behaviour and to the shape and extension of the perceptive field. Despite these differences, these two species do co-exist in food diluted areas, thus indicating alternative strategies to successfully thrive in pelagic oligotrophic environments.
Ecological Modelling, 2005
Ecological Modelling, 2009
Zooplankton encounter rates are dependent not only on both sensory and swimming performances of t... more Zooplankton encounter rates are dependent not only on both sensory and swimming performances of the organisms, but also on the distribution pattern of food particles. Increasing evidences indicate that, in natural conditions, phytoplankton is often aggregated in thin layers. In the present contribution we investigate the concomitant effects of motion complexity and habitat fragmentation on the number of encounters realised by virtual continuously moving copepods adopting different motion strategies. Our simulated organisms move in an environment characterised by the presence of thin patches of phytoplankton, and their swim follows five motion rules (pure random walk, correlated random walk with three different time scales, self-avoiding random walk), each characterised by a typical value of the three-dimensional fractal dimension D 3D. Compared to a uniform distribution, for a given motion rule the clustering of prey particles increases the variance of encounters, while no remarkable effect is reported in the average number of particles intercepted. These results broaden our understanding of the behavioural efficiency in freely swimming zooplankters and improve our knowledge of the functioning of aquatic systems.
Journal of the Fisheries Research Board of Canada, 1977
Journal of cell science, 1981
Differential cell adhesion, a suggested guiding force for tissue rearrangement during embryogenes... more Differential cell adhesion, a suggested guiding force for tissue rearrangement during embryogenesis, could be affected by desmosome frequency. A model system for studying embryonic tissue-positioning behaviour involves combining different tissues and following their rearrangements. We have previously shown that for one tissue, embryonic chick heart ventricle, direction of tissue positioning can be altered experimentally. Heart tissue precultured for 2.5 days tends to segregate internally, while tissue pre-cultured for just half a day tends to segregate externally. Also, intact fragments of tissue tend to segregate internally, while reaggregates of trypsin-disaggregated tissues tend to segregate externally. We show here that treatments that increase the tendency to internalize also increase the frequency of adherens junctions and treatments that increase the tendency to externalize decrease the frequency of junctions. An identical hierarchical ordering of the 4 experimental tissues o...
Virology, 1988
The genetic organization of the M RNA segment of snowshoe hare (SSH) virus, a member of the Bunya... more The genetic organization of the M RNA segment of snowshoe hare (SSH) virus, a member of the Bunyavirus genus of the family Bunyaviridae, has been determined. The middle (M) RNA segment has a single open reading frame (ORF) of 1441 amino acids. We have used amino- and carboxy-terminus sequencing and synthetic peptides to map proteins within the ORF. The order of the proteins translated from the single large open reading frame is G2, NSm, G1. The G2 protein extends from amino acids 14 to 299. The molecule is 286 residues long, with a computed nonglycosylated molecular weight of 31,973 Da. It is preceded by a cleaved 13 amino acid signal sequence. G2 includes a long highly hydrophobic sequence and contains three potential N-linked glycosylation sites. The G1 protein occupies the C-terminal end of the open reading frame from amino acids 474 to 1441 (968 amino acid residues) and has a computed nonglycosylated, molecular weight of 108,981 kDa. It has two potential N-linked glycosylation sites, and a potential transmembrane region followed by a potential cytoplasmic domain at the C-terminal end. If membrane associated it has an orientation of N-terminus outer, C-terminus inner. Limited trypsin digestion removes a 33-kDa fragment from the N-terminal end, leaving a virion-associated truncated G1 molecule (amino acids 762 to 1441) with a single N-linked glycosylation site. Between the G2 and G1 molecules there are 174 amino acids, sufficient to code for 19 kDa of protein. Some antibodies raised against peptides within this region react with proteins of 11 kDa (NSm) and 10 kDa present in infected cell lysates, but the exact relationship of these proteins to the open reading frame remains to be determined.
