̽��ֱ�� of Cambridge - pattern

Motion dazzle: spotting the patterns that help animals outsmart predators on the run

Anonymous — Wed, 09 Sep 2015 10:34:48 +0000

Many animals use the colours and patterns on their bodies to help them blend into the background and avoid the attention of predators. But this strategy, crypsis, is far from perfect. As soon as the animal moves, the camouflage is broken, and it is much easier for a predator to see and catch it. So how do animals protect themselves when they’re on the move?

Researchers are exploring whether high-contrast patterns during motion, such as stripes and zigzags, may be distorting the predator’s perception of where the animal is going. But, as little is known about such “motion dazzle”, we have built an online game to help shed light on it.

Lessons from war

̽��ֱ��idea is that it may be more effective for animals to focus on preventing capture, rather then preventing detection or recognition, is actually more than 100 years old. It was naturalist Abbott Thayer who suggested that high-contrast patterns may distort the perceived speed or direction of a moving object, making it harder to track and capture.

Such motion dazzle patterns were actually used in World War I and II, where some ships were painted with black and white geometric patterns in an attempt to reduce the number of successful torpedo attacks from submarines. However, due to many other factors affecting wartime naval losses, it is unclear whether motion dazzle patterns actually had the desired effect.

HMS Argus displaying a coat of dazzle camouflage in 1918. wikimedia

What about the natural world? Zebras have bold stripes, and scientists have debated the function of their patterns since Darwin’s time. A recent modelling study suggested that when zebras move, their stripes create contradictory signals about their direction of movement that is likely to confuse predators. There are potentially two visual illusions responsible for this, which could form the basis of motion dazzle effects: the wagon wheel effect and the barber pole illusion.

̽��ֱ��wagon wheel effect is named after Western movies, where the wheels on wagons often appear to be moving backwards. This is because the visual system takes “snapshots” over time and links them to create a continuous scene, in the same manner as recording film. If a wheel spoke moves forward rapidly between sampling events, it will appear to have moved backwards as it will be misidentified as the following spoke.

Wagon Wheel effect explained.

̽��ֱ��barber pole illusion (also known as the aperture effect) occurs because the moving stripes provide ambiguous information about the true direction of movement. These illusory effects produced by stripes could therefore lead to difficulties in judging the speed and movement of a moving target. However, the zebra study was entirely theoretical and didn’t test whether striped patterns actually affected the judgements of real observers.

Dazzle Bug

Surprisingly, the first experimental tests of the effectiveness of motion dazzle patterns weren’t carried out until recently. Some studies have shown that strikingly patterned targets can be more difficult to catch than targets with other patterns in studies using humans as “predators” playing touch screen computer games. However, other studies have found no clear advantage for motion dazzle patterns So although patterns can affect our perception of movement, it’s still not clear which are most effective at doing so.

Can you see the spider? Crypsis can be pretty effective - as long as you don’t move. J Kelley, Author provided

We are addressing the question of which patterns are best for avoiding predators during movement using Dazzle Bug – an online game that asks players to imagine themselves as a predator, trying to catch a moving bug as fast as possible. Each bug has a different body pattern as well as a random pattern of movement. Bugs with easy to catch patterns will disappear, whereas those that are particularly tricky to catch will survive ––just like in nature. Over time, the patterns on the bugs' body will evolve so that they become harder to catch with each successive generation.

This citizen science project will allow us to see what patterns are most effective at evading capture. We can then use these results to look at what visual effects these patterns have, and to see whether these patterns match up with those found on real animals in the wild.

Our findings will offer insight into the role of stripes, which are common in many species. While these patterns may have evolved to confuse the visual perception of a predator, they may also be a result of other selection pressures, such as attracting a mate or regulating body temperature. If striped patterns survive and evolve in the game, this would provide strong evidence that these patterns do act to confuse human predators, perhaps by producing the illusions described above. As motion perception seems to be highly conserved across a wide range of populations, these illusions may occur for many other predators too.

