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One Species Becomes Two, Inside an Insect

It’s easy to imagine how a physical barrier, like a river or a mountain range, could create new species. If two populations of the same creature get stuck on either side of the divide, they won’t be able to breed. They’ll evolve along their own separate paths, until the differences between them become so big that breeding would be impossible, even if they were to meet. One species becomes two.

There are also many examples where new species arise without any barrier—where one population splits in two even though all of its members share the same space. This is called sympatric speciation (from the Greek for “same fatherland”). It was proposed more than a century ago, and has been controversial for much of that time. But scientists have found more and more examples that support the concept, where new wasps, flies, fish and trees evolve side by side. Just last week, news broke about a deadbeat ant that branched off from its parent species, while living in the same colony.

The latest intriguing example comes from James Van Leuven and John McCutcheon at the University of Montana. It involves a bacterium called Hodgkinia that split into two distinct species, while living in the cells of an insect. There is no barrier. Sardines in a can have nothing on Hodgkinia. These bacteria are crammed into the same tightly packed microscopic structures, but somehow, they’ve managed to become two distinct species.

The two daughter species are like two halves of their ancestor. They’ve each lost genes that the original Hodgkinia had, but they’ve jettisoned different genes. Each compensates for the losses of its sister species. They complement each other perfectly—put them together, and you’d (almost) the complete genome of the ancestor.

Van Leuven and McCutcheon made their discovery by studying cicadas—insects known for their ear-splitting songs. About five years ago, they showed that one species of cicada has two bacteria living inside its cells—Sulcia and Hodgkinia. This is pretty normal. Many insects have helpful internal bacteria or “endosymbionts”. In sap-sucking groups like cicadas, these microbes act like dietary supplements, making nutrients that are missing from their diet.

Things got strange when Van Leuven and McCutcheon analysed DNA from a South American cicada called Tettigades undata. They found many fragments of Hodgkinia DNA but, try as they might, they couldn’t unite those pieces into a single genome. They always assembled into two separate ones. For simplicity, I’m going to call these H1 and H2.

The two genomes belong to different bacteria; they’re never found in the same cell The team confirmed this by using fluorescent molecules designed to label each genome—a yellow one for H1 and a blue one for H2. You can see the results in the image below. Each little dot is a separate bacterium, and each contains either H1 or H2, but never both. (The green dots are Sulcia, and the magenta ones belong to the cicada itself.)

Two Hodgkinia species (blue and yellow) in a cicada. Credit: Van Leuven et al, 2014.
Two Hodgkinia species (blue and yellow) in a cicada. Credit: Van Leuven et al, 2014.

These two bacteria diverged from a common ancestor, which I’ll call H0, around 5 million years ago. The duo got a good idea of what H0 looked like by studying a closely related species of cicada, which only has one Hodgkinia genome with 137 genes. Out of these, 20 are there in H1 but not H2, and 44 are in H2 but not H1. All of them (except one) are found in one or both of the daughter species.

This pattern looks a lot like what happens when a species duplicates its entire genome, as has happened many times in the evolution of flowers, fish, and more. Suddenly, the species carries two copies of each gene. Since it only needs one, the second is free to pick up mutations that disable and destroy it, which is often what happens. The result is a genome with almost the same number of genes, but packed into twice as much material.

That’s exactly what Van Leuven and McCutcheon saw in their cicadas. The original Hodgkinia doubled up into two distinct genomes that add back up to the original. But in cases of whole-genome duplication, the doubled-up DNA is still part of the same genome. Not so here; in this case, H1 and H2 are separate entities. The process that created them is a bit like splitting a coin along its edge, so you get a heads-only coin and a tails-only one. There’s no novelty. H1 and H2 don’t do anything that H0 couldn’t already do.

That’s abundantly clear if you look at their genes. H0 makes nutrients like vitamin B12 and methionine to feed its cicada host. It devotes many genes to the task, one for each step in the chain of chemical reactions that eventually produce the nutrients. Between them, H1 and H2 can do the same, but neither of them has the complete set of genes for any chain. Neither one alone can give its cicada the nutrients it needs. They have to work together, passing chemicals between them like a production line that snakes between two adjacent factories.

