̽��ֱ�� of Cambridge - butterfly

Spanish butterflies better at regulating their body temperature than their British cousins

sc604 — Tue, 09 Jan 2024 04:32:22 +0000

Butterfly populations in northern Spain are better than their UK counterparts at regulating their body temperature, but rising global temperatures may put Spanish butterflies at greater risk of extinction.

AI used to test evolution’s oldest mathematical model

sc604 — Wed, 14 Aug 2019 18:00:00 +0000

̽��ֱ��researchers, from the ̽��ֱ�� of Cambridge, the ̽��ֱ�� of Essex, the Tokyo Institute of Technology and the Natural History Museum London used their machine learning algorithm to test whether butterfly species can co-evolve similar wing patterns for mutual benefit. This phenomenon, known as Müllerian mimicry, is considered evolutionary biology’s oldest mathematical model and was put forward less than two decades after Darwin’s theory of evolution by natural selection.

̽��ֱ��algorithm was trained to quantify variation between different subspecies of Heliconius butterflies, from subtle differences in the size, shape, number, position and colour of wing pattern features, to broad differences in major pattern groups.

This is the first fully automated, objective method to successfully measure overall visual similarity, which by extension can be used to test how species use wing pattern evolution as a means of protection. ̽��ֱ��results are reported in the journal Science Advances.

̽��ֱ��researchers found that different butterfly species act both as model and as mimic, ‘borrowing’ features from each other and even generating new patterns.

“We can now apply AI in new fields to make discoveries which simply weren’t possible before,” said lead author Dr Jennifer Hoyal Cuthill from Cambridge’s Department of Earth Sciences. “We wanted to test Müller’s theory in the real world: did these species converge on each other’s wing patterns and if so how much? We haven’t been able to test mimicry across this evolutionary system before because of the difficulty in quantifying how similar two butterflies are.”

Müllerian mimicry theory is named after German naturalist Fritz Müller, who first proposed the concept in 1878, less than two decades after Charles Darwin published On the Origin of Species in 1859. Müller’s theory proposed that species mimic each other for mutual benefit. This is also an important case study for the phenomenon of evolutionary convergence, in which the same features evolve again and again in different species.

For example, Müller’s theory predicts that two equally bad-tasting or toxic butterfly populations in the same location will come to resemble each other because both will benefit by ‘sharing’ the loss of some individuals to predators learning how bad they taste. This provides protection through cooperation and mutualism. It contrasts with Batesian mimicry, which proposes that harmless species mimic harmful ones to protect themselves.

Heliconius butterflies are well-known mimics, and are considered a classic example of Müllerian mimicry. They are widespread across tropical and sub-tropical areas in the Americas. There are more than 30 different recognisable pattern types within the two species that the study focused on, and each pattern type contains a pair of mimic subspecies.

However, since previous studies of wing patterns had to be done manually, it hadn’t been possible to do large-scale or in-depth analysis of how these butterflies are mimicking each other.

“Machine learning is allowing us to enter a new phenomic age, in which we are able to analyse biological phenotypes - what species actually look like - at a scale comparable to genomic data,” said Hoyal Cuthill, who also holds positions at the Tokyo Institute of Technology and ̽��ֱ�� of Essex.

̽��ֱ��researchers used more than 2,400 photographs of Heliconius butterflies from the collections of the Natural History Museum, representing 38 subspecies, to train their algorithm, called ‘ButterflyNet’.

ButterflyNet was trained to classify the photographs, first by subspecies, and then to quantify similarity between the various wing patterns and colours. It plotted the different images in a multidimensional space, with more similar butterflies closer together and less similar butterflies further apart.

“We found that these butterfly species borrow from each other, which validates Müller’s hypothesis of mutual co-evolution,” said Hoyal Cuthill. “In fact, the convergence is so strong that mimics from different species are more similar than members of the same species.”

̽��ֱ��researchers also found that Müllerian mimicry can generate entirely new patterns by combining features from different lineages.