Biochimica Et Biophysica Acta-biomembranes - BBA-BIOMEMBRANES, 1982
Molecular and Biochemical Parasitology, 1982
As an assay for the surface deposition of newly synthesized major variable surface coat glycoprot... more As an assay for the surface deposition of newly synthesized major variable surface coat glycoprotein (VSCG) we have treated intact Trypanosoma brucei cells with the cleavable cross-linking reagent dithiobis-(succinimidyl propionate). Under appropriate conditions, surface VSCG is converted to oligomers of n not less than 8. The oligomeric protein, apparent molecular weight greater than 4 x 10(5), does not migrate more than 1 to 2 mm into a 3-15% linear polyacrylamide gradient gel containing 0.1% sodium dodecyl sulfate, hence the appearance of newly synthesized radiolabeled protein in the top 2 mm of the gel indicates the translocation of VSCG from the site of synthesis to the surface and the gross establishment of normal interactions among the molecules. In addition, purified VSCG treated with the cross-linking reagent yielded a dimeric product on gel electrophoresis. To examine the role of N-linked carbohydrate in the translocation of the protein and in intermolecular interactions we have allowed trypanosomes to incorporate L-[14C] serine into protein in the presence of the antibiotic tunicamycin. Our results show that N-linked carbohydrate is not essential to the transfer of VSCG to the cell surface nor does its absence interfere with gross intermolecular interactions in the short term. On the other hand N-linked carbohydrate does appear to play an essential role in dimer formation.
Marine Biology, 2002
The ability of planktonic copepods to detect and pursue remote prey is well documented, but there... more The ability of planktonic copepods to detect and pursue remote prey is well documented, but there are no empirical descriptions of their three-dimensional (3D) sensory fields. In this study, the attack volume of females of Euchaeta rimana Bradford, a planktonic calanoid copepod, was mapped by plotting the positions of attacked prey within a standardized 3D coordinate system defined by the body axes of E. rimana. This analysis was performed using videotaped observations of predatory interactions between free-swimming E. rimana and smaller copepod species. Attack by E. rimana was an oriented response, accurately directed toward remote prey within an ellipsoidal volume anterior to its paired first antennules. This attack volume enveloped the large mechanosensory setae projecting anteriorly from the first antennules, with attack distances averaging 1.5 mm, or less than one body length of the predator. E. rimana attacked a larger prey species, Acartia fossae, at significantly longer distances than it attacked a smaller species, Acrocalanus inermi, reflecting prey-specific perceptive volumes. Such perceptual biases may underlie the selective feeding patterns observed in E. rimana and other copepod species. These observations are consistent with mechanosensory mechanisms of prey identification and localization, suggesting that fluid disturbances provide the releasing and directing stimuli for E. rimana during predatory interactions. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.
Journal of Theoretical Biology, 2007
The encounter of individuals-prey, predators and mates-living in the surrounding environment is a... more The encounter of individuals-prey, predators and mates-living in the surrounding environment is a fundamental process in the life of an organism. Along with the sensory abilities, this process will be regulated by the movement rules adopted by the individual. In this work we discuss the encounter-enhancement effect due to different natatorial modes by calculating the number of encounters realised by differently convoluted trajectories in two homogeneous distributions of particles. Using numerically generated trajectories representative of specific swimming behaviour, we demonstrate that high values of three-dimensional fractal dimension D(3D)(>1.9) are beneficial only at high concentration, whereas at low concentration less tortuous tracks (D(3D) approximately 1.5) are almost equally efficient. In the light of our results it is possible to better understand the behavioural adaptations evolved by individuals to thrive in their environment.
Journal of Plankton Research, 2006
ABSTRACT Mating behaviour is an emerging topic in the study of copepod ecology, having important ... more ABSTRACT Mating behaviour is an emerging topic in the study of copepod ecology, having important consequences at both individual and population levels. Mate-finding has been shown to depend upon the perception of cues released by the conspecific, as well as on the swimming behaviour of both the male and the female. In order to understand the differences in the strategies adopted in the pre-copulatory phase by males and females, we analysed the swimming tracks of the freshwater calanoid Leptodiaptomus ashlandi. The three-dimensional trajectories described by males and females have been analysed in terms of their three-dimensional fractal dimension D 3D , a parameter which can synthetically but appropriately characterise the degree of contortion of a three-dimensional path. D 3D values for L. ashlandi males during the pre-detection phase are higher than the corresponding ones for females, indicating that the male explores more extended volumes of fluid thus increasing the probability of encountering a female.
