MONTREAL, CANADA—When taking a dip this summer you will probably swallow tens, possibly hundreds, of microscopic plankton called choanoflagellates. These common organisms have led to an uncommon insight into how multicellular organisms might have evolved. Bacteria can prompt single-celled choanoflagellates to divide into multicellular versions of themselves, University of California (UC), Berkeley, biologist Nicole King reported last week here at the 71st annual meeting of the Society for Developmental Biology. King hopes the work will prompt biologists to look more closely at the role of microorganisms in the evolution of multicellularity.
To the untrained eye, choanoflagellates look like animals. But they are less complex—the closest living relatives of animals but on an older branch of the tree of life. As such, these organisms can provide clues about what early animals looked like and can help reconstruct the events from more than 600 million years ago that led to the incredible diversity of the animal kingdom.
To investigate the transition to colony life, King decided to sequence the genome of a colony-forming choanoflagellate and compare it with the genome of a unicellular individual. But before sequencing, she asked undergraduate Richard Zuzow to purge the sample of everything but the plankton itself. When Zuzow added antibiotics to get rid of any bacteria, the choanoflagellate colonies disappeared. At first, “I didn’t believe him,” King recalls. But with repeated tests, she became convinced that “the bacteria are the important part of the [multicellular] story,” she says
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 salamanders, fish 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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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.
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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Diet has shaped human jaw bones; a result that could help explain why many people suffer with overcrowded teeth.
The study has shown that jaws grew shorter and broader as humans took on a more pastoral lifestyle.
Before this, developing mandibles were probably strengthened to give hunter-gatherers greater bite force.
The results were published in the Proceedings of the National Academy of Sciences.
“This is a fascinating study which challenges the common perception that there has been little recent change in the morphology of humans,” said anthropologist Jay Stock from the University of Cambridge.
Many scientists have suggested that the range of skull shapes that exist within our species is the result of exposure to different climates, while others have argued that chance played more of a role in creating the diversity we see in people’s profiles.
The new data, collected from over 300 skulls, across 11 populations, shows that jaws shortened and widened as humans moved from hunting and gathering to a more sedentary way of life.
The link between jaw morphology and diet held true irrespective of where people came from in the world, explained anthropologist Noreen von Cramon-Taubadel from the University of Kent.
It would be tempting to conclude that this is evidence for concurrent evolutionary change – where jaw bones have evolve to be shorter and broader multiple, independent times, she told BBC News.
But the sole author of the paper suggested that the changes in human skulls are more likely driven by the decreasing bite forces required to chew the processed foods eaten once humans switch to growing different types of cereals, milking and herding animals about 10,000 years ago.
“As you are growing up… the amount that you are chewing, and the pressure that your chewing muscles and bone [are] under, will affect the way that the lower jaw is growing,” explained Dr von Cramon-Taubadel.
She thinks that the shorter jaws of farmers meant that they have less space for their teeth relative to hunter-gatherers, whose jaws are longer.
“I have had four of my pre-molars pulled and that is the only reason that my teeth fit in my mouth,” said Dr von Cramon-Taubadel.
Ever since that time, she has wondered why so many people suffer with teeth-crowding.
“I think that’s the reason why this result resonates with people,” she said.
Dr Stock added: “[The finding] is particularly important in that it demonstrates that variation that we find in the modern human skeletal system is not solely driven by population history and genetics.”
These results fit with previous evidence of both a reduction in tooth and body size as humans moved to a more pastoral way of life.
It also helps explain why studies of captive primates have shown that animals tend to have more problems with teeth misalignment than wild individuals.
Further evidence comes from experimental studies that show that hyraxes – rotund, short-tailed rabbit-like creatures – have smaller jaws when fed on soft food compared to those fed on their normal diet.
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Scientists may be a step closer to understanding the origins of human social behaviour.
An analysis of over 200 primate species by a University of Oxford team suggests that our ancestors gave up their solitary existence when they shifted from being nocturnal creatures to those that are active during the day.
It is likely communal living was adopted to protect against day time predators, the researchers say.
The results are published in Nature.
From work on social insects and birds, some biologists have suggested that social groups begin to form when young do not leave their natal ground, but instead hang around and help raise their siblings.
Now, the latest evidence from primates suggests that this might not have been the case for our ancestors.
Leaping to sociality
By looking at whether closely related species share similar social structures, the Oxford team of evolutionary biologists shows that a common history is important in shaping the way animals behave in a group.
The team pinpointed the shift from non-social to social living to about 52 million years ago; a switch that appears to have happened in one step, and coincided with a move into daylight.
It did coincide with a change in family dynamics or female bonding, which emerged much later at about 16 million years ago.
“If you are a small animal active at night then your best strategy to avoid predation is to be difficult to detect,” explained Oxford’s Suzanne Shultz, who led the study.
“Once you switch to being active during the day, that strategy isn’t very effective, so an alternative strategy to reduce the risk of being eaten is to live in social groups,” she told BBC News.
Dr Shultz thinks that the move to day-time living in ancient primates allowed animals to find food more quickly, communicate better, and travel faster through the forest.
The link between sociality and a switch to daytime living might have been missed until now, she suspects, because biologists interested in this question have tended to work with Old World monkeys, like baboons, which are characterised by female bonded groups, which are not characteristic of many primate species.
