Biology subjects

Sponberg, S.

Publications and source records attributed to Sponberg, S..

23 records · Page 2Linked to original sources

bioRxiv2020

Wing damage affects flight kinematics but not flower tracking performance in hummingbird hawkmoths

The integrity of their wings is crucial to the many insect species that spend distinct portions of their life in flight. How insects cope with the consequences of wing damage is therefore a central question when studying how robust flight performance is possible with such fragile chitinous wings. It has been shown in a variety of insect species that the loss in lift-force production resulting from wing damage is generally compensated by an increase in wing beat frequency rather than amplitude. The consequences of wing damage for flight performance, however, are less well understood, and vary considerably between species and behavioural tasks. One hypothesis reconciling the varying results is that wing damage might affect fast flight manoeuvres with high acceleration, but not slower ones. To test this hypothesis, we investigated the effect of wing damage on the manoeuvrability of hummingbird hawkmoths (Macroglossum stellatarum) tracking a motorised flower. This assay allowed us to sample a range of movements at different temporal frequencies, and thus assess whether wing damage affected faster or slower flight manoeuvres. We show that hummingbird hawkmoths compensate for the loss in lift force mainly by increasing wing beat amplitude, yet with a significant contribution of wing beat frequency. We did not observe any effects of wing damage on flight manoeuvrability at either high or low temporal frequencies.

animal behavior and cognition↗

bioRxiv2019

Indirect actuation reduces flight power requirements in Manduca sexta via elastic energy exchange

In the vast majority of flying insects, wing movements are generated indirectly via the deformations of the exoskeleton. Indirect measurements of inertial and aerodynamic power requirements suggest that elastic energy exchange in spring-like structures may reduce the high power requirements of flight by recovering energy from one wingstroke to the next. We directly measured deformation mechanics and elastic energy storage in a hawkmoth Manduca sexta thorax by recording the force required to deform the thorax over a frequency range encompassing typical wingbeat frequencies. We found that a structural damping model, not a viscoelastic model, accurately describes the thoraxs linear spring-like properties and frequency independent dissipation. The energy recovered from thorax deformations is sufficient to minimize flight power requirements. By removing the passive musculature, we find that the exoskeleton determines thorax mechanics. To assess the factors that determine the exoskeletons spring-like properties, we isolated functional thorax regions, disrupted strain in an otherwise intact thorax, and compared results to a homogeneous hemisphere. We found that mechanical coupling between spatially separated thorax regions improves energy exchange performance. Furthermore, local mechanical properties depend on global strain patterns. Finally, the addition of scutum deformations via indirect actuation provides additional energy recovery without added dissipation.

biophysics↗

bioRxiv2019

Timing is (almost) everything in a comprehensive, spike-resolved flight motor program

Sequences of action potentials, or spikes, carry information in the number of spikes and their timing. Spike timing codes are critical in many sensory systems, but there is now growing evidence that millisecond-scale changes in timing also carry information in motor brain regions, descending decision-making circuits, and individual motor units. Across all the many signals that control a behavior how ubiquitous, consistent, and coordinated are spike timing codes? Assessing these open questions ideally involves recording across the whole motor program with spike-level resolution. To do this, we took advantage of the relatively few motor units controlling the wings of a hawk moth, Manduca sexta. We simultaneously recorded nearly every action potential from all major wing muscles and the resulting forces in tethered flight. We found that timing encodes more information about turning behavior than spike count in every motor unit, even though there is sufficient variation in count alone. Flight muscles vary broadly in function as well as in the number and timing of spikes. Nonetheless, each muscle with multiple spikes consistently blends spike timing and count information in a 3:1 ratio. Coding strategies are consistent. Finally, we assess the coordination of muscles using pairwise redundancy measured through interaction information. Surprisingly, not only are all muscle pairs coordinated, but all coordination is accomplished almost exclusively through spike timing, not spike count. Spike timing codes are ubiquitous, consistent, and essential for coordination.\n\nSignificance StatementBrains can encode precise sensory stimuli and specific motor systems also appear to be precise, but how important are millisecond changes in timing of neural spikes across the whole motor program for a behavior? We record every spike that the hawk moths nervous system sends to its wing muscles. We show that all muscles convey the majority of their information in spike timing. The number of spikes does play a role, but not in a coordinated way across muscles. Instead, all coordination is done using in the millisecond timing of in spikes. The importance and prevalence of timing across the motor program pose new questions for how nervous systems create precise, coordinated motor commands.

neuroscience↗

bioRxiv2019

History-dependent perturbation response in limb muscle

1Muscle mediates movement but movement is typically unsteady and perturbed. Muscle is known to behave non-linearly and with history dependent properties during steady locomotion, but the importance of history dependence in mediating muscles function during perturbations remains less clear. To explore muscles capacity to mitigate perturbations, we constructed a series of perturbations that varied only in kinematic history, keeping instantaneous position, velocity and time from stimulation constant. We discovered that muscles perturbation response is profoundly history dependent, varying by four fold as baseline frequency changes, and dissipating energy equivalent to ~ 6 times the kinetic energy of all the limbs (nearly 2400 W Kg-1). Muscles energy dissipation during a perturbation is predicted primarily by the force at the onset of the perturbation. This relationship holds across different frequencies and timings of stimulation. This history dependence behaves like a viscoelastic memory producing perturbation responses that vary with the frequency of the underlying movement.\n\nSummary StatementThe response of muscles to rapid, identical strain perturbations is history dependent, but is captured by a viscoelastic model with memory. Muscle function during perturbations therefore depends on locomotor frequency.

physiology↗

bioRxiv2018

Hawkmoth flight in the unsteady wakes of flowers

Flying animals maneuver and hover through environments where wind gusts and flower wakes produce unsteady flow. Although both flight maneuvers and aerodynamic mechanisms have been studied independently, little is known about how these interact in an environment where flow is already unsteady. Moths forage from flowers by hovering in the flowers wake. We investigate hawkmoths tracking a 3D-printed robotic flower in a wind tunnel. We visualize the flow in the wake and around the wings and compare tracking performance to previous experiments in a still air flight chamber. Like in still air, moths flying in the flower wake exhibit near perfect tracking at low frequencies where natural flowers move. However, tracking in the flower wake results in a larger overshoot between 2-5 Hz. System identification of flower tracking reveals that moths also display reduced-order dynamics in wind, compared to still air. Smoke visualization of the flower wake shows that the dominant vortex shedding corresponds to the same frequency band as the increased overshoot. Despite these large effects on tracking dynamics in wind, the leading edge vortex (LEV) remains bound to the wing throughout the wingstroke and does not burst. The LEV also maintains the same qualitative structure seen in steady air. Persistence of a stable LEV during decreased flower tracking demonstrates the interplay between hovering and maneuvering.\n\nSummary statementWe examined how moths maneuver in the wake of flowers and discover that flower tracking dynamics are simplified compared to still air, while the leading edge vortex does not burst and extends continuously across the wings and thorax.

animal behavior and cognition↗