How did this complicated set-up evolve? How did H1 and H2 arise from a population of H0 cells that were all living next to one another?

It’s hard to say for sure, but McCutcheon has an idea, illustrated in the diagram below. Each Hodgkinia bacterium contains thousands of copies of its genome (the green circles) in the same cell (the black outlines). At some point, one bacterium gets a mutation in just one of its genomes, which breaks one gene (marked in yellow in B). A second bacterium gets a mutation, again in just one genome, which breaks a different gene (marked in blue).

How one Hodgkinia species became two. Credit: Van Leuven et al, 2014.
How one Hodgkinia species became two. Credit: Van Leuven et al, 2014.

With so many genomes in each cell, these mutations don’t matter. They’re invisible to natural selection, and free to spread. As these bacteria divide, future generations of daughters might have two genomes with the mutation, then four, then eight (C).

Eventually, there’s some kind of bottleneck (D)—some event that produces lineages of cells where every genome has the yellow mutation or the blue one. Neither lineage is any use to the cicada on its own, because neither can make the full suite of nutrients that the insect demands. They have to work together, so they both stick around. They each start losing more and more genes, but always in a complementary way. They become H1 and H2.

It probably helps that cicadas can live for up to 17 years—long for an insect and an eternity for a bacterium. For most of those years, they live underground as immature nymphs that barely grow. In those years, the symbionts aren’t that important. They can change, evolve, and even build up detrimental mutations without affecting their host. The same symbiont shenanigans would be a much bigger problem for a short-lived insect like an aphid, and both the host and its deficient microbes would be quickly weeded out by natural selection. It’s probably no coincidence that, as McCutcheon puts it, “In the longest-lived cicadas, Hodgkinia genomes are off the deep end.”

“We think this is a very clear case of non-adaptive evolution,” he says. Hodgkinia didn’t gain anything from its split into two species, and neither did the cicada. It just happened through random events. It’s a great reminder that evolution isn’t a climb towards superior and more efficient forms. Sometimes, it leads to complexity for the sake of it. “This new symbiosis is not any better off than the simpler version,” says McCutcheon. “It’s just more complicated and it’s stuck.”

Reference: Van Leuven, Meister, Simon & McCutcheon. 2014. Sympatric Speciation in a Bacterial Endosymbiont Results in Two Genomes with the Functionality of One. Cell. http://dx.doi.org/10.1016/j.cell.2014.07.047

For another example of weird insect symbionts: Snug as a Bug in a Bug in a Bug

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Dozens of Insect Species Living Only On Two Types of Flower

Los Amigos Biological Station sits within the Peruvian Amazon—one of the planet’s richest hotspots for life. Countless species fly, scurry, climb and burrow through the surrounding rainforest. To be at the station is to be surrounded by life at its most diverse and wondrous.

But you don’t have to go into the forest to find diversity.

The research station has a kilometre-long airstrip, and its borders are thick with climbing squash vines descending from the trees. A team of scientists led by Marty Condon from Cornell College collected some 3,600 flowers from these vines, all belonging to just two species. They found entire worlds.

The flowers were home to 14 species of fly, which lived nowhere else. “When we go out in the field, we collect every flower, fruit and stem of this group. These particular flies have only come out of these two plants,” says Condon. Most were even restricted to either the male or female flowers of their chosen plant.

There was more. Condon also found 18 species of parasitic wasps, which attack the fly larvae and lay eggs inside their bodies. Two of the wasps were generalists that attacked a wide variety of hosts. But the vast majority were specialists that targeted just one of the 14 available fly species, even though there were several possible targets around.

It’s difficult for us humans to appreciate just how restricted and specialised creatures like this can be. We are a global species. When you can travel to the other side of the planet in less than a day, it’s hard to imagine how dozens of species can exist nowhere else but on a single type of flower.

Most of these species all looked the same. Condon’s team used their DNA to tell them apart. Specifically, they sequenced a gene called COI in all of the flies. Your version of COI is a 98 percent match for a chimp’s, but none of the fly species from the squash flowers shared more than 96 percent of their COI sequences. “A 4 percent different is huge,” says Condon. Once the DNA had split the lookalike flies into different groups, it became easier to find more visible differences between them, from subtle physical traits to distinctive mating rituals. “These flies really are extraordinarily different.”

