Ocean acidification impacts on sperm mitochondrial membrane potential bring sperm swimming behaviour near its tipping point

Broadcast spawning marine invertebrates are susceptible to environmental stressors such as climate change, as their reproduction depends on the successful meeting and fertilization of gametes in the water column. Under near-future scenarios of ocean acidification, the swimming behaviour of marine invertebrate sperm is altered. We tested whether this was due to changes in sperm mitochondrial activity by investigating the effects of ocean acidification on sperm metabolism and swimming behaviour in the sea urchin Centrostephanus rodgersii. We used a fluorescent molecular probe (JC-1) and flow cytometry to visualize mitochondrial activity (measured as change in mitochondrial membrane potential, MMP). Sperm MMP was significantly reduced in delta pH -0.3 (35% reduction) and delta pH -0.5 (48% reduction) treatments, whereas sperm swimming behaviour was less sensitive with only slight changes (up to 11% decrease) observed overall. There was significant inter-individual variability in responses of sperm swimming behaviour and MMP to acidified seawater. We suggest it is likely that sperm exposed to these changes in pH are close to their tipping point in terms of physiological tolerance to acidity. Importantly, substantial inter-individual variation in responses of sperm swimming to ocean acidification may increase the scope for selection of resilient phenotypes, which, if heritable, could provide a basis for adaptation to future ocean acidification.

Seawater carbonate chemistry and swimming behaviors of the raphidophyte Heterosigma akashiwo in a laboratory experiment

We investigated the effects of pH on movement behaviors of the harmful algal bloom causing raphidophyte Heterosigma akashiwo. Motility parameters from >8000 swimming tracks of individual cells were quantified using 3D digital video analysis over a 6-h period in 3 pH treatments reflecting marine carbonate chemistry during the pre-industrial era, currently, and the year 2100. Movement behaviors were investigated in two different acclimation-to-target-pH conditions: instantaneous exposure and acclimation of cells for at least 11 generations. There was no negative impairment of cell motility when exposed to elevated PCO2 (i.e., low pH) conditions but there were significant behavioral responses. Irrespective of acclimation condition, lower pH significantly increased downward velocity and frequency of downward swimming cells (p < 0.001). Rapid exposure to lower pH resulted in 9% faster downward vertical velocity and up to 19% more cells swimming downwards (p < 0.001). Compared to pH-shock experiments, pre-acclimation of cells to target pH resulted in ~30% faster swimming speed and up to 46% faster downward velocities (all p < 0.001). The effect of year 2100 PCO2 levels on population diffusivity in pre-acclimated cultures was >2-fold greater than in pH-shock treatments (2.2 × 105 µm**2/s vs. 8.4 × 104 µm**2/s). Predictions from an advection-diffusion model, suggest that as PCO2 increased the fraction of the population aggregated at the surface declined, and moved deeper in the water column. Enhanced downward swimming of H. akashiwo at low pH suggests that these behavioral responses to elevated PCO2 could reduce the likelihood of dense surface slick formation of H. akashiwo through reductions in light exposure or growth independent surface aggregations. We hypothesize that the HAB alga's response to higher PCO2 may exploit the signaling function of high PCO2 as indicative of net heterotrophy in the system, thus indicative of high predation rates or depletion of nutrients.

9-28 d of exposure to elevated pCO2 reduces avoidance of predator odour but had no effect on behavioural lateralization or swimming activity in a temperate wrasse(Ctenolabrus rupestris)

Most studies on the impact of near-future levels of carbon dioxide on fish behaviour report behavioural alterations, wherefore abnormal behaviour has been suggested to be a potential consequence of future ocean acidification and therefore a threat to ocean ecosystems. However, an increasing number of studies show tolerance of fish to increased levels of carbon dioxide. This variation among studies in susceptibility highlights the importance of continued investigation of the possible effects of elevated pCO2. Here, we investigated the impacts of increased levels of carbon dioxide on behaviour using the goldsinny wrasse (Ctenolabrus rupestris), which is a common species in European coastal waters and widely used as cleaner fish to control sea lice infestation in commercial fish farming in Europe. The wrasses were exposed to control water conditions (370 µatm) or elevated pCO2 (995 µatm) for 1 month, during which time behavioural trials were performed. We investigated the possible effects of CO2 on behavioural lateralization, swimming activity, and prey and predator olfactory preferences, all behaviours where disturbances have previously been reported in other fish species after exposure to elevated CO2. Interestingly, we failed to detect effects of carbon dioxide for most behaviours investigated, excluding predator olfactory cue avoidance, where control fish initially avoided predator cue while the high CO2 group was indifferent. The present study therefore shows behavioural tolerance to increased levels of carbon dioxide in the goldsinny wrasse. We also highlight that individual fish can show disturbance in specific behaviours while being apparently unaffected by elevated pCO2 in other behavioural tests. However, using experiments with exposure times measured in weeks to predict possible effects of long-term drivers, such as ocean acidification, has limitations, and the behavioural effects from elevated pCO2 in this experiment cannot be viewed as proof that these fish would show the same reaction after decades of evolution.

