Evolution Of Feeding Shapes Swimming Kinematics Of Barnacle Naupliar Larvae: A Comparison Between Trophic Modes

A central goal in evolutionary biology is connecting morphological features with ecological functions. For marine invertebrate larvae, appendage movement determines locomotion, feeding, and predator avoidance ability. Barnacle larvae are morphologically diverse, and the morphology of non-feeding lecithotrophic nauplii are distinct from those that are planktotrophic. Lecithotrophic larvae have a more globular body shape and simplified appendages when compared with planktotrophs. However, little is known about whether and how such morphological changes affect kinematics, hydrodynamics, and ecological functions. Here, we compared the nauplii kinematics and hydrodynamics of a lecithotrophic Rhizocephalan species, Polyascus planus, against that of the planktotrophic nauplii of an intertidal barnacle, Tetraclita japonica. High-speed, micro-particle image velocimetry analysis showed that the Polyascus nauplii swam faster and had higher amplitude and more synchronous appendage beating than the Tetraclita nauplii. This fast swimming was accompanied by a faster attenuation of induced flow with distance, suggesting reduced predation risk. Tetraclita nauplii had more efficient per beat cycles with less backward displacement during the recovery stroke. This “anchoring effect” resulted from the anti-phase beating of appendages. This movement, together with a high-drag body form, likely helps direct the suction flow toward the ventral food capturing area. In sum, the tradeoff between swimming speed and predation risks may have been an important factor in the evolution of the observed larval forms

Initial Geometrical Imperfections in Three-Storey Modular Steel Scaffolds

Modular steel scaffolds are commonly used as supporting scaffolds in building construction. They are highly susceptible to global and local instability, and traditionally, the load carrying capacities of these scaffolds are obtained from limited full-scale tests with little rational design. Structural failure of these scaffolds occurs from time to time due to inadequate design, poor installation and over-loads on sites. Initial geometrical imperfections are considered to be very important to the structural behaviour of multi-storey modular steel scaffolds. This paper presents an extensive numerical investigation on three different approaches in analyzing and designing multi-story modular steel scaffolds, namely, a) Notional Load Approach, b) Eigenmode Imperfection Approach, and c) Critical Load Approach. It should be noted that all these three approaches adopt different ways to allow for the presence of initial geometrical imperfections in the scaffolds when determining their load carrying capacities. Moreover, their suitability and accuracy in predicting the structural instability of typical modular steel scaffolds are presented and discussed in details

Neural processes of proactive and reactive controls modulated by motor-skill experiences

This study investigated the experience of open and closed motor skills on modulating proactive and reactive control processes in task switching. Fifty-four participants who were open-skilled

A Tail’s Tale: Biomechanical Roles Of Dorsal Thoracic Spine Of Barnacle Nauplii

Many marine invertebrates have complex life histories that begin with a planktonic larval stage. Similar to other plankton, these larval invertebrates often possess protruding body extensions, but their function beyond predator deterrence is not well-documented. For example, the planktonic nauplii of crustaceans have spines. Using the epibiotic pedunculate barnacle Octolasmis spp., we investigated how the dorsal thoracic spine affects swimming and fluid disturbance by comparing nauplii with their spines partially removed against those with intact spines. Our motion analysis showed that amputated Octolasmis spp. swam slower, in jerkier trajectories, and were less efficient per stroke cycle than those with intact spines. Amputees showed alterations in limb beat pattern: larger beat amplitude, increased phase lag, and reduced contralateral symmetry. These changes might partially help increase propulsive force generation and streamline the flow, but were insufficient to restore full function. Particle image velocimetry further showed that amputees had a larger relative area of influence, implying elevated risk by rheotactic predator. Body extensions and their interactions with limb motion play important biomechanical roles in shaping larval performance, which likely influences the evolution of form

Chapter 7 Review: Effects of Microplastic on Zooplankton Survival and Sublethal Responses

Microplastics (MPs) are a prolific contaminant in aquatic ecosystems across the globe. Zooplankton (including holoplankton and meroplankton) play vital ecological roles in marine and freshwater ecosystems and have been shown to readily consume MPs. The present review uses 88 pieces of published literature to examine and compare the effects of MPs on survival, growth, development, feeding rate, swimming speed, reproduction, organ damage and gene expression of different groups of zooplankton including copepods, daphnids, brine shrimp, euphausids, rotifers and the larvae of fishes, sea urchins, molluscs, barnacles, decapods and ascidians. Among the groups studied, daphnids and copepods are the most sensitive to MPs, with their feeding rate and fecundity significantly decreased at environmentally relevant MP concentrations. This might adversely affect daphnids and copepods populations in the long term. In contrast, molluscs, barnacles, brine shrimp and euphausids appear to be more tolerant to MPs. No clear impacts on survival, development time, growth or feeding rate can be observed in these zooplankton groups at any of the MP concentrations tested, suggesting that these groups might become more dominant with prolonged exposure to MP pollution. Leachates derived from MPs can induce severe abnormality in bivalve and sea urchin embryos. MPs have prominent effects on survival and fecundity of F1 offspring in bivalves, copepods and daphnids, indicating that MPs could incite transgenerational effects and drastically affect sustainability in zooplankton populations

Structural insights into the gating of DNA passage by the topoisomerase II DNA-gate.

