Biology subjects

Bhamla, S.

Publications and source records attributed to Bhamla, S..

10 recordsLinked to original sources

bioRxiv2026

Springtail-inspired compliant hinge enables terrain-adaptable takeoff in insect-scale robots

Springtails execute millisecond-scale escape jumps with a single appendage, the furca, on soil, snow, leaf litter, and water. Across 15 taxonomic families (n=552 individuals), relative furca length is bimodal. High-speed video and confocal imaging show that in some long-furca springtails, the resilin-rich manubrium-dens joint behaves as a compliant hinge. It bends during push-off to prolong contact, suppress pitch, and bias takeoff forward, whereas rigid joints drive backward launches with rapid body rotation. We translate this mechanism to a 20-mm, 84-mg jumping robot with an elastic robo-furca hinge. This flexible hinge reduces body rotation by [~] 90% on flat ground compared to rigid-hinge designs, while maintaining takeoff speed on gravel, springboards, leaves, and pine needles, enabling passive, terrain-adaptable launches for power-limited insect-scale robots without onboard sensing or active control.

animal behavior and cognition↗

bioRxiv2025

Decoding ultrasensitive self-assembly of the calcium-regulated Tetrahymena cytoskeletal protein Tcb2 using optical actuation.

EF-hand calcium binding proteins are key macromolecular components of many unique filament systems and ultrafast contractile structures found in protists. However, our biochemical understanding of these cytoskeletal systems has been hindered by the need for assays that can controllably generate spatiotemporal calcium dynamics to probe their behavior. Here, we define the quantitative requirements for calcium-dependent self-assembly of the Tetrahymena cortical cytoskeletal protein Tcb2 using a microscopy-based spatiotemporally controlled optical calcium release assay. Light-driven uncaging of the photolabile calcium chelator DMNP-EDTA stimulates rapid localized self-assembly of Tcb2 into micron-scale protein networks. We quantify how the growth, size, and lifetime of Tcb2 networks is controlled by the duration and intensity of the applied light pulse. Incorporating the fluorescent calcium indicator Rhod-5N allows inference of the spatiotemporal distribution of calcium-bound Tcb2 monomers during the reaction and identifies a sharp, ultrasensitive transition to Tcb2 self-assembly. By applying this assay to mutants in Tcb2s four EF hand domains, we show that D184 is the key calcium binding site that licenses Tcb2 for self-assembly and define quantitative roles for other binding sites in tuning Tcb2s calcium-responsiveness. Our approach reveals a rich space of structures and regulation available to a single-protein system through coupling calcium-binding to ultrasensitive self-assembly, opening new paths forward to understanding other protist filament networks and contractile myonemes.

biophysics↗

bioRxiv2025

Adhesion and injury cues enhance blackworm captureby freshwater planaria

In aquatic ecosystems, freshwater planarians (Dugesia spp.) function as predators, employing specialized adaptations for capturing live prey. This exploratory study examines the predatory interactions between the freshwater planarian Dugesia spp. and the California blackworm (Lumbriculus variegatus). Observations demonstrate that Dugesia is capable of capturing prey more than twice its own length. The predation process involves a dual adhesion mechanism whereby the planarian adheres simultaneously to the blackworm and the substrate, effectively immobilizing its prey. Despite the rapid escape response of blackworms, characterized by a reversing spiral swimming gait, planarian adhesion frequently prevents successful escape, although notably larger blackworms exhibit increased escape success. Subsequently, Dugesia employs an eversible pharynx to initiate ingestion, consuming the internal tissues of the blackworm through suction. Injury in blackworms emerged as a significant predictor of predation events, suggesting the potential involvement of chemical cues in prey detection, although this warrants further investigation. This study provides insights into the biomechanics and behaviors of predation involving two interacting muscular hydrostats, highlighting the critical adaptations that enable planarians to subdue and consume relatively large, mobile prey.

biophysics↗

bioRxiv2025

Rhagovelia uses interfacial run-and-tumble locomotionto improve prey capture in flowing environments

