scholarly journals Two swimming modes in Trachymedusae; bell kinematics and the role of giant axons

2021 ◽  
Author(s):  
M. E. Meech ◽  
C. E. Mills ◽  
S. H. D. Haddock ◽  
R. W. Meech
Keyword(s):  
Water Movement ◽  
Swimming Behaviour ◽  
Motor Axons ◽  
Laboratory Measurements ◽  
Video Footage ◽  
Swimming Motion ◽  
Evolutionary Context ◽  
Neural Anatomy

Although members of the Rhopalonematidae family (Cnidaria, Hydrozoa, Trachymedusae) are known to exhibit unusually powerful jet swimming in addition to their more normal slow swimming behaviour, for the most part reports are rare and anecdotal. Many species are found globally at depths of 600 - 2000 m and so observation and collection depends on using remotely operated submersible vehicles. With a combination of in-situ video footage and laboratory measurements, we have quantified kinematic aspects of this dual swimming motion and its electrophysiology. The species included are from two Rhopalonematidae clades; they are Colobonema sericeum, Pantachogon haeckeli, Crossota millsae and two species of Benthocodon. Comparison is made with Aglantha digitale, a species from a third Rhopalonematidae clade brought to the surface by natural water movement. We find that although all Rhopalonematidae appear to have two swimming modes there are marked differences in their neural anatomy, kinematics and physiology. Giant motor axons, known to conduct impulses during fast swimming in A. digitale, are absent from C. sericeum and P. haeckeli. Slow swimming is also different; in C. sericeum and its relatives it is driven by contractions restricted to the base of the bell. These behavioural differences are related to the position of the different clades on a ribosomal DNA-based phylogenetic tree. This finding allows us to pinpoint the phylogenetic branch point leading to the appearance of giant motor axons and escape swimming. They place the remarkable dual swimming behaviour of members of the Rhopalonematidae family into an evolutionary context.

Sponge Behavior and the Chemical Basis of Responses: A Post-Genomic View

2019 ◽  
Vol 59 (4) ◽  
pp. 751-764 ◽  
Author(s):  
Sally P Leys ◽  
Jasmine L Mah ◽  
Paul R McGill ◽  
Laura Hamonic ◽  
Fabio C De Leo ◽  
...  
Keyword(s):  
Signaling Pathways ◽  
Atmospheric Pressure ◽  
Water Movement ◽  
Whole Body ◽  
Signal Pathways ◽  
Chemical Signaling ◽  
Electrical Signaling ◽  
Complex Signaling

Abstract Sponges perceive and respond to a range of stimuli. How they do this is still difficult to pin down despite now having transcriptomes and genomes of an array of species. Here we evaluate the current understanding of sponge behavior and present new observations on sponge activity in situ. We also explore biosynthesis pathways available to sponges from data in genomes/transcriptomes of sponges and other non-bilaterians with a focus on exploring the role of chemical signaling pathways mediating sponge behavior and how such chemical signal pathways may have evolved. Sponge larvae respond to light but opsins are not used, nor is there a common photoreceptor molecule or mechanism used across sponge groups. Other cues are gravity and chemicals. In situ recordings of behavior show that both shallow and deep-water sponges move a lot over minutes and hours, and correlation of behavior with temperature, pressure, oxygen, and water movement suggests that at least one sponge responds to changes in atmospheric pressure. The sensors for these cues as far as we know are individual cells and, except in the case of electrical signaling in Hexactinellida, these most likely act as independent effectors, generating a whole-body reaction by the global reach of the stimulus to all parts of the animal. We found no evidence for use of conventional neurotransmitters such as serotonin and dopamine. Intriguingly, some chemicals synthesized by symbiont microbes could mean other more complex signaling occurs, but how that interplay might happen is not understood. Our review suggests chemical signaling pathways found in sponges do not reflect loss of a more complex set.

Sticking to the rules

2020 ◽  
Vol 14 (2) ◽  
Author(s):  
Jeanette Landgrebe ◽  
Rainar Rye Marstrand
Keyword(s):  
Professional Practice ◽  
Video Footage ◽  
Moment Interaction ◽  
Mere Presence ◽  
The Moment ◽  
Professional Workplace ◽  
Different Levels ◽  
Material Form

In this paper, we take an ethnomethodological perspective to analysing members’ competence in a professional practice. We propose an approach which systematises different levels of analysis to identify the underlying management rules, principles and procedures that are significant for the way members in a Lean department meeting organise their in situ activity. Authentic video footage, on-site observations and ethnographic material form the basis of our research focus. Our analysis suggests that the mere presence of an inscribed post-it within an activity does not automatically render it into an object which facilitates discussions, organises activities or records outcomes, but that it is embedded within the members’ taken-for-granted knowledge and routine ways of doing. As such, it is the larger organisational context and the activity at hand which determine the role of the post-it in the moment-to-moment interaction. In conclusion, we suggest going beyond the conventional understanding of context and participation framework in analysing work practices, as an approach to broadening our understanding of what constitutes context from members’ own perspectives in a professional workplace practice.