Journal of Marine Systems, 2010
The calanoid Clausocalanus furcatus and the cyclopoid Oithona plumifera are species dominating th... more The calanoid Clausocalanus furcatus and the cyclopoid Oithona plumifera are species dominating the copepod assemblage in oligotrophic environments but displaying contrasting swimming behaviour. C. furcatus moves almost continuously along very convoluted trajectories, while O. plumifera sinks slowly with occasional brief relocating jumps. To evaluate the efficiency of such opposing behaviour in encountering potential prey, the swimming performances of both species
Journal of Clinical Investigation, 1996
Preconditioning with brief ischemia before a sustained period of ischemia reduces infarct size in... more Preconditioning with brief ischemia before a sustained period of ischemia reduces infarct size in the perfused heart. A cultured chick ventricular myocyte model was developed to investigate the role of adenosine receptor subtypes in cardiac preconditioning. Brief hypoxic exposure, termed preconditioning hypoxia, prior to prolonged hypoxia, protected myocytes against injury induced by the prolonged hypoxia. Activation of the adenosine A1 receptor with CCPA or the A3 receptor with C1-IB-MECA can replace preconditioning hypoxia and simulate preconditioning, with a maximal effect at 100 nM. While activation of the A2a receptor by 1 microM CGS21680 could not mimic preconditioning, its stimulation during preconditioning hypoxia, however, attenuated the protection against hypoxia-induced injury. Blockade of A2a receptors with the selective antagonist CSC (1 microM) during preconditioning hypoxia enhanced the protective effect of preconditioning. Nifedipine, which blocked the A2a receptor-mediated calcium entry, abolished the A2a agonist-induced attenuation of preconditioning. Isoproterenol, forskolin, and BayK 8644, which stimulated calcium entry, also attenuated preconditioning. Nifedipine blocked the increase in calcium uptake by these agents as well as their attenuating effect on preconditioning. The present study provides the first evidence that the adenosine A3 receptor is present on ventricular myocytes and can mediate simulation of preconditioning. The data demonstrate, for the first time, that activation of the A2a receptor antagonizes the preconditioning effect of adenosine, with increased calcium entry during the preconditioning stimuli as a novel mechanism.
Hydrobiologia, 2011
Daphnia swimming behaviour is controlled by a variety of external factors, including light, prese... more Daphnia swimming behaviour is controlled by a variety of external factors, including light, presence of food and predators. Temperature represents a key driver in the dynamics of Daphnia populations, as well as on their motion. In this study, we have investigated the behavioural adaptations of adult Daphnia pulicaria to two different temperatures, representative of the mean winter (3°C) and summer (22°C) temperatures to which these organisms are exposed to in the real environment. Video observations were conducted both in the presence and in the absence of light to investigate possible day/night modifications in the motion strategy. Analyses of mean speed, velocity power spectral density and trajectory fractal dimension point out specific adaptations that allow D. pulicaria to successfully adjust to the changing conditions of the environment. Independently of the light conditions, in cold waters D. pulicaria swim almost vertically with defined motional frequencies, likely to increase the encounter with food items diluted in the fluid. A similar behaviour is displayed by the animals at summertime temperatures in the presence of light; however, in this case the vertical swimming is coupled with the absence of peaks in the power spectra and might be exploited to avoid predators. In contrast, at 22°C in dark conditions D. pulicaria move horizontally with lateral motions to take advantage of possible patches of phytoplankton. This information sheds new light into the complex and dynamic adaptations of D. pulicaria in response to external stimuli.
Ecological Modelling, 2005
Several natural processes, such as swimming and flying, occur in a three-dimensional reference fr... more Several natural processes, such as swimming and flying, occur in a three-dimensional reference frame and thus describe three-dimensional trajectories. Analysing such tracks is no easy task. To this aim, here we propose a new technique, based on the box-counting approach, by which to estimate the three-dimensional fractal dimension (D 3D ) of spatially-evolving routes. This technique has been preliminary tested on two sets of random walks (pure and correlated). Then, our approach has been utilised to characterise the swimming trajectories performed by the freshwater cladoceran Daphnia pulex under two light conditions. Morphologically different tracks attain statistically different D 3D values, smoother paths having lower values than more tortuous ones; therefore, our proposed methodology proves to be fruitful in direct comparisons. Moreover D 3D can highlight bizarre situations, in which differently convoluted tracks are characterised by the same degree of contortion.
