Predator visual adaptations for breaking camouflage

Overview

Understanding the sensory ecology of camouflage provides a unique window into the evolutionary ecology of predator-prey interactions. Much recent research has investigated how prey coloration defends against predators. However, predator adaptations for breaking camouflage have been relatively understudied. This project will investigate the role of two visual adaptations that have been hypothesized to beat camouflage – stereopsis and a sensitivity to second-order motion.

Stereopsis is the ability to calculate depth by comparing the views of the two eyes. It has been shown in several vertebrates and one insect predator: the praying mantis. Importantly, it has been suggested to enable predators to spot perfectly camouflaged items since they stand out in relief. Yet the advantage it conveys against camouflage has not been explicitly tested.

Camouflage could also interfere with the ability to intercept moving objects. Predators can easily track a black target on a grey background. However, intercepting targets matching the background (e.g. grey on grey) is more difficult. This is achieved by an ability to exploit ‘second-order motion’ cues, correlating more complex visual statistics over time. This ability is known in humans and has recently been discovered in mantises, but we know little about how it helps against different forms of camouflage.

Our recent research has developed computational models for both stereopsis and second-order motion in insects. In this project, we will modify them to see which components are essential for camouflage breaking (Aim 1). Using a 3D insect cinema, we will then investigate how predator stereopsis breaks camouflage (Aim 2). We will further develop an evolutionary simulation where virtual prey will be tested against live insects and humans to investigate the evolution of camouflage in response to these visual adaptations (Aim 3). Finally, we will examine whether traits such as iridescence and specular reflections defend against these visual adaptations (Aim 4). The project thus combines behavioural and sensory ecology with computational approaches to reveal the coevolution of patterns and visual systems.

Methodology

Computational models of vision developed by JR and VN will be modified and tested on different camouflaged stimuli to assess which aspects of visual processing enable camouflage breaking (Aim 1). The capability of stereopsis of predators (mantises and humans) to break camouflage will be tested in a 3D cinema set-up (Aim 2). Using a computer screen and 3D glasses, predators will be presented camouflaged moving prey with or without stereo depth cues. Predator accuracy will be measured throughout using the latency, angle and probability of a response. For Aim 3, virtual stimuli varying along multiple dimensions (spatial frequency, speed, contrast) will be presented to predators. Their responses will exert a selection pressure on prey visual characteristics. This will form an evolutionary simulation revealing adaptive forms of camouflage. Finally, behavioural experiments with mantises and real and 3D printed prey will be conducted in the lab to test how iridescence and specular reflections interfere with prey capture (Aim 4). JH, VN and JR will supervise the student on psychophysics and visual programming. JS, KK, JH and VN will supervise the student on the theory underlying iridescence and the design of behavioural experiments.

Project Timeline

Year 1

Month 1-6: Literature review, introduction to insect care and construction of set-up. Month 7-9: Iridescence and prey capture experiments. Month 10-12: Specular reflections and prey capture experiments.

Year 2

Month 1-5: Experiments on 3D disparity and camouflage breaking in the 3D insect cinema. Month 6-12: Experiments assessing camouflage effectiveness against computational models of vision. Attending a national/European conference.

Year 3

Month 1-3: Developing the evolutionary simulation. Month 4-12: Running evolutionary simulations. Attending a training course and an international conference.

Year 3.5

Month 1-6: Thesis write-up

Training
& Skills

The supervisory team is uniquely interdisciplinary and several of them have successfully collaborated before. They can thus train students from different disciplines (ecology/psychology/physics) and the student will be trained in a suite of experimental and computational skills and areas including: 1) Behavioural and sensory ecology 2) Programming of visual stimuli and computational approaches to ecology 3) Machine-learning based video analysis 4) Insect care and maintenance 5) Data processing and statistical analysis 6) Scientific writing 7) Presentation skills through conferences, lab meetings, and public outreach

References & further reading

Nityananda V, O’Keeffe J, Umeton D, Simmons A, Read JCA. Second-order cues to figure motion enable object detection during prey capture by praying mantises. Proceedings of the National Academy of Sciences of the United States of America 2019, 116(52), 27018-27027.

Nityananda V, Tarawneh G, Henriksen S, Umeton D, Simmons A, Read JCA. A Novel Form of Stereo Vision in the Praying Mantis. Current Biology 2018, 28(4), 588-593.

Troscianko J, Skelhorn J, Stevens M. Camouflage strategies interfere differently with observer search images. Proceedings of the Royal Society Series B 2018, 285, 20181386.

Rowland HM, Burriss RP, Skelhorn J. The antipredator benefits of postural camouflage in peppered moth caterpillars. Scientific Reports 2020, 10, 21654

Halpin, C. G., Penacchio, O., Lovell, P. G., Cuthill, I., Harris, J., Skelhorn, J. & Rowe, C., Pattern contrast influences wariness in naïve predators towards aposematic patterns, 2020, Scientific Reports. 10, 8 p., 9246.

Kjernsmo, K., Whitney, H.M., Scott-Samuel, N.E., Hall, J.R., Knowles, H., Talas, L. & Cuthill, I.C. 2020. Iridescence as camouflage. Current Biology 30, 551-555.

Further Information

Informal enquiries are very welcome. Any interested applicants are strongly encouraged to contact Dr Vivek Nityananda (vivek.nityananda@newcastle.ac.uk, +441912086246)

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