Buzzing bees scare elephants away

It’s a myth that elephants are afraid of mice, but new research shows that they’re not too keen on bees. Even though they fearlessly stand up to lions, the mere buzzing of bees is enough to send a herd of elephants running off. Armed with this knowledge, African farmers may soon be able to use strategically placed hives or recordings to minimise conflicts with elephants.

Elephants turn tail at the sound of beesIain Douglas-Hamilton and Fritz Vollrath from Kenyan conservation charity Save the Elephants first suspected this elephantine phobia in 2002, when they noticed that elephants were less likely to damage acacia trees that contained beehives.

Animals as powerful as the African elephant can go largely untroubled by predators. Their bulk alone protects them from all but the most ambitious of lion prides.

But these defences do nothing against the African bees, which can sting them in their eyes, behind their ears and inside their trunks. Against these aggressive insects, the elephants are well justified in their caution and local people have reported swarms of bees chasing elephants for long distances.

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Trout with salmon parents could help to revive endangered fish species

Japanese researchers have developed a way of using one species of fish as a surrogate parent for an endangered one by transplanting the sexual equivalent of stem cells. If enough of these cells can be preserved, an extinct species could be resurrected.

Getting excited when fish produce sperm would usually get you strange looks. But for Tomoyuki Okutsu and colleagues at the Tokyo University of Marine Science and Technology, it’s all part of a day’s work. They are trying to use one species of fish as surrogate parents for another, a technique that could help to preserve species that are headed for extinction.

Baby trout can be born from salmon parents using transplanted sex cells.Okutsu works on salmonids, a group of fish that includes salmon and trout. Many members of this tasty clan have suffered greatly from over-fishing in the last few decades, and their populations are dwindling their way to extinction.

If stocks fall below a critical level, they may need a jump-start. One strategy is to freeze some eggs to be fertilised artificially, in the way that many human eggs are in fertility clinics. But it’s much harder for fish eggs – they are large and have lots of fat, which makes them difficult to freeze effectively.

Okutsu’s group have hit on a more effective solution. They use transplanted sexual stem cells to turn another species of fish into surrogate parents for the endangered ones.

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Genetic study puts damper on gray whales’ comeback

The eastern Pacific gray whale has bounced back from the brink of extinction to a healthy population of 22,000 individuals. But by measuring the genetic diversity of these whales, scientists have estimated that the original population was up to five times larger. The whales aren’t out of the danger zone yet, and climate change may explain why.

Twenty-two thousand sounds like a huge number. It’s happens to be number of eastern Pacific gray whales currently swimming off the coast of North America. It’s certainly much larger than 140, the number of whales that aboriginal people of this area are allowed to hunt. And it’s far, far bigger than zero, the population size that the whales were rapidly approaching in the mid 20th century.

The gray whale hasn’t fully recovered from a century or more of huntingObviously, it’s all relative. Twenty-two thousand is still much less than ninety-six thousand. That’s the size of the original gray whale population and it’s three to five times the current count. Not exactly cause for conservational complacency, then.

Previously, conservationists and whalers alike could only speculate on the number of whales that lived before their flirtation with extinction. But now, Elizabeth Alter and Stephen Palumbi from Stanford University have managed to pin down a figure by looking at the genetic diversity of living whales. And their results suggest that despite a rebound that Hollywood would envy, the grays are still a pale shadow of their former strength.

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Is a virus responsible for the disappearing bees?

A group of scientists have found that a virus – IAPV – may be responsible for Colony Collapse Disorder, the mysterious condition that’s emptying the hives of European and American beekeepers.

A bee sits on a readout of its own genetic material.In 2006, American and European beekeepers started noticing a strange and worrying trend – their bees were disappearing. Their hives, usually abuzz with activity, were emptying.

Like honeycombed Mary Celestes, there was no trace of the workers or their corpses either in or around the ghost hives, which still contained larvae and plentiful stores of food. It seemed that entire colonies of bees had apparently chosen not to be.

The cause of the aptly named ‘Colony Collapse Disorder’, or CCD, has been hotly debated over the last year. Fingers were pointed at a myriad of suspects including vampiric mites, pesticides, electromagnetic radiation, GM crops, climate change and poor beekeeping practices. And as usual, some people denied that there was a problem at all.

But a large team of US scientists led by Diana Cox-Foster and Ian Lipkin have used modern genomics to reveal the main villain in this entomological whodunnit – a virus called Israeli Acute Paralysis Virus or IAPV.

