Eye gaze is an important source of information for animals, implicated in communication, cooperation, hunting and antipredator behaviour. Gaze perception and its cognitive underpinnings are much ...studied in primates, but the specific features that are used to estimate gaze can be difficult to isolate behaviourally. We photographed 13 laboratory-housed tufted capuchin monkeys (
) to quantify chromatic and achromatic contrasts between their iris, pupil, sclera and skin. We used colour vision models to quantify the degree to which capuchin eye gaze is discriminable to capuchins, their predators and their prey. We found that capuchins, regardless of their colour vision phenotype, as well as their predators, were capable of effectively discriminating capuchin gaze across ecologically relevant distances. Their prey, in contrast, were not capable of discriminating capuchin gaze, even under relatively ideal conditions. These results suggest that specific features of primate eyes can influence gaze perception, both within and across species.
Eyes convey important information about the external and internal worlds of animals. Individuals can follow the gaze of others to learn about the location of salient objects as well as assess eye ...qualities to evaluate the health, age or other internal states of conspecifics. Because of the increasing prevalence of artificial lighting at night (ALAN), urbanized individuals can potentially garner information from conspecific eyes under both daylight and ALAN. We tested this possibility using a visual modeling approach in which we estimated the maximum distance at which individuals could detect conspecific eyes under daylight and high levels of ALAN. We also estimated the minimum light level at which individuals could detect conspecific eyes. Great-tailed grackles (Quiscalus mexicanus) were used as our study species because they are highly social and are unusual among birds in that they regularly gather at nocturnal roosts in areas with high levels of ALAN. This visual modelling approach revealed that grackles can detect conspecific eyes under both daylight and ALAN, regardless of iris coloration. The grackles could detect conspecific eyes at farther distances in daylight compared to ALAN. Our results highlight the potential importance of lighting conditions in shaping social interactions.
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•Many animals use information from conspecific eyes for visual communication.•Visual models estimated eye detectability under artificial light at night (ALAN).•A songbird can detect conspecific eyes under high and low levels of ALAN.•They can detect conspecific eyes at farther distances under daylight.
Eyes are communicative. But what happens when eyes are camouflaged? In the present study, while either wearing sunglasses (that camouflaged the eyes) or clear glasses, participants were presented ...with sexually provocative and neutral images, which they viewed in the presence of another person who they knew was observing their eyes. Unbeknownst to the participants, however, we also surreptitiously monitored and recorded their eye gaze in both conditions. People spontaneously looked more and for longer at the sexually provocative images when their eyes were camouflaged by sunglasses. This finding provides convergent evidence for the proposal that covert attention operates in service of overt social attention, and suggests that decoupling overt and covert attention is much more prevalent than previously assumed. In doing so it also sheds light on the relation between the evolution of human eye morphology and systems of attention.
Abstract
Visually dependent dim-light foraging has evolved repeatedly, broadening the ecological niches of some species. Many dim-light foraging lineages evolved from diurnal ancestors, requiring ...immense visual sensitivity increases to compensate for light levels a billion times dimmer than daylight. Some taxa, such as bees, are anatomically constrained by apposition compound eyes, which function well in daylight but not in starlight. Even with this constraint, the bee genus Megalopta has incredibly sensitive eyes, foraging in light levels up to nine orders of magnitude dimmer than diurnal relatives. Despite many behavioural studies, variation in visual sensitivity and eye morphometry has not been investigated within and across Megalopta species. Here we quantify external eye morphology (corneal area and facet size) for sympatric species of Megalopta, M. genalis and M. amoena, which forage during twilight. We use electroretinograms to show that males, despite being smaller than females, have equivalent visual sensitivity and increased retinal responsivity. Although males have relatively larger eyes compared with females, corneal area and facet size were not correlated with retinal responsivity, suggesting that males have additional non-morphological adaptations to increase retinal responsiveness. These findings provide the foundation for future work into the neural and physiological mechanisms that interface with morphology to influence visual sensitivity, with implications for understanding niche exploitation.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The eyes of frogs and toads (Anura) are among their most fascinating features. Although several pupil shapes have been described, the diversity, evolution, and functional role of the pupil in anurans ...have received little attention. Studying photographs of more than 3200 species, we surveyed pupil diversity, described their morphological variation, tested correlation with adult habits and diel activity, and discuss major evolutionary patterns considering iris anatomy and visual ecology. Our results indicate that the pupil in anurans is a highly plastic structure, with seven main pupil shapes that evolved at least 116 times during the history of the group. We found no significant correlation between pupil shape, adult habits, and diel activity, with the exception of the circular pupil and aquatic habits. The vertical pupil arose at least in the most-recent common ancestor of Anura + Caudata, and this morphology is present in most early-diverging anuran clades. Subsequently, a horizontal pupil, a very uncommon shape in vertebrates, evolved in most neobatrachian frogs. This shape evolved into most other known pupil shapes, but it persisted in a large number of species with diverse life histories, habits, and diel activity patterns, demonstrating a remarkable functional and ecological versatility.
•Children prefer to cooperate with others who have white sclera vs dark sclera.•Children prefer to cooperate with others who have white sclera vs larger irises.•Children’s judgements of cuteness ...follow a similar but not identical pattern.•These results provide general support for the cooperative eye hypothesis.