Of course, with over a million known insect species, and many millions more left to discover, we expect insects to be diverse. Even so, Condon was astonished by what she found. If two flies exploit exactly the same resource, you’d expect the more efficient competitor to eventually oust its rival. In this way, species partition themselves into distinct niches—each one specialised to a certain area, or food source, or time of day. They can co-exist because they each do their own thing.

“That’s the standard scenario: there should be one thing on each kind of resource,” says Condon. “But when we got our samples in, we thought: Whoa, this is not like that at all. We found multiple insects feeding on exactly the same tissues of exactly the same species.” For example, the male flowers of Gurania spinulosa are home to 9 of the flies and 12 of the wasps. “That was totally unexpected,” says Condon. This town ain’t big enough for two, let alone nine or twelve.

Why so much diversity? The team found a big clue when they dissected almost 400 fly pupae. They found that many wasps actually do lay eggs in the larvae of several fly species—it’s just that the wasp larvae can only survive in the right host. If they get implanted into the wrong one, they’re dead. The host kills them, perhaps by mounting some sort of immune defence.

That explains why there are so many wasps on the two flowers: the majority of them are adapted to parasitise a single fly species, and the others are inhospitable.

But why are so many species of flies? Condon’s hunch is that this group of flies is ancient and widespread. They have been feeding on the same sorts of flowers throughout South and Central America for around 6 million years. That period saw the rise of the Andes, and regular waves of drought and rain. These changing conditions would have regularly fragmented the local plant populations, and the flies could have adapted to these isolated pockets. “Then previously isolated plant habitats come back together and bingo, there are multiple fly species on same host plants,” says Condon.

Alternatively, the flies could be diversifying because of the wasps. Each adapts into an “enemy-free space”, becoming impervious to the existing wasps. The wasps counter-adapt, so that both parasites and hosts foster extra diversity in each other. They’re caught up in an evolutionary game of cat and mouse (or wasp and fly), diversifying into new forms as they play. As Andrew Forbes, who was involved in this study, has previously show, diversity can create itself.

It’s a fascinating study. Different species can be separated by physical barriers like mountains or by rivers, or because they’re active at different times of the day, or even because they harbour different gut microbes. But in this case, it seems that the tangled interactions between parasites and hosts create the barriers that keep species apart, and set up entire webs of life on single flowers.

That’s the basic idea, but there’s a lot still to discover about these insects. For example, how do the flies kill the wasps? And how do the generalist wasps manage to target so many different flies with impunity. And why would the specialist wasps ever occasionally lay eggs on the wrong fly? The team found that they only ever did this on plants that also contained the right host. So, Condon believes that the wasps are tracking down their hosts with some sort of chemical cue, but once they’re in the right ballpark, they sometimes get confused. “They think, ‘It looks like I can put my babies here somewhere’, and they make mistakes,” she says.

“I think it’s pretty outrageous how much diversity could be out there,” says Condon. If just two flowers could play host to so many species of insect, just think about how many more are lurking on or in the other plants of the rainforest. How many are there, and how would we ever find them all?

Reference: Condon, Scheffer, Lewis, Wharton, Adam & Forbes. 2014. Lethal Interactions Between Parasites and Prey Increase Niche Diversity in a Tropical Community. Science http://dx.doi.org/10.1126/science.1245007

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Sneaky Spotted Cat Has Been Disguised As Another Species

Cats are known for being elusive and stealthy, but the southern tigrina takes those qualities to a new level. For decades, this South American feline has been hiding in plain sight, mistaken for a close relative called the tigrina or oncilla.

Physically, the two species are almost indistinguishable—both look like domestic cats with leopard-like spots. There southern tigrina is slightly darker than its north-eastern cousin, its spots are slightly larger, its tail is slightly shorter, and its ears are slightly rounder. But there’s more physical variation within each species than between them.

It’s their DNA that reveals the gulf between them. By analysing the genes of 115 “tigrinas” from all over Brazil, Tatiane Trigo showed those in the north-east are genetically distinct from those in the south and south-east, and the genetic differences between them are as large as those between other cat species. Although both tigrinas are found in central Brazil, some unknown barrier stops them from mating and they have not bred for some time.