Ecological Modelling, 2009
Correlated random walks Fractal dimension Encounters Patches a b s t r a c t Zooplankton encounte... more Correlated random walks Fractal dimension Encounters Patches a b s t r a c t Zooplankton encounter rates are dependent not only on both sensory and swimming performances of the organisms, but also on the distribution pattern of food particles. Increasing evidences indicate that, in natural conditions, phytoplankton is often aggregated in thin layers. In the present contribution we investigate the concomitant effects of motion complexity and habitat fragmentation on the number of encounters realised by virtual continuously moving copepods adopting different motion strategies. Our simulated organisms move in an environment characterised by the presence of thin patches of phytoplankton, and their swim follows five motion rules (pure random walk, correlated random walk with three different time scales, self-avoiding random walk), each characterised by a typical value of the three-dimensional fractal dimension D 3D . Compared to a uniform distribution, for a given motion rule the clustering of prey particles increases the variance of encounters, while no remarkable effect is reported in the average number of particles intercepted. These results broaden our understanding of the behavioural efficiency in freely swimming zooplankters and improve our knowledge of the functioning of aquatic systems.
Journal of Plankton Research, 2004
Three-dimensional swimming, in 20 trajectories of Daphnia pulex, was characterized in terms of it... more Three-dimensional swimming, in 20 trajectories of Daphnia pulex, was characterized in terms of its kinematic properties. Results show that the random component was stronger than the deterministic component at time scales >1-2 s. Such random movements may have evolved to outwit potential predators and prey.
Journal of Marine Systems, 2010
The calanoid Clausocalanus furcatus and the cyclopoid Oithona plumifera are species dominating th... more The calanoid Clausocalanus furcatus and the cyclopoid Oithona plumifera are species dominating the copepod assemblage in oligotrophic environments but displaying contrasting swimming behaviour. C. furcatus moves almost continuously along very convoluted trajectories, while O. plumifera sinks slowly with occasional brief relocating jumps. To evaluate the efficiency of such opposing behaviour in encountering potential prey, the swimming performances of both species are here simulated with a Lagrangian, individual-based approach, implemented to simulate the realistic motion and perceptive fields of the two species. For each modelled swimming trajectory, we calculate the number of realised encounters and the associated search efficiency in uniform and patchy distributions of virtual prey. C. furcatus will perform better than O. plumifera in terms of realised encounters, but its search efficiency will be lower owing to the peculiar motion behaviour and to the shape and extension of the perceptive field. Despite these differences, these two species do co-exist in food diluted areas, thus indicating alternative strategies to successfully thrive in pelagic oligotrophic environments.
Ecological Modelling, 2005
Ecological Modelling, 2009
Zooplankton encounter rates are dependent not only on both sensory and swimming performances of t... more Zooplankton encounter rates are dependent not only on both sensory and swimming performances of the organisms, but also on the distribution pattern of food particles. Increasing evidences indicate that, in natural conditions, phytoplankton is often aggregated in thin layers. In the present contribution we investigate the concomitant effects of motion complexity and habitat fragmentation on the number of encounters realised by virtual continuously moving copepods adopting different motion strategies. Our simulated organisms move in an environment characterised by the presence of thin patches of phytoplankton, and their swim follows five motion rules (pure random walk, correlated random walk with three different time scales, self-avoiding random walk), each characterised by a typical value of the three-dimensional fractal dimension D 3D. Compared to a uniform distribution, for a given motion rule the clustering of prey particles increases the variance of encounters, while no remarkable effect is reported in the average number of particles intercepted. These results broaden our understanding of the behavioural efficiency in freely swimming zooplankters and improve our knowledge of the functioning of aquatic systems.
