Biology subjects

Wan, K. Y.

Publications and source records attributed to Wan, K. Y..

15 recordsLinked to original sources

bioRxiv2026

Adaptive motility and feeding strategies of deep-branching predatory protists

Heterotrophic flagellates play a major role in nutrient recycling and shaping aquatic microbial communities. Many motile species have evolved diverse predatory strategies to exploit microbial prey, from bacteria to small eukaryotes. Excavates, deep-branching eukaryotic lineages with distinctive biflagellate morphology and conserved cytoskeletal features, exhibit varied feeding behaviours, including grazing, raptorial feeding, and filter-feeding. However, the temporal dynamics of their motility, feeding, and spatial distribution in relation to bacterial population density remain under-explored. Here, we quantify the behavioural ecology of excavates using high-resolution, single-cell tracking and quantitative analysis. Focussing on two Discoba species - the marine Jakoba libera and freshwater Reclinomonas americana - we identify different behavioural patterns: J. libera swims, forages and feeds, while R. americana swims and feeds. Prey availability differentially affects motility: J. libera increases the number of swimming cells when food is scarce, while R. americana shows the opposite trend. Spatial statistics reveal fundamental differences in their feeding and redistribution strategies. J. libera acts as an active forager, whereas R. americana behaves as a strict filter feeder. A third species, the anaerobic Kipferlia bialata (from a different clade), adopts a foraging strategy similar to J. libera. Together, these results elucidate the adaptive relationship between prey availability, feeding modes, and motility in bacteriovorous excavate flagellates, offering new insights into the ecological and evolutionary dynamics of microbial predators.

biophysics↗

bioRxiv2026

Mechanosensation, habituation, and behavioural plasticity in tintinnid ciliates

Unicellular organisms sense, integrate and respond to environmental cues despite lacking neurons or a nervous system. Several species, notably ciliates, are capable of adaptive behaviours normally associated with multicellular animals. Integral to marine ecosystems are planktonic ciliates called tintinnids, which feed on microbes and serve as prey for larger predators. In nature, they swim, feed, hunt, and build ornate loricas, while experiencing varied mechanical and flow perturbations from encounters with other organisms and their environment. Here, we investigated mechanosensory responses in tintinnids at single-cell resolution using temporally controlled touch and vibrational stimuli. Localised touch stimulation of the ciliary band triggered stereotyped ciliary reversals and beat frequency elevation, but strong vibrational stimuli elicited rapid whole-cell contractions. Repeated stimulation produced a progressive decline in response probability that depends on stimulus frequency, with spontaneous recovery if stimulation is withheld. Our work identifies a novel form of cilia-associated habituation response to mechanical stimulation in tintinnids that is distinct from contractile whole-body responses previously reported in other protists. The results show how motility and sensory feedback are tightly coupled to coordinate cellular information processing and a hierarchy of mechanosensory responses in a single-celled organism.

biophysics↗

bioRxiv2026

Simulation-driven discovery of morphology-function relationships in microswimmers

For more than a billion years, microorganisms have evolved complex strategies for navigating aquatic habitats, despite the fundamental limitations and constraints imposed by their physical environment. A common theme across these strategies is the use of active slender appendages (cilia, flagella, archaella) to generate self-propulsion. Diverse selection pressures and evolutionary trajectories have driven the emergence of drastically different morphologies of biological microswimmers, each tailored for distinct functions ranging from motility to taxis to prey capture to feeding. Despite the biological and ecological significance of these intricate microscale processes, realistic computational modelling of these organisms and their behaviours is still in its infancy. Here, we present a comprehensive open-source simulation platform for motile microswimmers, that faithfully captures the universal hydrodynamic principles shared by such systems. We illustrate the predictive power and versatility of this approach to resolve and explore morphology-function relationships across different microswimmer species and provide new insights into the diversification of locomotion strategies in early eukaryotes.

