Spatially invariant feature detection is a property of many visual systems that rely on visual information provided by two eyes. However, how information across both eyes is integrated for invariant feature detection is not fully understood. Here we investigate spatial invariance of looming responses in descending neurons (DNs) of Drosophila melanogaster. We find multiple looming responsive DNs integrate looming information across both eyes, even though their dendrites are restricted to a single visual hemisphere. One DN, the giant fiber (GF), responds invariantly to looming stimuli across tested azimuthal locations. We confirm visual information propagates to the GF from the contralateral eye through an unidentified pathway and demonstrate that the absence of this pathway alters GF responses to looming stimuli presented to the ipsilateral eye. Our data highlight a role for bilateral visual integration in generating consistent, looming-evoked escape responses that are robust across different stimulus locations and parameters.

Visual features detected by the early visual system must be combined into higher order representations to guide behavioral decision. Although key developmental mechanisms that enable the separation of visual feature channels in early visual circuits have been discovered, relatively little is known about the mechanisms that underlie their convergence in later stages of visual processing. Here we explore the development of a functionally well-characterized sensorimotor circuit in Drosophila melanogaster, the convergence of visual projection neurons (VPNs) onto the dendrites of a large descending neuron called the giant fiber (GF). We find two VPNs encoding different visual features that target the same giant fiber dendrite establish their territories on the dendrite, in part, through sequential axon arrival during development prior to synaptogenesis. Physical occupancy is important to maintain territories, as we find the ablation of one VPN results in expanded dendrite territory of the remaining VPN, and that this compensation enables the GF to remain responsive to ethologically relevant visual stimuli. Our data highlight temporal mechanisms for visual feature convergence and promote the GF circuit, and the Drosophila optic glomeruli where VPN to GF connectivity resides, as an ideal developmental model for investigating complex wiring programs and plasticity in visual feature convergence.

An animals nervous system recognizes visual features regardless of where the visual feature is located. However, the underlying mechanisms that enable location invariant feature detection are not fully understood, particularly when visual feature information contributed by each eye needs to be resolved. Here we investigate directional invariance of looming responses in descending neurons (DN) of Drosophila melanogaster. We find multiple looming responsive DN integrate looming information across both eyes, even though their dendrites are unilateral. One DN in particular, the giant fibers (GF), generates invariant looming responses across approach directions. We confirm visual information propagates to the GF from the contralateral eye through an as of yet unidentified pathway and demonstrate the absence of this pathway alters GF responses to looming stimuli from the ipsilateral eye. Our data highlight a role for bilateral visual integration in generating consistent escape responses that are robust across a wide range of stimulus locations and parameters.