“Intuitively, you would expect that there would be fewer wing patterns where species are mimicking each other, but we see exactly the opposite, which has been an evolutionary mystery,” said Hoyal Cuthill. “Our analysis has shown that mutual co-evolution can actually increase the diversity of patterns that we see, explaining how evolutionary convergence can create new pattern feature combinations and add to biological diversity.

“By harnessing AI, we discovered a new mechanism by which mimicry can produce evolutionary novelty. Counterintuitively, mimicry itself can generate new patterns through the exchange of features between species which mimic each other. Thanks to AI, we are now able to quantify the remarkable diversity of life to make new scientific discoveries like this: it might open up whole new avenues of research in the natural world.”

Reference:
Jennifer F. Hoyal Cuthill et al. ‘Deep learning on butterfly phenotypes tests evolution’s oldest mathematical model.’ Science Advances (2019). DOI: 10.1126/sciadv.aaw4967

Researchers have used artificial intelligence to make new discoveries, and confirm old ones, about one of nature’s best-known mimics, opening up whole new directions of research in evolutionary biology.

We can now apply AI in new fields to make discoveries which simply weren’t possible before

Jennifer Hoyal Cuthill

J Hoyal Cuthill, photo credits S Ledger and R Crowther

Butterfly co-mimic pairs from the species Heliconius erato (odd columns) and Heliconius melpomene (even columns). Illustrated butterflies are sorted by greatest similarity (along rows, top left to bottom right)

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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̽��ֱ��butterflies are coming

ta385 — Thu, 25 Jul 2019 05:00:00 +0000

Climate change poses a major threat to butterflies but a new generation of Cambridge scientists is working to unlock their secrets and help them thrive.

Butterflies are genetically wired to choose a mate that looks just like them

ta385 — Fri, 08 Feb 2019 10:35:48 +0000

A team of academics from the ̽��ֱ�� of Cambridge, in collaboration with the Smithsonian Tropical Research Institute in Panama, observed the courtship rituals and sequenced the DNA from nearly 300 butterflies to find out how much of the genome was responsible for their mating behaviour.

̽��ֱ��research, published in PLOS Biology, is one of the first ever genome studies to look at butterfly behaviour and it unlocks the secrets of evolution to help explain how new species are formed. Scientists sequenced the DNA from two different species of Heliconius butterflies which live either side of the Andes mountains in Colombia. Heliconians have evolved to produce their own cyanide which makes them highly poisonous and they have distinct and brightly coloured wings which act as a warning to would-be predators.

Professor Chris Jiggins, one of the lead authors on the paper and a Fellow of St John’s College, said: “There has previously been lots of research done on finding genes for things like colour patterns on the butterfly wing, but it’s been more difficult to locate the genes that underlie changes in behaviour. What we found was surprisingly simple – three regions of the genome explain a lot of their behaviours. There’s a small region of the genome that has some very big effects.”

̽��ֱ��male butterflies were introduced to female butterflies of two species and were scored for their levels of sexual interest directed towards each. ̽��ֱ��scientists rated each session based on the number of minutes of courtship by the male – shown by sustained hovering near or actively chasing the females.

Unlike many butterflies which use scented chemical signals to identify a mate, Heliconians use their long-range vision to locate the females, which is why it’s important each species has distinct wing markings. When a hybrid between the two species was introduced, the male would most commonly show a preference for a mate with similar markings to itself. ̽��ֱ��research showed the same area of the genome that controlled the coloration of the wings was responsible for defining a sexual preference for those same wing patterns.

Dr Richard Merrill, one of the authors of the paper, based at Ludwig-Maximilians-Universität, Munich, said: “It explains why hybrid butterflies are so rare – there is a strong genetic preference for similar partners which mostly stops inter-species breeding. This genetic structure promotes long-term evolution of new species by reducing intermixing with others.”

