Category: News stories

Plant has evolved a specialist bird perch

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New research sheds light on the world’s most specialised bird perch.

The researchers suspect that the vertical, branchless stem of a South African plant – locally called the Rat’s Tail – has evolved to encourage pollinating birds to visit its flowers.

The birds hang upside down from this perch and fertilise the plant when they thrust their beaks into the red flowers to drink nectar.

The international team reports the findings in the Annals of Botany.

Plants go to great lengths to attract animals to pollinate them; they seduce insects, birds and small mammals with colourful, shapely, sweet-smelling flowers.

Some plants even wave at passing pollinators.

On first seeing the deep red, long-tubular flowers of Babiana ringens in 2003, botanist Spencer Barrett from the University of Toronto, Canada, suspected that he was dealing with a plant that was pollinated exclusively by birds.

But the position of the flowers at the base of the plant perplexed him.

Most birds avoid feeding on or close to the ground to keep clear of ground-dwelling predators; plants reliant on bird-pollination tend to keep their flowers up high.

Dr Barrett and his colleague Bruce Anderson from University of Stellenbosch in South Africa, wondered if the curious perch-like structure had evolved to give pollinating birds a foothold from which to feed.

Crouching among the shrubs of the Cape of South Africa, binoculars in hand, Dr Barrett and his team confirmed that the flowers were exclusively pollinated by sunbirds.

“When we saw a bird visiting we were completely enchanted,” said Dr Barrett.

Relaxed selection

Still unconvinced that the stick-like protrusion had evolved as a perch, the team set about to gather further evidence.

They set out to look at the full distribution of B. ringens across the Cape, and found that in the east, where sunbirds have a greater variety of flowering plants to choose between, B. ringens‘ perches were smaller than in the west, where plants can rely on regular visits from sunbirds.

Dr Barrett suspects that in the absence of pollinating birds, the plants do not need to invest in maintaining the perch, and so it shrinks over many generations – an example of what is called relaxed selection.

With time, this branch might return to its ancestral form, which the researchers suspect was a central stem with flowers at its top, much like many of B. ringens’close relatives.

“It’s a fascinating piece of work,” said plant biologist Professor Simon Hiscock from the University of Bristol.

This study poses questions about the influence of pollinators on the structures of flowers and on plants’ reproductive strategies, he added.

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Waving robotic crab arm attracts females

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A vigorous wave of the claw can be the key to mating success for male fiddler crabs, report researchers at the 13th Congress of the European Society for Evolutionary Biology.

Male crabs advertise their quality as a potential mate to passing females by waving their large yellow claws.

Using robotic arms, researchers evaluated how the size and speed of the waving claw affected mating success.

The results may help explain why males protect their smaller neighbours.

To the fiddler crab Uca mjoebergi, the Australian mudflats in the north of the country are a heaving dance floor, where a male must rely on his moves to attract a mate.

Males stand outside their burrows and use their enlarged claw to attract females by moving it in circles.

If a female likes the look of a male, she will come closer and disappear down his burrow in the sand, possibly staying to mate.

Wave of waving

When a female wanders through a neighbourhood, “you see part of the mudflat light up” with waving yellow claws, said ecologist Sophie Callander from the Australian National University in Canberra.

Dr Callander and her colleagues used a fully adjustable robotic arm – called Robocrab – to determine what female crabs are looking for in a mate.

Dr Callander set up three robotic arms around a female crab, and sat beneath the unforgiving Australian sun for many hours recording the females’ reactions to different combinations of wave speeds and claw size.

Females approaching from 20cm preferred males with a higher wave rate and larger claws. Intriguingly, this preference increased in strength when the male was flanked by more slowly waving, smaller-clawed crabs.

Fiddler crabs also use these claws in displays of dominance and fighting prowess.

Previous work has shown that larger males sometimes go to the aid of smaller males when an intruder is trying to steal a smaller male’s burrow.

