Fruitflies evolve number sense

US and Canadian researchers have evolved a population of fruitflies that can count. The result, presented on 9 July at the First Joint Congress on Evolutionary Biology in Ottawa, Canada, supports the notion that the neural mechanisms underlying basic arithmetic skills first emerged hundreds of millions of years ago. It could also eventually offer a key to understanding why some people have problems with numbers.

Few doubt that our closest animal relatives have some capacity to count. A variety of clever studies have also revealed the numerical skills of more distant species, including salamandersfish and bees. But until now, no one has ever tried to genetically enhance an animal’s counting ability.

To tackle the challenge, evolutionary geneticists Tristan Long, of Wilfrid Laurier University in Waterloo, Canada, and William Rice, of the University of California, Santa Barbara, teamed up to try to create a race of numerically savvy insects. During a 20-minute training period, flies were exposed to either two, three or four flashes of light — two and four flashes coincided with a vigorous shake administered by placing a electric toothbrush next to the box containing the flies. After a brief rest, the flies were returned to box and shown the light flashes. Despite a dislike for being shaken, most of the flies were not able to learn to associate the negative stimulus with the number of flashes. But 40 generations later, they could.

The researchers caution that the work is preliminary and that they do yet know what genetic changes are behind the insects’ evolved number sense.

“The obvious next step is to see how [the flies’] neuro-architecture has changed,” explains Long. He then hopes to look for genetic differences between control and experimentally selected flies to pin down the genes responsible for their enhanced counting ability.

Neuroscientists have long speculated that human mathematical ability is built on an innate foundation that predates language and complex reasoning. Dyscalculia, a poorly understood disorder that affects a person’s ability to learn and perform basic arithmetic operations, may in some cases be related to an impairment of this innate foundation. If so, says Long, fruitflies could help to uncover genetic links to the disorder.

“This project was really about getting people interested in using fruitflies as a model system for understanding numerical competence and its evolution,” he adds.

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Resistant bed-bugs ‘from tropics’

New results suggest that insecticide use in the tropics is to blame for the re-emergence of bed-bug infestations.

Exposure to treated bed nets and linens meant that populations of bed-bugs had become resistant to the chemicals used to kill them, researchers said.

The findings could help convince pest controllers to find alternative remedies to deal with the problem.

The results were presented at the American Society of Tropical Medicine and Hygiene’s 60th annual meeting.

Since almost vanishing from homes in industrialised countries in the 1950s, populations of the common bed-bug have become re-established in these regions over the past decade or so.

These mostly nocturnal feeders are difficult to control, not only because they are adept at avoiding detection by crawling into creases of soft furnishing but also because they have developed a resistance to many of the chemicals that have been used to kill them.

Findings presented at the gathering in Philadelphia showed that 90% of 66 populations sampled from 21 US states were resistant to a group of insecticides, known as pyrethroids, commonly used to kill unwanted bugs and flies.

Bed-bugs in furniture (Image: Richard Naylor/University of Sheffield)
Female bed-bugs, hidden in furniture creases, can each lay up to 300 eggs


One of the co-authors – evolutionary biologist Warren Booth, from North Caroline State University in Raleigh – explained that the genetic evidence he and his colleagues had collected showed that the bed-bugs infecting households in the US and Canada in the last decade were not domestic bed bugs, but imports.

“If bed-bugs emerged from local refugia, such as poultry farms, you would expect the bed-bugs to be genetically very similar to each other,” explained entomologist and co-author Coby Schal, also from North Carolina State University. “This isn’t what we found.”

In samples collected from across the eastern US, the team discovered populations of bed-bugs that were genetically very diverse.

This suggested that the bugs originated from elsewhere, and relatively recently because the different populations had not had time to interbreed, Dr Schal explained.

He suggested that the source for the new outbreaks was warmer climes, where the creatures would have probably developed a resistance to chemicals.

“The obvious answer is the tropics, where they have used treated bed nets [and] high levels of insecticides on clothing and bedding to protect the military,” Dr Booth told BBC News.

He explained that although bed-bugs were essentially eradicated from industrialised countries in the 1950s, they continued to thrive in Africa and Asia.

“Its very likely that it is from one of these areas where insecticide resistance evolved,” he said.


However, UK-based pest management specialist Clive Boase questioned that hypothesis.

He said bed nets, to protect against mosquito-transmitted malaria and dengue, were only used in parts of Africa that were hot, where the tropical bed-bug (Cimex hemipterus) was found.