̽��ֱ��paper is one of two published in PLOS Biology and funded by the European Research Council which brought together ten years of research by Professor Jiggins and his team. ̽��ֱ��second study investigated how factors including mate preference act to prevent genetic mixing between the same two species of butterfly. They discovered that despite the rarity of hybrid butterflies – as a result of their reluctance to mate with one another – a surprisingly large amount of DNA has been shared between the species through hybridisation. There has been ten times more sharing between these butterfly species than occurred between Neanderthals and humans.

Dr Simon Martin, one of the authors of the second paper, from the ̽��ֱ�� of Edinburgh, explained: “Over a million years a very small number of hybrids in a generation is enough to significantly reshape the genomes of the these butterflies.”

Despite this genetic mixing, the distinct appearance and behaviours of the two species remain intact, and have not become blended. ̽��ֱ��researchers found that there are many areas of the genome that define each species, and these are maintained by natural selection, which weeds out the foreign genes. In particular, the part of the genome that defines the sex of the butterflies is protected from the effects of inter-species mating. As with the genetics that control mating behaviour, these genes enable each butterfly type to maintain its distinctiveness and help ensure long-term survival of the species. But can the findings translate into other species including humans?

Professor Jiggins said: “In terms of behaviour, humans are unique in their capacity for learning and cultural changes but our behaviour is also influenced by our genes. Studies of simpler organisms such as butterflies can shed light on how our own behaviour has evolved. Some of the patterns of gene sharing we see between the butterflies have also been documented in comparisons of the human and Neanderthal genomes, so there is another link to our own evolution.”

“Next we would like to know how novel behaviour can arise and what kind of genetic changes you need to alter behaviour. We already know that you can make different wing patterns by editing the genes. These studies suggest that potentially new behaviours could come about by putting different genes together in new combinations.”

References

Martin, S et al. Recombination rate variation shapes barriers to introgression across butterfly genomes. PLOS Biology; 7 Feb 2019; DOI: 10.1371/journal.pbio.2006288

Merrill, R et al. Genetic dissection of assortative mating behavior. PLOS Biology; 7 Feb 2019; DOI: 10.1371/journal.pbio.2005902

Male butterflies have genes which give them a sexual preference for a partner with a similar appearance to themselves, according to new research.

There’s a small region of the genome that has some very big effects

Chris Jiggins

Heliconius melpomene amaryllis

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Attribution

Genetic switch that turned moths black also colours butterflies

tdk25 — Thu, 02 Jun 2016 04:00:22 +0000

̽��ֱ��same gene that enables tropical butterflies to mimic each other’s bright and colourful patterning also caused British moths to turn black amid the grime of the industrial revolution, researchers have found.

Writing in the journal Nature, a team of researchers led by academics at the Universities of Cambridge and Sheffield, report that a fast-evolving gene known as “cortex” appears to play a critical role in dictating the colours and patterns on butterfly wings.

A parallel paper in the same journal by researchers from the ̽��ֱ�� of Liverpool shows that this same gene also caused the peppered moth to turn black during the mid-19th century, when it evolved to find new ways to camouflage itself; a side-effect of industrial pollution at the time.

̽��ֱ��finding offers clues about how genetics plays a role in making evolution a predictable process. For reasons the researchers have yet to understand in full, the cortex gene, which helps to regulate cell division in butterflies and moths, has become a major target for natural selection acting on colour and pattern on the wings.

Chris Jiggins, Professor of Evolutionary Biology and a Fellow of St John’s College, ̽��ֱ�� of Cambridge, said: “What’s exciting is that it turns out to be the same gene in both cases. For the moths, the dark colouration developed because they were trying to hide, but the butterflies use bright colours to advertise their toxicity to predators. It raises the question that given the diversity in butterflies and moths, and the hundreds of genes involved in making a wing, why is it this one every time?”

