Biology subjects

Nordstrom, K.

Publications and source records attributed to Nordstrom, K..

12 recordsLinked to original sources

bioRxiv2026

Parallel descending neurons differentially encode target and looming information in the hoverfly visual system

Detecting small, fast-moving objects is crucial for behaviors such as pursuit, territorial defence, and predator avoidance. At long range, however, potential mates, rivals, and predators produce remarkably similar visual signals, potentially making them difficult to distinguish. Nevertheless, many flying insects, including the hoverfly Eristalis tenax, can respond rapidly and appropriately to these ambiguous visual cues, implying specialised neural pathways that extract behaviorally relevant information. Descending neurons link visual processing to motor output, thus transforming visual signals into behavioral actions. In E. tenax, both target selective descending neurons (TSDNs) and looming-sensitive descending neurons respond to small targets, yet their respective contributions to target processing remain unclear. Using electrophysiological recordings, we compared receptive field organization and sensitivity to target size and motion direction across these neuronal populations. Although TSDNs and looming-sensitive descending neurons differed systematically in their target coding, a subset of looming-sensitive descending neurons closely resembled TSDNs, sharing small receptive fields and sharp target tuning despite retaining sensitivity to looming stimuli. These findings reveal previously unrecognized diversity among descending neurons tuned to small targets and suggest that parallel descending pathways encode distinct information from similar visual cues. Such an organization may enable common visual inputs to support both target pursuit and the detection of approaching threats.

neuroscience↗

bioRxiv2026

Hoverfly responses to looming stimuli depend on elevation and speed

An object on immediate collision course generates a rapidly expanding visual stimulus on the retina, which will typically trigger a fast reaction, such as an evasive behavior. In hoverflies, for example, visual looming stimuli may be generated if the insect is about to collide with a stationary object in the surround, by an approaching predator, or by conspecifics during territorial interactions. Supporting these behavioral responses is a diverse range of looming sensitive descending neurons that project information from the optic lobes and central brain to the motor control centers in the thoracic ganglia. We here show that the looming sensitive descending neurons are predominantly sensitive to looming stimuli located in the ventral visual field. To investigate if this is matched by behavior, we recorded how tethered hoverflies responded to looming stimuli presented dorsally or ventrally on a visual monitor, at four different speeds (l/|v| of 10 - 667 ms), covering a naturalistic range. We found that ventral stimuli, especially at intermediate speeds (l/|v| = 50 or 200 ms), triggered much stronger behavioral responses than dorsally displayed stimuli. The behavioral data thus not only match the receptive fields of the neurons likely to support the behavior, but also highlight that behavioral output is not entirely reflexive but is strongly modulated by stimulus speed and elevation. Significance StatementIf someone throws a ball at you, this generates a rapidly expanding object across your visual field, which will make you react before you have even had time to think. You may for example duck, dip or dive to avoid the ball, or bring your hands up to grab it. Similarly, many insects respond to rapidly approaching objects. We here show that hoverfly reactions to such looming stimuli depend on stimulus speed and elevation, with the strongest response to stimuli approaching from below. We further demonstrate that the neurons likely supporting these behaviors show highest sensitivity in the ventral visual field, suggesting a close match between neural tuning and behavioral output.

animal behavior and cognition↗

bioRxiv2026

Single-Cell and Tissue-Specific CRISPR Editing Analyses Unveil New Insights to Off-Targets and Translocations