biophysics↗

bioRxiv2025

Embodied behavioural complexity in a ciliated microorganism

Most animals coordinate behaviour using neural computations. Yet, single-celled organisms also exhibit stimulus-responsive, even cognitive, actions. To understand how a single cell can coordinate and drive complex behaviours without any neural encoding, we study an algal protist - a motile cell with four extremely long cilia. The organism displays a surprisingly rich locomotor repertoire, emerging from the intricate dynamics of the cilia, which form a tight bundle when swimming. We leverage high-speed quantitative live imaging to extract the spectrum of possible ciliary beating patterns, and derive a dispersion relation coupling the temporal frequency and spatial wavelength of cilia oscillations. We further reconstruct the attractor manifold embedded in the behavioural space, showing that despite the range and complexity of ciliary beating modes, the underlying behavioural manifold is intrinsically low-dimensional with elaborate topological structure. Dynamic and excitable transitions in motility behaviour are encoded as trajectories in this space.

biophysics↗

bioRxiv2025

Light-dependent switching of circling handedness in microswimmer navigation

Many swimming microorganisms navigate their environment by modulating the curvature of their swimming trajectories in response to external cues. Here, we show that the biflagellate alga Chlamy-domonas reinhardtiiswims in circles and actively switches its trajectory handedness in response to orthogonal illumination: the cell swims counterclockwise at low light intensities yet clockwise at high light intensities. This handedness switching arises from light-dependent modulation of flag-ellar beating, including changes in beat extension, phase, and--crucially--beat plane orientation. Using high-speed imaging and hydrodynamic modeling, we reveal that this beat plane reorientation is critical for Chlamydomonas to swim orthogonally to light as well as to dynamically modulate its trajectory curvature, enabling transitions between global exploration and localized searching in spatially structured light fields. Our results establish beat plane reorientation as a novel mechanism for curvature control in microswimmer navigation.

biophysics↗

bioRxiv2025

Dynamics and emergence of metachronal waves in the ciliary band of a metazoan larva

Both natural and synthetic ciliary arrays exhibit diverse coordination patterns. Proper coordination of cilia is essential for the normal physiology of many organisms, from single cells to humans. Yet despite decades of research the mechanisms of cilia coordination remains disputed, particularly the question of how coordinated waves of activity known as metachronal waves arise in different ciliated systems. In many aquatic larvae that rely on ciliary motility to swim, the cilia are often arranged ornately in arrays or bands, within which robust metachronal waves propagate. Here, to resolve the origins of ciliary metachronism, we target the equatorial ciliary band of the marine annelid, Platynereis dumerelii, using whole-body high-speed imaging, and physical and biological manipulations. The results reveal an unprecedented wave structure featuring strong coupling within individual multiciliated cells that breaks down across cell boundaries, and absence of global coupling across the organism. Using laser ablation to create gaps in the ciliary band, we quantify the resulting disruption to wave propagation, revealing the extent of interciliary phase-locking and implicating steric interactions as an important contributor to coordination. The larvae also exhibit spontaneous whole-body ciliary arrests which allow us to study wave emergence and re-establishment for the first time, revealing a novel role of the animals nervous system in the dynamic coupling of cilia.

biophysics↗

bioRxiv2025

A scotophobic response characterised by body contraction and ciliary arrest in Acropora coral larvae

Planulae of the reef-building coral Acropora millepora exhibit whole-body contraction and ciliary arrest after exposure to sudden light dimming. Quantitative behavioural assays confirmed reductions in swimming speed and alterations in vertical and horizontal movement under alternating light and dark conditions. High-speed microscopy revealed that ciliary activity ceases upon dimming, while the typically elongated body contracts into a rounded form, altering swimming behaviour. These larval responses suggest an adaptive mechanism to regulate positioning within the highly structured and complex light environment of reef habitats, critical for coral recruitment and survival.

neuroscience↗

bioRxiv2024

Diversity of motility patterns in benthic diatoms

Diatoms, a highly successful group of photosynthetic algae, contribute to a quarter of global primary production. Many species are motile, despite having no appendages and a completely rigid cell body. Cells move to seek out nutrients, locate mating partners, and undergo vertical migration. To explore the natural diversity of diatom motility, we perform a comparative study across five common biofilm-forming species. Combining morphological measurements with high-resolution cell tracking, we establish how gliding movements relate to the morphology of the raphe - a specialised slit in the cell wall responsible for motility generation. Our detailed analyses reveal that cells exhibit a rich but species-dependent phenotype, switching stochastically between four stereotyped motility states. We model this behaviour and use stochastic simulations to predict how heterogeneity in microscale navigation patterns leads to differences in long-time diffusivity and dispersal. In a representative species, we extend these findings to quantify diatom gliding in complex, naturalistic 3D environments, suggesting that cells may exploit these distinct motility signatures to achieve niche segregation in nature.