Dr Nicola Nadeau, a NERC Research Fellow from the ̽��ֱ�� of Sheffield added: “It’s amazing that the same gene controls such a diversity of different colours and patterns in butterflies and a moth. Our study, together with the findings from the ̽��ֱ�� of Liverpool, shows that the cortex gene is important for colour and pattern evolution in this whole group of insects.”

Butterflies and moths comprise the order of insects known as Lepidoptera. Nearly all of the 160,000 types of moth and 17,000 types of butterfly have different wing patterns, which are adapted for purposes like attracting mates, giving off warnings, camouflage (also known as “crypsis”), and thermal regulation.

These wing patterns are actually made up of tiny coloured scales arranged like tiles on a roof. Although they have been studied by biologists for over a century, the molecular mechanisms which control their development are only now starting to be uncovered.

̽��ֱ��peppered moth is one of the most famous examples of evolution by natural selection. Until the 19th Century, peppered moths were predominantly pale-coloured, and used this to camouflage themselves against lichen-covered tree trunks, which made them almost invisible to predators.

During the industrial revolution, however, the lichen on trees in some parts of the country was killed by pollution, and soot turned the trunks black. A corresponding change was seen in the in peppered moths which turned black as well, helping them to remain camouflaged from birds. ̽��ֱ��process is known as industrial melanism – melanism meaning the development of dark coloured pigmentation.

̽��ֱ��Liverpool-led team found that this colour change was produced by a mutation in the cortex gene, which occurred during the mid 1800s, just before the first reported sighting of black peppered moths. Fascinatingly, however, the Cambridge-Sheffield study has now shown that exactly the same gene also influences the extremely bright and colourful patterns of Heliconius – the name given to about 40 different closely-related species of beautiful, tropical butterflies found in South America.

Heliconius colour patterns are used to send a signal to potential predators that the butterflies are toxic if eaten, and different types of Heliconius butterfly mimic one another by using their bright colours as warning signals. Unlike the dark colouring of the peppered moth, it is therefore an evolutionary development that is meant to be seen.

̽��ֱ��researchers carried out fine-scale mapping, looking for parts of the DNA sequence that were specifically different in butterflies with different patterns, in three different Heliconius species, and in each case the cortex gene was found to be responsible for this adaptation in their patterning.

Because Heliconius species are extremely diverse, the study of what causes variations in their patterning can provide more general clues about the genetic switches that control diversification in species.

In most cases, the genes responsible for these processes are known as “transcription factors” – meaning that they are responsible for turning other genes on and off. Intriguingly, what made cortex such an elusive switch to spot was the fact that it does not do this. Instead, it is a cell cycle regulator, which means that it controls when cells divide and thus when different coloured scales develop within a butterfly wing.

“It’s a different gene to the one we might have expected and we still need to do more to understand exactly what it’s doing, and how it’s doing it,” Jiggins said. Dr Nadeau added “Our results are even more surprising because the cortex gene was previously thought to only be involved in producing egg cells in female insects, and is very similar to a gene that controls cell division in everything from yeast to humans.”

Reference

Nadeau N. et al. ̽��ֱ��gene cortex controls mimicry and crypsis in butterflies and moths. Nature, 2 June 2016; DOI: 10.1038/nature17961

Additional image: ̽��ֱ��study reveals that the black colour of the moth (above) and the yellow patches on the butterfly (below) were caused by the same gene, known as “cortex”. Credits: Yikrazuul and Loz, both via Wikimedia Commons.

Heliconius butterflies have evolved bright yellow colours to deter predators, while peppered moths famously turned black to hide from birds. A new study reveals that the same gene causes both, raising fascinating questions about how evolution by natural selection occurs in these species.

It raises the question that given the diversity in butterflies and moths, and the hundreds of genes involved in making a wing, why is it this one every time?

Chris Jiggins

Chris Jiggins, ̽��ֱ�� of Cambridge

Heliconius Melpomene.