Journal of the Fisheries Research Board of Canada, 1977
Journal of cell science, 1981
Differential cell adhesion, a suggested guiding force for tissue rearrangement during embryogenes... more Differential cell adhesion, a suggested guiding force for tissue rearrangement during embryogenesis, could be affected by desmosome frequency. A model system for studying embryonic tissue-positioning behaviour involves combining different tissues and following their rearrangements. We have previously shown that for one tissue, embryonic chick heart ventricle, direction of tissue positioning can be altered experimentally. Heart tissue precultured for 2.5 days tends to segregate internally, while tissue pre-cultured for just half a day tends to segregate externally. Also, intact fragments of tissue tend to segregate internally, while reaggregates of trypsin-disaggregated tissues tend to segregate externally. We show here that treatments that increase the tendency to internalize also increase the frequency of adherens junctions and treatments that increase the tendency to externalize decrease the frequency of junctions. An identical hierarchical ordering of the 4 experimental tissues o...
Virology, 1988
The genetic organization of the M RNA segment of snowshoe hare (SSH) virus, a member of the Bunya... more The genetic organization of the M RNA segment of snowshoe hare (SSH) virus, a member of the Bunyavirus genus of the family Bunyaviridae, has been determined. The middle (M) RNA segment has a single open reading frame (ORF) of 1441 amino acids. We have used amino- and carboxy-terminus sequencing and synthetic peptides to map proteins within the ORF. The order of the proteins translated from the single large open reading frame is G2, NSm, G1. The G2 protein extends from amino acids 14 to 299. The molecule is 286 residues long, with a computed nonglycosylated molecular weight of 31,973 Da. It is preceded by a cleaved 13 amino acid signal sequence. G2 includes a long highly hydrophobic sequence and contains three potential N-linked glycosylation sites. The G1 protein occupies the C-terminal end of the open reading frame from amino acids 474 to 1441 (968 amino acid residues) and has a computed nonglycosylated, molecular weight of 108,981 kDa. It has two potential N-linked glycosylation sites, and a potential transmembrane region followed by a potential cytoplasmic domain at the C-terminal end. If membrane associated it has an orientation of N-terminus outer, C-terminus inner. Limited trypsin digestion removes a 33-kDa fragment from the N-terminal end, leaving a virion-associated truncated G1 molecule (amino acids 762 to 1441) with a single N-linked glycosylation site. Between the G2 and G1 molecules there are 174 amino acids, sufficient to code for 19 kDa of protein. Some antibodies raised against peptides within this region react with proteins of 11 kDa (NSm) and 10 kDa present in infected cell lysates, but the exact relationship of these proteins to the open reading frame remains to be determined.
Biochimica Et Biophysica Acta-biomembranes - BBA-BIOMEMBRANES, 1982
Molecular and Biochemical Parasitology, 1982
As an assay for the surface deposition of newly synthesized major variable surface coat glycoprot... more As an assay for the surface deposition of newly synthesized major variable surface coat glycoprotein (VSCG) we have treated intact Trypanosoma brucei cells with the cleavable cross-linking reagent dithiobis-(succinimidyl propionate). Under appropriate conditions, surface VSCG is converted to oligomers of n not less than 8. The oligomeric protein, apparent molecular weight greater than 4 x 10(5), does not migrate more than 1 to 2 mm into a 3-15% linear polyacrylamide gradient gel containing 0.1% sodium dodecyl sulfate, hence the appearance of newly synthesized radiolabeled protein in the top 2 mm of the gel indicates the translocation of VSCG from the site of synthesis to the surface and the gross establishment of normal interactions among the molecules. In addition, purified VSCG treated with the cross-linking reagent yielded a dimeric product on gel electrophoresis. To examine the role of N-linked carbohydrate in the translocation of the protein and in intermolecular interactions we have allowed trypanosomes to incorporate L-[14C] serine into protein in the presence of the antibiotic tunicamycin. Our results show that N-linked carbohydrate is not essential to the transfer of VSCG to the cell surface nor does its absence interfere with gross intermolecular interactions in the short term. On the other hand N-linked carbohydrate does appear to play an essential role in dimer formation.