Thanks to its genes, a second tigrina species has blinked into view, like a reverse Cheshire cat.

Trigo is assigning the classic name—tigrina (Leopardus tigrinus)—to the  north-eastern cats, and she has named the others southern tigrinas (Leopardus guttulus).

These felines are the latest examples of cryptic species, where a single animal actually turns out to be two or more, largely thanks to genetic studies. There are two species of African elephants, two Nile crocodiles, and possibly many species of killer whales and giraffes.

Things get even more complicated when you consider two other small cats that live in South America. Geoffroy’s cat (Leopardus geoffroyi) is larger and stockier than the tigrinas, and its spots are solid dots rather than open rosettes. The pampas cat (Leopardus colocolo) is even more distinctive—it has stripes on its legs, pointed ears, and a shorter tail.

Geoffroy's cat. Credit: Charles Barilleaux.
Geoffroy’s cat. Credit: Charles Barilleaux.

Trigo showed that some of the genes in the tigrinas (but not the southern ones) came from the pampas cats. Although the two species don’t mate any more, they must have hybridised at some point in their history. This may have been important for the tigrinas. Unlike their forest-dwelling southern cousins, they live in open plains… and so do the pampas cats. Maybe they gained important adaptations for life in the open after their ancestors bred with plains specialists. “This is an intriguing possibility in this case, and we plan to further investigate it,” says Trigo.

The team also found that Geoffroy’s cat is still hybridising with the southern tigrinas! Southern Brazil, where the two species overlap, is effectively a “hybrid swarm”—a zone where almost all southern tigrinas and Geoffroy’s cats are partial hybrids of the two.

So, do they still count as separate species? Trigo thinks so. Their genes tell a story of separation and reunion. The two cats did properly split off from each other some time ago. But after the last Ice Age, the southern tigrinas experienced a population boom, and started expanding into southern Brazil where they met up with their long-separated Geoffroy’s cat cousins. They bred, and their offspring are clearly fertile. But there are still strong genetic differences between the two cats in parts of their range outside the contact zone. They’re not going to merge back into a single species.

Trigo’s priority now is to find out more about the north-eastern tigrinas, which have been poorly studied compared to their southern kin. How does it live? How many are there? Is it in need of protection? There are still many secrets to be learned from biodiversity, including cryptic species in groups that are thought to be well-known, such as wild cats,” she says.

The team are now planning to study other South American cats, like the ocelot and margay. They’ve already found some interesting genetic divisions within both species throughout their range, although nothing definitive yet. On the flipside, they’ve found some evidence that the pampas cat is not, as others have suggested, two or three distinct species.

Reference: Trigo, Schneider, Oliveira, Lehugeur, Silveira, Freitas & Eizirik. 2013. Molecular Data Reveal Complex Hybridization and a Cryptic Species of Neotropical Wild Cat. Current Biology http://dx.doi.org/10.1016/j.cub.2013.10.046

More on hybrids and cryptic species:

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On the Origin of Really Shiny Species

Starlings. From left to right and top to bottom: Common starling by Pierre Selim; Iris glossy starling by Doug Janson; Golden-breasted starling by Perry Quan; Superb starling by Sumeet Moghe; Violet-backed starling by Doug Janson; and Long-tailed glossy starling by Thom Haslam.

If you talk about a starling, most people in Europe and North America will picture a small bird with glossy  black plumage. But that’s the common starling. It’s just one of 113 starling species, many of which have far more spectacular feathers. Just take a look at the selection above.

These resplendent plumes don’t just catch the eye. They may also explain why these birds are so diverse. According to a new study from Rafael Maia at the University of Akron, the starlings’ colours have made them more evolvable, accelerating their split into more and more species.

Many birds produce beautiful feathers using pigments that selectively absorb and reflect different colours of light. But starlings owe their most stunning colours to the structures of the feathers themselves.

As light hits the feathers, it encounters several layers. At each one, some light gets reflected and the rest passes through. If the layers are evenly spaced, the reflected beams amplify each other to produce exceptionally strong colours, which can easily change depending on the distance between the layers or the angle they’re viewed from. This effect is called iridescence. You can see it on the vivid throats of hummingbirds, the tail feathers of peacocks and the plumage of many starlings.

