Predator vision and defensive coloration: from mechanism to function
Lead Research Organisation:
University of Cambridge
Department Name: Zoology
Abstract
Few things are more important to an animal than avoiding predation. The various strategies involved in reducing the risk of predation include camouflage to hinder detection or recognition, startle displays and eyespots to scare predators, and 'dazzle' markings making it difficult for predators to judge how fast the prey is moving. As soon as Darwin and Wallace presented their theory of evolution by natural selection, around 150 years ago, the numerous ways of avoiding predation provided crucial examples for illustrating and defending natural selection and adaptation. The study of animal coloration has also influenced many areas of human applications and culture. For example, camouflage is of great importance in military applications, and has influenced peaceful areas of culture such as art and fashion. Conspicuous displays, like startle responses and eyespots, can also influence applications, such as producing non-harmful deterrents for avian crop pests. However, as the Darwinian anniversary approaches (200 years since Darwin's birth, and 150 years since the Origin of Species was published), researchers still know surprisingly little about many areas of protective coloration. This project has three main aims. The first is to investigate how various forms of defensive coloration reduce the risk of predation in terms of predator vision. Birds are the principle predators used in this project, and represent the main visual predation threat for many animals. Considering their visual abilities is crucial because, unlike humans, birds can perceive ultraviolet light and have a more sophisticated colour vision system than humans. By understanding what specific processes of predator vision are exploited, we can explain the form, function, and evolution of different defensive strategies in nature. The second aim is to investigate how different defensive strategies can be combined on the same animal (such as camouflage and conspicuous signals), and how they relate to each other. In most previous work, different defensive strategies have been considered in isolation, despite the fact that most animal markings result from a range of selection pressures and fulfil multiple functions. The third aim is to extrapolate the principles learned from the study of defensive coloration to other areas of behaviour and signalling. The model system used here is brood parasitism, where a parasitic bird 'tricks' other species into caring for its young. This has, over co-evolution, often led to hosts having increasing ability to recognise and reject foreign eggs, and counter-adaptations in parasites to evade host defences, including egg mimicry. First, I will create simulations of evolution, where computer generated prey on artificial backgrounds are subjected to selection pressure (to be hidden against the background or to prevent capture when moving) by an artificial 'predator', based on features of real predator visual systems. Prey which survive, then reproduce, with some offspring incurring mutations for new colour patterns. Over time, those markings most successful in preventing predation will spread, further evolve, and optimise their defensive capability. In this way, I will predict what types of prey coloration evolve under different selection pressures and how they exploit specific aspects of predator vision. Second, artificial prey, designed to a bird's visual system, will be presented to bird predators in aviaries and the field. These are not intended to resemble real species, but to derive general principles about what types of marking are most effective in preventing predation, including what makes effective camouflage markings and startle displays. Finally, in extending the principles of defensive signals, I will ask how closely the egg of a brood parasite must match those of its host to prevent being detected as an intruder, and how cuckoo chick markings both increase host provisioning and decrease the risk of predation.
Technical Summary
Avoiding predation is a crucial aspect of many animals fitness, with defensive strategies including camouflage, startle displays, and 'motion dazzle' markings. This project aims to: (1) base explanations of animal defensive coloration in formal mechanistic terms of how the visual signals are perceived by a predator, (2) use the principles derived to understand the form of defensive signals in nature, and (3) apply these principles to other areas of behaviour and signalling, using parental care and brood parasitism as a model system. Birds are the principle receivers used in this project. By understanding what mechanisms of the predator's vision are exploited, we can explain the form, function, and evolution of different defensive strategies in nature. In addition, defensive strategies have generally been considered in isolation, despite the fact that most animal markings typically result from multiple selection pressures and fulfil several functions. Understanding how defensive signals work can allow the derivation of general principles to be applied to other areas of behaviour and signalling. Simulations of prey evolution will involve computer generated prey, with 'genes' coding for their appearance, being subjected to selection pressure based on features of real predator visual systems. These will predict what types of prey coloration evolve under different selection pressures, and the specific aspects of predator vision they exploit. Artificial prey will be presented to avian predators in field sites and aviaries to derive general principles about what markings are most effective in preventing predation, including camouflage and startle displays. Finally, experiments will investigate how closely a cuckoo egg must match those of its host to prevent detection, and how the markings of cuckoo chicks can increase host provisioning. The project links behaviour, evolution and visual signalling, to theories from visual psychology and techniques from computer science.
Organisations
People |
ORCID iD |
Martin Stevens (Principal Investigator) |
Publications
Winters A
(2014)
Maternal effects and warning signal honesty in eggs and offspring of an aposematic ladybird beetle
in Functional Ecology
Wilson-Aggarwal JK
(2016)
Escape Distance in Ground-Nesting Birds Differs with Individual Level of Camouflage.
in The American naturalist
Walker LK
(2013)
A window on the past: male ornamental plumage reveals the quality of their early-life environment.
in Proceedings. Biological sciences
Troscianko J
(2015)
Image calibration and analysis toolbox - a free software suite for objectively measuring reflectance, colour and pattern.
in Methods in ecology and evolution
Troscianko J
(2016)
Camouflage predicts survival in ground-nesting birds.
in Scientific reports
Troscianko J
(2016)
Nest covering in plovers: How modifying the visual environment influences egg camouflage.
in Ecology and evolution
Troscianko J
(2013)
Defeating crypsis: detection and learning of camouflage strategies.
