Realised hypothetical phenotypes and the adaptive value of Batesian mimicry

Lead Research Organisation: University of Nottingham
Department Name: School of Life Sciences

Abstract

Many animals, such as venomous snakes or stinging wasps, advertise to potential predators that they are well defended by displaying bright, bold colour patterns. Other animals, known as "mimics", have evolved to deceive predators by displaying patterns similar to the dangerous "models", despite being harmless. Studying the evolution of mimicry has the potential to tell us much about how natural selection leads to adaptation in wild animals.

Among mimics, we see many prominent and beautiful examples of the extreme adaptations that evolution can produce. However, some mimics, including many hoverflies that mimic wasps, only approximately resemble their model. We expect natural selection to favour the most convincing mimics, because less good ones ought to be recognised and picked off by predators: so why are some mimics inaccurate? Perhaps predators (such as birds) do not pay attention to all aspects of the prey's appearance, so the mimic does not have to be accurate in every way. Birds might avoid all prey that are roughly similar to a particularly nasty model, so beyond a certain point, further accuracy is unnecessary. Alternatively, the best chances of survival may gained by mimics which approximately resemble several nasty model species, rather than those which are perfect mimics of one particular model.

To test these ideas, we need to know not only how successful existing mimics are, but also the performance of alternative mimics with different combinations of features to the existing ones. Would a more accurate mimic survive better? What if it were perfect except for its colour? This is an example of a more general problem in evolutionary biology, of predicting how non-existent, but theoretically plausible, organisms might perform in comparison to those that we observe in nature.

To explore the evolutionary potential of mimics, our project brings together recently-developed technologies in a way never exploited before by biologists. First, we will photograph hoverflies and wasps from multiple angles and assemble 3D digital representations. We will then create new "morphed" images of plausible, but imaginary, intermediates between hoverflies and wasps which vary in similarity to the wasps. Thirdly, we will use 3D printing to create models of these intermediates (as well as the "real" insects) that are realistic in terms of their size, colour, pattern and shape. Lastly, we will measure the "survival" of these 3D models in a variety of experiments.

We will test the response of predators by training birds to "attack" models of hoverflies, but avoid those of wasps, in order to gain food rewards. Having learnt that distinction, the birds will then be tested for how they behave towards 3D models of intermediate appearance. The longer the birds hesitate before attacking, the more effective is the mimicry, because in the wild such delays would give the insect an opportunity to escape. We will look at predator behaviour both in the wild, where natural communities of birds with varying levels of experience are foraging for food, and in the laboratory, where we can control the experiences of each individual and watch how they learn. We will also repeat the experiments using praying mantises in place of birds, to investigate whether insect predators judge mimicry differently.

Our project addresses a long-standing biological question about the evolution of inaccurate mimicry, but will also provide broader insights into evolutionary processes. What is it about existing species that mean they survived when others either did not survive, or never evolved in the first place? This in turn allows us to understand how evolution produced the combinations of characteristics of existing species, and to predict the direction that evolution might take in the future. Our novel method will provide a framework for other evolutionary biologists to explore similar questions in a wide range of different organisms.

Planned Impact

Our proposed research is "Discovery Science": the primary motivation is curiosity regarding fundamental questions about the way organisms evolve. As with all such "blue skies" research, it has the potential for wide-ranging economic and societal impact in the future in ways that are difficult to predict, but which are no less important as a result.

In addition to this, because we are studying a highly accessible and intuitive example of evolution by natural selection (Batesian mimicry), our project provides the perfect opportunity for outreach and increasing the public understanding of science (especially evolution). We will run experiments in schools to teach children about evolutionary processes, and enthuse them about scientific experiments. Replicating our laboratory experiments in the school environment will increase interest and excitement from the learners, because they can see that they are participating in ongoing research with an uncertain outcome. Crucially, our partner schools are part of the "Widening Participation" scheme at the University of Nottingham, which aims to stimulate interest in university education amongst pupils from disadvantaged backgrounds. Our colleagues in the School of Life Sciences have shown that getting these children actively involved in novel scientific research is especially effective at both engendering enthusiasm for science and improving subject knowledge [1].

Batesian mimicry is an ideal case study for teaching about evolution, as the variation in question is on show in a visually striking way, and the principles behind the fitness benefits that mimicry brings (increased protection through deceiving predators) are easily understood. FG, TR and CT have all had great success in the past in using Batesian mimicry in teaching sessions for school children (of a range of ages). For example, CT has presented practical sessions based on the topic of mimicry at the Sutton Trust Summer School, which is aimed at increasing interest and enthusiasm for higher education among year 12 students from state-maintained schools. These sessions received excellent feedback, indicating that the attendees were more likely to consider studying a similar topic at university as a result. TR has run an experiment in primary schools, in which children play the role of a "predator" in a computer game, to test hypotheses about mimicry [2]. This experiment was embedded in a class activity about the principles of evolution, which stimulated fascinating debate amongst pupils. We plan to create a modified version of the above computer game for use during school sessions, and will also publicise the game more widely in order to engage and educate the general public in the topic of evolution.

1. Devonshire, I.M., et al. (2014). PLoS ONE, 9: e103640.
2. Morris, R. & Reader, T. (in prep) [Available online at http://ecology.nottingham.ac.uk/NERC]

Publications

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Taylor C (2022) Body size in Batesian mimicry in Evolutionary Ecology

 
Description In nature, there are some animals that look like other, more dangerous animals to protect themselves from being eaten by predators. This is called mimicry. However, not all mimics are equally good at looking like their models. Scientists have been puzzled about why some mimics don't look very much like the animals they're trying to imitate. They've had a hard time figuring this out because it's tricky to study animals that don't exist anymore.