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Restoring predator numbers by culling their prey

Helping out a threatened predator by culling their prey seems like a really stupid idea. But Scandinavian scientists have found that it might be the best strategy for helping some of our ailing fish stocks.

Lennart Persson and colleagues from Umeå University came up with this counterintuitive idea by running a 26-year natural experiment with the fish of Lake Takvatn, Norway.

The brown trout increases the numbers of its prey by eating it!At the turn of the 20th century, the top predator in Lake Takvatn was the brown trout. Over-fishing sent its numbers crashing, and it was virtually gone by 1980.

In its place, a smaller fish – the Arctic char ­– was introduced in 1930. Char should make a good meal for trout, so it was surprising that when the trout were reintroduced they failed to flourish despite an abundance of food.

It was only in the 1980s, when the researchers removed over 666,000 char from the lake that the trout started bouncing back. While their prey population fell by 80%, the trout have increased in number by 30 times. The lake’s temperature and nutrient levels were mostly constant during this time, so why did the trout do better when they prey was culled?

Persson believes that it’s not the numbers of the char, but their size that matters, and that changed irrevocably when the trout first vanished.

More predation means more prey?

Paradoxically, predators like trout, can actually increase the numbers of small prey by eating them. It seems like a strange idea, but it happens because the remaining prey face less competition for food. As a result, they grow more rapidly, mature faster and give rise to more young.

By growing too large, the Arctic char muscled the trout out of Lake Takvatn.This means the population becomes, on average, smaller, since individuals spend less time growing and fill the water with baby fish. And that’s good news for predators. But take the predator out and the whole system grinds to a halt.

Conservationists often like to believe that an over-hunted predator will just bounce back into its original niche once hunting is stopped. But things are rarely that simple. In the predator’s absence, other species will rush in to fill the gap and the entire system can settle down into a new balance, which the predator can find very hard to slot back into.

Practicalities

In Lake Tyvatn, the absence of the trout meant that the char population faced no threats and competed heavily for resources. They grew and reproduced slowly, reaching sizes too large for the trout to tackle. The proportions of small char fell to a level which could not support reintroduced trout. Essentially, while the predator was away, the prey took it easy and locked the door so it couldn’t get back.

When the char were culled, this mimicked the effects of trout predation by removing the largest individuals. As a result, the numbers of smaller, trout-friendly char doubled and began to dominate the lake. And that shift finally allowed the trout to regain a foothold (or finhold) in the lake. The two fish have now established a balance in numbers for over 15 years.

Persson’s study clearly shows that removing a predator from its habitat (an all-too common occurrence) doesn’t create a predator-shaped hole in the ecosystem, ready to be filled again. Instead, it causes drastic changes to local food webs, that can only be reversed with counter-intuitive and ingenious strategies.

Stocks of predatory fish, including sharks, salmon, cod and trout, are threatened by over-fishing all over the world, and Persson believes that his strategy could help them to recover.

For example, the falling cod population in the Baltic sea could potentially be restored by fishing for its prey, like herring or sprat. It’s so crazy, it just might work.

 

Reference: Persson, Amundsen, de Roos, Klemetsen, Knudsen & Primicerio. 2007. Culling prey promotes predator recovery – alternative states in a whole-lake experiment. Science 316: 1743- 1746.

Related post on over-fishing:
Shark-hunting harms animals at bottom of the food chain
and others on changing ecosystems:
Attack of the killer mice – introduced rodents eat seabird chicks alive
The fox and the island: an Aleutian fable
Farmed salmon decimate wild populations by exposing them to parasites

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Climate change responsible for decline of Costa Rican amphibians and reptiles

Amphibians around the world are facing extinction from habitat loss and a killer fungus. Now, climate change joins their list of enemies. In Costa Rica, warmer and wetter days have led to a loss of rainforest leaf litter that has sent amphibian and reptile populations crashing.

Miners used to take canaries into unfamiliar shafts to act as early warning systems for the presence of poisons. Today, climate scientists have their own canaries – amphibians.

The golden toad was one of the first casualties in the great amphibian decline.Amphibians – the frogs, toads and salamanders – are particularly susceptible to environmental changes because of their fondness for water, and their porous absorbing skins. They are usually the first to feel the impact of environmental changes.

And feel it they have. They are one of the most threatened groups of animals and one in three species currently faces extinction. The beautiful golden toad (right) was one of the first casualties and disappeared for good in 1989. Even though they are less glamorous than tigers, pandas or polar bears, amphibians are a top priority for conservationists.