Rhagovelia oriander is a freshwater water strider native to the rivers and streams of North and South America, known for its distinctive skating movement on the waters surface. This movement resembles the correlated random-walk pattern seen in microorganisms such as Escherichia coli. Previous studies have primarily focused on limb adaptations and biomechanics, leaving the ecological significance inadequately addressed. We combine field observations with controlled laboratory experiments using a flow mill to investigate the dynamics of R. oriander under typical flow conditions. Our findings indicate that this insect exhibits a two-dimensional run-and-tumble motion, often incorporating lateral tumbles following straight runs (run distance: 30.7 {+/-} 9.3 mm). We find that this behavior is resilient to changes in flow speed. In-silico simulations of particle interception demonstrated that this locomotion method enhances encounter rates compared to linear movement, particularly when the simulated food particle is following a rapid flow field. Our results document run-and-tumble locomotion in a millimeter-scale organism, showcasing a unique example of convergent behavior across diverse taxonomic groups and providing valuable insights into locomotion ecology while serving as a source of inspiration for bioinspired robotics and environmental exploration algorithms.

biophysics↗

bioRxiv2025

Hexapods shift to increasingly stable gaits when climbing on inclined substrates

When terrestrial organisms locomote in natural settings, they must navigate complex surfaces that vary in incline angles and substrate roughness. Variable surface structures are common in arboreal environments and can be challenging to traverse. This study examines the walking gait of katydids (Tettigoniidae) as they traverse a custom-built platform with varying incline angles (30{degrees}, 45{degrees}, 60{degrees}, 75{degrees}, 90{degrees}) and substrate roughness (40, 120, and 320 grit sandpaper). Our results show that katydids walk more slowly as the incline angle increases and as katydid mass increases, with a decrease of around 0.3 BL/s for every 1{degrees} increase in incline. At steeper inclines and larger sizes, katydids are also less likely to use an alternating tripod gait, opting instead to maintain more limbs in contact with the substrate during walking. Katydids also increased average duty factor when climbing steeper inclines and with increasing body mass. However, substrate roughness did not affect walking speed or gait preference in our trials. These findings provide insights into how environmental factors influence locomotor strategies in katydids and enhance our understanding of effective locomotor strategies in hexapods.

animal behavior and cognition↗

bioRxiv2025

Three-dimensional Tracking Method for Water-Hopping Mudskippers in Natural Habitats

We present a portable, non-invasive, and low-cost three-dimensional tracking method to quantify in situ water-hopping kinematics of mudskippers. By combining dual-camera video recordings with tracking fish path, Gaussian Splatting terrain reconstruction and epipolar geometric analysis, we capture detailed 3D trajectories of mudskippers in their natural tidal-flat habitats. Our proposed method resolves complex hopping motions, including both straight and curved escape paths, and reveals that horizontal distance, hopping height, and speed are strongly influenced by fish size and local terrain features. These results highlight both the biomechanical and ecological significance of water-hopping in mudskippers, demonstrating how a simple, deployable 3D approach can resolve complex amphibious movements in challenging field environments.

animal behavior and cognition↗

bioRxiv2025

Light-induced reversible assembly and actuation in ultrafast Ca2+-driven chemomechanical protein networks

Programming rapid, repeatable motions in soft materials has remained a challenge in active matter and biomimetic design. Here, we present a light-controlled chemomechanical network based on Tetrahymena thermophila calcium-binding protein 2 (Tcb2), a Ca2+-sensitive contractile protein. These networks--driven by Ca2+-triggered structural rearrangements--exhibit dynamic selfassembly, spatiotemporal growth, and contraction rates comparable to actomyosin systems. By coupling light-sensitive chelators for optically triggered Ca2+ release, we achieve precise growth and repeatable mechanical contractility of Tcb2 networks, revealing emergent phenomena such as boundary-localized active regions and density gradient-driven reversals in motion. A coupled reaction-diffusion and elastic model explains these dynamics, highlighting the interplay between chemical network assembly and mechanical response. We further demonstrate active transport of particles via network-mediated forces in vitro and implement reinforcement learning to program seconds-scale spatiotemporal actuation in silico. These results establish a platform for designing responsive active materials with rapid chemomechanical dynamics and tunable optical control, with applications in synthetic cells, sub-cellular force generation, and programmable biomaterials.