CRISPR-Cas9 holds promise for treating genetic disease, but rare off-target mutations and structural variants remain as key safety concerns, especially at scales relevant to therapy. We established workflows to resolve Cas9 off-target activity in vitro at single-cell resolution and in vivo across different tissues. Using clonally expanded electroporated mouse embryos and embryonic stem cells, we reveal that individual cells exhibit unique off-target and translocation profiles, including events missed in bulk analyses. Integrating single-cell editing with chromatin accessibility, transcription, and DNA methylation measurements suggested that sequence-independent features modulate Cas9 access and cleavage, with preferential editing in regions characterized by open chromatin and lower methylation. In Cas9-inducible mouse models, editing analyses revealed organ-distinct off-target spectra, DNA repair pathway usage, indel patterns, and markedly varying translocation propensity between tissues. These findings demonstrate that off-target activity is heterogeneous across cells and context-dependent across organs, motivating sensitive single-cell analyses and organ-specific evaluation in preclinical development to more accurately assess risk and improve the safety of CRISPR-based genomic medicines.

genomics↗

bioRxiv2025

Sexual dimorphism in sensorimotor transformation of optic flow

Motion vision underpins a wide range of adaptive behaviours essential for individual and species survival. In hoverflies, some visual behaviours are sexually dimorphic, including for example male high-speed pursuit of conspecifics, matched by improved optics, and faster photoreceptors. Other visual behaviours are sexually monomorphic, with for example similar foraging flight speeds in male and female hoverflies. However, whether the descending neurons responsible for sensorimotor transformation of optic flow are sexually dimorphic is unknown. To address this, we combined morphological analysis with electrophysiology of optic flow sensitive descending neurons and compared neural responses to the behavioural output in tethered hoverflies. We found that while optomotor flight behaviour is largely sexually monomorphic, the underlying neural responses are sexually dimorphic, especially at higher optic flow velocities. Additionally, behavioural responses were noticeably slower than neural responses. Together, our findings uncover a nuanced, sex- and stimulus- dependant sensorimotor transformation, shaped by both neural architecture and behavioural demands.

neuroscience↗

bioRxiv2025

Conserved but mechanistically diverse piRNA defence against gypsy LTR retrotransposons in insect ovaries

Organisms have evolved highly adaptable defence systems to silence mobile genetic elements such as transposons. While individual transposons may emerge and vanish over time, the long-term evolutionary stability of the pathways that suppress them remains poorly understood. In the ovarian somatic cells of Drosophila, envelope-carrying gypsy long terminal repeat (LTR) retrotransposons are silenced by the Piwi-interacting RNA (piRNA) pathway, which depends exclusively on Piwi - an evolutionary derivative of an Aubergine/Piwi gene duplication unique to flies. Recent studies, however, have revealed that envelope-carrying gypsy elements are widespread across metazoans and particularly abundant in insect genomes, raising questions about the origin of ovarian somatic piRNA defence. Here we demonstrate that Aedes and Anopheles mosquitoes, as well as stingless bees and crickets, all produce piRNAs targeting gypsy elements in ovarian somatic cells, indicating a continuous arms race in this cellular niche for more than 400 million years of insect evolution. Notably, in Aedes aegypti, ovarian somatic cells express the same piRNA clusters as other somatic tissues, where they are known to target RNA viruses - suggesting a shared origin of anti-viral and anti-retrotransposon defences. Furthermore, we reveal striking lineage-specific differences in ovarian somatic piRNA biogenesis: slicing-independent phasing dominates in dipterans, ping-pong amplification in bees, and slicing-dependent phasing in crickets. Together, these findings indicate that distinct piRNA pathways have independently evolved at different timepoints to silence the same class of retrotransposons in insect evolution.