The usual factors – introduced predators and vanishing habitats – are partially to blame, but many populations have plummeted in parts of the world untouched by pesky humans.

More recently, a large number of these deaths have been pinned on a fatal fungal disease called chytridiomycosis. Hapless individuals become infected when they swim in water used by diseased peers, and fungal spores attach to their skins. The disease had decimated amphibians across the Americans.

A third of the world’s amphibians face extinction, if not more.The extent of the damage may be even worse than we think. We have very little long-term data on the population sizes of many amphibian species, particularly in the tropics, where the greatest diversity exists. One of the few sites to buck the trend of ignorance is La Selva Biological Station in Costa Rica, which has been monitoring amphibian populations since the 1950s.

Steven Whitfield and colleagues from Florida International University used the La Selva data to analyse the populations of a species living among the leaf litter that covers the local rainforest floor. The team ran their census of about 30 species of amphibians, as well as many reptiles (lizards and snakes).

To their astonishment, the populations of these species had plummeted by 75% in 35 years. This massive decline is worrying for many reasons, the least of which is that La Selva sits within a protected area. Habitat destruction is non-existent here, so something else must be happening.

Nor is chytridiomycosis to blame. The fungus doesn’t tolerate high temperatures and only grows in temperate regions or mountainous ones. La Selva is neither. The killer fungus marks its presence with rapid falls in amphibian numbers within months, but these declines took place over decades.

And most tellingly of all, the reptiles suffered population losses as great as those of the amphibians. With their dry, scaly skins, reptiles lack the amphibian vulnerability to chemicals and chytridiomycosis. Something else is afoot.

Warmer and wetter days are diminishing the leaf litter that amphibians and reptiles call home.Whitfield believes that climate change is the answer. Over the past 35 years, La Selva has experienced wetter and warmer days. Temperatures have gone up by one degree Celsius, which slows the growth of local trees, and reduces the volume of leaves that they shed. The number of dry days has halved, and with more rainfall, the leaves that do fall decay faster.

So these combined climate changes have conspired to reduce the levels of leaf litter in the forest, robbing amphibians and reptiles alike of their homes. Even in this protected area, habitat destruction is going on right under our feet.

The climate change idea explains another odd finding. Whitfield saw that amphibian and reptile numbers had not declined in nearby abandoned cacao plantations. That’s because cacao trees shed their leaves throughout the year and provide a continual supply of new leaf litter.

The picture for the world’s amphibians seemed bleak enough, but it seems that we have been ignoring a larger simmering danger in the face of the immediate threat of chytridiomycosis. It is telling that all but one of the disappearing species in this study are listed as ‘least concern’ by the World Conservation Union (IUCN). Whitfield’s study should be a call to action for conservationists.

Reference: Whitfield, Bell, Phillippi, Sasa, Bolanos, Chaves, Savage & Donnelly. 2007. Amphibian and reptile declines over 35 years at La Selva, Costa Rica. PNAS doi.0611256104.

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Attack of the killer mice – introduced rodents eat seabird chicks alive

On Gough island, introduced mice have developed a grisly appetite for seabird chicks and could well drive local species to extinction.

As Charles Darwin learned several centuries ago, islands are havens for evolution. Newcomers to these isolated worlds find themselves unshackled from the predators that dogged them on the mainland. They celebrate their freedom by diversifying into a great variety of species.

A Gough Island mice sites amid a grisly pile of chick bodies.But predators still have ways of tracking them down, and following the footsteps of sailors is one of them. By killing adults and eating eggs, introduced predators such as rats, cats and stoats are responsible for nine in ten of the bird extinctions since 1600.

Now, conservation agencies are getting serious about introduced predators. As an example, they have spent increasingly large budgets in recent years on the eradication of rats from troubled islands.

Smaller stowaways like mice typically escape the conservationists’ wrath, and between 2001 and 2005, twenty-five times less money was spent on dealing with them. After all, mice are smaller and less opportunistic than rats and pose very little threat to seabirds.

Or at least that was what scientists used to think. In 2005, Ross Wanless, Peter Ryan and colleagues from the University of Cape Town found that on Gough Island in the south Atlantic, mice had developed sinister appetites. They were eating the chicks of local seabirds alive (see image below).

Infrared footage shows mice feeding on a chick.

House mice were introduced to Gough Island, now a World Heritage Site, in 1888 and are the only introduced mammals there. They share the island with large seabird colonies including many endangered species, and the last breeding populations of the Tristan albatross and the Atlantic petrel.