bioengineering↗

bioRxiv2024

Mastering the Manu - How humans create large splashes

Manu jumping, a popular water diving style amongst M[a]ori people in New Zealand, focuses on creating large splashes. Divers perform aerial maneuvers such as the "utkatasana" pose, entering the water in a V-shape, and executing underwater maneuvers to maximize the splash size. Our study explores the underlying fluid dynamics of Manu jumping and demonstrates how two key parameters, the V-angle and the timing of body opening, can maximize the Worthington jet formation. To accurately replicate human manu jumping, we studied water entry of both passive solid objects with varying V angles and an active body opening robot (Manubot). The analysis revealed that a 45-degree V angle is optimal for maximizing Worthington jet formation, consistent with human diving data. This angle balances a large cavity size and a deep pinch-off depth. The body opening within a timing window of [Formula] synchronizes the robots potential energies to be timely transferred to the cavity formation, producing the strongest and most vertical, i.e., ideal, Worthington jets. Based on our experimental findings, we propose optimal parameters for generating the largest Manu splashes. These insights offer engineering perspectives on how to modulate underwater cavity dynamics using both passive and active body formations.

biophysics↗

bioRxiv2024

Fishnet mesh of centrin-Sfi1 drives ultrafast calcium-activated contraction of the giant cell Spirostomum ambiguum

Spirostomum is a giant unicellular ciliate that contracts to a quarter of its body length in less than five milliseconds, achieving an order of magnitude higher fractional shortening rate than actomyosin-based systems. This ultrafast contraction is powered by myonemes, calcium-activated protein networks at the cortex whose biochemical mechanism remain unclear. We quantify changes in cortical microtubules, membrane ruffles, and the fishnet-like myoneme mesh during contraction, and develop multiscale models that connect local myoneme shortening to whole-cell shape change. Centrin and an Sfi1 homolog co-localize with the myoneme by immunofluorescence and localize to the myoneme by immunogold electron microscopy. Coarse-grained mesh simulations reproduce the measured deformations and show that fishnet geometry, together with volume conservation, leads to uniform contraction. Finally, we reconstitute a Spirostomum centrin-Sfi1 repeat complex in vitro and measure calcium-dependent compaction and self-association, supporting a molecular basis for myoneme contractility. Together, these results support a multiscale model in which calcium-responsive centrin- Sfi1 structures are the central contractile element in Spirostomum and suggest design principles for fast, calcium-triggered, chemomechanical contractile networks that operate without actomyosin or ATP. SIGNIFICANCE STATEMENTMany cells change shape using actomyosin, but some protists contract using calcium-activated protein networks called myonemes. We combine quantitative imaging, electron microscopy, multiscale modeling, and in vitro reconstitution to link molecular-scale mechanisms to the millisecond shortening of the giant ciliate Spirostomum. Centrin and an Sfi1 homolog co-localize in a fishnet-like cortical mesh, and simulations show that this geometry can reproduce the observed whole-cell shape change under volume conservation. Purified centrin-Sfi1 complexes undergo calcium-dependent compaction and self-association, supporting a protein-scale switch that can drive myoneme contraction. These results connect calcium signaling to whole-cell mechanics and suggest principles for designing fast, ATP-independent bioin-spired actuators and synthetic cellular machinery.

cell biology↗

bioRxiv2019

Biophysical mechanism of ultrafast helical twisting contraction in the giant unicellular ciliate Spirostomum ambiguum

The biophysical mechanism of cytoskeletal structures has been fundamental to understanding of cellular dynamics. Here, we present a mechanism for the ultrafast contraction exhibited by the unicellular ciliate Spirostomum ambiguum. Powered by a Ca2+ binding myoneme mesh architecture, Spirostomum is able to twist its two ends in the same direction and fully contract to 75% of its body length within five milliseconds, followed by a slow elongation mechanism driven by the uncoiling of the microtubules. To elucidate the principles of this rapid contraction and slow elongation cycle, we used high-speed imaging to examine the same-direction coiling of the two ends of the cell and immunofluorescence techniques to visualize and quantify the structural changes in the myoneme mesh, microtubule arrays, and the cell membrane. Lastly, we provide support for our hypotheses using a simple physical model that captures key features of Spirostomums ultrafast twisting contraction. SIGNIFICANCEUltrafast movements are ubiquitous in nature, and some of the most fascinating ultrafast biophysical systems are found on the cellular level. Quantitative studies and models are key to understand the biophysics of these fast movements. In this work, we study Spirostomums ultrafast contraction by using high-speed imaging, labeling relevant cytoskeletal structures, and building a physical model to provide a biophysical mechanism especially of the helical same direction twisting of this extremely large single cell organism. Deeper understanding of how single cells can execute extreme shape changes hold potential for advancing basic cell biophysics and also inspire new cellular inspired actuators for engineering applications.

biophysics↗