biophysics↗

bioRxiv2022

Ciliary propulsion and metachronal coordination in reef coral larvae

Larval dispersal is critical to the survival of coral reefs. As the only motile stage of the reproductive cycle, coral larvae choose a suitable location to settle and mature into adult corals. Here, we present the first detailed study of ciliary propulsion in the common stony reef coral Acropora millepora. Using high-speed, high-resolution imaging, particle image velocimetry, and electron microscopy, we reveal the arrangement of the densely packed cilia over the larval body surface, and their organisation into diaplectic (transversely propagating) metachronal waves. We resolve the individual-ciliums beat dynamics and compare the resultant flows with a computational model of a ciliary array, and show that this form of ciliary metachronism leads to near-maximal pumping efficiency.

biophysics↗

bioRxiv2022

Distinct gaits of self-propelled quadriflagellate microswimmers

Legged animals often coordinate multiple appendages for both underwater and terrestrial loco-motion. Quadrupeds in particular, change their limb movements dynamically to achieve a number of gaits, such as the gallop, trot, and pronk. Surprisingly, micron-sized unicellular algae are also capable of coordinating four flagella to produce microscale versions of these gaits for swimming. Here we present a fully-3D model of a quadriflagellate microswimmer comprising five beads and systematically investigate the effect of gait on swimming dynamics, propulsion speed, efficiency, and induced flow patterns. We find that by changing gait alone, distinct motility patterns emerge from the same basic microswimmer design. Our findings suggest that different species of morphologically-similar microorganisms (e.g. with identical number and placement of appendages) evolved distinct flagellar coordination patterns as a consequence of different ecological drivers. By comparing the flagella-induced flows in terms of volumetric clearance rate, we further explore the implications of distinct gaits for single-cell dispersal, feeding, and predator-avoidance.

biophysics↗

bioRxiv2021

Phenotyping single-cell motility in microfluidic confinement

At all scales, the movement patterns of organisms serve as dynamic read-outs of their behaviour and physiology. We devised a novel droplet microfluidics assay to encapsulate single algal microswimmers inside closed arenas, and comprehensively studied their roaming behaviour subject to a large number of environmental stimuli. We compared two model species, Chlamydomonas reinhardtii (freshwater alga, 2 cilia), and Pyramimonas octopus (marine alga, 8 cilia), and detailed their highly-stereotyped behaviours and the emergence of a trio of macroscopic swimming states (smooth-forward, quiescent, tumbling or excitable backward). Harnessing ultralong timeseries statistics, we reconstructed the species-dependent reaction network that underlies the choice of locomotor behaviour in these aneural organisms, and discovered the presence of macroscopic non-equilibrium probability fluxes in these active systems. We also revealed for the first time how microswimmer motility changes instantaneously when a chemical is added to their microhabitat, by inducing deterministic fusion between paired droplets - one containing a trapped cell, and the other, a pharmacological agent that perturbs cellular excitability. By coupling single-cell entrapment with unprecedented tracking resolution, speed and duration, our approach offers unique and potent opportunities for diagnostics, drug-screening, and for querying the genetic basis of micro-organismal behaviour.

biophysics↗

bioRxiv2021

A minimal robophysical model of quadriflagellate self-propulsion

Locomotion at the microscale is remarkably sophisticated. Microorganisms have evolved diverse strategies to move within highly viscous environments, using deformable, propulsion-generating appendages such as cilia and flagella to drive helical or undulatory motion. In single-celled algae, these appendages can be arranged in different ways around an approximately 10 {micro}m cell body, and coordinated in distinct temporal patterns. Inspired by the observation that some quadriflagellates (bearing four flagella) have an outwardly similar morphology and flagellar beat pattern, yet swim at different speeds, this study seeks to determine whether variations in swimming performance could arise solely from differences in swimming gait. Robotics approaches are particularly suited to such investigations, where the phase relationships between appendages can be readily manipulated. Here, we developed autonomous, algae-inspired robophysical models that can self-propel in a viscous fluid. These macroscopic robots (length and width = 8.5 cm, height = 2 cm) have four independently actuated flagella that oscillate back and forth under low-Reynolds number conditions (Re[~] [O] (10-1)). We tested the swimming performance of these robot models with appendages arranged in one of two distinct configurations, and coordinated in one of three distinct gaits. The gaits, namely the pronk, the trot, and the gallop, correspond to gaits adopted by distinct microalgal species. When the appendages are inserted perpendicularly around a central body, the robot achieved a net performance of 0.15 - 0.63 body lengths per cycle, with the trot gait being the fastest. Robotic swimming performance was found to be comparable to that of the algal microswimmers across all gaits. By creating a minimal robot that can successfully reproduce cilia-inspired drag-based swimming, our work paves the way for the design of next-generation devices that have the capacity to autonomously navigate aqueous environments.