Type IIA topoisomerases (Top2s) manipulate the handedness of DNA crossovers by introducing a transient and protein-linked double-strand break in one DNA duplex, termed the DNA-gate, whose opening allows another DNA segment to be transported through to change the DNA topology. Despite the central importance of this gate-opening event to Top2 function, the DNA-gate in all reported structures of Top2-DNA complexes is in the closed state. Here we present the crystal structure of a human Top2 DNA-gate in an open conformation, which not only reveals structural characteristics of its DNA-conducting path, but also uncovers unexpected yet functionally significant conformational changes associated with gate-opening. This structure further implicates Top2's preference for a left-handed DNA braid and allows the construction of a model representing the initial entry of another DNA duplex into the DNA-gate. Steered molecular dynamics calculations suggests the Top2-catalyzed DNA passage may be achieved by a rocker-switch-type movement of the DNA-gate

Firestorms on Social Media: Effects of Social Information Characteristics on Customer Responses

Firestorms on social media have become one of the biggest challenges for organizations engaging with such online platforms. Handling a firestorm on social media has not been easy because customers\u27 responses towards the incident is influenced by not only the original content, but also others’ responses towards the firestorm on the platform. Drawing on social impact theory and the dual-process model of social influences, this study develops a conceptual framework and explores the effects of social information characteristics (i.e., strength, number, and immediacy) on the customers\u27 perceptions of social influences (i.e., social proof and social pressure), and then their immediate and distal responses towards the organization. The conceptual framework will be tested with social media users using a focus group study and an experiment. This study is expected to contribute to the growing body of knowledge of firestorms on social media and provide organizations with insights into tackling such firestorm

Kinematic analysis of the Pakuashan fault tip fold, west central Taiwan: Shortening rate and age of folding inception

The Pakuashan anticline is an active fault tip fold that constitutes the frontal most zone of deformation along the western piedmont of the Taiwan Range. Assessing seismic hazards associated with this fold and its contribution to crustal shortening across central Taiwan requires some understanding of the fold structure and growth rate. To address this, we surveyed the geometry of several deformed strata and geomorphic surfaces, which recorded different cumulative amounts of shortening. These units were dated to ages ranging from ~19 ka to ~340 ka using optically stimulated luminescence (OSL). We collected shallow seismic profiles and used previously published seismic profiles to constrain the deep structure of the fold. These data show that the anticline has formed as a result of pure shear with subsequent limb rotation. The cumulative shortening along the direction of tectonic transport is estimated to be 1010 ± 160 m. An analytical fold model derived from a sandbox experiment is used to model growth strata. This yields a shortening rate of 16.3 ± 4.1 mm/yr and constrains the time of initiation of deformation to 62.2 ± 9.6 ka. In addition, the kinematic model of Pakuashan is used to assess how uplift, sedimentation, and erosion have sculpted the present-day fold topography and morphology. The fold model, applied here for the first time on a natural example, appears promising in determining the kinematics of fault tip folds in similar contexts and therefore in assessing seismic hazards associated with blind thrust faults

An in vivo intracellular study of auditory thalamic neurons

The intrinsic electrophysiological properties of medial geniculate body (MGB) neurons and their responses to noise bursts/pure tones were examined in the pentobarbital anesthetized guinea pig through intracellular recording. Discharge rate was calculated in the absence of acoustic stimuli over varied membrane potentials which were changed by intracellular injection of current or through automatic drifting. The non-acoustically-driven firing rate was 45.8±23.3 Hz (mean±S.D., n=8) at membrane potentials of -45 mV, 30.6±19.4 Hz (n=14) at -50 mV, 18.0±12.9 Hz (n=14) at -55 mV, and significantly decreased to 5.7±7.4 Hz at -60 mV, and to 0.7±1.5 Hz (n=10) at -65 mV (ANOVA, P<0.001). The maximum non-acoustically-driven rate observed in the present study was 160 Hz. The auditory responsiveness of the MGB neurons was examined at membrane potentials over a range of -45 to -75 mV: the higher the membrane potential, the greater the responsiveness and vice versa. A putative non-low-threshold calcium spike (non-LTS) burst was observed in the present study. It showed significantly longer inter-spike intervals (11.6±6.0 ms, P<0.001, t -test) than those associated with the putative LTS bursts (6.7±2.4 ms, P<0.001, t-test). The dependence of the temporal structure of the spikes/spike bursts on the stimulus may provide insight into the temporal coding of sound information in the auditory system. © 2003 Elsevier Ltd. All rights reserved.published_or_final_versio