This behaviour is unlikely to be an altruistic form of neighbourhood watch, and Dr Callander thinks that her experiment could offer an explanation.

“If larger males can retain smaller neighbours they might… increase their mating success,” she told BBC News.

For fiddler crabs at least, it pays to keep close to the small and weak.

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Bed bugs protect their sperm from bacteria

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Bed bugs protect their sperm against sexually transmitted infections by producing germ-busting ejaculates, scientists have found.

Bacteria covering bed bugs’ bodies are transmitted to the female, along with the sperm, during mating.

The new work shows that without the protection of antibacterial agents in the bug’s ejaculate, 40% of sperm die.

The results were presented at the 13th Congress of the European Society for Evolutionary Biology.

Bed bugs, and the related bat bugs that live in African caves, are renowned for their bizarre sex lives.

‘Traumatic insemination’

Males, instead of penetrating the female’s vagina, pierce her underside and deposit sperm inside the female, where it swims through the insect’s blood system to the ovaries to fertilise the eggs.

Female bed bugs protect themselves against the diseases that males transmit with a structure on their bellies that guides the penis into a mass of germ-fighting cells.

Males, it seems, have also evolved a way to fend off the effects of sexually transmitted infections, evolutionary biologist Oliver Otti from the University of Sheffield, UK, told conference attendees in Germany.

Suspecting that males load their ejaculates with proteins that protect sperm, Dr Otti carefully extracted sperm from a number of male bed bugs, being sure not to mix it with the seminal fluid that usually makes up the rest of the ejaculate.

He then mixed the sperm with a “soup” of micro-organisms that he had collected from the outer skin of the bed bugs.

To half of these samples he added lysozyme, a bacteria-killing enzyme known to be active in bed bugs, and saw that 40% more sperm survived in its presence.

Females didn’t gain any protection from these introduced bacteria-busting enzymes, he explained; the presence of lysozyme in the ejaculate seemed to be purely to protect sperm.

But other work by Dr Otti’s colleague Michael Siva-Jothy, who is also based at the University of Sheffield, shows that females protect themselves from the infections introduced during sex with their own lysozymes.

In fact, females ramp up their lysozyme activity just before they are about to feed. Dr Siva-Jothy explained that this is probably because in the bed bug world, feeding is generally always followed by mating.

“Wounding is a very frequent event during and after copulation, and generally genitals are not that clean, ” Dr Otti told BBC News.

He explained that the research that has focused on human sexual transmitted diseases has tended to ignore the microbes that coexist with us on our skin; these microbes are likely also transferred during sex.

“It is not clear what the cost of having them around is,” Dr Otti added.

The advantage of studying bed bugs, he said, is that we share many components of our immune system. As a result, scientists can learn much from manipulating the bugs’ sex lives to study the consequences on lifespan and offspring production – some of these trade-offs could be relevant to humans.

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Insects use antibacterial secretions to protect young

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Scientists have confirmed that so-called burying beetles coat their young’s food with an antibacterial substance to guarantee their survival.

Burying beetles lay their eggs on the carcasses of small animals, such as birds and rodents.

The researchers show that without the anti-microbial secretions the young fail to gain weight and die.

The results were presented the 13th Congress of the European Society for Evolutionary Biology.

Most animals try to do the best for their young, but burying beetles, in the genus Nicrophorus, which are found in temperate regions in Europe and North America, are truly doting parents.

As a prospective parent, burying beetles find a dead animal, such as a mouse or bird, and roll the carcass into a ball.

They then bury the carcass, hiding it from predators that might eat it or fancy it for a nursery for their own young – no small feat for a beetle that is only 15mm long.

The beetles then lay their eggs in the flesh of the animal and wait to welcome their young into the world.

But a buried carcass is not going to stay fresh for very long, and the bacterial communities that colonise it are likely to threaten the beetle’s developing larvae.