If we find that patterns other than stripes – such as speckles, splotches or zigzags – are most effective in preventing capture, this then leads to new and interesting questions about how these patterns may act to confuse or mislead. Whatever the outcome, Dazzle Bug will provide insight into how bodily patterns may have evolved to help animals to survive life on the go.

Laura Kelley, Research Fellow, ̽��ֱ�� of Cambridge

This article was originally published on ̽��ֱ��Conversation. Read the original article.

̽��ֱ��opinions expressed in this article are those of the individual author(s) and do not represent the views of the ̽��ֱ�� of Cambridge.

A new online game is helping researchers explore whether high-contrast patterns during motion, such as stripes and zigzags, help to protect animals from predators.

Dazzle Bug asks players to imagine themselves as a predator, trying to catch a moving bug as fast as possible

Laura Kelley

Eric Dietrich/wikimedia

Zebras on the run can razzle-dazzle their enemies

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Birds evolve ‘signature’ patterns to distinguish cuckoo eggs from their own

fpjl2 — Wed, 18 Jun 2014 09:36:32 +0000

For some birds, recognising their own eggs can be a matter of life or death.

In a new study, scientists have shown that many birds affected by the parasitic Common Cuckoo - which lays its lethal offspring in other birds’ nests - have evolved distinctive patterns on their eggs in order to distinguish them from those laid by a cuckoo cheat.

̽��ֱ��study reveals that these signature patterns provide a powerful defense against cuckoo trickery, helping host birds to reject cuckoo eggs before they hatch and destroy the host’s own brood.

To determine how a bird brain might perceive and recognize complex pattern information, Dr Mary Caswell Stoddard at Harvard ̽��ֱ�� and Professor Rebecca Kilner and Dr Christopher Town at the ̽��ֱ�� of Cambridge developed a new computer vision tool, NATUREPATTERNMATCH. ̽��ֱ��tool extracts and compares recognizable features in visual scenes, recreating processes known to be important for recognition tasks in vertebrates.

“We harnessed the same computer technology used for diverse pattern recognition tasks, like face recognition and image stitching, to determine what visual features on a bird’s eggs might be easily recognised,” explained Stoddard.

Using the tool, the researchers studied the pigmentation patterns on hundreds of eggs laid by eight different bird species (hosts) targeted by the Common Cuckoo.

They discovered that some hosts, like the Brambling, have evolved highly recognisable egg patterns characterised by distinctive blotches and markings. By contrast, other hosts have failed to evolve recognisable egg patterns, instead laying eggs with few identifiable markings. Those hosts with the best egg pattern signatures, the researchers found, are those that have been subjected to the most intense cuckoo mimicry.

̽��ֱ��Common Cuckoo and its hosts are locked in different stages of a co-evolutionary arms race. If a particular host species – over evolutionary time – develops the ability to reject foreign cuckoo eggs, the cuckoo improves its ability to lay eggs that closely match the colour and patterning of those laid by its host.

“ ̽��ֱ��ability of Common Cuckoos to mimic the appearance of many of their hosts’ eggs has been known for centuries. ̽��ֱ��astonishing finding here is that hosts can fight back against cuckoo mimicry by evolving highly recognisable patterns on their own eggs, just like a bank might insert watermarks on its currency to deter counterfeiters,” said Stoddard.

“ ̽��ֱ��surprising discovery of this study is that hosts achieve egg recognition in different ways” said Kilner, from Cambridge’s Department of Zoology.

Some host species have evolved egg patterns that are highly repeatable within a single clutch, while other species have evolved eggs with patterns that differ dramatically from female to female in a population. Still other host species produce egg patterns with high visual complexity. Each strategy is effective, increasing the likelihood that a given host will identify and reject a foreign egg. “Some species use two of these strategies, but none uses all three,” continued Kilner. “A signature like this would be too complex to be easily recognised”.

̽��ֱ��patterns on bird eggs are just one type of visual signature. Identity signatures are common in the animal world, but how they are encoded and recognised is poorly understood. In the future, computational tools like NATUREPATTERNMATCH - which account for important aspects of visual and cognitive processing - will be crucial for understanding the evolution of visual signals in diverse biological populations.