But, he added, it was not the tropical bed-bug that was the problem in the US and UK; instead it was their temperate cousin, Cimex lectularius.

Dr Boase explained that comprehensive records showed that infestations of bed-bugs in Europe were less pervasive in the 1970s and 80s, but they were still present.

By continually exposing these populations to insecticides, which came on the market in the late 1970s, these creatures likely developed resistance, he said.

“We don’t have to invoke stories of disease control programmes in Africa; all the evidence here in the UK is that our problem is home-grown.”

Dr Boase wondered that if the US had similar long-term records whether the researchers would have reached a different conclusion.

Evolutionary biologist Richard Naylor from the University of Sheffield agreed: “I am kind of surprised by [their interpretation].

“It doesn’t seem that difficult to develop resistance or lose it; in lab cultures, if you stop exposing [bed-bugs] to pyrethroids it drops out of lab populations very quickly,” he said.

Mr Naylor asked that if the US bed bugs had been exposed to the chemicals elsewhere in the past, “why would they still be resistant?”

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A rare he-she butterfly is born in London’s NHM

A half-male, half-female butterfly has hatched at London’s Natural History Museum.

A line down the insect’s middle marks the division between its male side and its more colourful female side.

Failure of the butterfly’s sex chromosomes to separate during fertilisation is behind this rare sexual chimera.

Once it has lived out its month-long life, the butterfly will join the museum’s collection.

Only 0.01% of hatching butterflies are gynandromorphs; the technical term for these strange asymmetrical creatures.

“So you can understand why I was bouncing off of the walls when I learned that… [it] had emerged in the puparium,” said butterfly enthusiast Luke Brown from London’s Natural History Museum.

Mr Brown built his first butterfly house when he was seven, and has hatched out over 300 thousand butterflies; this is only his third gynandromorph.

Half and half

It is not only the wings that are affected, he explained. The butterfly’s body is split in two, its sexual organs are half and half, and even its antennae are different lengths.

“It is a complete split; part-male, part-female… welded together inside,” he told the BBC.

The dual-sex butterfly is an example of a Great Mormon, Papilio memnon –a species that is native to Asia.

With a shortage of butterfly-specific gender neutral pronouns, the butterfly is being referred to as “it”, and is already middle-aged at three and a half week’s old.

So the public has only a narrow window of opportunity to see it alive.

Though rare, gynandromorphy isn’t unique to butterflies; individual crabs, lobsters, spiders and chickens have all been found with a mix of two sexes.

There are likely many more cases in the natural world, but sexual chimeras are more difficult to spot in animals where females and males look alike.

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Scientists to sequence thousands of insect genomes

Thousands of insects are being lined up to have their genomes sequenced.

The five-year project will help researchers pinpoint vulnerable regions of insects’ genomes, which could be targeted with pesticides.

The project’s leaders hope the initiative will make a dent in the $50bn spent globally each year to control diseases transmitted by insects.

The final list of six-legged critters has yet to be finalised.

The project, called the 5000 Insect and Other Arthropod Genome Initiative, comes at a time when the costs of genome sequencing have fallen substantially and it is feasible to cheaply sequence large numbers of animals and plants.

Handfuls of bugs

Among the list of agriculturally important insects and other arthropods – animals with exoskeletons – to be sequenced are handfuls of bugs that act as disease vectors.

By comparing the genomes of these insects with those of their close relatives that don’t carry pathogens, researchers hope to pinpoint the genes that make one insect a disease-vector and another not.

What’s more, knowing the genes involved will help researchers better predict how insect immune systems will evolve in response to biopesticide control measures, such as Beauveria bassiana, a fungus used to control mosquitoes in malaria-ridden countries in Africa.

It is also hoped that the project will aid the search for suitable compounds for use as pesticides; ones that kill a targeted pest but leave the beneficial pollinating insects that also visit the crop plants unharmed.

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The Earliest Touchdown

Three hundred million years ago, a flying insect skidded to a landing on a muddy patch of earth and preserved a 3.5-centimeter-long imprint for eternity. From the position of the legs, the curve of the abdomen, and the lack of wing marks, the researchers suspect that the imprint was made by an ancient mayfly that held its wings upright when at rest. Collected in southeastern Massachusetts, the fossil is the oldest known full-body impression of a flying insect, the team reports online today in the Proceedings of National Academy of Sciences. The ability of today’s insects to skim the surface of water is thought to be a modern invention. But the discovery of tiny drag marks (see inset) that suggest that mayflies likely slide before stopping is at least enough to prompt some paleontologists to keep an open mind on the matter.