evolutionary biology↗

bioRxiv2025

Fast adaptation in invertebrate looming-sensitive descending neurons

Motion vision plays a crucial role in guiding dynamic behaviors, such as determining when to escape from predators, pursue prey, navigate obstacles, or adjust flight patterns during migration. Adaptation to repetitive motion stimuli is a crucial aspect of this process, allowing animals to efficiently process new stimuli while avoiding sensory overload. This helps animals remain responsive to novel or important stimuli, ensuring appropriate behavioral reactions. Adaptation to looming stimuli, which often signal an approaching threat through the rapid expansion of an objects image on the retina, allows animals to distinguish harmless from harmful stimuli. While neural adaptation has been extensively studied in the flys optic lobes, less is known about how descending neurons, which link the optic lobes to the motor centers in the thoracic ganglia, adapt. To address this gap, we investigate adaptation in looming-sensitive descending neurons in the hoverfly Eristalis tenax. Using intracellular recordings, we show that these descending neurons adapt to looming stimuli with inter-stimulus intervals of 1-3 s. We show that the level of adaptation depends on the ISI, with shorter intervals leading to greater adaptation. Specifically, we find that adaptation leads to decreased response duration, with a pronounced delayed response onset. We identified descending neurons that responded to looming stimuli either unilaterally or bilaterally and used this to show that most of the adaptation takes place within the neuron itself, rather than its pre-synaptic inputs. Finally, we found that the wing beat amplitude of tethered hoverflies did not appear to adapt to repetitive looming stimuli. Significance StatementRapidly expanding looming objects often signal approaching threats, and appropriate detection is therefore critical for survival across species. Adaptation to repetitive looming cues allows animals to filter out irrelevant information, ensuring they respond only to significant threats. While adaptation has been well studied in the brain, how descending neurons, which connect the brain with the body, adapt to looming stimuli remains poorly understood. Here, we investigate looming-sensitive descending neurons in the hoverfly Eristalis tenax and show that they adapt strongly when looming stimuli are repeated in quick succession. We show that most of the adaptation takes place within the descending neuron itself. Our research establishes a foundation for future exploration of the neural mechanisms underlying behavior in constantly changing environments.

neuroscience↗

bioRxiv2024

Innate floral object identification in the generalist solitary hoverfly pollinator Eristalinus aeneus

All animals must locate and identify food for their survival. Most insects are solitary. Newly emerged solitary insects must therefore employ innate identification of food cues to locate relevant nutritive objects from a distance. Innate preferences for food cues should be both specific enough to allow discrimination between food and non-food objects and general enough to allow for the variety of food objects relevant to each species ecology. How insects with small nervous systems are able to encode these cues innately is an area of intense study for ecologists and neuroscientists alike. Here, we used the solitary generalist pollinator Eristalinus aeneus to understand how the innate search template used to identify multiple floral species can arise through a small number of sensory cues spanning multiple modalities. We found that innate floral choices of the hoverfly E. aeneus are a product of contextual integration of broad, plant-based olfactory cues and visual cues, where a combination of radial symmetry and reflection in the 500-700 nm wavelength range was particularly important. Our study, therefore, shows how tiny brains can efficiently encode multimodal cues to identify multiple relevant objects without prior experience.

animal behavior and cognition↗

bioRxiv2024

Combining Unity with machine vision to create low latency, flexible, and simple virtual realities

O_LIIn recent years, virtual reality arenas have become increasingly popular for quantifying visual behaviors. By using the actions of a constrained animal to control the visual scenery, the animal is provided the perception of moving through a simulated environment. As the animal is constrained in space, this allows detailed behavioral quantification. Additionally, as the world is generally computer-generated this allows for mechanistic quantification of visual triggers of behavior. C_LIO_LIWe created a novel virtual arena combining machine vision with the gaming engine Unity. For tethered flight, we enhanced an existing multi-modal virtual reality arena, MultiMoVR (Kaushik et al., 2020) but tracked hoverfly wing movements using DeepLabCut-live (DLC-live, Kane et al., 2020). For trackball experiments, we recorded the motion of a ball that a tethered crab was walking on using FicTrac (Moore et al., 2014). In both cases, real-time tracking was interfaced with Unity to control the movement of the tethered animals avatars in the virtual world. We developed a user-friendly Unity Editor interface, CAVE, to simplify experimental design and data storage without the need for coding. C_LIO_LIWe show that both the DLC-live-Unity and the FicTrac-Unity configurations close the feedback loop effectively with small delays, less than 50 ms. Our FicTrac-Unity integration highlighted the importance of closed-loop feedback by reducing behavioral artifacts exhibited by the crabs in open-loop scenarios. We show that Eristalis tenax hoverflies, using the DLC-live-Unity integration, navigate towards flowers. The effectiveness of our CAVE interface is shown by implementing experimental sequencing control based on avatar proximity to virtual structures. C_LIO_LIOur results show that combining Unity with machine vision tools such as DLC-live and FicTrac provides an easy and flexible virtual reality (VR) environment that can be readily adjusted to new experiments and species. This can be implemented programmatically in Unity, or by using our new tool CAVE, which allows users to design and implement new experiments without programming in code. We provide resources for replicating experiments and our interface CAVE via GitHub, together with user manuals and instruction videos, for sharing with the wider scientific community. C_LI

