Across diverse animal taxa, gaze stabilization is an essential behavioural reflex to ensure that optic flow on the retina of moving animals is stabilized. During rapid maneuvers, this reduces motion blur in the visual field. In insects, gaze stabilization is achieved largely via compensatory head movements as their eyes are relatively fixed with respect to their heads. Typically, insects stabilize rotational optic flow to retrieve important translational optic flow cues such as heading and depth perception. In Diptera, several behavioural, anatomical and electrophysiological studies have revealed the role of multiple sensory modalities in ensuring head stabilization around the roll axis. These modalities include the compound eyes and the halteres, the modified hindwing in flies that has evolved into a mechanosensory organ. Whereas visual feedback is crucial during slow movements, halteres provide faster feedback about body rotations. Interestingly, electrophysiological recordings from some neck motor neurons suggest non-linear interaction between visual and haltere feedback. Because halteres are a unique adaptation in Diptera, these findings raise an intriguing question: What sensory inputs contribute to head stabilization in non-Dipteran insects which lack halteres? The question is especially pertinent in nocturnal insects, in which visual transduction is slow. Previous work has implicated antennal mechanosensors as being crucial for insect flight stability, and also other locomotory behaviors e.g. in head stabilization of walking crickets. Using high-speed videography and behavioural measurements in the nocturnal Oleander hawkmoth, Daphnis nerii, we tested the hypothesis that antennal mechanosensors contribute to the control of head movements. Specifically, tethered moths were oscillated around their roll axis at two ambient light intensities and two frequencies of body oscillations. This assay enabled us to track the head movements in response to specific manipulations to their visual and antennal mechanosensory feedback. Our results suggest that visual and antennal mechanosensory feedback affect head stabilization in a frequency-dependent way, similar to the combined role of visual and haltere feedback in flies. Moreover, the antennal feedback is derived from Johnstonâs organ, the mechanosensory organs present at the antennal base, which have been previously implicated in flight control. These data show that head movements, and therefore gaze stablization, requires both visual and antennal mechanosensory inputs, suggesting the multimodal feedback system for gaze stabilization in hawkmoths. We also observed small-amplitude head oscillations or head wobble in the hawkmoths. Head wobble occurs in tethered flying moths irrespective of external perturbations and are dependent on sensory feedback processes, which is consistent with our hypothesis of multimodal feedback system in rapid head positioning reflexes.
In a separate project, we measured the frequency response of the visual system in a comparative framework. Through electroretinography recordings from the retinal surface, we conducted a survey of Flicker Fusion Frequencies in diverse Lepidoptera (moths and butterflies). Flicker Fusion Frequency is a measure of temporal resolution at the level of photoreceptors. Because the Order Lepidoptera houses both diurnal (primarily butterflies) and nocturnal (primarily moths) members, it is an ideal system to compare FFF. We tested the hypothesis that Flicker Fusion Frequency (FFF) depends on the diel activity patterns of the insects. Alternatively, they may be phylogenetically constrained. Based on temporal response profiles from 25 species across 6 families of Lepidoptera, we show that the FFF are phylogenetically constrained, such that the FFF in nocturnal butterflies resembles their diurnal relatives, whereas the FFF in diurnal moths resembles their nocturnal relatives.
LOCATION:Remote Video Conference END:VEVENT END:VCALENDAR