Diversity in Primate External Eye Morphology: Previously Undescribed Traits and Their Potential Adaptive Value

García, Juan Olvido Perea; Danel, Dariusz; Monteiro, Antónia

doi:10.3390/sym13071270

Cited by 14 publications

(28 citation statements)

References 47 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition, the degree to which eye direction, independent of head direction, can be interpreted as a social cue in non-human primates is unclear, sparsely researched in most species and has been challenged 6 . Instead, scleral pigment may represent an alternative function such as photo-regulation 19,20 with exceptions delineating in line with the strength of self-domestication processes 11 .…”

Section: Discussionmentioning

confidence: 99%

“…A further minor limitation in using online primate facial photographs is that these images may be biased by the aesthetic preferences of the human photographer and/or uploader, a bias that may particularly influence photographed eye characteristics, as, even when looking at non-human animals, humans often attend to the eyes 43 . In addition, it remains possible that ocular morphologies in addition to the sclera, such as the limbus or temporal wedge 19 , may be captured in analyses due to the presumable variation in the presentation of these features between primate species, which have not been described to our knowledge. However, this is also a limitation common to every previous study concerning divergent ocular morphologies in primates [1][2][3][4][5][6]10 .…”

Section: Discussionmentioning

confidence: 99%

“…As evidence, authors note the metabolic cost required to synthesise pigment which may indicate an adaptive function 2 . No function of scleral pigment has yet, to our knowledge, been comparatively determined, though it has been suggested that ocular pigment may instead provide protection against UV radiation 19,20 .…”

mentioning

confidence: 99%

See 2 more Smart Citations

The evolutionary drivers of primate scleral coloration

Mearing

Burkart

Dunn

et al. 2022

Sci Rep

View full text Add to dashboard Cite

The drivers of divergent scleral morphologies in primates are currently unclear, though white sclerae are often assumed to underlie human hyper-cooperative behaviours. Humans are unusual in possessing depigmented sclerae whereas many other extant primates, including the closely-related chimpanzee, possess dark scleral pigment. Here, we use phylogenetic generalized least squares (PGLS) analyses with previously generated species-level scores of proactive prosociality, social tolerance (both n = 15 primate species), and conspecific lethal aggression (n = 108 primate species) to provide the first quantitative, comparative test of three existing hypotheses. The ‘self-domestication’ and ‘cooperative eye’ explanations predict white sclerae to be associated with cooperative, rather than competitive, environments. The ‘gaze camouflage’ hypothesis predicts that dark scleral pigment functions as gaze direction camouflage in competitive social environments. Notably, the experimental evidence that non-human primates draw social information from conspecific eye movements is unclear, with the latter two hypotheses having recently been challenged. Here, we show that white sclerae in primates are associated with increased cooperative behaviours whereas dark sclerae are associated with reduced cooperative behaviours and increased conspecific lethal violence. These results are consistent with all three hypotheses of scleral evolution, suggesting that primate scleral morphologies evolve in relation to variation in social environment.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

The evolutionary drivers of primate scleral coloration

Mearing

Burkart

Dunn

et al. 2022

Sci Rep

View full text Add to dashboard Cite

show abstract

“…1 ); nevertheless, two decades later our understanding of the drivers underlying said diversity remains poor. This diversity includes variation in shape of the eye outline, in conjunctival and iridial colouration, and in other traits for which we lack adaptive explanations or hypotheses 8 (Fig. 2 ).…”

Section: Introductionmentioning

confidence: 99%

“…For instance blue irises have been associated with reduced incidence of seasonal affective disorder in people living far from the equator 29 . Latitudes farther from the equator receive less overall solar irradiance of all wavelengths with less short wavelength (blue) radiation 28 , and the circadian-rhythm hypothesis suggests that bluer irises in primates should be found at higher latitudes to maximise the incidence of blue light entering the eyeball 8 . Greater incidence of short-wave (blue) light results in the activation of intrinsically photosensitive retinal ganglion cells 27 which, by suppressing melatonin release, increase wakefulness.…”

Section: Introductionmentioning

confidence: 99%

Ecological factors are likely drivers of eye shape and colour pattern variations across anthropoid primates

García

Ramarajan

Kret

et al. 2022

Sci Rep

Self Cite

View full text Add to dashboard Cite

External eye appearance across primate species is diverse in shape and colouration, yet we still lack an explanation for the drivers of such diversity. Here we quantify substantial interspecific variation in eye shape and colouration across 77 primate species representing all extant genera of anthropoid primates. We reassess a series of hypotheses aiming to explain ocular variation in horizontal elongation and in colouration across species. Heavier body weight and terrestrial locomotion are associated with elongated eye outlines. Species living closer to the equator present more pigmented conjunctivae, suggesting photoprotective functions. Irises become bluer in species living further away from the equator, adding to existing literature supporting a circadian clock function for bluer irises. These results shift the current focus from communicative, to ecological factors in driving variation in external eye appearance in anthropoid primates. They also highlight the possibility that similar ecological factors contributed to selection for blue eyes in ancestral human populations living in northern latitudes.

show abstract

Attention Towards Pupil Size in Humans and Bonobos (Pan paniscus)

2022

View full text Add to dashboard Cite

Previous work has established that humans have an attentional bias towards emotional signals, and there is some evidence that this phenomenon is shared with bonobos, our closest relatives. Although many emotional signals are explicit and overt, implicit cues such as pupil size also contain emotional information for observers. Pupil size can impact social judgment and foster trust and social support, and is automatically mimicked, suggesting a communicative role. While an attentional bias towards more obvious emotional expressions has been shown, it is unclear whether this also extends to a more subtle implicit cue, like changes in pupil size. Therefore, the current study investigated whether attention is biased towards pupils of differing sizes in humans and bonobos. A total of 150 human participants (141 female), with a mean age of 19.13 (ranging from 18 to 32 years old), completed an online dot-probe task. Four female bonobos (6 to 17 years old) completed the dot-probe task presented via a touch screen. We used linear mixed multilevel models to examine the effect of pupil size on reaction times. In humans, our analysis showed a small but significant attentional bias towards dilated pupils compared to intermediate-sized pupils and intermediate-sized pupils when compared to small pupils. Our analysis did not show a significant effect in bonobos. These results suggest that the attentional bias towards emotions in humans can be extended to a subtle unconsciously produced signal, namely changes in pupil size. Due to methodological differences between the two experiments, more research is needed before drawing a conclusion regarding bonobos.

show abstract

Diversity in Primate External Eye Morphology: Previously Undescribed Traits and Their Potential Adaptive Value

Cited by 14 publications

References 47 publications

The evolutionary drivers of primate scleral coloration

The evolutionary drivers of primate scleral coloration

Ecological factors are likely drivers of eye shape and colour pattern variations across anthropoid primates

Attention Towards Pupil Size in Humans and Bonobos (Pan paniscus)

Contact Info

Product

Resources

About