animal behavior and cognition↗

bioRxiv2023

Neural responses to reconstructed target pursuits

Many animals use motion vision information to control dynamic behaviors. Predatory animals, for example, show an exquisite ability to detect rapidly moving prey followed by pursuit and capture. Such target detection is not only used by predators but can also play an important role in conspecific interactions. Male hoverflies (Eristalis tenax), for example, vigorously defend their territories against conspecific intruders. Visual target detection is believed to be subserved by specialized target tuned neurons that are found in a range of species, including cats, zebrafish, and insects. However, how these target-tuned neurons respond to actual pursuit trajectories is currently not well understood. To redress his, we recorded extracellularly from target selective descending neurons (TSDNs) in male Eristalis tenax hoverflies. We show that the neurons have dorso-frontal receptive fields, with a preferred direction up and away from the visual midline. We next reconstructed visual flow-fields as experienced during pursuits of artificial targets (black beads). We recorded TSDN responses to six reconstructed pursuits and found that each neuron responded consistently at remarkably specific time points, but that these time points differed between neurons. We compared the observed spike probability with the spike probability predicted from each neurons receptive field and size tuning, and found a correlation coefficient of 0.35. Interestingly, however, the overall response rate was low, with individual neurons responding to only a small part of each reconstructed pursuit. In contrast, the TSDN population responded to a substantially larger proportion of the pursuits (up to a median of 23%). This large variation between neurons could be useful if different neurons control different parts of the behavioral output. Significance statementDescending neurons constitute less than 1% of the nervous system, yet have to convey all requisite information from the brain to the body. They are therefore a crucial bottleneck in sensorimotor transformation. Descending target tuned neurons in male hoverflies (Eristalis tenax), for example, are believed to play a key role in territory defense and pursuit of conspecifics. However, this has not been tested using visual stimuli resembling reconstructed target pursuits. We here found that the observed neural responses to reconstructed pursuits are stronger than those predicted from responses to simpler stimuli. In addition, while the responses to simple stimuli suggested a homogenous population of neurons, the reconstructed pursuits showed important differences between individual neurons. Our data thus highlight the need for using more naturalistic stimuli when deciphering neural function.

neuroscience↗

bioRxiv2022

Dual receptive fields underlying target and motion sensitivity in looming sensitive descending neurons

Responding rapidly to visual stimuli is fundamental for many animals. For example, predatory birds and insects alike have amazing target detection abilities, with incredibly short neural and behavioral delays, enabling efficient prey capture. Similarly, looming objects need to be rapidly avoided to ensure immediate survival, as these could represent approaching predators. Male Eristalis tenax hoverflies are non-predatory, highly territorial insects, that perform high-speed pursuits of conspecifics and other territorial intruders. During the initial stages of the pursuit the retinal projection of the target is very small, but grows to a larger object before physical interaction. Supporting such behaviors, E. tenax and other insects have both target-tuned and loom-sensitive neurons in the optic lobes and the descending pathways. We here show that these visual stimuli are not necessarily encoded in parallel. Indeed, we describe a class of descending neurons that respond to small targets, to looming and to widefield stimuli. We show that these neurons have two distinct receptive fields where the dorsal receptive field is sensitive to the motion of small targets and the ventral receptive field responds to larger objects or widefield stimuli. Our data suggest that the two receptive fields have different pre-synaptic input, where the inputs are not linearly summed. This novel and unique arrangement could support different behaviors, including obstacle avoidance, flower landing, target pursuit or capture. Significance StatementIf you are playing baseball, when the ball is far away, it appears as a very small object on your retina. However, as the ball gets closer, its image becomes a rapidly expanding object. Here, we show that within the hoverfly visual system, a single neuron could respond to both of these images. Indeed, we found a class of descending neurons with dual sensitivity, separated into two distinct parts of the visual field. The neurons have a more dorsal receptive field that is sensitive to small targets and a more ventral receptive field that is sensitive to larger objects.