Human societies likely descended from similar large, loosely aggregated creatures, Dr Shultz explained, but the key difference, she pointed out, is that our closest cousins’ societies do not vary within a species, while humans’ do.
“In human societies we have polygyny… we have monogamy, and in some places we have females leaving the group they were born in, and in others males leave,” she said.
Why this difference exist is still unclear.
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Scientists have shown that women who were first to settle in a new land had more children and grandchildren than those who followed.
Researchers analysed the family trees of French settlers who colonised Canada in the 17th and 18th centuries.
Their results could help to explain why some rare genetics diseases are common in communities established by migrations.
The findings have been published in the journal Science.
The team of researchers from Canada and Europe relied on data collected by the parish councils of Charlevoix and Saguenay Lac Saint-Jean, a region 170km north of Quebec, Canada.
The towns not only boast dairy farms, charming villages and sandy beaches but some of the best ever-kept marriage records – comprising more than a million people.
By building a picture of marriages and how many children the pairings produced, the researchers showed that woman who arrived as part of the first wave of immigration had 15% more children than those who arrived a generation later.
The pioneering woman married younger and benefited from scooping up the best local resources, they added.
But the study also found that the pioneering women’s children also had more children.
Lead author Laurent Excoffier, from the University of Bern in Switzerland, explained that the children of women at the front of the wave inherited their mother’s higher rate of fertility.
Yet, the researchers added, there was no such correlation between generations that arrived 30 years later behind the first wave.
Dr Excoffier drew parallels with cane toads. Scientists have observed that the toads at the edge of their range have bigger front legs and stronger back legs; all the better to invade new areas.
And when toads at the frontiers breed, their offspring inherit these longer, stronger limbs.
Such an effect is not unexpected, but until now no one has seen this phenomenon in humans.
“This was a rare chance to study a relatively recent human migration,” said co-author Damian Labuda, a geneticist from the University of Montreal, Canada.
Population geneticist Montgomery Slatkin from University of California, who was not involved in the work, called the study one of the “most interesting, detailed studies” he had seen.
“I think what happened [here] could easily have happened in other populations,” he added.
The findings suggest that families at the front of the wave of migration contributed more to the contemporary gene pool than those that were slower to arrive, explained Dr Labuda.
This could help explain why some rare genetic diseases are more common than expected in the Charlevoix and Saguenay Lac Saint-Jean regions.
That is because any disease causing mutations carried by people by the frontiers would be pass onto their descendents, who make up a large proportion of subsequent generations in the population.
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Scientists have found tiny bubbles beneath the blubber of dolphins that have beached themselves.
The bubbles were discovered by taking ultrasound scans of the animals within minutes of stranding off Cape Cod, US.
The team’s findings help confirm what many researchers have long suspected: dolphins avoid the bends by taking long, shallow decompression dives after feeding at depth.
The study is reported in Proceedings of the Royal Society B.
Many biologists believe that marine mammals do not struggle, as human divers do, with decompression sickness – “the bends” – when ascending from great depths.
In humans, breathing air at the comparatively high pressures delivered by scuba equipment causes more nitrogen to be absorbed into the blood and the body’s tissues, and this nitrogen comes back out as divers ascend.
If divers ascend too quickly, the dissolved nitrogen forms bubbles in the body, causing decompression sickness.
But marine mammals such as whales, dolphins, and seals are highly adept at dealing with the pressures of the deep.
They slow their hearts, collapse the tiny air-filled chambers in their lungs, and channel blood to essential organs – like the brain – to conserve oxygen, and limit the build-up of nitrogen bubbles in the blood that happens at depth.
However, veterinary scientist Michael Moore from Woods Hole Oceanographic Institute in the US, thinks that it is “naive” to think that diving mammals do not also struggle with these laws of chemistry.
Even marine mammals ascending from the deep must rid themselves of the gas that has built up in their tissues, or risk developing the bends.
If dolphins, he explained, come up too quickly then there is evidence that they “grab another gulp of air and go back down again,” in much the same way a human diver would “re-tank and re-ascend” to try to prevent the bends.
“But there’s one place you can’t do that [if you are a dolphin] and that’s sitting on the beach,” Dr Moore told BBC News.
And so when he and his team scanned eight Atlantic white-sided dolphins and 14 short-beaked common stranded dolphins using ultrasound, they were not surprised to find tiny bubbles below the blubber of the animals.
Because three of the dolphins were scanned within minutes of their stranding, the team ruled out the possibility that the air pockets were a result of beaching, and instead think that they formed while the animals were still in the water.
Sascha Hooker, a marine mammal ecologist with the Sea Mammal Research Unit in St Andrews, UK, commented: “This study is much less about why animals strand, and much more about using stranded animals to give us a bit more insight [into] what is going on inside live marine mammals.
“[What’s] particularly interesting from this is that the animals that were released… survived.
“So it looks like these animals are able to deal with some bubbles.”
She explained that studying the behaviour and physiology of diving animals is incredibly difficult because researchers cannot follow them down to the deep.
Stranded animals, therefore, offer researchers rare access to these expert divers to measure what changes they undergo to avoid the bends.
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