Performance of Scheduling Policies in Adversarial Networks with Non-synchronized Clocks

In this paper we generalize the Continuous Adversarial Queuing Theory (CAQT) model (Blesa et al. in MFCS, Lecture Notes in Computer Science, vol. 3618, pp. 144–155, 2005) by considering the possibility that the router clocks in the network are not synchronized. We name the new model Non Synchronized CAQT (NSCAQT). Clearly, this new extension to the model only affects those scheduling policies that use some form of timing. In a first approach we consider the case in which although not synchronized, all clocks run at the same speed, maintaining constant differences. In this case we show that all universally stable policies in CAQT that use the injection time and the remaining path to schedule packets remain universally stable. These policies include, for instance, Shortest in System (SIS) and Longest in System (LIS). Then, we study the case in which clock differences can vary over time, but the maximum difference is bounded. In this model we show the universal stability of two families of policies related to SIS and LIS respectively (the priority of a packet in these policies depends on the arrival time and a function of the path traversed). The bounds we obtain in this case depend on the maximum difference between clocks. This is a necessary requirement, since we also show that LIS is not universally stable in systems without bounded clock difference. We then present a new policy that we call Longest in Queues (LIQ), which gives priority to the packet that has been waiting the longest in edge queues. This policy is universally stable and, if clocks maintain constant differences, the bounds we prove do not depend on them. To finish, we provide with simulation results that compare the behavior of some of these policies in a network with stochastic injection of packets.

Performance of Scheduling Policies in Adversarial Networks with Non-synchronized Clocks

In this paper we generalize the Continuous Adversarial Queuing Theory (CAQT) model (Blesa et al. in MFCS, Lecture Notes in Computer Science, vol. 3618, pp. 144–155, 2005) by considering the possibility that the router clocks in the network are not synchronized. We name the new model Non Synchronized CAQT (NSCAQT). Clearly, this new extension to the model only affects those scheduling policies that use some form of timing. In a first approach we consider the case in which although not synchronized, all clocks run at the same speed, maintaining constant differences. In this case we show that all universally stable policies in CAQT that use the injection time and the remaining path to schedule packets remain universally stable. These policies include, for instance, Shortest in System (SIS) and Longest in System (LIS). Then, we study the case in which clock differences can vary over time, but the maximum difference is bounded. In this model we show the universal stability of two families of policies related to SIS and LIS respectively (the priority of a packet in these policies depends on the arrival time and a function of the path traversed). The bounds we obtain in this case depend on the maximum difference between clocks. This is a necessary requirement, since we also show that LIS is not universally stable in systems without bounded clock difference. We then present a new policy that we call Longest in Queues (LIQ), which gives priority to the packet that has been waiting the longest in edge queues. This policy is universally stable and, if clocks maintain constant differences, the bounds we prove do not depend on them. To finish, we provide with simulation results that compare the behavior of some of these policies in a network with stochastic injection of packets.

Super-Resolution in Respiratory Synchronized Positron Emission Tomography

Respiratory motion is a major source of reduced quality in positron emission tomography (PET). In order to minimize its effects, the use of respiratory synchronized acquisitions, leading to gated frames, has been suggested. Such frames, however, are of low signal-to-noise ratio (SNR) as they contain reduced statistics. Super-resolution (SR) techniques make use of the motion in a sequence of images in order to improve their quality. They aim at enhancing a low-resolution image belonging to a sequence of images representing different views of the same scene. In this work, a maximum a posteriori (MAP) super-resolution algorithm has been implemented and applied to respiratory gated PET images for motion compensation. An edge preserving Huber regularization term was used to ensure convergence. Motion fields were recovered using a B-spline based elastic registration algorithm. The performance of the SR algorithm was evaluated through the use of both simulated and clinical datasets by assessing image SNR, as well as the contrast, position and extent of the different lesions. Results were compared to summing the registered synchronized frames on both simulated and clinical datasets. The super-resolution image had higher SNR (by a factor of over 4 on average) and lesion contrast (by a factor of 2) than the single respiratory synchronized frame using the same reconstruction matrix size. In comparison to the motion corrected or the motion free images a similar SNR was obtained, while improvements of up to 20% in the recovered lesion size and contrast were measured. Finally, the recovered lesion locations on the SR images were systematically closer to the true simulated lesion positions. These observations concerning the SNR, lesion contrast and size were confirmed on two clinical datasets included in the study. In conclusion, the use of SR techniques applied to respiratory motion synchronized images lead to motion compensation combined with improved image SNR and contrast, without any increase in the overall acquisition times.