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

Yes

Natural selection sculpts genetic information to limit diversity

tdk25 — Fri, 13 May 2016 13:30:35 +0000

A study of tropical butterflies has added to growing evidence that natural selection reduces species’ diversity by moulding parts of their genetic structure, including elements that have no immediate impact on their survival.

̽��ֱ��research, by a ̽��ֱ�� of Cambridge-led team of academics, focused on genetic data from South American Heliconius butterflies. It showed that when these butterflies develop a beneficial adaptation through a mutation in their DNA, other parts of the same chromosome – the long strings of DNA that make up the butterfly’s genome – may end up being defined by the fact that they are “linked” to the point where the mutation took place. Natural selection ends up influencing the fate of these linked sites, even though they have no impact on the species’ fitness and long-term survival prospects.

As the adaptation is passed down through the generations as a result of natural selection, this collection of linked genetic sites can be passed on intact, removing genetic variation that previously existed in the population at these sites. This effectively limits the overall amount of variation in the butterfly population.

̽��ֱ��study complements similar findings in other species, including humans and fruit flies, which together offer one possible solution to a long-standing paradox in population genetics. This is the fact that while species with bigger populations should be more genetically diverse – because there is more potential for new mutations to occur – in practice they often only exhibit as much diversity as smaller populations.

For example, in the Cambridge-led study, the researchers found that the genetic diversity of Heliconius butterflies is very similar to that of fruit flies, even though fruit flies are far more numerous. They also estimated that the amount of adaptation within Heliconius butterflies caused by natural selection is probably about half that of fruit flies. In other words, because natural selection affects the fruit flies more, reducing variation, they end up exhibiting roughly the same amount of genetic diversity, even though there are more of them.

̽��ֱ��researchers stress that this explanation for variable levels of genetic diversity between different species is still, at the moment, a theory. Not all scientists are convinced that natural selection has this effect and argue that the variable diversity of species relative to population size may well have other causes.

Understanding more about what these causes are will, however, help to answer even more fundamental scientific questions – such as how and why species vary in the first place, and when they can really be said to have become distinct enough from their ancestors to represent a species in their own right.

Dr Simon Martin, a Research Fellow at St John’s College, Cambridge, who led the study, said: “We will only be able to understand this fully if we can compare results from across different species. Extending our knowledge to butterflies is a step towards explaining these much broader patterns in nature; it’s only by doing this kind of research that we will know whether these ideas are right or not.”

Martin and his colleagues examined a very large data set of 79 whole genome sequences representing 12 related species of Heliconius butterfly. This large-scale data has only become available in recent years, as a result of advances in genome sequencing which have made the process both easier and more affordable.

̽��ֱ��study involved scouring the sequences for an apparent pattern of association between particular sites within the genome and low variation. “That acts as a kind of signature,” Martin said. “If you can see that in a genome, then as far as we can tell it is an indication of selection.”

In addition, the researchers compared the number of variations in the parts of the genome where proteins are coded – and therefore may be responsible for adaptations – with the number of variations in other parts of the genome. It is possible to predict what this ratio would be if variations only occurred by chance. ̽��ֱ��difference between that prediction, and the actual statistics, suggests the extent to which natural selection has shaped species differences.

̽��ֱ��study estimated that around 30% of the protein differences between species of Heliconius are adaptations caused by natural selection. In keeping with theories about diversity in the population of other species, this turned out to be about half the number of protein variations in fruit flies – a larger population with less genetic diversity overall.

Intriguingly, the study effectively suggests that natural selection could limit a species' ability to adapt to future environmental change by removing linked variations that, despite having no immediate beneficial impact on the species, could become relevant to its survival and capacity to cope with its environment in the future.

“Variation is a kind of raw material and you don’t necessarily use it all at any one time,” Martin explained. “It’s something that could be used to adapt and change in the future.”

“Something that has turned up during the last few years in research of this kind is a phenomenon where we see that a species has adapted, and we discover, when we look for the origin of that adaptation, that the mutation was not actually new. Instead, it was a variation that previously existed in the population. So while we cannot forecast the future, an emerging idea is that mutations that have no effect on survival today may be a source of beneficial variation in the future.”

