I take on the challenges of studying complex biological designs using integrative approaches, with the ultimate goal of uncovering the interplay between biological and physical principles in evolution. I frame research questions within an evolutionary context, and use both experimental physics and mathematical modeling to obtain answers.
My research falls into three overlapping areas: (1) Evolution of complex functional systems across cellular to organismal levels. (2) Biophysics, morphogenesis and evolution of novel structure at the cellular and subcellular levels. (3) Ecology and biomechanics of novel performances within contexts of dispersal, feeding and predator-prey interactions.
General areas: biomechanics, evolution, morphogenesis, physiology, biofluids, behavioral ecology
Specific areas: Biomechanics and evolution of locomotor systems (flapping flight, controlled aerial locomotion, legged locomotion, flagellated locomotion), Interfacial fluid mechanics, Collective motility, Intracellular morphogenesis
Biomechanics, Evolution & Morphogenesis at Cellular Level
Evolution and morphogenesis of a high-performance intracellular fiber
The hagfishes defend themselves against predators with their slime, a composite material formed within 0.1 second. The strength of slime is imparted by the slime threads, which rival spider silk in strength and are the longest known intracellular fibers (i.e., reaching ~20 cm in length, which is >1,000 times the size of the cell). My ongoing research addresses the development, morphogenesis and evolution of hagfish slime thread by asking: (1) How do the threads develop, coil and package within the cytoplasmic space, and (2) what is the evolutionary origin of slime thread?
Keywords biofiber, evolution, intracellular morphogenesis, predator-prey interaction
Body size-dependent evolution of thread and thread cells: Zeng, Y., Petrichko, S., Nieders, K., Plachetzki, D., Fudge, D. (2021) Evolution of a remarkable intracellular polymer and extreme cell allometry in hagfishes. Current Biology.
Rolling locomotion in bacterial aggregates
I discovered a mode of locomotion built on division-of-labor in the bacterium Caulobacter crescentus. These organisms have two types of cells; immotile stalked cells and flagellated cells. They form aggregates and disperse by rolling on liquid-solid interfaces. I captured images of the rolling aggregates using high-speed microscopy and was able to reconstruct the 3D kinematics for hydrodynamic modeling. C. crescentus wheel-like rolling is driven by flagellar motors and represented by far the smallest wheeled locomotion found in any living systems.
Keywords microorganism movement, hydrodynamics, dispersal, multicellularity, micro-robotics
Biomechanics, Evolution & Morphogenesis at Organismal Level
Evolution and biomechanics of insect flight
The earliest winged insects left no trace in the fossil record, yet we know that the first winglets somehow gained size and acquired flapping motion leading to flight. To understand the evolution from winglessness to flapping flight, I examined extant insects undergoing flight reduction. By sampling from intermediate morphologies, I studied how flight biomechanics varied with wing size in evolution.
Evolution and biomechanics of insect flight along ecological gradient
The tropical stick insect Asceles tanarata Brock, 1999 represents one of the few well-documented cases of discrete intra-specific variation in flight-related morphology along an environmental gradient. From lowland Singapore (~50 m) to Cameron Highland (~1600 m), they exhibit a transition from fully-winged to miniaturized winged morphology. My research addresses the evolutionary transitions in flight-related morphology and flight biomechanics in this species group.
Keywords aerodynamics, flight, evolution, sexual dimorphism
Evolution of flight morphology
The stick insects exhibit diverse wing sizes. What is the general pattern of wing size variation and what are the underlying selections? My research showed the variation in wing size depends on sex and correlates with body size. It also explained why there are so few insects with intermediate-sized wings.
Keywords evolution, flight, sexual dimorphism
Biomechanics of aerial righting reflex
Aerial righting maneuver using appendages as aerodynamic surfaces is an essential step in flight evolution. In nymphal stick insect Extatosoma tiaratum, I showed complex leg behaviors with significant aerodynamic utilities for initiating rapid righting rotation and decelerating the rotation afterward. This research demonstrated complex neuromechanical mechanisms can be involved in controlled aerial behaviors as simple as falling upside-down.
Keywords aerodynamics, maneuverability, flight, legs, micro aero-robotics
Functional implication of the evolution of a novel body plan: Biomechanics of omnidirectional strike in flat spiders
Predator-prey interactions promote the evolution of novel movement capabilities. In a group of spiders with flat bodies and widespread legs, we discovered the ‘omnidirectional strikes,’ where the spiders can attack within 0.12 seconds prey coming from any direction. Such a locomotion system likely evolved to effectively ambush prey on open surfaces, such as rocks and tree trunks, where these spiders commonly hunt. This study has already inspired new studies in biomechanics and robotics.
Keywords maneuverability, legged locomotion, multi-body mechanics
Ecology and biomechanics of gliding in wingless animals
Many wingless arboreal invertebrates glide. My research addresses why they glide in the first place and how such ecological context may lead to powered flight in evolution.
Keywords aerodynamics, behavioral ecology, control
Zeng, Y., Chang, S. W., Williams, J. Y., Nguyen, L. Y. -N., Tang, J., Naing, G., Kazi, C., and Dudley, R. (2020). Canopy parkour: movement ecology of post-hatch dispersal in a gliding nymphal stick insect, Extatosoma tiaratum. Journal of Experimental Biology.
A Minimal Framework for Describing Living Systems
We propose a conceptual approach based on four identified resources—energy, conductance, storage, and information (ECSI)—to reintegrate biological studies with the aim of unifying life sciences under resource limitations.
Keywords energy, scale, living systems
A first systematic investigation on the entomology of Nuosu (彝) people, a minority group living in mountain villages of southern Sichuan, China.