Germ-free

So burying beetles use secretions from their anal glands to coat the fur or feathers with substances that guarantee the carcass stays germ-free and fresh for longer.

Now scientists from the University of Manchester have worked out what makes these secretions so good at killing germs.

The researchers extracted secretions from the anal glands of a species of burying beetle called Nicrophorus vespilloides, and showed that when this substance was added to bacterial cells, they were destroyed.

Evolutionary biologists Andres Arce, who led the study, and his colleagues, suspecting that they were dealing with a enzyme that “chops up microbial cell walls”, investigated and confirmed that the secretions were rich in lysozymes.

These are anti-microbial enzymes, and a common component of animals’ immune systems.

Lysozymes are also secreted in mammals’ breast milk and in human tears.

The team showed that larva raised in the absence of either their parents secretions were 40% more likely to die before adulthood.

Dr Arce explained that for a non-social insect, these burying beetles are already known to show quite substantial levels of parental care.

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Lager-brewing yeast identified in Argentina

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Scientists have identified a yeast that led to the discovery of lager.

The researchers isolated the new species in the frozen forests of Patagonia in South America.

Their discovery suggests that this yeast crossed the Atlantic hundreds of years ago and combined with one traditionally used in Europe to make ale.

The discovery is described in the Proceedings of the National Academy of Sciences.

A lucky find

The workhorse of brewing, the yeast Saccharomyces cerevisiae, is used worldwide to ferment fruit and grains to make wine, cider and ale.

Lager, which is fermented more slowly and at lower temperatures than ale, is presumed to be a later invention, and was likely stumbled upon when Bavarian monks moved their beer barrels into caves for storage.

In those caves, Saccharomyces cerevisiae, which prefers to grow just above room temperature, is presumed to have been outcompeted in the fermenting beer by a species that thrived at cooler climes.

The modern-day lager-brewing yeast, Saccharomyces pastorianus, which is a fully domesticated species, is probably a hybrid of this cool-loving strain and the ale-brewing species, and survives because brewers keep back a little of the lager each time to seed the next batch with the same yeast.

Lager’s cradle

“The hybrid almost definitely formed accidentally and people adopted it because the beer came out differently,” said evolutionary biologist Chris Hittinger from the University of Wisconsin in Madison, US, who was one of the team behind the discovery.

But researchers have long wondered where the original cool-loving yeast species came from.

That is until Dr Hittinger and his colleagues isolated it from a beech tree in the forests of Patagonia this year.

These forests, where daily lows average around -2C, are the perfect cradle for modern-day lager-brewing yeast. The species has been designated Saccharomyces eubayanus.

“I personally prefer lagers to ales, and I am very grateful that these two distant cousins met up in a Bavarian cellar hundreds of years ago,” Dr Hittinger told BBC News.

Knowing the ancestral strain to the modern day lager-brewing yeast will help scientists pinpoint the effects of domestication in the genome of brewing yeasts.

And there is also the possibility that there are other undiscovered species of yeast in those Patagonia forests that could become the next best brew.

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Species flee warming faster than previously thought

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Animals and plants are shifting their natural home ranges towards the cooler poles three times faster than scientists previously thought.

In the largest study of its kind to date, researchers looked at the effects of temperature on over 2,000 species.

They report in the journal Science that species experiencing the greatest warming have moved furthest.

The results helped to “cement” the link between climate change and shifts in species’ global ranges, said the team.

Scientists have consistently told us that as the climate warms we should expect animals to head polewards in search of cooler temperatures.

Animals like the British comma butterfly, for example, has moved 220km northward from central England to southern Scotland in the last two decades.

An uphill struggle

There is also evidence that more species seem to be moving up mountains than down, explained conservation biologist Chris Thomas from the University of York, UK, who led the study.

But studies had stopped short of showing that rising temperatures are responsible for these shifts in range, he added.

Now he and his team have made this link.

