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Jonathan H. Booth1,2,3, Andrew Meek1,2, Nils M. Kronenberg1,2, Stefan R. Pulver3✉*, Malte C. Gather1,2✉*
1) Centre of Biophotonics, SUPA, School of Physics and Astronomy, University of St Andrews, Fife, United Kingdom.
2) Humboldt Centre for Nano- and Biophotonics, Institute for Physical Chemistry, University of Cologne, Germany.
3) School of Psychology and Neuroscience, University of St Andrews, Fife, United Kingdom.
* Denotes equal contribution ✉sp96@st-andrews.ac.uk & malte.gather@uni-koeln.de
This work was supported by EPSRC Doctoral Training grant (EP/L505079/1), a European
Research Council Grant to MCG (640012) and the Alexander von Humboldt Foundation via
the Humboldt Award. We would like to extend thanks to Dr. Marcus Bischoff and Prof.
Francoise Payre for technical advice.
Introduction
Wavelength Alternating Resonance Pressure Microscopy Spatiotemporal Ground Reaction Force Dynamics of Peristaltic Waves
Bilateralism Anchors Conclusions
Protopodial Deployment Dynamics
Larvae exhibit transient substrate
interactions during turning
associated with anchoring to
mitigate instability induced from
bilateral contractions.
(representative of 3 bilateralisms)
As well as peristalses, larvae can produce bilateral asymmetric
contractions to turn their head.
This raises the question of how animals prevent rolling via instability as
a consequence of these behaviours.
This is characterised
by low force but large
contact area
interactions
suggestive of body
mass re-organisation
TP engage to provide a transient terminal
segment allowing subsequent movement,
preventing reaction forces from impeding the
initial impetus for progression.
During ST, the protopodia plants and produces
a transient force disproportionate to the contact
area, akin to anchoring.
During SI, protopodia retract into a
sequestration pocket, but not before producing
a disproportionate force relative to the contact
area akin to vaulting.
Core Questions:
What are the ground
reaction forces generated by
larvae during movement?
How do larvae mitigate
excess friction from
denticles?
How do larvae overcome
reaction forces to prevent
interference of progression?
Protopodia also plant across the
left and right axes, unfolding over
time rather than all at once.
(n=5)
Soft bodied animals solve complex motor problems by controlling how their bodies contract
and interact with their substrates in order to give rise to movement. Measurements of ground
reaction forces (GRFs) in multiple species have revealed general principles of substrate
interactions [1], especially those which were not readily apparent by simple observation.
However, so far, the severely low spatio-temporal resolution of GRF measurement
technologies has limited progress. What progress has been made has proven inspirational to
the developing field of biomimetic robotics [2].
We have developed a non-contact technique based on Elastic Resonator Interference Stress
Microscopy (ERISM) [3] and Wavelength Alternating Resonance Pressure (WARP)
microscopy, allowing widefield, video-rate GRF measurement [4] and high spatial resolution [5]
at the substrate interface without probing the animal.
We apply this technique to study the substrate interaction in Drosophila melanogaster larvae.
Drosophila larvae have large cuticular processes, bespeckled with actin protrusions
called denticles (right). We refer to these structures as protopodia, due to their
superficial similarity to myopodia in nemertine worms.
These animals move by a series of contractions called peristaltic waves, for which the
neurophysiology is beginning to be well understood [6]. However, the biomechanics
underlying such behaviours remains understudied, with little literature discussing the
GRFs produced by these animals [7].
Drosophila larvae must interact with their substrate in an intricate manner to overcome
the friction created by denticles in an energetically viable manner. They must also
anchor parts of their body while others are in motion in order to prevent reaction forces
from interfering with forward progress. To our knowledge, how such interaction is
accomplished is unknown until now.
1. Lin, H. and Trimmer, B., 2010. The substrate as a skeleton: ground reaction forces from a soft-bodied legged animal. Journal of Experimental Biology, 213(7), pp.1133-1142.
2. Kim, S., Laschi, C., & Trimmer, B. (2013). Soft robotics: a bioinspired evolution in robotics. Trends in Biotechnology, 31(5), 287294. https://doi.org/https://doi.org/10.1016/j.tibtech.2013.03.002
3. Kronenberg, N. M., Liehm, P., Steude, A., Knipper, J. A., Borger, J. G., Scarcelli, G., Franze, K., Powis, S. J., & Gather, M. C. (2017). Long-term imaging of cellular forces with high
precision by elastic resonator interference stress microscopy. Nature Cell Biology. 19, pp 864872.
4. Meek, A. T., Kronenberg, N. M., Morton, A., Liehm, P., Murawski, J., Dalaka, E., Booth, J. H., Powis, S. J., & Gather, M. C. (2021). Real-time imaging of cellular forces using optical
interference. Nature Communications, 12(1), 3552
5. Dalaka, E., Kronenberg, N. M., Liehm, P., Segall, J. E., Prystowsky, M. B., & Gather, M. C. (2020). Direct measurement of vertical forces shows correlation between mechanical activity
and proteolytic ability of invadopodia. Science Advances, 6(11), eaax6912.
WARP allows video-rate force
map calculation with micrometre
spatial resolution, nanonewton
force sensitivity and millisecond
temporal resolution in freely
behaving Drosophila larvae.
We found that Drosophila larvae
move by a dynamic pattern of
protopodial contact and release
Allowing anchorage and
movement with low friction!
Mode Calculation
Interference Mapping Cotangent Map Calculation
6. Hunter, I., Coulson, B., Zarin, A. A., & Baines, R. A. (2021). The Drosophila Larval Locomotor Circuit Provides a Model to
Understand Neural Circuit Development and Function. Frontiers in Neural Circuits, 15.
7. Khare, S. M., Awasthi, A., Venkataraman, V., & Koushika, S. P. (2015). Colored polydimethylsiloxane micropillar arrays for
high throughput measurements of forces applied by genetic model organisms. Biomicrofluidics, 9(1), 14111.
Protopodia exert forces disproportionate to the
contact area during swing initiation (SI; blue)
and swing termination of a wave (ST; red).
(single trial but representative of n=5)
The SI force and contact area is often
less than the ST force and area. Each
protopodia exerts around 1-8 µN
(n=5).
SI peaks depended
on wave duration for
the posterior abdomen,
but ST peaks did not
vary with wave
duration. (n=5)
Posterior
(TP) not previously known as
locomotor appendages act as
transient terminal
segments
The ST and SI peaks are not homogenously distributed across the
protopodia, instead the locus of peak force is medial.
Protopodia plant in aheel-toe process, akin to feet. (n=5)
250 µm
100 µm
200 µm
200 µm 100 µm
100 µm
FEM
Calculation
Lambda Phi
100 µm
Scan for video
Scan for video
Scan for video
stance swing stance stanceswing
stance swing stance stanceswing
stance swing stance swing
R2=0.91
R2=0.91
R2=0.87
