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Duran E, Perea-García JO, Piepenbrock D, Veefkind C, Kret ME, Massen JJM. Preliminary evidence that eye appearance in parrots (Psittaciformes) co-varies with latitude and altitude. Sci Rep 2024; 14:12859. [PMID: 38834673 DOI: 10.1038/s41598-024-63599-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Accepted: 05/30/2024] [Indexed: 06/06/2024] Open
Abstract
External eye appearance in avian taxa has been proposed to be driven by social and ecological functions. Recent research in primates suggests, instead, that, photoprotective functions are important drivers of external eye appearance. Using similar methods, we examined the variation in external eye appearance of 132 parrot species (Psittaciformes) in relation to their ecology and sociality. Breeding systems, flock size and sexual dimorphism, as well as species' latitude and maximum living altitude, and estimated UV-B incidence in species' ranges were used to explore the contribution of social and ecological factors in driving external eye appearance. We measured the hue and brightness of visible parts of the eye and the difference in measurements of brightness between adjacent parts of the eye. We found no link between social variables and our measurements. We did, however, find a negative association between the brightness of the inner part of the iris and latitude and altitude. Darker inner irises were more prevalent farther away from the equator and for those species living at higher altitudes. We found no link between UV-B and brightness measurements of the iris, or tissue surrounding the eye. We speculate that these results are consistent with an adaptation for visual functions. While preliminary, these results suggest that external eye appearance in parrots is influenced by ecological, but not social factors.
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Affiliation(s)
- Elif Duran
- Department of Psychology, Izmir University of Economics, Izmir, Turkey
| | - Juan Olvido Perea-García
- Institute of Psychology, Cognitive Psychology Unit, Leiden University, Wassenaarseweg 52, Leiden, 2333 AK, The Netherlands.
| | - Diede Piepenbrock
- Animal Behaviour and Cognition, Department of Biology, Utrecht University, Utrecht, The Netherlands
| | - Celine Veefkind
- Animal Behaviour and Cognition, Department of Biology, Utrecht University, Utrecht, The Netherlands
| | - Mariska E Kret
- Institute of Psychology, Cognitive Psychology Unit, Leiden University, Wassenaarseweg 52, Leiden, 2333 AK, The Netherlands
- Leiden Institute of Brain and Cognition (LIBC), Leiden, The Netherlands
| | - Jorg J M Massen
- Animal Behaviour and Cognition, Department of Biology, Utrecht University, Utrecht, The Netherlands
- Vogelpark Avifauna, Alphen Aan Den Rijn, The Netherlands
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2
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Pletcher JS, Zimmer JL, Liu CC, Beierschmitt A, Lewin AC. Ocular examination findings and selected ophthalmic diagnostic tests in African green monkeys (Chlorocebus aethiops sabaeus). Vet Ophthalmol 2024; 27:158-169. [PMID: 37442802 DOI: 10.1111/vop.13132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2023] [Revised: 06/26/2023] [Accepted: 07/04/2023] [Indexed: 07/15/2023]
Abstract
OBJECTIVE To document ocular lesions and establish ophthalmic diagnostic test reference values in a colony of African green monkeys (Chlorocebus aethiops sabaeus). ANIMALS STUDIED Fifty one geriatric (GAGM, 19-30 years old), 10 adult (AAGM, 5-9 years old) and 10 juvenile (JAGM, <2 years old) African green monkeys housed in a single Caribbean research colony. PROCEDURES Ocular biomicroscopy, indirect fundoscopy, Schirmer tear test (STT), rebound tonometry (TonoVet®) and corneal fluorescein staining were performed. Mixed ANCOVA tests were performed to compare STT and IOP between groups. RESULTS Common ocular lesions in GAGM included vitreal degeneration (27/51, 51/102 eyes) and cataracts (21/51, 32/102 eyes). Vitreal degeneration was also common in AAGM (8/10, 16/20 eyes) and infrequent in JAGM (3/10, 6/20 eyes). Cataracts were not present in any JAGM or AAGM. All eyes in all three groups had perilimbal corneal pigmentation and faint lace-like anterior corneal stromal opacification. Median (range) STT values were 16.0 (18) mm/min in GAGM. Mean (SD) STT values were 14.2 (4.6) mm/min in AAGM, and 8.9 (3.4) mm/min in JAGM. Median (range) IOP values were 16.5 (27) mmHg in GAGM. Mean (SD) IOP values were 18.0 (2.8) mmHg in AAGM, and 14.1 (2.2) mmHg in JAGM. JAGM had significantly lower STT and IOP values compared to AAGM (p = .0449, .0057, respectively) and GAGM (p = .0002, .0130, respectively). CONCLUSIONS Spontaneous ocular lesions were common in geriatric monkeys in this research colony. IOP and STT values were lower in juvenile African green monkeys relative to adult or geriatric animals.