Analysing the range shifts of more than 2,000 species – ranging from butterflies to birds, algae to mammals – across Europe, North and South America and Malaysia over the last four decades, they show that organisms that experience the greatest change in temperatures move the fastest.

The team found that on average organisms are shifting their home ranges at a rate of 17km per decade away from the equator; three times the speed previously thought.

Organisms also moved uphill by about 1m a year.

“Seeing that species are able to keep up with the warming is a very positive finding,” said biologist Terry Root from Stanford University in California, US.

She added that it seemed that species were able to seek out cooler habitats as long as there was not an obstacle in their way, like a highway.

Out of range

But what about the animals that already live at the poles, or at the top of mountains?

“They die,” said Dr Thomas. Take the polar bear, it does most of its hunting off the ice, and that ice is melting – this July was the lowest ever recorded Arctic ice cover – it has nowhere to go.

However, the loss of this one bear species, although eminently emblematic, seems insignificant when compared to the number of species that are threatened at the top of tropical mountains.

On Mount Kinabalu in Borneo, Dr Thomas’ graduate student, I-Ching Chen, has been following the movement of Geometrid moths uphill as temperatures increase. Their natural ranges have shifted by 59m in 42 years.

These moths “don’t have options; they are being forced up, and at some point they will run out of land,” reflected Dr Thomas.

The British scientist said that it was really too early to start generalising about the characteristics of the species that had shifted their distribution to stay within their optimal temperature range.

“But we know that the species which have expanded the most and fastest are the species that are not particularly fussy about where they live,” he told BBC News.

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Swedish wolves threatened by under-reported poaching

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Illegal poaching accounts for over half of all deaths of Swedish wolves, suggests a new study.

Basing their estimates on long-term wolf counts, the researchers reveal that two-thirds of poaching goes undetected.

The study suggests that without the past decade of persecution Swedish wolves would be four times more abundant than they are today.

The study’s findings are reported in Proceedings of the Royal Society B.

“Many have speculated that poaching levels are high for many threatened species of carnivores,” said Chris Carbone from the Zoological Society of London.

“This study presents an important step in trying to quantify this hidden threat,” he added.

The new study predicts the size of the wolf Swedish population each year based on counts from the previous year.

These counts are based on radio-tracked wolves and the more traditional ‘footprint count’, used in Sweden for over 10 years to estimate wolf numbers.

Counting canines

The researchers’ estimates took account of confirmed cases of wolf mortality – such as when a wolf is killed on the road, dies from disease or is found killed.

However, when the team, based at Grimso Wildlife Research Station in Sweden, compared the expected numbers produced by their models to the actual number of wolves in the wild, they found they were over estimating the size of the population.

Conservation biologist Guillaume Chapron, and one of the team, suspects that ‘cryptic poaching’, poaching that goes undetected, accounts for this difference.

The poaching we see is the “tip of the iceberg,” he said.

The researchers predict that without the last decade of poaching, wolves would have numbered around a thousand by 2009, four times the number reported that year.

Wolves are known to kill the dogs that many Swedes use to hunt moose, and despite up to four year prison sentence if caught poaching, a few people do not hestitate to take a shot at a wolf.

Founding fins

Poaching is not the only threat to the Swedish wolf.

These large carnivores went extinct in Sweden in the 1970s, and the population has since re-established itself after a handful of migratory Finnish wolves took over the empty territories.

Today, all 250 or so Swedish wolves have descended from these few founding individuals.

And so the population is highly inbred and suffers from skeletal abnormalities and problems reproducing.

Further reducing the number of wolves by poaching leaves this population very vulnerable to further inbreeding, explained Dr Chapron.

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Spermless mosquitoes hold promise to stop malaria

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Scientists have created spermless mosquitoes in an effort to curb the spread of malaria.

Experts say that this is an important first step toward releasing sterile males into the wild to reduce the size of mosquito populations.

Malaria kills around one million people worldwide every year, and in Africa alone, accounts for 20% of all childhood deaths.