The layers mostly consist of small pigmented structures called melanosomes, which are found in all bird feathers. In their simplest form, they’re shaped like solid rods. But the starlings have added three types of deluxe features on top of this basic model. Some have evolved flatter melanosomes, which lets them pack more layers into the same space. Others have hollow melanosomes, which provide even more layers as light passes through solid walls and empty interiors. Yet others have melanosomes that are hollow and flattened.

When Maia thought about these structural colours, he was struck by how easy it would be for a starling to evolve a completely different palette. “It just needs to change how thick the layers are, or how spaced apart they are,” he says. By contrast, it would be very difficult to start making new pigments. You’d need ways of ushering the right starting ingredients through a new set of chemical reactions—the equivalent of building an entirely new factory just to make a car of a slightly different model. To evolve a new structural colour, you just need to rearrange the parts a little.

By looking at the starling family tree, Maia found that the basic melanosomes have evolved into the three complex types many times over. And although the complex types can change between themselves, they never revert back into the original solid rods. “I thought that maybe you’d have a lot of changing back-and-forth,” he says, “but actually, once these complex structures evolve, they stick.”

As the melanosomes moved from simple to complex shapes, the starlings’ colours became around 80 percent brighter. Their palette also expanded, which you can see in the image below. Each dot represents the colour of a starling feather, and species with complex melanosomes (red, blue and green dots) carry a broader range of colours than those with solid ones (purple dots). “Once you have a certain evolutionary step, you open up the range of colours you can produce,” says Maia.

Top: Four different types of melanosomes: solid rods; flattened; hollow; hollow and flattened. Bottom: colours produced by the four melanosome types; white dots represent non-iridescent colours.
Top: Four different types of melanosomes: solid rods; flattened; hollow; hollow and flattened.
Bottom: colours produced by the four melanosome types; white dots represent non-iridescent colours.

But the starlings with hollow or flattened melanosomes don’t just have a more diverse palette—they also have a palette that diversifies faster. Maia found that their colours change at 10 to 40 times the rate of their cousins with simple melanosomes. They also produced new species at the fastest rates.

This all makes sense. Once they evolved the more complex melanosomes, the starlings could produce dramatic differences in colour by tweaking tiny details, like the thickness of the walls or the density of the layers. Natural selection suddenly had more variation to tinker with. And since starlings rely on colours to recognise each other and choose their mates, their fast-changing palettes would more quickly accentuate the differences between separate populations accelerating their split into new species.

This probably wouldn’t have happened if the starlings’ colours were produced by pigments. Consider a canary. It gets its yellow colour from pigments called carotenoids, which play important roles in their immune systems. If an individual can cope with shunting these substances into its feathers, it must be in good health, which makes the colour an honest sign of quality. A sickly canary simply cannot afford to be as yellow as a healthy one. But once the bird uses this honest signal, it’s hard to evolve a new one that is equally truthful. It would need to produce an entirely new set of chemicals that are both visible to an onlooker and tied to the bird’s health.

Starlings also use their structural colours as honest signals. Healthy, well-fed birds produce stronger iridescent colours than sickly, starving ones. But these birds prove their quality by making an even template. It doesn’t matter if their melanosomes give off a blue or purple or green iridescence, as long as they built to the same specifications and arranged evenly. The structure matters. The strength of the iridescence matter. The colour does not. This means that starlings can make an entire spectrum of colours that are all equally honest. They were free to diversity into ever more resplendent forms without sacrificing the reliability of their messages within their plumage.

Reference: Maia, Rubenstein & Shawkey. 2013. Key ornamental innovations facilitate diversification in an avian radiation. PNAS http://dx.doi.org/doi/10.1073/pnas.1220784110

More on iridescence:

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Stickleback genome reveals detail of evolution’s repeated experiment

Apathy, weary sighs, and fatigue: these are the symptoms of the psychological malaise that Carl Zimmer calls Yet Another Genome Syndrome. It is caused by the fast-flowing stream of publications, announcing the sequencing of another complete genome.