The cooperative eye hypothesis posits that human eye morphology evolved to facilitate cooperation. Although it is known that young children prefer stimuli with eyes that contain white sclera, it is unknown whether white sclera influences children’s perception of a partner’s cooperativeness specifically. In the current studies, we used an online methodology to present 5-year-old children with moving three-dimensional face models in which facial morphology was manipulated. Children found “alien” faces with human eyes more cooperative than faces with dark sclera (Study 2) but not faces with enlarged irises (Study 1). For more human-like faces (Study 3), children found human eyes more cooperative than either enlarged irises or dark sclera and found faces with enlarged irises cuter (but not more cooperative) than eyes with dark sclera. Together, these results provide strong support for the cooperative eye hypothesis.
The scleral ossicle rings function has been related to mechanical protection, muscle fixation, support for eyeball shape and visual accommodation. There are few morphobiometric reports on these rings ...in different Testudines species, and we performed ultrasound (US) and computed tomography (CT) of the scleral ossicle rings in one green turtle (Chelonia mydas), one black-bellied slider (Trachemys dorbigni) and one red-footed tortoise (Chelonoidis carbonarius). The US and CT of the ossicle rings were performed for anatomical identification. The thickness, density, width, and diameters of each ring were measured. The US and CT of the scleral ossicle rings of three animals showed single and continuous circular structures, located in the anterior pole. These structures were easily observed in C. mydas, whose rings were the biggest, thickest and widest. The T. dorbigni CT presented decreased dimensions and the ossicles were the most difficult to identify. Bone density in the superior region was greater than in the inferior of each ring in all animals. Non-invasive imaging exams are good tools to study the anatomy of the ocular skeleton. The scleral ossicle rings of the three specimens presented general morphological similarities and CT enabled visualizing a greater number of details of the ring bone morphology.
RESUMO: Os anéis de ossículos esclerais têm sua função relacionada à proteção mecânica, fixação muscular, suporte para o formato do bulbo ocular e acomodação visual, contudo existem poucos relatos morfobiométricos sobre esses anéis em diferentes espécies de Testudines. Desta forma, foi realizada a avaliação morfobiométrica, por ultrassom (US) e tomografia computadorizada (TC), dos anéis de ossículos esclerais em uma tartaruga verde (Chelonia mydas), um tigre-d’água (Trachemys dorbigni) e um jabuti-piranga (Chelonoidis carbonarius). Foram realizadas US e TC dos anéis esclerais dos três animais para identificação anatômica, espessura, densidade, largura e diâmetros. A US e a TC dos três animais mostraram estruturas circulares únicas e contínuas, localizadas no polo anterior. Estas estruturas foram facilmente observadas na C. mydas, cujos anéis eram os maiores, mais espessos e mais largos. A TC da T. dorbigni apresentou dimensões reduzidas e os ossículos foram dificilmente identificados. A densidade óssea na região superior foi maior comparativamente a parte inferior de cada anel, em todos os animais. Exames de imagem não invasivos mostraram-se bons instrumentos para estudo do esqueleto escleral. Os anéis de ossículos esclerais dos três espécimes apresentaram semelhanças morfológicas gerais e a TC permitiu visualizar um maior número de detalhes da morfologia óssea do anel.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Animals vary widely in body size within and across species. This has consequences for the function of organs and body parts in both large and small individuals. How these scale, in relation to body ...size, reveals evolutionary investment strategies, often resulting in trade-offs between functions. Eyes exemplify these trade-offs, as they are limited by their absolute size in two key performance features: sensitivity and spatial acuity. Due to their size polymorphism, insect compound eyes are ideal models for studying the allometric scaling of eye performance. Previous work on apposition compound eyes revealed that allometric scaling led to poorer spatial resolution and visual sensitivity in small individuals, across a range of insect species. Here, we used X-ray microtomography to investigate allometric scaling in superposition compound eyes-the second most common eye type in insects-for the first time. Our results reveal a novel strategy to cope with the trade-off between sensitivity and spatial acuity, as we show that the eyes of the hummingbird hawkmoth retain an optimal balance between these performance measures across all body sizes.
In this study, we assessed eye morphology and retinal topography in two flamingo species, the Caribbean flamingo (Phoenicopterus ruber) and the Chilean flamingo (P. chilensis). Eye morphology is ...similar in both species and cornea size relative to eye size (C:A ratio) is intermediate between those previously reported for diurnal and nocturnal birds. Using stereology and retinal whole mounts, we estimate that the total number of Nissl‐stained neurons in the retinal ganglion cell (RGC) layer in the Caribbean and Chilean flamingo is ~1.70 and 1.38 million, respectively. Both species have a well‐defined visual streak with a peak neuron density of between 13,000 and 16,000 cells mm−2 located in a small central area. Neurons in the high‐density regions are smaller and more homogeneous compared to those in medium‐ and low‐density regions. Peak anatomical spatial resolving power in both species is approximately 10–11 cycles/deg. En‐face images of the fundus in live Caribbean flamingos acquired using spectral domain optical coherence tomography (SD‐OCT) revealed a thin, dark band running nasotemporally just dorsal to the pecten, which aligned with the visual streak in the retinal topography maps. Cross‐sectional images (B‐scans) obtained with SD‐OCT showed that this dark band corresponds with an area of retinal thickening compared to adjacent areas. Neither the retinal whole mounts, nor the SD‐OCT imaging revealed any evidence of a central fovea in either species. Overall, we suggest that eye morphology and retinal topography in flamingos reflects their cathemeral activity pattern and the physical nature of the habitats in which they live.
We investigated eye morphology and retinal topography in Caribbean and Chilean flamingos. Both species have a well‐defined visual streak, with the peak retinal ganglion cell densities located in a small central area. The organization of the visual system in these birds reflects their cathemeral activity pattern and the physical nature of the habitats in which they live.
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