Biology subjects

Belusic, G.

Publications and source records attributed to Belusic, G..

6 recordsLinked to original sources

bioRxiv2026

The Effective Visual Acuity of Butterflies in Flight

The spatial visual acuity of an eye is determined by both the spatial sampling density of the retina and the angular sensitivity of individual photoreceptors. In insect compound eyes, these are respectively characterised by the interommatidial angle, {Delta}{varphi}, and photoreceptor acceptance angle, {Delta}{rho}. During movement, however, finite photoreceptor integration times cause retinal image motion to broaden the effective acceptance angle, potentially degrading spatial resolution beyond its anatomical limit. This problem is especially acute in flying insects, which experience large rotational velocities during locomotion and must actively stabilise gaze to limit retinal image motion. Butterflies present a particularly demanding case because their flight is characterised by large, wingbeat-coupled thoracic oscillations. Here, we quantify how gaze stabilisation limits motion blur in freely flying Monarch butterflies Danaus plexippus by combining free-flight kinematic reconstruction of the head and thorax with separate intracellular measurements of photoreceptor acceptance angles and integration times from quiescent butterflies. We found that, without head compensation, thoracic oscillations would broaden the effective photoreceptor acceptance angle from its quiescent value of 2.17{degrees} to 9.38{degrees} during take-off. Compensatory head movements substantially reduced this motion-induced broadening, limiting the effective acceptance angle to 5.28{degrees}. Nevertheless, this 2.4-fold broadening of effective photoreceptor acceptance angle represents a substantial degradation of spatial acuity in flight, highlighting motion blur as an important constraint on the visual ecology of flying butterflies.

neuroscience↗

bioRxiv2025

Spectral Matched Filtering in the Butterfly Visuomotor System

Color provides an important dimension for object detection and classification. In most animals, color- and motion-vision are largely separated throughout early stages of visual processing. However, accumulating evidence indicates crosstalk between chromatic and achromatic pathways. Here we investigate the spectral sensitivity of the butterfly motion-vision pathway at the level of pre-motor descending neurons (DNs), which connect the brain to thoracic motor centres. Butterflies engage in fast agile flight within often-colorful visual ecologies, which may heighten evolutionary pressure to integrate color- and motion-vision. Indeed, we observed a separation of spectral sensitivities that matches the functional properties of butterfly DNs, such that wide-field optic flow-sensitive DNs involved in stabilisation reflexes have effectively broadband spectral responses, whilst target-selective DNs involved in target-tracking are comparatively narrowband and match conspecific wing coloration. Our findings demonstrate an integration of color- and motion-vision within a pre-motor neuronal bottleneck that controls behavior.

neuroscience↗

bioRxiv2025

Electrophysiological recordings reveal photoreceptor coupling in the dorsal rim areas of honeybee and bumblebee eyes

Many insects rely on skylight polarization patterns to navigate their habitats. To perform this vital task, most insect species have evolved specialized ommatidia in the dorsal rim area (DRA) of their compound eyes that are adapted to detect linearly polarized light in large patches of sky. In this study, we conducted electrophysiological recordings of honeybee (Apis mellifera) and bumblebee (Bombus terrestris) photoreceptors in the DRA and other regions of the compound eye to map their receptive fields. For both species, we report novel evidence for photoreceptor coupling, i.e., spatial summation, present in the retinal layer of the DRA. We explore spatial summation as a possible, eye-region-specific mechanism to increase the effective size of DRA ommatidia receptive fields; a crucial functional feature of the polarization compass.

neuroscience↗

bioRxiv2022

Behavioral responses of free flying Drosophila melanogaster to shiny, reflecting surfaces

Active locomotion plays an important role in the life of many animals since it permits to explore the environment and find vital resources. Most insect species rely on a combination of visual cues such as celestial bodies, landmarks, or linearly polarized light to navigate or to orient themselves in their surroundings. In nature, linearly polarized light can arise either from atmospheric scattering or from reflections off shiny non-metallic surfaces like water or shiny foil. Although multiple reports described different behavioral responses of various insects to such shiny surfaces, little is known about the retinal detectors or the underlying neural circuits. Our goal was to quantify the behavioral responses of free flying Drosophila melanogaster, a molecular genetic model organism that allows for systematic dissection of neural circuitry. Fruit flies were placed in a custom-built arena with controlled environmental parameters (temperature, humidity, and light intensity). Flight densities and landings were quantified for hydrated and dehydrated fly populations when separately exposed to three different stimuli such as a diffusely-reflecting matt plate, a small patch of shiny foil, versus real water. Our analysis reveals for the first time that flying fruit flies indeed use vision to guide their flight maneuvers around shiny surfaces.

animal behavior and cognition↗

bioRxiv2022

Opponent processing in the retinal mosaic of nymphalid butterflies

The eyes of nymphalid butterflies, investigated with incident illumination, show colourful facet reflection patterns, the eye shine, which is uniform or heterogeneous, dependent on the species. Facet colours suggest that the ommatidia contain different sets of photoreceptors and screening pigments, but how the colours and the cell characteristics are associated has not been clearly established. Here we analyse the retinae of two nymphalids, Apatura ilia, which has a uniform eyeshine, and Charaxes jasius, a species with a heterogeneous eye shine, using single-cell recordings, spectroscopy and optical pupillometry. Apatura has UV, blue and green-sensitive photoreceptors, allocated into three ommatidial types. The UV and blue-sensitive cells are long visual fibres (LVFs), receiving opponent input from the green-sensitive short visual fibres (SVFs). Charaxes has an expanded set of photoreceptors, allocated into three additional, red-reflecting ommatidial types. All red ommatidia contain green-sensitive LVFs, receiving opponent input from red receptors. In both species, the SVFs do not receive any opponent input. The simple retina of Apatura with three ommatidial types and two colour-opponent channels can support trichromatic vision. Charaxes has six ommatidial types and three colour-opponent channels. Its expanded receptor set can support tetrachromatic vision.

neuroscience↗

bioRxiv2022

Generating spatiotemporal patterns of linearly polarised light at high frame rates for insect vision research

Polarisation vision is commonplace among invertebrates; however, most experiments focus on determining behavioural and/or neurophysiological responses to static polarised light sources rather than moving patterns of polarised light. To this end, we designed a polarisation stimulation device based on superimposing polarised and non-polarised images from two projectors, which can display moving patterns at frame rates exceeding invertebrate flicker fusion frequencies. A linear polariser fitted to one projector enables moving patterns of polarised light to be displayed, whilst the other projector contributes arbitrary intensities of non-polarised light to yield moving patterns with a defined polarisation and intensity contrast. To test the device, we measured receptive fields of polarisation sensitive Argynnis paphia butterfly photoreceptors for both non-polarised and polarised light. We then measured local motion sensitivities of the optic flow-sensitive lobula plate tangential cell H1 in Calliphora vicina blowflies under both polarised and non-polarised light, finding no polarisation sensitivity in this neuron.

neuroscience↗