A novel method for comparative analysis of retinal specialization traits from topographic maps.

Vertebrates possess different types of retinal specializations that vary in number, size, shape, and position in the retina. This diversity in retinal configuration has been revealed through topographic maps, which show variations in neuron density across the retina. Although topographic maps of about 300 vertebrates are available, there is no method for characterizing retinal traits quantitatively. Our goal is to present a novel method to standardize information on the position of the retinal specializations and changes in retinal ganglion cell (RGC) density across the retina from published topographic maps. We measured the position of the retinal specialization using two Cartesian coordinates and the gradient in cell density by sampling ganglion cell density values along four axes (nasal, temporal, ventral, and dorsal). Using this information, along with the peak and lowest RGC densities, we conducted discriminant function analyses (DFAs) to establish if this method is sensitive to distinguish three common types of retinal specializations (fovea, area, and visual streak). The discrimination ability of the model was higher when considering terrestrial (78%-80% correct classification) and aquatic (77%-86% correct classification) species separately than together. Our method can be used in the future to test specific hypotheses on the differences in retinal morphology between retinal specializations and the association between retinal morphology and behavioral and ecological traits using comparative methods controlling for phylogenetic effects.

Visual detection of UV cues by adult zebrafish (Danio rerio).

Visual sensitivity to ultraviolet (UV) light is widespread in the animal kingdom. Many studies on UV vision have utilized physiological and/or anatomical methods to determine whether animals are visually sensitive to UV wavelengths. However, ultimately behavioral methods can reveal whether retinal UV sensitivity results in perceptual detection of UV stimuli. For the widely studied zebrafish (Danio rerio), the adult retina possesses cone photoreceptors that are sensitive to UV light. Here, we used a behavioral technique, the escape response assay, to test whether adult zebrafish can visually detect and behaviorally respond to visual cues that reflect UV. We found that adult zebrafish robustly respond to UV reflecting cues under UV light while showing no responses to the same cues under no UV light. From our results, we confirm that adult zebrafish can visually detect UV reflecting cues and show that UV perceptual sensitivity is functional in adult zebrafish. Our study highlights the utility of the fish escape response assay for UV visual behavior research.

Sex-specific visual performance: female lizards outperform males in motion detection.

In animal communication, complex displays usually have multiple functions and, male and female receivers often differ in their utilization and response to different aspects of these displays. The perceptual variability hypothesis suggests that different aspects of complex signals differ in their ability to be detected and processed by different receivers. Here, we tested whether receiver male and female Sceloporus graciosus lizards differ in visual motion detection by measuring the latency to the visual grasp response to a motion stimulus. We demonstrate that in lizards that largely exhibit complex motions as courtship signals, female lizards are faster than males at visually detecting motion. These results highlight that differential signal utilization by the sexes may be driven by variability in the capacity to detect different display properties.