News reports about such publications tend to follow the same pattern. Scientists have deciphered the full genome of Animal X, which is known for Traits Y and Z, which could include commercial importance, social behaviour, being closely related to us, or just being exceptionally weird. By understanding X’s collection of As, Gs, Cs and Ts, we may gain insights into the genetic basis of Y and Z, which will be terribly important and there will be parties and cake.

Note the future tense. The value in sequencing yet another genome is almost never in the act itself, but in enabling an entire line of subsequent research. It’s the harbinger of news; it’s rarely news itself.

But there are exceptions. This week, there’s a paper about a new animal genome that goes the extra mile. It includes not just one full sequence, but twenty-one. It doesn’t just spell out the creature’s DNA, but also uses it to address some big questions in evolutionary biology. And its protagonist is a small, unassuming fish – the three-spined stickleback.


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In a scalding spring, one species of microbe is becoming two

In a cauldron of boiling, acidic water, kneeling at the foot of a Russian volcano, one species of microbe is on the cusp of becoming two.

Sulfolobus islandicus is an archaeon – one of many single-celled microbes that thrive in extreme environments. Mutnovsky volcano is certainly one such place. Found at the far eastern end of Russia, it’s full of churning, scalding springs that are nonetheless teeming with microscopic life. S.islandicus thrives in these springs, feasting on the sulphur within the water.

Now, Rachel Whitaker from the University of Illinois has found that the species has pretty much split into two separate lineages. Both share the same water, and they can trade genes with one another, but they have started to part ways and are becoming increasingly distant. In this hot, hostile and acidic world, the origin of the species is playing out before our eyes.


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Nile crocodile is actually two species (and the Egyptians knew it)

The Nile crocodile is a truly iconic animal. Or, more accurately, two iconic animals. As I’ve just written over at Nature News:

The iconic Nile crocodile actually comprises two different species — and they are only distantly related. The large east African Nile crocodile (Crocodylus niloticus) is in fact more closely related to four species of Caribbean crocodile than to its small west African neighbour, which has been named (Crocodylus suchus).

Evon Hekkala of Fordham University in New York and her colleagues revealed evidence for the existence of the second species by sequencing the genes of 123 living Nile crocodiles and 57 museum specimens, including several 2,000-year-old crocodile mummies.

The results resolve a centuries-old debate about the classification of the Nile crocodile, and have important implications for the conservation of both species.


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One generation, new species – all-female lizard bred in a lab

In a lab in Kansas, Aracely Lutes has created a new species of all-female lizard that reproduces by cloning itself. There wasn’t any genetic engineering involved; Lutes did it with just a single round of breeding.

This feat stands in stark contrast to the slow pace at which species usually arise. Here’s the typical story: different populations become separated in some way, whether by space, time, predators, sexual preferences, or an inability to understand one another. Differences gradually build up between them, until they can no longer produce fit and fertile offspring. Voila – where there was once one species, there are now two.


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In African rivers, an electric Tower of Babel

The rivers and lakes of Africa are filled with conversations that you cannot hear or take part in. These chats are conducted by fishes called mormyrids or elephantfishes, which can produce and sense electric fields. They use their abilities to navigate through murky waters, hunt their prey, and talk to one another. It’s clearly a successful lifestyle, for there are over 200 species of mormyrid alive today.

Bruce Carlson from Washington University in St Louis thinks that the origin of these diverse species lay in the diversity of their electric songs. Different species of mormyrid communicate with different electric signals, which work as badges of identity. When they’re ready to mate, they find partners of their own kind by listening out for their preferred electric dialect.

The evolution of these diverse signals hinged in turn on changes in the mormyrids’ brains and sense organs. These allowed them to pick up subtler differences in their electric signals and talk to each other in more varied ways. This opened up a world of communication, but it was also the mormyrid equivalent of the Tower of Babel. By gaining the ability to communicate in different dialects, the species of mormyrid grew apart.


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Single gene creates snake-resistant mirror-image snails, and maybe some new species


In the novel Dr. No, the titular villain explains to James Bond that he once survived an assassination attempt because his heart was in the wrong place. The good doctor had a condition called situs inversus – his organs were mirror images of their normal versions, found on the opposite side of his body. His heart, being on the right, was unharmed when his would-be murderer stabbed the left side of his chest. Having a mirror-image body can be useful when someone’s out to kill you and while that’s true for criminal masterminds, it also applies to snails.