̽��ֱ��findings of this study are reported in the journal Nature Communications.

Inset image: Reed Warbler caring for Cuckoo chick. Credit: David Kjaer

Using new ‘pattern recognition algorithm,’ latest research highlights how birds are ‘fighting back’ against the parasitic Common Cuckoo in what scientists describe as an evolutionary ‘arms race’. They found that birds with the most sophisticated and distinctive egg patterning are those most intensely targeted by the cuckoo’s egg mimicry.

̽��ֱ��surprising discovery of this study is that hosts achieve egg recognition in different ways

Rebecca Kilner

Mary Caswell Stoddard/Natural History Museum

NATUREPATTERNMATCH extracts visual features, here represented by magenta vectors (left). Three eggs each (represented in different rows) laid by three different Great Reed Warblers are shown here (right).

̽��ֱ��text in this work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page. For image rights, please see the credits associated with each individual image.

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Plants and patterning: how shapes are made

amb206 — Mon, 11 Mar 2013 08:00:00 +0000

Plants come in a fabulous array of shapes and sizes – from the tiny moss to the huge oak, from the tree-like structure to the delicate beauty of orchids. All these living things start with a single cell. How does this variety happen and what can we learn from it?

̽��ֱ��tiny molecular mechanisms that determine the forms of plants lie in the cell wall, the strong fibrous material that surrounds each cell. ̽��ֱ��cell wall and its shape give the plant its shape, allowing it to grow upwards, outwards and downwards in certain ways so that the resulting plant has the characteristic shape we associate with it, whether a twining vine or a giant Redwood.

In a talk this Wednesday (13 March) evening, taking place as part of Cambridge Science Festival, molecular biologist Dr Siobhan Braybrook will explore how plants grow shapes by following an intricate process of patterning – as cells multiply and build the structures that make up their component parts. In particular, she will look at the mathematics, physics, and chemistry that underlie this patterning, including the development of Fibonacci patterns in plants.

̽��ֱ��lecture – titled ‘Biological design: the history and future of plant architecture’ - will give an overview of the fundamental processes of plant growth – and explore what we know, how we make use of this knowledge in agriculture, and what remains to be discovered.

Dr Braybrook will then go on to discuss how mankind has domesticated crops – such as maize – to produce higher yields. Research can contribute to this process by providing a better understanding of plant shape and form as a basis for future crop breeding.

Finally, she will look at the exciting possibilities that exist in developing new technologies – and smart materials in particular – that mimic the structures and mechanisms in plants. “ ̽��ֱ��ways in which plants grow and make use of the environment around them with a minimal output of energy represent huge potential for exploring new technologies,” she said.

“For example, we can look at how fig bark self-heals using latex, how wax coating on leaves protects them from water, how spores walk and jump, and how the hinges of the Venus fly trap are perfectly balanced to snap shut.”

Dr Braybrook leads a research group at Cambridge ̽��ֱ��’s Sainsbury Laboratory, an interdisciplinary research centre dedicated to understanding plant development. Its teams include physicists, computer scientists, geneticists, molecular biologists, mathematicians and biochemists.

“We look at development in plants from a set of unique viewpoints to explore the new frontiers of plant science,” says Dr Braybrook. “My own area of expertise within this broad spectrum is to contribute to understanding the plant as a growing material, and I’m keen to put this across to the public in an accessible and entertaining way, while not forgetting that plants are vital to life.”

‘Biological design: the history and future of plant architecture’ will take place at the Sainsbury Laboratory on Wednesday 13 March, 7.30-8.30pm. ̽��ֱ��free talk is suitable for ages 16 and upwards. Advance booking essential: http://www.cam.ac.uk/sciencefestival/events/

A Cambridge Science Festival lecture on Wednesday (13 March 2013) will look at how plants grow through repeating patterns and discuss what we can learn from them in developing smart materials.

We can look at how fig bark self-heals using latex, how wax coating on leaves protects them from water, how spores walk and jump.

Dr Siobhan Braybrook

Siobhan Braybrook

Scanning electron micrograph image of sunflower head developing.

This work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page.

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