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Santhanakrishnan A.,Georgia Institute of Technology | Dollinger M.,University of North Carolina at Chapel Hill | Hamlet C.L.,North Carolina State University | Colin S.P.,Roger Williams University | And 2 more authors.
Journal of Experimental Biology

Quantifying the flows generated by the pulsations of jellyfish bells is crucial for understanding the mechanics and efficiency of their swimming and feeding. Recent experimental and theoretical work has focused on the dynamics of vortices in the wakes of swimming jellyfish with relatively simple oral arms and tentacles. The significance of bell pulsations for generating feeding currents through elaborate oral arms and the consequences for particle capture are not as well understood. To isolate the generation of feeding currents from swimming, the pulsing kinematics and fluid flow around the benthic jellyfish Cassiopea spp. were investigated using a combination of videography, digital particle image velocimetry and direct numerical simulation. During the rapid contraction phase of the bell, fluid is pulled into a starting vortex ring that translates through the oral arms with peak velocities that can be of the order of 10?cm?s-1. Strong shear flows are also generated across the top of the oral arms throughout the entire pulse cycle. A coherent train of vortex rings is not observed, unlike in the case of swimming oblate medusae such as Aurelia aurita. The phase-Averaged flow generated by bell pulsations is similar to a vertical jet, with induced flow velocities averaged over the cycle of the order of 1-10?mm?s-1. This introduces a strong near-horizontal entrainment of the fluid along the substrate and towards the oral arms. Continual flow along the substrate towards the jellyfish is reproduced by numerical simulations that model the oral arms as a porous Brinkman layer of finite thickness. This two-dimensional numerical model does not, however, capture the far-field flow above the medusa, suggesting that either the three-dimensionality or the complex structure of the oral arms helps to direct flow towards the central axis and up and away from the animal. © 2012. Published by The Company of Biologists Ltd. Source

Thestrup T.,Max Planck Institute of Neurobiology | Thestrup T.,Howard Hughes Medical Institute | Litzlbauer J.,Max Planck Institute of Neurobiology | Bartholomaus I.,Max Planck Institute of Neurobiology | And 19 more authors.
Nature Methods

The quality of genetically encoded calcium indicators (GECIs) has improved dramatically in recent years, but high-performing ratiometric indicators are still rare. Here we describe a series of fluorescence resonance energy transfer (FRET)-based calcium biosensors with a reduced number of calcium binding sites per sensor. These 'Twitch' sensors are based on the C-terminal domain of Opsanus troponin C. Their FRET responses were optimized by a large-scale functional screen in bacterial colonies, refined by a secondary screen in rat hippocampal neuron cultures. We tested the in vivo performance of the most sensitive variants in the brain and lymph nodes of mice. The sensitivity of the Twitch sensors matched that of synthetic calcium dyes and allowed visualization of tonic action potential firing in neurons and high resolution functional tracking of T lymphocytes. Given their ratiometric readout, their brightness, large dynamic range and linear response properties, Twitch sensors represent versatile tools for neuroscience and immunology. © 2014 Nature America, Inc. All rights reserved. Source

Colin S.P.,Roger Williams University | Colin S.P.,Whitman Center | Costello J.H.,Whitman Center | Costello J.H.,Providence College | And 5 more authors.

Flexible bell margins are characteristic components of rowing medusan morphologies and are expected to contribute towards their high propulsive efficiency. However, the mechanistic basis of thrust augmentation by flexible propulsors remained unresolved, so the impact of bell margin flexibility on medusan swimming has also remained unresolved. We used biomimetic robotic jellyfish vehicles to elucidate that propulsive thrust enhancement by flexible medusan bell margins relies upon fluid dynamic interactions between entrained flows at the inflexion point of the exumbrella and flows expelled from under the bell. Coalescence of flows from these two regions resulted in enhanced fluid circulation and, therefore, thrust augmentation for flexible margins of both medusan vehicles and living medusae. Using particle image velocimetry (PIV) data we estimated pressure fields to demonstrate a mechanistic basis of enhanced flows associated with the flexible bell margin. Performance of vehicles with flexible margins was further enhanced by vortex interactions that occur during bell expansion. Hydrodynamic and performance similarities between robotic vehicles and live animals demonstrated that the propulsive advantages of flexible margins found in nature can be emulated by human-engineered propulsors. Although medusae are simple animal models for description of this process, these results may contribute towards understanding the performance of flexible margins among other animal lineages. © 2012 Colin et al. Source

Sutherland K.R.,University of Oregon | Costello J.H.,Providence College | Costello J.H.,Whitman Center | Colin S.P.,Whitman Center | And 2 more authors.
Journal of Plankton Research

Planktonic organisms are exposed to turbulent water motion that affects the fundamental activities of swimming and feeding. The goal of this study was to measure the influence of realistic turbulence levels on (i) swimming behavior and (ii) fluid interactions during feeding by the lobate ctenophore, Mnemiopsis leidyi, a highly successful suspension-feeding predator. A laboratory turbulence generator produced turbulence (ε = 0.5-1.4 × 10-6 W kg-1) representative of a field site in Woods Hole, MA, USA. Compared with still water, M. leidyi avoided regions in the experimental vessel where turbulence was greatest (ε = 1.1-1.4 × 10-6 W kg-1) by increasing its swimming speeds and accelerations. Both laboratory and in situ particle image velocimetry data demonstrated that feeding currents of M. leidyi were eroded by ambient fluid motions. Despite this, the overall flux to the feeding structures remained constant due to higher swimming speeds in turbulent conditions. Instantaneous shear deformation rates produced by background turbulence were higher than those produced by ctenophore feeding currents and frequently exceeded the published escape thresholds of copepod prey. Feeding current erosion and fluid mechanical signal noise within turbulent flows affect the mechanics of predator-prey interactions during suspension feeding by the ctenophore M. leidyi. © The Author 2014. Source

Elemans C.P.H.,National Oceanic and Atmospheric Administration | Elemans C.P.H.,University of Southern Denmark | Mensinger A.F.,Whitman Center | Mensinger A.F.,University of Minnesota | And 2 more authors.
Journal of Experimental Biology

Sound communication is fundamental to many social interactions and essential to courtship and agonistic behaviours in many vertebrates. The swimbladder and associated muscles in batrachoidid fishes (midshipman and toadfish) is a unique vertebrate sound production system, wherein fundamental frequencies are determined directly by the firing rate of a vocal-acoustic neural network that drives the contraction frequency of superfast swimbladder muscles. The oyster toadfish boatwhistle call starts with an irregular sound waveform that could be an emergent property of the peripheral nonlinear sound-producing system or reflect complex encoding in the central nervous system. Here, we demonstrate that the start of the boatwhistle is indicative of a chaotic strange attractor, and tested whether its origin lies in the peripheral sound-producing system or in the vocal motor network. We recorded sound and swimbladder muscle activity in awake, freely behaving toadfish during motor nerve stimulation, and recorded sound, motor nerve and muscle activity during spontaneous grunts. The results show that rhythmic motor volleys do not cause complex sound signals. However, arrhythmic recruitment of swimbladder muscle during spontaneous grunts correlates with complex sounds. This supports the hypothesis that the irregular start of the boatwhistle is encoded in the vocal pre-motor neural network, and not caused by peripheral interactions with the sound-producing system. We suggest that sound production system demands across vocal tetrapods have selected for muscles and motorneurons adapted for speed, which can execute complex neural instructions into equivalently complex vocalisations. © 2014, Company of Biologists Ltd. All rights reserved. Source

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