in PloS one
Teasdale LC
(2013)
Discrete colour polymorphism in the tawny dragon lizard (Ctenophorus decresii) and differences in signal conspicuousness among morphs.
in Journal of evolutionary biology
Tanaka K
(2011)
Rethinking visual supernormal stimuli in cuckoos: visual modeling of host and parasite signals
in Behavioral Ecology
Stoddard MC
(2011)
Avian vision and the evolution of egg color mimicry in the common cuckoo.
in Evolution; international journal of organic evolution
Description | This fellowship was transferred to Exeter Uni while still in progress. It has revealed many of the features that make camouflage effective, how a host of a brood parasite detects a foreign egg, and developed methods to quantify visual signals. Full details are in the submission for BB/G022887/2 |
Exploitation Route | Future research, outreach |
Sectors | Education |
Description | This fellowship was transferred to Exeter Uni midway. Please see BB/G022887/2 By research community and for schools outreach, citizen science, and media. |
First Year Of Impact | 2009 |
Sector | Education |
Impact Types | Cultural |
Description | How to optimise imperfect camouflage |
Amount | £376,743 (GBP) |
Funding ID | BB/P018319/1 |
Organisation | Biotechnology and Biological Sciences Research Council (BBSRC) |
Sector | Public |
Country | United Kingdom |
Start | 09/2017 |
End | 09/2020 |
Description | Predator learning of camouflage types Grant Ref: BB/L017709/1 |
Amount | £371,695 (GBP) |
Funding ID | BB/L017709/1 |
Organisation | Biotechnology and Biological Sciences Research Council (BBSRC) |
Sector | Public |
Country | United Kingdom |
Start | 09/2014 |
End | 09/2017 |
Title | Data and code for Caves, Dixit, Colebrook-Robjent, Hamusikili, Stevens, Thorogood, and Spottiswoode: Hosts elevate either within-clutch consistency or between-clutch distinctiveness of egg phenotypes in defence against brood parasites |
Description | In host-parasite arms races, hosts can evolve signatures of identity to enhance detection of parasite mimics. In theory, signatures are most effective when within-individual variation is low ("consistency"), and between-individual variation is high ("distinctiveness"). However, empirical support for positive covariation in signature consistency and distinctiveness across species is mixed. Here we attempt to resolve this puzzle by partitioning distinctiveness according to how it is achieved: (1) greater variation within each trait, contributing to elevated "absolute distinctiveness" or (2) combining phenotypic traits in unpredictable combinations ("combinatorial distinctiveness"). We tested how consistency covaries with each type of distinctiveness by measuring variation in egg colour and pattern in two African bird families (Cisticolidae and Ploceidae) that experience mimetic brood parasitism. Contrary to predictions, parasitised species, but not unparasitised species, exhibited a negative relationship between consistency and combinatorial distinctiveness. Moreover, regardless of parasitism status, consistency was negatively correlated with absolute distinctiveness across species. Together, these results suggest that (i) selection from parasites acts on how traits combine rather than absolute variation in traits, (ii) consistency and distinctiveness are alternative rather than complementary elements of signatures, and (iii) mechanistic constraints may explain the negative relationship between consistency and absolute distinctiveness across species. |
Type Of Material | Database/Collection of data |
Year Produced | 2021 |
Provided To Others? | Yes |
URL | http://datadryad.org/stash/dataset/doi:10.5061/dryad.02v6wwq34 |
Description | BBC 1 TV Appearance |
Form Of Engagement Activity | A press release, press conference or response to a media enquiry/interview |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Public/other audiences |
Results and Impact | I appeared on BBC 1 'The One Show' about my work on camouflage and colour change in rockpool goby fish. no actual impacts realised to date |
Year(s) Of Engagement Activity | 2014 |
Description | BBC online coverage |
Form Of Engagement Activity | A press release, press conference or response to a media enquiry/interview |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Media (as a channel to the public) |
Results and Impact | Coverage of paper on cuckoo eggs no actual impacts realised to date |
Year(s) Of Engagement Activity | 2010 |
Description | BBC2 TV Appearance |
Form Of Engagement Activity | A press release, press conference or response to a media enquiry/interview |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Media (as a channel to the public) |
Results and Impact | Appearance on a BBC 2 TV programme as part of a series called 'Inside the Animal Mind' no actual impacts realised to date |
Year(s) Of Engagement Activity | 2014 |
Description | Media output |
Form Of Engagement Activity | A press release, press conference or response to a media enquiry/interview |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Media (as a channel to the public) |
Results and Impact | BBC Online coverage of paper no actual impacts realised to date |
Year(s) Of Engagement Activity | 2010 |
Description | Science, is it for me? 2014 |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Schools |
Results and Impact | An event to inspire school children to study science while redefining the stereotype of scientists in lab coats. My lab and I presented some of the work we do in our project. 60 students from several local schools were invited to the University of Exeter where scientists organised sessions for the pupils to experience and learn about the research being conducted at the university. Our Group provided a series of activities including; an introduction to signalling and camouflage, a session on search images, discussion on startle displays and an activity to appreciate camouflage on different habitats. Presentation and camouflage games illustrating research. no actual impacts realised to date |
Year(s) Of Engagement Activity | 2014 |
Description | TV appearance |
Form Of Engagement Activity | A press release, press conference or response to a media enquiry/interview |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Media (as a channel to the public) |
Results and Impact | National Geographic television programme ('Jurassic CSI') - I appeared in one episode of the series discussing bird vision and coloration no actual impacts realised to date |
Year(s) Of Engagement Activity | 2011 |