The work is reported in Proceedings of the National Academy of Sciences.

Insect sterilisation isn’t new: scientists have attempted to control the sleeping sickness-carrying tsetse fly by exposing them to radiation to render them sterile.

A similar approach has been successfully used against the potatoes weevil in Japan and the tropical screwworm that attacks cattle.

Frail fly

However, exposing mosquitoes to radiation has tended to leave male mosquitoes frail, and unable to compete in the frenzied mating aerobatics that Anopheles gambiae – the world’s most efficient malaria vector – enjoys.

Now scientists have developed an alternative route to mosquito sterility.

Entomologist Flaminia Catteruccia from Imperial College London enlisted the help of her graduate student Janis Thailayil in the search for how to make male mosquitoes sterile but leave them otherwise unharmed.

Mr Thailayil injected 10,000 mosquito embryos with tiny fragments of RNA designed to turn off a gene – called zpg – that is essential for normal sperm development.

After months of laborious work, the researchers created around 100 spermless mosquitoes, and showed that females were just as willing to mate with these males as with fertile ones.

Dr Catteruccia explains that female mosquitoes mate only once in their lives. If scientists can trick them into thinking that they have successfully mated, then they will continue to lay their eggs without knowing that they have not been fertilised.

“You [could] in principle release large numbers of sterile males over many generations… and eventually all the females will have mated with the sterile males and…you can really reduce the number of mosquitoes,” explained Dr Catteruccia.

This would gradually reduce the number of hatching mosquitoes. And hopefully help eradicate what many consider to be the single most dangerous insect species for mankind.

However, Dr Catterucci warns that this is only a proof of principle. The method her team used to create the spermless males would be far too labour-intensive to flood wild populations with enough spermless males to have any effect on their numbers.

However, knowing that females don’t notice whether they are receiving sperm or not is still an important step, she said.

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How bloodsuckers find their blood

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Scientists have identified the heat-sensitive facial nerves used by vampire bats to detect their next meal.

The nerves allow bats to pinpoint where the blood flows closest to their prey’s skin so they can feed more efficiently.

Vampire bats are among a handful of animals that use infrared sensors to locate their next meal, but are unique in the way they do it.

The findings are reported in the journal Nature.

Native to Central and South America, the Common Vampire Bat, Desmodus rotundus, needs to take a sanguineous slurp every night to survive.

Researchers believe that the bats rely solely on detecting their next meal in the dark by listening out for their prey’s breathing.

Having located a prey individual the bats crawls along the ground and onto the animal.

Once atop their prey, the bats are capable of using their heat-adapted nerves in their upper lip and nose to detect blood up to 20cm under their prey’s flesh.

The new finding has pinpointed the molecule that is responsible – heat-sensitive TRPV1. TRPV1, a protein, usually helps animals detect dangerously high temperatures (those over 43 degrees C), but in the bats, some of the TRPV1 molecules have been mutated into a version that is sensitive to lower temperatures, those around 30 degrees C.

Lots of blood-sucking animals search out their next meal using heat-detecting molecules, but they all seem to do it in a different way, said bat biologist, Brock Fenton from the University of Western Ontario, who was not involved in the work.

He said that perceptual world of bats undoubtedly has many more intriguing secrets.

  • The Common Vampire Bat (Desmodus rotundus) is one of three species of vampire bat: The Hairy-legged Vampire Bat (Diphylla ecaudata), and the White-winged Vampire Bat (Diaemus youngi)
  • All three live in the Central and South America
  • D. rotundus feeds mainly on domestic animals, using its razor sharp teeth to make small (5mm) cuts in their prey – most often around the neck or vulva – and secretes an anticoagulant into the wound so it can draw enough blood to the surface
  • D. rotundus drinks its body weight in blood each night, secreting blood plasma in its urine as it feeds to lighten the load
  • Scientists have developed a anti-clotting drug from the saliva of vampire bats that could help stroke patients

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