In Japan, Satsuma snails have shells that mostly coil in the same direction. If you put your finger in the shell’s centre and follow the spiral outwards, you would probably move in a clockwise circle. And Iwasaki’s snail-eating snake knows it.


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Gut bacteria change the sexual preferences of fruit flies


Imagine taking a course of antibiotics and suddenly finding that your sexual preferences have changed. Individuals who you once found attractive no longer have that special allure. That may sound far-fetched, but some fruit flies at Tel Aviv University have just gone through that very experience. They’re part of some fascinating experiments by Gil Sharon, who has shown that the bacteria inside the flies’ guts can actually shape their sexual choices.

The guts of all kinds of animals, from flies to humans, are laden with bacteria and other microscopic passengers. This ‘microbiome’ acts as a hidden organ. It includes trillions of genes that outnumber those of their hosts by hundreds of times. They affect our health, influencing the risk of obesity and chronic diseases. They affect our digestion, by breaking down chemicals in our food that we wouldn’t normally be able to process. And, at least in flies, they can alter sexual preferences, perhaps even contributing to the rise of new species.


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Malawi cichlids – how aggressive males create diversity


This is an old article, reposted from the original WordPress incarnation of Not Exactly Rocket Science. I’m on holiday for the moment, but you can expect a few new pieces here and there (as well as some exciting news…)

Certain groups of animals show a remarkable capacity for quickly evolving into new species to seize control of unexploited niches in the environment. And among these ecological opportunists, there are few better examples than the cichlids, a group of freshwater fishes that are one of the most varied group of back-boned animals on the planet.

In the words of Edward O. Wilson, the entire lineage seems “poised to expand.” The Great Lakes of Africa – Tanganyika, Malawi and Victoria – swarm with a multitude of different species; Lake Malawi alone houses over 500 that live nowhere else in the world. All of these forms arose from a common ancestor in a remarkably short span of time. Now, a new study suggests that this explosive burst of diversity has been partly fuelled by rivalry between hostile males.


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Genetic flip produces two plants for the price of one


On the western coast of America, a combination of cool fog and salty sea spray keeps the soil moist all year round. In these wet conditions, you’ll find an unassuming plant called the yellow monkeyflower. Drive further inland, and the climate changes considerably. It’s hotter and drier, and every summer brings a harsh drought. But here too, the yellow monkeyflower blooms but its lifespan is shorter and its leaves are less luscious. Despite their different habitats and lifestyles, both groups of monkeyflowers are members of the same species. But that might eventually change.

David Lowry from Duke University discovered the secret of the monkeyflower’s dual identities lies in a flipped chunk of DNA. A large chunk of the plant’s genome, containing around 360 genes, has been flipped upside-down, effectively giving it two genomes for the price of one.


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Spots plus spots equals maze: how animals create living patterns

Fish-patternsWhat happens if you cross a fish that has white spots on a black body with another fish that has black spots on a white body? You might think that you’d get a fish with a single uniform colour, or one with both types of spots. But the hybrid’s skins are very different and far more beautiful. It does not inherit its parents’ palettes, overlaid on top of each other; instead, it gets a mesmeric swirl of black and white that looks like a maze on its skin.

To understand where these hybrid patterns come from, you need to look at how fish decorate their skins in the first place. These patterns can be very complicated, as even the briefest swim through a coral reef will tell you, but they also vary from individual to individual – one trout will have a slightly different array of spots to another. These differences tell us that intricate patterns aren’t stamped onto a fish’s skin according to a genetically encoded blueprint. They’re living patterns, generated through a lively dance between a handful of molecules.


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Holy hybrids Batman! Caribbean fruit bat is a mash-up of three species


Most mammals can trace their origins to a single ancestral species. But in the Caribbean islands of the Lesser Antilles, there is a fruit bat with a far more complex family tree. Artibeus schwartzi’s genome is a hybrid mish-mash of DNA inherited from no less than three separate ancestors. One of these is probably extinct and the other two of which still live on the same island chain. It’s a fusion bat, a sort of fuzzy, winged spork.