Color is necessary for specialized face learning in the Northern paper wasp, Polistes fuscatus

Visual individual recognition requires animals to distinguish among conspecifics based on appearance. Though visual individual recognition has been reported in a range of taxa, the features that animals rely on to discriminate between individuals are often not well understood. Northern paper wasp females, Polistes fuscatus, possess individually distinctive color patterns on their faces, which mediate individual recognition. It is currently unclear what facial features P. fuscatus use to distinguish individuals. The anterior optic tubercle, a chromatic processing brain region, is especially sensitive to social experience during development, suggesting that color may be important for recognition in this species. We sought to test the roles of color in wasp facial recognition. Color may be important simply because it creates a pattern. If this is the case, then wasps should perform similarly when discriminating color or grayscale images of the same faces. Alternatively, color itself may be important for recognition, which would predict poorer performance on grayscale image discrimination relative to color images. We found wasps trained on grayscale faces, unlike those trained on color images, did not perform better than chance. Suggesting that color is necessary for the recognition of an image as a face by the wasp visual system.

Colors everywhere: enhanced chromatic processing across the first visual synapse in the zebrafish central brain

SummaryLarval zebrafish (Danio rerio) are an ideal organism to study color vision, as their eye possesses four types of cone photoreceptors, covering most of the visible range and into the UV [1,2]. Additionally, their entire eye and nervous system are accessible to imaging, given they are naturally transparent [3–5]. Relying on this advantage, recent research has found that, through a set of color specific horizontal, bipolar and retinal ganglion cells (RGCs) [6–8], the eye then relays tetrachromatic information to several retino-recipient areas (RAs) [9,10]. The main RA is the optic tectum, receiving 97% of the RGC axons via the neuropil mass termed Arborization Field 10 (AF10) [11,12]. In this work, we aim to understand the processing of color signals at the interface between RGCs and their targets in the brain. We used 2-photon calcium imaging to separately measure the responses of RGCs and neurons in the dorsal brain to stimulation with four different colors in awake animals. We find that color information is widespread throughout the larval brain, with a large variety of color responses among RGCs, and an even greater diversity in their targets. Specific combinations of response types are localized to specific nuclei, but we observe no single color processing structure. In the main interface in this pathway, the connection between Arborization Field 10 and the tectum, we observe key elements of color processing such as enhanced signal decorrelation and improved decoding [13,14]. Finally, when presenting a richer set of stimuli, we identify parallel processing of color, motion and luminance information in the same cells/terminals, evidence of a rich color vision machinery in this small vertebrate brain.

Strain variations in cone wavelength peaks in situ during zebrafish development

There are four cone morphologies in zebrafish, corresponding to UV (U), blue (B), green (G), and red (R)-sensing types; yet genetically, eight cone opsins are expressed. How eight opsins are physiologically siloed in four cone types is not well understood, and in larvae, cone physiological spectral peaks are unstudied. We use a spectral model to infer cone wavelength peaks, semisaturation irradiances, and saturation amplitudes from electroretinogram (ERG) datasets composed of multi-wavelength, multi-irradiance, aspartate-isolated, cone-PIII signals, as compiled from many 5- to 12-day larvae and 8- to 18-month-old adult eyes isolated from wild-type (WT) or roy orbison (roy) strains. Analysis suggests (in nm) a seven-cone, U-360/B1-427/B2-440/G1-460/G3-476/R1-575/R2-556, spectral physiology in WT larvae but a six-cone, U-349/B1-414/G3-483/G4-495/R1-572/R2-556, structure in WT adults. In roy larvae, there is a five-cone structure: U-373/B2-440/G1-460/R1-575/R2-556; in roy adults, there is a four-cone structure, B1-410/G3-482/R1-571/R2-556. Existence of multiple B, G, and R types is inferred from shifts in peaks with red or blue backgrounds. Cones were either high or low semisaturation types. The more sensitive, low semisaturation types included U, B1, and G1 cones [3.0–3.6 log(quanta·μm−2·s−1)]. The less sensitive, high semisaturation types were B2, G3, G4, R1, and R2 types [4.3-4.7 log(quanta·μm−2·s−1)]. In both WT and roy, U- and B- cone saturation amplitudes were greater in larvae than in adults, while G-cone saturation levels were greater in adults. R-cone saturation amplitudes were the largest (50–60% of maximal dataset amplitudes) and constant throughout development. WT and roy larvae differed in cone signal levels, with lesser UV- and greater G-cone amplitudes occurring in roy, indicating strain variation in physiological development of cone signals. These physiological measures of cone types suggest chromatic processing in zebrafish involves at least four to seven spectral signal processing pools.