Abstract
Predatory snakes are argued to have been largely responsible for the origin of primates via selection favoring expansion of the primate visual system, and even today snakes can be deadly to primates. Neurobiological research is now beginning to reveal the mechanisms underlying the ability of primates (including humans) to detect snakes more rapidly than other stimuli. However, the visual cues allowing rapid detection of snakes, and the cognitive and ecological conditions contributing to faster detection, are unclear. Since snakes are often partially obscured by vegetation, the more salient cues are predicted to occur in small units. Here we tested for the salience of snake scales as the smallest of potential visual cues by presenting four groups of wild vervet monkeys (Chlorocebus pytherythrus) with a gopher snake (Pituophis catenifer) skin occluded except for no more than 2.7 cm, in natural form and flat, the latter to control for even small curvilinear cues from their unusual body shape. Each of these treatments was preceded by a treatment without the snakeskin, the first to provide a baseline, and the second, to test for vigilance and memory recall after exposure to the snakeskin. We found that (1) vervets needed only a small portion of snakeskin for detection, (2) snake scales alone were sufficient for detection, (3) latency to detect the snakeskin was longer with more extensive and complex ground cover, and (4) vervets that were exposed to the snakeskin remembered where they last saw “snakes”, as indicated by increased wariness near the occluding landmarks in the absence of the snakeskin and more rapid detection of the next presented snakeskin. Unexpectedly, adult males did not detect the snakeskin as well as adult females and juveniles. These findings extend our knowledge of the complex ecological and evolutionary relationships between snakes and primates.
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Acknowledgments
This research was supported by the National Science Foundation (BCS 99-03949 and BCS 1266389) and was conducted under local affiliation with the Kenya Wildlife Service and with permission to conduct research in Kenya from NACOSTI (permit no. NACOSTI/P/I5/5820/4650). The study has IACUC approval (protocol no. 19172) from the University of California, Davis. We are grateful to Margaret Kinnaird, Dino Martins, the staff at Mpala Research Centre, and Truman Young for logistical support, Wilson Longor for help in identifying the HP individuals, Jessica Alvarez, David Madry, Chyna Oyola, and Mariel Viano for scoring the videos, Brianne Beisner, Richard Coss, Harry Greene, and Truman Young for helpful discussions and comments on earlier drafts, two anonymous reviewers for their insightful comments, and, of course, the monkeys.
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Isbell, L.A., Etting, S.F. Scales drive detection, attention, and memory of snakes in wild vervet monkeys (Chlorocebus pygerythrus). Primates 58, 121–129 (2017). https://doi.org/10.1007/s10329-016-0562-y
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DOI: https://doi.org/10.1007/s10329-016-0562-y