Marine Biology, 2002
The ability of planktonic copepods to detect and pursue remote prey is well documented, but there... more The ability of planktonic copepods to detect and pursue remote prey is well documented, but there are no empirical descriptions of their three-dimensional (3D) sensory fields. In this study, the attack volume of females of Euchaeta rimana Bradford, a planktonic calanoid copepod, was mapped by plotting the positions of attacked prey within a standardized 3D coordinate system defined by the body axes of E. rimana. This analysis was performed using videotaped observations of predatory interactions between free-swimming E. rimana and smaller copepod species. Attack by E. rimana was an oriented response, accurately directed toward remote prey within an ellipsoidal volume anterior to its paired first antennules. This attack volume enveloped the large mechanosensory setae projecting anteriorly from the first antennules, with attack distances averaging 1.5 mm, or less than one body length of the predator. E. rimana attacked a larger prey species, Acartia fossae, at significantly longer distances than it attacked a smaller species, Acrocalanus inermi, reflecting prey-specific perceptive volumes. Such perceptual biases may underlie the selective feeding patterns observed in E. rimana and other copepod species. These observations are consistent with mechanosensory mechanisms of prey identification and localization, suggesting that fluid disturbances provide the releasing and directing stimuli for E. rimana during predatory interactions. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.
Journal of Theoretical Biology, 2007
The encounter of individuals-prey, predators and mates-living in the surrounding environment is a... more The encounter of individuals-prey, predators and mates-living in the surrounding environment is a fundamental process in the life of an organism. Along with the sensory abilities, this process will be regulated by the movement rules adopted by the individual. In this work we discuss the encounter-enhancement effect due to different natatorial modes by calculating the number of encounters realised by differently convoluted trajectories in two homogeneous distributions of particles. Using numerically generated trajectories representative of specific swimming behaviour, we demonstrate that high values of three-dimensional fractal dimension D(3D)(>1.9) are beneficial only at high concentration, whereas at low concentration less tortuous tracks (D(3D) approximately 1.5) are almost equally efficient. In the light of our results it is possible to better understand the behavioural adaptations evolved by individuals to thrive in their environment.
Journal of Plankton Research, 2006
ABSTRACT Mating behaviour is an emerging topic in the study of copepod ecology, having important ... more ABSTRACT Mating behaviour is an emerging topic in the study of copepod ecology, having important consequences at both individual and population levels. Mate-finding has been shown to depend upon the perception of cues released by the conspecific, as well as on the swimming behaviour of both the male and the female. In order to understand the differences in the strategies adopted in the pre-copulatory phase by males and females, we analysed the swimming tracks of the freshwater calanoid Leptodiaptomus ashlandi. The three-dimensional trajectories described by males and females have been analysed in terms of their three-dimensional fractal dimension D 3D , a parameter which can synthetically but appropriately characterise the degree of contortion of a three-dimensional path. D 3D values for L. ashlandi males during the pre-detection phase are higher than the corresponding ones for females, indicating that the male explores more extended volumes of fluid thus increasing the probability of encountering a female.
Journal of Marine Systems, 2010
The calanoid Clausocalanus furcatus and the cyclopoid Oithona plumifera are species dominating th... more The calanoid Clausocalanus furcatus and the cyclopoid Oithona plumifera are species dominating the copepod assemblage in oligotrophic environments but displaying contrasting swimming behaviour. C. furcatus moves almost continuously along very convoluted trajectories, while O. plumifera sinks slowly with occasional brief relocating jumps. To evaluate the efficiency of such opposing behaviour in encountering potential prey, the swimming performances of both species
Journal of Clinical Investigation, 1996
Preconditioning with brief ischemia before a sustained period of ischemia reduces infarct size in... more Preconditioning with brief ischemia before a sustained period of ischemia reduces infarct size in the perfused heart. A cultured chick ventricular myocyte model was developed to investigate the role of adenosine receptor subtypes in cardiac preconditioning. Brief hypoxic exposure, termed preconditioning hypoxia, prior to prolonged hypoxia, protected myocytes against injury induced by the prolonged hypoxia. Activation of the adenosine A1 receptor with CCPA or the A3 receptor with C1-IB-MECA can replace preconditioning hypoxia and simulate preconditioning, with a maximal effect at 100 nM. While activation of the A2a receptor by 1 microM CGS21680 could not mimic preconditioning, its stimulation during preconditioning hypoxia, however, attenuated the protection against hypoxia-induced injury. Blockade of A2a receptors with the selective antagonist CSC (1 microM) during preconditioning hypoxia enhanced the protective effect of preconditioning. Nifedipine, which blocked the A2a receptor-mediated calcium entry, abolished the A2a agonist-induced attenuation of preconditioning. Isoproterenol, forskolin, and BayK 8644, which stimulated calcium entry, also attenuated preconditioning. Nifedipine blocked the increase in calcium uptake by these agents as well as their attenuating effect on preconditioning. The present study provides the first evidence that the adenosine A3 receptor is present on ventricular myocytes and can mediate simulation of preconditioning. The data demonstrate, for the first time, that activation of the A2a receptor antagonizes the preconditioning effect of adenosine, with increased calcium entry during the preconditioning stimuli as a novel mechanism.