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Affiliation(s)
- Jacklin S Pletcher
- Matthew J. Ryan Veterinary Hospital, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Jennifer L Zimmer
- Oakland Veterinary Referral Services, Bloomfield Township, Michigan, USA
| | - Chin-Chi Liu
- Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA
| | - Amy Beierschmitt
- Behavioural Science Foundation, Estridge Estate, Saint Kitts and Nevis
| | - Andrew C Lewin
- Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA
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Konno A, Aoki H, Suzuki E, Furuta S, Ueda S. Are dark-eyed dogs favoured by humans? Domestication as a potential driver of iris colour difference between dogs and wolves. ROYAL SOCIETY OPEN SCIENCE 2023; 10:230854. [PMID: 38126061 PMCID: PMC10731317 DOI: 10.1098/rsos.230854] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Accepted: 11/27/2023] [Indexed: 12/23/2023]
Abstract
Comparative studies have shown that the eye morphology of primates has been shaped by a variety of selection pressures (e.g. communication, environmental factors). To comprehensively elucidate the complex links between ocular morphology and its evolutionary drive, attention should be paid to other phylogenetic groups. Here, we address a new question regarding the evolution of eye colour patterns in the oldest domesticated animal, namely, the domestic dog (Canis familiaris). In this study, we conducted an image analysis of dogs and their closest relatives, grey wolves (Canis lupus), to compare the colours of their irises, with the aim of assessing whether eye colours of dogs affect how humans perceived dogs. We found that the irises of dogs were significantly darker than those of wolves. We also found that facial images of dark-eyed dogs were perceived as more friendly and immature, potentially eliciting caregiving responses from humans. Our findings are consistent with our expectation that humans favour dark-eyed dogs over light-eyed ones and provide an updated hypothesis that dogs with dark eyes may have evolved by acquiring a facial trait that sends a non-threatening gaze signal to humans.
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Affiliation(s)
- Akitsugu Konno
- Department of Animal Sciences, Teikyo University of Science, Yamanashi, Japan
| | - Hitomi Aoki
- Department of Animal Sciences, Teikyo University of Science, Yamanashi, Japan
| | - Emiri Suzuki
- Department of Animal Sciences, Teikyo University of Science, Yamanashi, Japan
| | - Seiya Furuta
- Department of Animal Sciences, Teikyo University of Science, Yamanashi, Japan
| | - Sayoko Ueda
- The Mt. Fuji Institute for Nature and Biology, Showa University, Yamanashi, Japan
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Caspar KR, Hüttner L, Begall S. Scleral appearance is not a correlate of domestication in mammals. ZOOLOGICAL LETTERS 2023; 9:12. [PMID: 37248525 PMCID: PMC10228120 DOI: 10.1186/s40851-023-00210-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Accepted: 05/15/2023] [Indexed: 05/31/2023]
Abstract
Numerous hypotheses try to explain the unusual appearance of the human eye with its bright sclera and transparent conjunctiva and how it could have evolved from a dark-eyed phenotype, as is present in many non-human primates. Recently, it has been argued that pigmentation defects induced by self-domestication may have led to bright-eyed ocular phenotypes in humans and some other primate lineages, such as marmosets. However, it has never been systematically studied whether actual domesticated mammals consistently deviate from wild mammals in regard to their conjunctival pigmentation and if this trait might therefore be part of a domestication syndrome. Here, we test this idea by drawing phylogenetically informed comparisons from a photographic dataset spanning 13 domesticated mammal species and their closest living wild relatives (n ≥ 15 photos per taxon). We did not recover significant differences in scleral appearance or irido-scleral contrast between domesticated and wild forms, suggesting that conjunctival depigmentation, unlike cutaneous pigmentation disorders, is not a general correlate of domestication. Regardless of their domestication status, macroscopically depigmented conjunctivae were observed in carnivorans and lagomorphs, whereas ungulates generally displayed darker eyes. For some taxa, we observed pronounced intraspecific variation, which should be addressed in more exhaustive future studies. Based on our dataset, we also present preliminary evidence for a general increase of conjunctival pigmentation with eye size in mammals. Our findings suggest that conjunctival depigmentation in humans is not a byproduct of self-domestication, even if we assume that our species has undergone such a process in its recent evolutionary history.