To tackle this problem, we came up with a new way to study how well different mimics fool predators. We made detailed, lifelike models of insects using 3D printing technology. As well as real species, we were able to extrapolate to create models which looked more or less like dangerous animals than existing mimics.

We tested how our 3D models fooled real predators, like birds. We discovered that wild birds are very good at noticing small differences in how insects look, meaning that even very good mimics may not be protected from predation. Our laboratory experiments suggested that birds pay more attention to the colours and sizes of mimics, and less attention to patterns and body shapes.

Surprisingly, we found that mimics don't get extra protection by looking a little like multiple dangerous animals. It seems that predators don't necessarily get confused by these "hybrid" mimics.

When it comes to smaller predators like praying mantises and spiders, we found that they could tell the difference between good mimics and bad ones, but were more likely to be fooled by very accurate mimics. This suggests that the types of predators in an area play a big role in why some mimics aren't very convincing.
Exploitation Route The 3D imaging, morphing and "printing" techniques we have developed provide an exciting model for future studies of evolution, function and ecology of complex traits in organisms. Using our techniques would allow scientists to capture, manipulate and re-create life-like morphologies for a wide range of species, facilitating experiments asking questions about how and why these morphologies have evolved.

Our findings about the evolutionary origins of imperfect mimicry suggest several important lines of enquiry for future research in this field. First, our data suggest that differences among predators in perception and cognitive abilities might be crucial in explaining how accurate mimicry needs to be. However, current knowledge of which species are actually important in generating natural selection on mimicry is very poor. Second, our results show that there are large differences in the importance or salience of different types of cue (e.g. colour, pattern, size, shape) to predators, and further research is required to understand better these differences and their implications for selection on mimicry. Similarly, adapting the framework we have developed to incorporate other potentially mimetic traits, such as behaviour and odour, is necessary to produce a comprehensive understanding of the evolution of mimicry.
Sectors Education

Environment

 
Description 3D images generated by our project have been used to create virtual reality and web-based 3D simulations in which participants encounter insects. These simulations were created as part of a separate BBSRC-funded citizen science project, and have been deployed to the public in two science festivals and one public science installation. The same images are now being used by Computer Scientists to build a holographic display to be deployed at a local nature reserve; this work is due to be funded by an EU grant (pending). The physical 3D models we created for experiments funded by this grant have been used to create an installation for presentation to school children and the general public at the Theatre Royal and Concert Hall in Nottingham. The aim of this installation was to stimulate non-scientists to think about the evolution of the diversity of life and the nature of biodiversity.
First Year Of Impact 2020
Sector Digital/Communication/Information Technologies (including Software),Education,Culture, Heritage, Museums and Collections
Impact Types Cultural

Societal

 
Description BBC 'Wild Isles' Performance - Call to animate foyer spaces at the Theatre Royal Concert Hall before/after concert
Amount £779 (GBP)
Organisation University of Nottingham 
Sector Academic/University
Country United Kingdom
Start 02/2024 
End 03/2024
 
Description Swat or Not? Identifying Insects in Virtual Reality
Amount £19,937 (GBP)
Funding ID BB/T019085/1 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 02/2020 
End 06/2020
 
Description Nottingham Festival of Science and Creativity 2020 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact We provided members of the public visiting the festival with access to an immersvie, interactive Virtual Reality (VR) simulation. Participants wore a VR headset, played a game, and discussed the scientific significance with project members and student volunteer helpers. We provided a leaflet to all participants with more information about the project and the underlying science.
Year(s) Of Engagement Activity 2020
URL https://nottsfosac.co.uk/
 
Description Nottingham Festival of Science and Creativity 2021 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact We hosted an interactive 3D simulation on a website which was promoted as an activity forming part of the Nottingham Festival of Science and Creativity, which was hosted online in 2021 (rather than in person) because of the pandemic. We had good levels of engagement from members of the public, but it is not easy to assess any impact, because the last-minute nature of the arrangements meant that we did not have time to gain ethical clearance to ask users for feedback.
Year(s) Of Engagement Activity 2021
URL https://swatornot.co.uk/
 
Description Sustainability showcase installation 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact We created an installation piece about the evolution of mimicry, using 3D printed models, and presented this to a group of ~50 school children and several hundred members of the public at the Theatre Royal and Concert Hall in Nottingham. The installation was part of a showcase of research related to sustainability which was presented alongside a BBC orchestra performance (Wild Isles in Concert) of music from David Attenborough TV series.
Year(s) Of Engagement Activity 2024
URL https://trch.co.uk/whats-on/bbcco-wild-isles/
 
Description University of the third age lecture 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact I was invited to give a lecture and lead a discussion about this grant and associated research to an audience of interested retired members of the public.
Year(s) Of Engagement Activity 2023
 
Description Virtual Reality installation 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Over the course of three months, we demonstrated our Virtual Reality simulation to the general public at the Green Light in the City pop-up installation in Nottingham city centre. The intention was to provide an entertaining and thought-provoking addition to the installation, which aims to get helpful information and share ideas about the city's green future. The demonstration was a success, provoking lots of interest from the public in our research, and has helped us to formulate plans for future engagement activities.
Year(s) Of Engagement Activity 2021,2022
URL https://greenlightnottingham.co.uk/