̽��ֱ��study appears in the May 2016 issue of Genetics.

A study of butterflies suggests that when a species adapts, other parts of its genetic make-up can be linked to that adaptation, limiting diversity in the population.

While we cannot forecast the future, an emerging idea is that mutations that have no effect on survival today may be a source of beneficial variation in the future

Simon Martin

Chris Jiggins, ̽��ֱ�� of Cambridge.

Heliconius Melpomene, a tropical butterfly found in South America. ̽��ֱ��study shows how its genetic structure has been defined by natural selection, even in areas that have no bearing on its survival prospects.

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

Yes

Genetic ‘paint box’ shuffled between butterfly species to create new wing patterns

fpjl2 — Fri, 15 Jan 2016 19:01:08 +0000

New research on butterfly genomes has revealed that the genetic components that produce different splotches of colour on wings can be mixed up between species by interbreeding to create new patterns, like a "genetic paint box".

Research on Amazonian Heliconius butterflies has shown that two of the most common colour patterns, found in combination on the wings of many Heliconius species – the dennis red patch on the base of the forewing, and the ray red streaks that fan out across the hindwing – are controlled by separate genetic switches that arose in completely different species.

A team of researchers has traced the merging of these two wing pattern elements to interbreeding between butterfly species that occurred almost two million years ago.

It has been known for some time that exchange of genes between species can be important for evolution: humans have exchanged genes with our now extinct relatives which may help survival at high altitudes, and Darwin's Finches have exchanged a gene that influences beak shape. In butterflies, the swapping of wing pattern elements allows different species to share common warning signs that ward off predators – a phenomenon known as mimicry.

However, the new study, published today in the journal PLOS Biology, is the first to show such mixing of genetic material can produce entirely new wing patterns, by generating new combinations of genes.

"We found that different colour patches on the wings are controlled by different genetic switches that can be turned on and off independently. As these switches were shared between species they got jumbled up into different combinations, making new wing patterns," said senior author Professor Chris Jiggins, from Cambridge ̽��ֱ��'s Department of Zoology.

̽��ֱ��researchers sequenced the genomes from 142 individual butterflies across 17 Heliconius species and compared the DNA data, focusing on the regions associated with the two red colour patterns of dennis and ray on the forewing and hindwing. "In each butterfly genome, we narrowed down around 300 million base pairs of DNA to just a few thousand," said Jiggins.

They found that the genetic switches for these distinct wing splotches operated independently, despite being located next to each other in the genome. ̽��ֱ��sequencing revealed that the switch for each colour splotch had evolved just once, and in separate species, but had been repeatedly shared across all the Heliconius species at occasional points of interbreeding dating back almost two million years.

"By identifying the genetic switches associated with bits of wing pattern, when they evolved and how they diverged, we can actually map onto the species tree how these little regions of colour have jumped between species - and we can see they are jumping about all over the place," said Jiggins.

̽��ֱ��key to this evolutionary butterfly painting is the independence of each genetic switch. " ̽��ֱ��gene that these switches are controlling is identical in all these butterflies, it is coding for the same protein each time. That can't change as the gene is doing other important things," said lead author Dr Richard Wallbank, also from Cambridge's Department of Zoology.

"It is the switches that are independent, which is much more subtle and powerful, allowing evolutionary tinkering with the wing pattern without affecting parts of the genetic software that control the brain or eyes.

"This modularity means switching on a tiny piece of the gene's DNA produces one piece of pattern or another on the wings – like a genetic paint box," Wallbank said.

Reference:
Wallbank RWR, Baxter SW, Pardo-Diaz C, Hanly JJ, Martin SH, Mallet J, et al. (2016) Evolutionary Novelty in a Butterfly Wing Pattern through Enhancer Shuffling. PLoS Biol 14(1): e1002353. doi:10.1371/journal.pbio.1002353

Research finds independent genetic switches control different splotches of colour and pattern on Heliconius butterfly wings, and that these switches have been shared between species over millions of years, becoming “jumbled up” to create new and diverse wing displays.