Hydrobiologia, 2011
Daphnia swimming behaviour is controlled by a variety of external factors, including light, prese... more Daphnia swimming behaviour is controlled by a variety of external factors, including light, presence of food and predators. Temperature represents a key driver in the dynamics of Daphnia populations, as well as on their motion. In this study, we have investigated the behavioural adaptations of adult Daphnia pulicaria to two different temperatures, representative of the mean winter (3°C) and summer (22°C) temperatures to which these organisms are exposed to in the real environment. Video observations were conducted both in the presence and in the absence of light to investigate possible day/night modifications in the motion strategy. Analyses of mean speed, velocity power spectral density and trajectory fractal dimension point out specific adaptations that allow D. pulicaria to successfully adjust to the changing conditions of the environment. Independently of the light conditions, in cold waters D. pulicaria swim almost vertically with defined motional frequencies, likely to increase the encounter with food items diluted in the fluid. A similar behaviour is displayed by the animals at summertime temperatures in the presence of light; however, in this case the vertical swimming is coupled with the absence of peaks in the power spectra and might be exploited to avoid predators. In contrast, at 22°C in dark conditions D. pulicaria move horizontally with lateral motions to take advantage of possible patches of phytoplankton. This information sheds new light into the complex and dynamic adaptations of D. pulicaria in response to external stimuli.
Ecological Modelling, 2005
Several natural processes, such as swimming and flying, occur in a three-dimensional reference fr... more Several natural processes, such as swimming and flying, occur in a three-dimensional reference frame and thus describe three-dimensional trajectories. Analysing such tracks is no easy task. To this aim, here we propose a new technique, based on the box-counting approach, by which to estimate the three-dimensional fractal dimension (D 3D ) of spatially-evolving routes. This technique has been preliminary tested on two sets of random walks (pure and correlated). Then, our approach has been utilised to characterise the swimming trajectories performed by the freshwater cladoceran Daphnia pulex under two light conditions. Morphologically different tracks attain statistically different D 3D values, smoother paths having lower values than more tortuous ones; therefore, our proposed methodology proves to be fruitful in direct comparisons. Moreover D 3D can highlight bizarre situations, in which differently convoluted tracks are characterised by the same degree of contortion.
Ecological Modelling, 2009
Correlated random walks Fractal dimension Encounters Patches a b s t r a c t Zooplankton encounte... more Correlated random walks Fractal dimension Encounters Patches a b s t r a c t Zooplankton encounter rates are dependent not only on both sensory and swimming performances of the organisms, but also on the distribution pattern of food particles. Increasing evidences indicate that, in natural conditions, phytoplankton is often aggregated in thin layers. In the present contribution we investigate the concomitant effects of motion complexity and habitat fragmentation on the number of encounters realised by virtual continuously moving copepods adopting different motion strategies. Our simulated organisms move in an environment characterised by the presence of thin patches of phytoplankton, and their swim follows five motion rules (pure random walk, correlated random walk with three different time scales, self-avoiding random walk), each characterised by a typical value of the three-dimensional fractal dimension D 3D . Compared to a uniform distribution, for a given motion rule the clustering of prey particles increases the variance of encounters, while no remarkable effect is reported in the average number of particles intercepted. These results broaden our understanding of the behavioural efficiency in freely swimming zooplankters and improve our knowledge of the functioning of aquatic systems.
Journal of Plankton Research, 2004
Three-dimensional swimming, in 20 trajectories of Daphnia pulex, was characterized in terms of it... more Three-dimensional swimming, in 20 trajectories of Daphnia pulex, was characterized in terms of its kinematic properties. Results show that the random component was stronger than the deterministic component at time scales >1-2 s. Such random movements may have evolved to outwit potential predators and prey.