Mechanical actuator for biomimetic propulsion and the effect of the caudal fin elasticity on the swimming performance

This paper presents a mechanical actuator for the biomimetic propulsion of swimming devices and the experimental study of the effect of the caudal fin elasticity on the overall performance. The design of the proposed drive allows the DC motor to operate at constant speed, so all the power of the motor is spent only for the motion of the caudal fin. A prototype of the actuator, in which the caudal fin serves as a driving element, is manufactured and tested in both laboratory and natural conditions. The swimming speed, the thrust efficiency and the maneuverability are evaluated for caudal fins with different stiffness. The caudal fin whose rigidity varies relative to both vertical and horizontal cross-section, exhibits the best performance. The achieved results also confirm that the proposed actuator could be of great interest to applications in the field of underwater operation, ocean investigation and environmental protection.

A new procedure for race analysis in swimming based on individual distance measurements

biomecanica de la natación

Effect of yoga and swimming on body temperature of pregnant women

Physical activity for pregnant women should be controlled and adapted in order to minimize the risk of loss of balance and fetal trauma (Davies, Wolfe, Mottola, y MacKinnon, 2003). Noninvasive technologies are required for understanding better the effects of physical activity on pregnant women. Infrared thermography allows, remotely, securely and without any contact, to measure and display accurate temperatures on the human skin.

Effects of different swimming race constraints on turning movements

The aim of this study was to investigate the effects of different swimming race constraints on the evolution of turn parameters. One hundred and fifty-eight national and regional level 200-m (meters) male swimming performances were video-analyzed using the individualized-distance model in the Open Comunidad de Madrid tournament. Turn (p < .001, ES = 0.36) and underwater distances (p < .001, ES = 0.38) as well as turn velocity (p < .001, ES = 0.69) significantly dropped throughout the race, although stroke velocity and underwater velocity were maintained in the last lap of the race (p > .05). Higher expertise swimmers obtained faster average velocities and longer distances in all the turn phases (p < .001, ES = 0.59), except the approach distance. In addition, national level swimmers showed the ability to maintain most of the turn parameters throughout the race, which assisted them in improving average velocity at the end of races. Therefore, the variations in the turning movements of a swimming race were expertise-related and focused on optimizing average velocity. Turning skills should be included in the swimming race action plan.

Minimum size limit for useful locomotion by free-swimming microbes

Formulas are derived for the effect of size on a free-swimming microbe’s ability to follow chemical, light, or temperature stimuli or to disperse in random directions. The four main assumptions are as follows: (i) the organisms can be modeled as spheres, (ii) the power available to the organism for swimming is proportional to its volume, (iii) the noise in measuring a signal limits determination of the direction of a stimulus, and (iv) the time available to determine stimulus direction or to swim a straight path is limited by rotational diffusion caused by Brownian motion. In all cases, it is found that there is a sharp size limit below which locomotion has no apparent benefit. This size limit is estimated to most probably be about 0.6 μm diameter and is relatively insensitive to assumed values of the other parameters. A review of existing descriptions of free-floating bacteria reveals that the smallest of 97 motile genera has a mean length of 0.8 μm, whereas 18 of 94 nonmotile genera are smaller. Similar calculations have led to the conclusion that a minimum size also exists for use of pheromones in mate location, although this size limit is about three orders of magnitude larger. In both cases, the application of well-established physical laws and biological generalities has demonstrated that a common feature of animal behavior is of no use to small free-swimming organisms.

Recurrent excitatory postsynaptic potentials induced by synchronized fast cortical oscillations

Gamma frequency (about 20–70 Hz) oscillations occur during novel sensory stimulation, with tight synchrony over distances of at least 7 mm. Synchronization in the visual system has been proposed to reflect coactivation of different parts of the visual field by a single spatially extended object. We have shown that intracortical mechanisms, including spike doublet firing by interneurons, can account for tight long-range synchrony. Here we show that synchronous gamma oscillations in two sites also can cause long-lasting (>1 hr) potentiation of recurrent excitatory synapses. Synchronous oscillations lasting >400 ms in hippocampal area CA1 are associated with an increase in both excitatory postsynaptic potential (EPSP) amplitude and action potential afterhyperpolarization size. The resulting EPSPs stabilize and synchronize a prolonged beta frequency (about 10–25 Hz) oscillation. The changes in EPSP size are not expressed during non-oscillatory behavior but reappear during subsequent gamma-oscillatory events. We propose that oscillation-induced EPSPs serve as a substrate for memory, whose expression either enhances or blocks synchronization of spatially separated sites. This phenomenon thus provides a dynamical mechanism for storage and retrieval of stimulus-specific neuronal assemblies.