Towards understanding the role of turbulence on droplets in clouds: In situ and laboratory measurements

2010 ◽  
Vol 97 (4) ◽  
pp. 426-437 ◽  
Author(s):  
H. Siebert ◽  
S. Gerashchenko ◽  
A. Gylfason ◽  
K. Lehmann ◽  
L.R. Collins ◽  
...  
Keyword(s):  
Laboratory Measurements

scholarly journals The role of algae in fine sediment flocculation: In-situ and laboratory measurements

2019 ◽  
Vol 413 ◽  
pp. 71-84 ◽  
Author(s):  
Zhirui Deng ◽  
Qing He ◽  
Zeinab Safar ◽  
Claire Chassagne
Keyword(s):  
Fine Sediment ◽  
Laboratory Measurements

{10-12} Twinning Mechanism During In Situ Micro-Tensile Loading of Pure Mg: Role of Basal Slip and Twin-Twin Boundary Interaction

2020 ◽  
Author(s):  
Nicolò Maria della Ventura ◽  
Szilvia Kalácska ◽  
Daniele Casari ◽  
Thomas Edward James Edwards ◽  
Johann Michler ◽  
...  
Keyword(s):  
Twin Boundary ◽  
Basal Slip ◽  
Tensile Loading ◽  
Boundary Interaction

Saturated Hydraulic Conductivity of Clayey Tills and the Role of Fractures

1990 ◽  
Vol 21 (2) ◽  
pp. 119-132 ◽  
Author(s):  
Johnny Fredericia
Keyword(s):  
Hydraulic Conductivity ◽  
American Studies ◽  
Field Measurements ◽  
Present Knowledge ◽  
Saturated Hydraulic Conductivity ◽  
Field Observations ◽  
Laboratory Measurements ◽  
Vertical Hydraulic Conductivity ◽  
Data Field

The background for the present knowledge about hydraulic conductivity of clayey till in Denmark is summarized. The data show a difference of 1-2 orders of magnitude in the vertical hydraulic conductivity between values from laboratory measurements and field measurements. This difference is discussed and based on new data, field observations and comparison with North American studies, it is concluded to be primarily due to fractures in the till.

The role of (bio)surfactant sorption in promoting the bioavailability of nutrients localized at the solid-water interface

1999 ◽  
Vol 39 (7) ◽  
pp. 91-98 ◽  
Author(s):  
Ryan N. Jordan ◽  
Eric P. Nichols ◽  
Alfred B. Cunningham
Keyword(s):  
Mass Transfer ◽  
Cell Membrane ◽  
Substrate Concentration ◽  
Water Interface ◽  
Industrial Systems ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Surfactant Sorption

Bioavailability is herein defined as the accessibility of a substrate by a microorganism. Further, bioavailability is governed by (1) the substrate concentration that the cell membrane “sees,” (i.e., the “directly bioavailable” pool) as well as (2) the rate of mass transfer from potentially bioavailable (e.g., nonaqueous) phases to the directly bioavailable (e.g., aqueous) phase. Mechanisms by which sorbed (bio)surfactants influence these two processes are discussed. We propose the hypothesis that the sorption of (bio)surfactants at the solid-liquid interface is partially responsible for the increased bioavailability of surface-bound nutrients, and offer this as a basis for suggesting the development of engineered in-situ bioremediation technologies that take advantage of low (bio)surfactant concentrations. In addition, other industrial systems where bioavailability phenomena should be considered are addressed.

THE ROLE OF BACTERIAL COMMUNITIES ON IN-SITU ARSENIC AND IRON CYCLING IN RIVERBANKS ALONG THE MEGHNA RIVER, BANGLADESH

2020 ◽  
Author(s):  
Kimberly D. Myers ◽  
◽  
Katrina Lee Jewell ◽  
P.S.K. Knappett ◽  
Mehtaz M. Lipsi ◽  
...  
Keyword(s):  
Bacterial Communities ◽  
Iron Cycling

scholarly journals Modelling of speleothems failure in the Hotton cave (Belgium). Is the failure earthquake induced?

2001 ◽  
Vol 80 (3-4) ◽  
pp. 315-321 ◽  
Author(s):  
J.F. Cadorin ◽  
D. Jongmans ◽  
A. Plumier ◽  
T. Camelbeeck ◽  
S. Delaby ◽  
...  
Keyword(s):  
Natural Frequencies ◽  
Quantitative Information ◽  
Rigid Bodies ◽  
Tensile Failure ◽  
Future Research ◽  
Geometrical Parameters ◽  
Laboratory Measurements ◽  
Ground Acceleration ◽  
Strong Ground

AbstractTo provide quantitative information on the ground acceleration necessary to break speleothems, laboratory measurements on samples of stalagmite have been performed to study their failure in bending. Due to their high natural frequencies, speleothems can be considered as rigid bodies to seismic strong ground motion. Using this simple hypothesis and the determined mechanical properties (a minimum value of 0.4 MPa for the tensile failure stress has been considered), modelling indicates that horizontal acceleration ranging from 0.3 m/s2 to 100 m/s2 (0.03 to 10g) are necessary to break 35 broken speleothems of the Hotton cave for which the geometrical parameters have been determined. Thus, at the present time, a strong discrepancy exists between the peak accelerations observed during earthquakes and most of the calculated values necessary to break speleothems. One of the future research efforts will be to understand the reasons of the defined behaviour. It appears fundamental to perform measurements on in situ speleothems.

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