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Affiliation(s)
- Kai R Caspar
- Institute of Cell Biology, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
- Department of General Zoology, University of Duisburg-Essen, Essen, Germany.
- Department of Game Management and Wildlife Biology, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Praha, Czech Republic.
| | - Lisa Hüttner
- Department of General Zoology, University of Duisburg-Essen, Essen, Germany
| | - Sabine Begall
- Department of General Zoology, University of Duisburg-Essen, Essen, Germany
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Clark IR, Lee KC, Poux T, Langergraber KE, Mitani JC, Watts D, Reed J, Sandel AA. White sclera is present in chimpanzees and other mammals. J Hum Evol 2023; 176:103322. [PMID: 36706647 PMCID: PMC9998187 DOI: 10.1016/j.jhevol.2022.103322] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2022] [Revised: 12/22/2022] [Accepted: 12/23/2022] [Indexed: 01/27/2023]
Affiliation(s)
- Isabelle R Clark
- Department of Anthropology, University of Texas at Austin, 2201 Speedway, Austin, TX 78712, USA
| | - Kevin C Lee
- School of Human Evolution and Social Change and Institute of Human Origins, Arizona State University, 900 S. Cady Mall, Tempe, AZ 85281, USA
| | - Tucker Poux
- Tufts University, 419 Boston Ave, Medford, MA 02155, USA
| | - Kevin E Langergraber
- School of Human Evolution and Social Change and Institute of Human Origins, Arizona State University, 900 S. Cady Mall, Tempe, AZ 85281, USA
| | - John C Mitani
- Department of Anthropology, University of Michigan, 1085 S. University Ave., Ann Arbor, MI 48109, USA
| | - David Watts
- Department of Anthropology, Yale University, P.O. Box 208277, New Haven, CT 06520, USA
| | - James Reed
- Underdog Films Ltd, 2 St. Paul's Road, Bristol, BS8 1LT, UK
| | - Aaron A Sandel
- Department of Anthropology, University of Texas at Austin, 2201 Speedway, Austin, TX 78712, USA.
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Zijlstra TW, van Berlo E, Kret ME. Attention Towards Pupil Size in Humans and Bonobos ( Pan paniscus). AFFECTIVE SCIENCE 2022; 3:761-771. [PMID: 36519142 PMCID: PMC9743857 DOI: 10.1007/s42761-022-00146-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2022] [Accepted: 08/07/2022] [Indexed: 05/29/2023]
Abstract
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. Supplementary Information The online version contains supplementary material available at 10.1007/s42761-022-00146-1.