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Parasite Invasion Caught on Camera

For the first time, the tiny malaria parasite, Plasmodium falciparum, has been caught on camera breaking and entering a red blood cell. High resolution 3D images reveal that once the three components of the parasite—nucleus (blue), other organelles (red), and the green pore the parasite brings with it and through which it invades (green)—have attached to the cell, a switch is triggered and the parasite is free to burrow through the cell’s membrane. From this point on, the parasite is unstoppable, multiplying within the cell until it breaks out of its host to invade fresh red blood cells. The new imaging technique will allow researchers to see the effects of novel drugs on this final stage in the parasite’s invasion strategy, researchers report online on this week in Cell Host & Microbe. They hope that this will help scientists develop better drugs to alleviate the suffering of the 400 million people who contract malaria each year.

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Sleepy Bees Lose Their Rhythm

Sleep deprived and having trouble communicating? You aren’t alone. Drowsy honey bees (Apis mellifera) are incoherent, too, researchers report online today in the Proceedings of the National Academy of Sciences. Every morning, the bees set off on their daily foraging trips and return to the nest to perform a waggle dance. The angle of the bee’s body relative to the sun indicates the direction its comrades must fly in to find the good flowers, and the duration of its dance tells how far away they are. Sleep-deprived bees—kept up all night by researchers agitating them—made more errors when communicating the direction of the flower than did well-rested bees; at least until they had caught up on their sleep. Experiments to demonstrate whether bee insomnia is bad for the colony’s survival are underway; until the results are in, worker bees are advised to be tucked up in a hive, with a hot cup of nectar by 9 p.m.

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Rethinking Brain Evolution in Insects

As surprising at it may seem, wasps, bees, and even ants have relatively large and complex brains. That allows these “social insects” to keep track of the intricate relationships between the thousands of individuals in their colony—or so researchers thought. A new study indicates that these insects didn’t grow big brains to cope with social living; they evolved them millions of years earlier when they were solitary parasites.

The link between brain size and social living was first noted in 1850, when scientists identified mushroom bodies in the insect brain. Aptly named because they’re shaped like mushrooms, the structures contain thousands of neurons responsible for processing and remembering smells and sights. Social insects tend to have larger mushroom bodies than solitary ones, leading researchers to believe that the transition from solitary to social living increased the size of these brain regions.

But Sarah Farris has found a different explanation. Instead of comparing social insects with solitary ones, Farris, a neurobiologist at West Virginia University in Morgantown, looked into the past. To get a sense of how the wasp brain evolved over time, she and taxonomist Susanne Schulmeister of the American Museum of Natural History in New York City compared the mushroom bodies of parasitic wasps with those of nonparasitic wasps, which represent the very oldest form of wasp. The parasitic wasps had consistently larger and more elaborate mushroom bodies than the nonparasites, the duo reports online today in the Proceedings of the Royal Society B. In particular, the caps, called calyces, of the parasitic mushroom bodies were twice the size of nonparasites.

Farris points out that parasitism evolved 90 million years before social insects appear, and so “insects had big mushroom bodies for quite a while before sociality arose.” This is the first evidence that parasitism, and not sociality, was the driver of insect mushroom body complexity, she says. That may be because well-developed mushroom bodies help parasitic wasps better locate the nests of the larvae they lay their eggs in.

Francis Ratnieks, an evolutionary biologist at the University of Sussex in the United Kingdom agrees with the study’s findings, but he thinks the researchers need to also look at the brains of social insects. It would be useful, for example, to compare the brains of social worker bees, which process vast quantities of visual information as they fly from flower to flower, with those of parasitic wasps. If bees have even larger mushroom bodies than parasitic wasps, he says, this would suggest that social insects have further improved on the brains that they inherited from their ancestors.

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Maggots Are Covered With Eyes

Fruitfly larvae typically spend their short existence head first in a piece of rotten fruit devouring yeast. That’s perilous: If they can’t see the sun, they’re likely to shrivel under the elements. Luckily the maggots have eyes in the back of their heads—and pretty much everywhere else on their bodies. Reporting online today in Nature, researchers have found that the larvae sport light-sensitive cells (green) that run from head to tail. The cells are especially sensitive to the wavelengths common in bright sunshine, allowing the maggots to squirm into the fruit before the heat desiccates them.

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