We can actually map onto the species tree how these little regions of colour have jumped between species

Chris Jiggins

Jiggins group

A range of wing patterns across Heleconius butterfly species.

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

Yes

How the butterflies got their spots

bjb42 — Thu, 04 Feb 2010 00:00:00 +0000

Heliconius, or passion-vine butterflies, live in the Americas - from the southern United States to southern South America. Although they cannot interbreed, H. melpomene and H. erato have evolved to mimic one another perfectly.

These delicate butterflies have splashes of red and yellow on their black wings, signaling to birds that they contain toxins and are extremely unpalatable. They mimic one another's colour and pattern to reinforce these warning signals.

Scientists have studied these butterflies since the 1860s as a classic case of evolution in action, but only now is modern sequencing technology unlocking the underlying genetics.

̽��ֱ��Cambridge-led team of researchers from UK and US universities, which has been breeding the butterflies in Panama for the past decade, has been searching for the genes responsible for the butterflies' wing patterns and the answer to the question of whether the same genes in two different species are responsible for the mimicry.

According to Dr Chris Jiggins of the Department of Zoology at the ̽��ֱ�� of Cambridge, one of the authors of the study: " ̽��ֱ��mimicry is remarkable. ̽��ֱ��two species that we study - erato and melpomene - are quite distantly related, yet you can't tell them apart until you get them in your hand. ̽��ֱ��similarity is incredible - even down to the spots on the body and the minute details of the wing pattern."

That the two species have evolved to look exactly the same is due to predation by birds. " ̽��ֱ��birds will try anything that looks different in the hope that it's good, so they learn that certain wing patterns are unpalatable and avoid them, but anything that deviates slightly from what they've experienced before is more likely to be attacked," he explains.

These butterflies have been studied since Darwin's day because they are such a striking example of adaptation. For years, scientists have pondered whether when different species evolve to look the same, they share a common genetic mechanism.

According to Jiggins: "It's interesting because it tells us how flexible evolution is. If you get the same wing pattern evolving independently in different populations, do you expect the same genes to be involved?"

Because there are thousands of genes in the butterflies' genome, most scientists felt it was unlikely that the same genes should be involved. But the results of this study suggest that this is, in fact, the case.

̽��ֱ��new results - published today in two parallel papers in the journal PLoS Genetics - show that the regions of the genome associated with the wing patterns are very small - akin to genetic "hotspots".

"This tells us something about the limitations on evolution, and how predictable it is. Our results imply that despite the many thousands of genes in the genome there are only one or two that are useful for changing this colour pattern. It seems like evolution might be concentrated in quite small regions of the genome - or hotspots - while the rest of it does not change very much," says Jiggins.

This is not the only unexpected element of the study. ̽��ֱ��team was also surprised that the obvious candidate genes - such as those involved in colour or wing pattern in other species - do not seem to be involved in the passion-vine butterflies' mimicry.

According to Jiggins: "We think it's more likely to be some novel method of cellular signaling, which is quite intriguing and could be important in many other insect species."

̽��ֱ��next stage of the research is to look at other traits, such as behaviour, because the butterflies have preferences for particular colours and use wing patterns to select mates. "It seems the same regions of the genome control this behaviour as well as the wing pattern. We'd like to understand this," he says.

̽��ֱ��results are published in PLoS Genetics on 5 February 2010.

How two butterfly species have evolved exactly the same striking wing colour and pattern has intrigued biologists since Darwin's day. Now, scientists at Cambridge have found "hotspots" in the butterflies' genes that they believe will explain one of the most extraordinary examples of mimicry in the natural world.

It's interesting because it tells us how flexible evolution is.

Dr Chris Jiggins

whologwhy from Flickr

BUTTERFLY

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