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Affiliation(s)
- T. W. Zijlstra
- Cognitive Psychology Unit, Institute of Psychology, Leiden University, Leiden, the Netherlands
- Leiden Institute for Brain and Cognition (LIBC), Leiden, the Netherlands
| | - E. van Berlo
- Cognitive Psychology Unit, Institute of Psychology, Leiden University, Leiden, the Netherlands
- Leiden Institute for Brain and Cognition (LIBC), Leiden, the Netherlands
- Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, the Netherlands
| | - M. E. Kret
- Cognitive Psychology Unit, Institute of Psychology, Leiden University, Leiden, the Netherlands
- Leiden Institute for Brain and Cognition (LIBC), Leiden, the Netherlands
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Wacewicz S, Perea-García JO, Lewandowski Z, Danel DP. The adaptive significance of human scleral brightness: an experimental study. Sci Rep 2022; 12:20261. [PMID: 36424405 PMCID: PMC9691750 DOI: 10.1038/s41598-022-24403-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2022] [Accepted: 11/15/2022] [Indexed: 11/27/2022] Open
Abstract
Homogeneously depigmented sclerae have long been proposed to be uniquely human-an adaptation to enable cooperative behaviour by facilitating interpersonal coordination through gaze following. However, recent evidence has shown that deeply pigmented sclerae also afford gaze following if surrounding a bright iris. Furthermore, while current scleral depigmentation is clearly adaptive in modern humans, it is less clear how the evolutionarily intermediate stages of scleral pigmentation may have been adaptive. In sum, it is unclear why scleral depigmentation became the norm in humans, while not so in sister species like chimpanzees, or why some extant species display intermediate degrees of pigmentation (as our ancestors presumably did at some point). We created realistic facial images of 20 individually distinct hominins with diverse facial morphologies, each face in the (i) humanlike bright sclera and (ii) generalised apelike dark sclera version. Participants in two online studies rated the bright-sclera hominins as younger, healthier, more attractive and trustworthy, but less aggressive than the dark-sclera hominins. Our results support the idea that the appearance of more depigmented sclerae promoted perceived traits that fostered trust, increasing fitness for those individuals and resulting in depigmentation as a fixed trait in extant humans.
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Affiliation(s)
- Slawomir Wacewicz
- Center for Language Evolution Studies, Nicolaus Copernicus University, Toruń, Poland.
| | - Juan Olvido Perea-García
- The Cognitive Psychology Unit, Faculty of Social Sciences, Leiden University, Leiden, The Netherlands
| | - Zdzisław Lewandowski
- Department of Human Biology, Wroclaw University of Health and Sport Sciences, Wroclaw, Poland
| | - Dariusz P Danel
- Department of Anthropology, Hirszfeld Institute of Immunology and Experimental Therapy, Polish Academy of Sciences, Wroclaw, Poland
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8
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Mearing AS, Burkart JM, Dunn J, Street SE, Koops K. The evolutionary drivers of primate scleral coloration. Sci Rep 2022; 12:14119. [PMID: 35982191 PMCID: PMC9388658 DOI: 10.1038/s41598-022-18275-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2022] [Accepted: 08/08/2022] [Indexed: 11/09/2022] Open
Abstract
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.
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Affiliation(s)
- Alex S Mearing
- Department of Archaeology, Fitzwilliam Street, University of Cambridge, Cambridge, CB2 1QH, UK.
| | - Judith M Burkart
- Department of Anthropology, University of Zurich, 8057, Zurich, Switzerland
| | - Jacob Dunn
- Department of Archaeology, Fitzwilliam Street, University of Cambridge, Cambridge, CB2 1QH, UK.,School of Life Sciences, Anglia Ruskin University, Cambridge, CB1 1PT, UK.,Department of Cognitive Biology, University of Vienna, 1090, Vienna, Austria
| | - Sally E Street
- Department of Anthropology, University of Durham, Durham, DH1 3LE, UK
| | - Kathelijne Koops
- Department of Archaeology, Fitzwilliam Street, University of Cambridge, Cambridge, CB2 1QH, UK.,Department of Anthropology, University of Zurich, 8057, Zurich, Switzerland
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Kano F, Furuichi T, Hashimoto C, Krupenye C, Leinwand JG, Hopper LM, Martin CF, Otsuka R, Tajima T. What is unique about the human eye? Comparative image analysis on the external eye morphology of human and nonhuman great apes. EVOL HUM BEHAV 2021. [DOI: 10.1016/j.evolhumbehav.2021.12.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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