neuroscience↗

bioRxiv2022

Male hoverflies (Eristalis tenax) do not use heuristic rules based on retinal size and speed to initiate indoor pursuits of artificial targets

The ability to visualize small moving objects is vital for the survival of many animals, as these could represent predators or prey. For example, predatory insects, including dragonflies, robber flies and killer flies, perform elegant, high-speed pursuits of both biological and artificial targets. Many non-predatory insects, including male hoverflies and blowflies, also pursue targets during territorial or courtship interactions. To date, most hoverfly pursuits were studied outdoors. To investigate naturalistic hoverfly (Eristalis tenax) pursuits under more controlled settings, we constructed an indoor arena that was large enough to encourage naturalistic behavior. We presented artificial beads of different sizes, moving at different speeds, and filmed pursuits with two cameras, allowing subsequent 3D reconstruction of the hoverfly and bead position as a function of time. We show that male E. tenax hoverflies are unlikely to use strict heuristic rules based on angular size or speed to determine when to start pursuit, at least in our indoor setting. We found that hoverflies pursued faster beads when the trajectory involved flying downwards towards the bead. Furthermore, we show that target pursuit behavior can be broken down into two stages. In the first stage the hoverfly attempts to rapidly decreases the distance to the target by intercepting it at high speed. During the second stage the hoverflys forward speed is correlated with the speed of the bead, so that the hoverfly remains close, but without catching it. This may be similar to dragonfly shadowing behavior, previously coined motion camouflage.

animal behavior and cognition↗

bioRxiv2020

Now you see me, now you don't: Modulation of neural responses to targets moving in three-dimensional optic flow

For the human observer, it can be difficult to follow the motion of small objects, especially when they move against background clutter. In contrast, insects efficiently do this, as evidenced by their ability to capture prey, pursue conspecifics, or defend territories, even in highly textured surrounds. We here recorded from target selective descending neurons (TSDNs) which likely subserve these impressive behaviors. To simulate the type of background optic flow that would be generated by the pursuers own movements through the world, we used the coherent motion of a perspective distorted sparse dot field. We show that hoverfly TSDN responses to target motion are suppressed when such background optic flow moves in the same direction as the target. Indeed, the neural responses are strongly attenuated against both translational sideslip as well as rotational yaw. More strikingly, we show that TSDNs are facilitated by background optic flow in the opposite direction to the target, if the target moves horizontally. Furthermore, we show that a small, frontal spatial window of background optic flow is enough to fully facilitate or attenuate TSDN responses to target motion. We argue that the TSDN response facilitation could be beneficial in modulating corrective turns during target pursuit. Significance statementTarget detection in visual clutter is a difficult computational task that insects, with their poor resolution compound eyes and small brains, do successfully and with extremely short behavioral delays. We here show that the responses of target selective descending neurons are attenuated by background motion in the same direction as target motion, but facilitated by opposite direction background motion. This finding is important for understanding conspecific pursuit behavior, since these descending neurons likely control behavioral output. The facilitation that we describe would come into effect if the hoverfly is subjected to background motion in one direction, but the target it is pursuing moves in the opposite direction, and could therefore be used to modulate gaze stabilizing corrective turns.

neuroscience↗