biophysics↗

bioRxiv2020

Control of helical navigation by three-dimensional flagellar beating

Helical swimming is a ubiquitous strategy for motile cells to generate self-gradients for environmental sensing. The model biflagellate Chlamydomonas reinhardtii rotates at a constant 1 - 2 Hz as it swims, but the mechanism is unclear. Here, we show unequivocally that the rolling motion derives from a persistent, non-planar flagellar beat pattern. This is revealed by high-speed imaging and micromanipulation of live cells. We construct a fully-3D model to relate flagellar beating directly to the free-swimming trajectories. For realistic geometries, the model reproduces both the sense and magnitude of the axial rotation of live cells. We show that helical swimming requires further symmetry-breaking between the two flagella. These functional differences underlie all tactic responses, particularly phototaxis. We propose a control strategy by which cells steer towards or away from light by modulating the sign of biflagellar dominance.

biophysics↗

bioRxiv2020

Functional Exploration of Heterotrimeric Kinesin-II in IFT and Ciliary Length Control in Chlamydomonas

Heterotrimeric organization of kinesin-II is essential for its function in anterograde IFT in ciliogenesis. However, the molecular basis of forming this complex for its function is not well understood. In addition, the anterograde IFT velocity varies significantly in different organisms, but how motor speed affects ciliary length is not clear. We show that Chlamydomonas kinesin-II (CrKinesin-II) involves distinct mechanisms from mammals and C. elegans in its assembly to necessitate its function in IFT. Furthermore, chimeric CrKinesin-II with human kinesin-II motor domains functioned in vitro and in vivo, leading to a ~2.8-fold reduced anterograde IFT velocity and a similar fold reduction in IFT injection rate that supposedly correlates with ciliary assembly activity. However, the ciliary length was only mildly reduced (~15%). Modelling analyses suggest that such a non-linear scaling relationship between IFT velocity and ciliary length can be accounted for by limitation of the motors and/or its ciliary cargoes, e.g. tubulin.

cell biology↗

bioRxiv2019

Reorganisation of complex ciliary flows around regenerating Stentor coeruleus

The phenomenon of ciliary coordination has garnered increasing attention in recent decades, with multiple theories accounting for its emergence in different contexts. The heterotrich ciliate Stentor coeruleus is a unicellular organism which boasts a number of features which present unrivalled opportunities for biophysical studies of cilia coordination. With their cerulean colour and distinctive morphology, these large protists possess a characteristic differentiation between cortical rows of short body cilia used for swimming, and an anterior ring structure of fused oral cilia forming a membranellar band. The oral cilia beat metachronously to produce strong feeding currents. In addition to this complex body plan, Stentor have remarkable regenerative capabilities. Minute fragments of single cells can over the period of hours or days, regenerate independently into new, proportional individuals. Certain environmental perturbations elicit a unique programmed response known as oral regeneration wherein only the membranellar band is shed and a new, ciliated oral primordium formed on the side of the body. Here, we target oral regeneration induced by sucrose-shock to reveal the complex interplay between ciliary restructuring and hydrodynamics in Stentor, which accompanies the complete developmental sequence from band formation, elongation, curling, and migration toward the cell anterior.\n\n\"When the anterior part is open, one may perceive about its Edges a very lively Motion; and when the Polyps presents itself in a certain manner, it discovers, on either side of these edges of its anterior part, somewhat very much resembling the wheels of a little Mill, that move with great velocity.\"\n\nA. Trembley F.R.S describing the membranellar band of Stentor, Phil. Soc. Trans. Royal Society (London), 1744.

biophysics↗