The mice seemed to be co-existing peacefully until the turn of the millennium, when some of the seabirds started experiencing massive breeding losses.

Wanless investigated and by watching about 300 nests, he found video evidence that the mice have developed a taste for albatross, petrel and shearwater chicks. They were attacking and eating chicks up to 300 times their weight, and often en masse.

Albatross chicks are not defenceless and will often ward off much larger avian hunters like the sub-Antarctic skua or the southern giant petrel. But they have also been spoilt through an evolutionary history free of mammalian dangers. The chicks have no idea how to react to mice, let alone defend themselves, hapless and helpless.

To save endangered birds like the albatross, ALL introduced predators must be dealt with.In fact, Wanless describes the mice as parasites rather than predators. They often don’t kill the chicks outright but slowly feed from open wounds over the course of days.

Typically, 60-75% of Tristan albatross young survive their first year. But thanks to the voracious mice, only 27% now do so on Gough Island. As a result, the population of this already vulnerable bird has crashed by over a quarter since the 1960s.

The birds of Gough Island will clearly need some assistance. Meanwhile, Wanless is sounding the alarm for other islands where introduced mice roam free.

On islands where they are not alone, larger introduced predators like cats or rats may be helping to keep their numbers down. The danger then, is that when conservationists get rid of these larger problems, they may unwittingly unleash a smaller foe on the native animals.

This very situation seems to be playing out on Marion Island in the South Indian ocean. In the 1990s introduced cats were finally eradicated from the island, leaving mice as the only mammal aliens around.

And sure enough, Ryan has found that several wandering albatross chicks have died of wounds consistent with mouse attacks. These attacks could be much more widespread than we had realised.

The message is clear – eradication programmes for introduced animals should target all potential predators, whether big or small. As in the case of sharks and scallops dealt with elsewhere in this blog, the removal of top predators can often doom animals at the bottom of the food chain by releasing hunters in the middle tier.

Reference: Wanless, Angel, Cuthbert, Hilton & Ryan. 2007. Can predation by invasive mice drive seabird extinctions? Biology Letters doi:10.1098/rsbl.2007.0120

Corals survive acid oceans by switching to soft-bodied mode

Biologists fear that the world’s beautiful coral reefs may be early victims of climate change, succumbing to the increasing acidity of the planet’s oceans. But new research provides a small glimmer of hope, by showing that corals may be able to weather the upcoming storm by shifting to a temporary soft-bodied lifestyle.

Climate change is not just about surface warming and glacial melting. The carbon dioxide that human activity is pumping into the atmosphere also dissolves in the world’s oceans, slowly increasing their acidity over time. And that spells trouble for corals.

Corals, like this brain coral, find it harder to build their shells in acid water

Corals may seem like immobile rock, but these hard fortresses are home to soft-bodied animals. These creatures – the coral polyps – build their mighty reefs of calcium carbonate using carbonate ions drawn from the surrounding water.

But as the water’s pH levels fall, these ions become depleted and the corals start to run out of their chemical mortar. The upshot is that in acid water, corals find it hard to build their homes.

Scientists have predicted that if carbon dioxide levels double, the reef-building powers of the world’s corals could fall by up to 80%. If they can’t rebuild quickly enough to match natural processes of decay and erosion, the reefs will start to vanish.

Now, Maoz Fine and Dan Tchernov from the Interuniversity Institute of Marine Science, Israel, have found that they have a way of coping with homelessness.

They grew some fragments form two European coral species under normal Mediterrenean conditions, and others in water slightly more acidic, by a mere 0.7 pH units.

In acid water, corals lose their shells and live as soft-bodied polyps.Those that spent a month in the acidic tank were quickly transformed. The skeleton dissolved and the colony split apart. The exposed and solitary polyps, looking like little sea anemones, still remained attached to rocky surfaces. When the going gets tough, the tough clearly go soft.

Even without their protective skeletons, they survived for over a year and seemed to be going about business as usual. They thrived, they reproduced normally and they still kept the symbiotic algae that allow them to produce energy through photosynthesis.

And when they were put back in normal conditions, they readily gave up their independence and re-formed both colonies and hard shells.

Fine and Tchernov’s findings suggest that corals may be able to survive upcoming climate changes by adopting soft-bodied, free-living lifestyles. And there is evidence that they have used this trick before.

The species supported by coral reefs may die off if the corals switch to a soft-bodied life.The hard shells of coral reefs fossilise easily, but the fossil record still has large gaps where no reefs are found. These may represent periods of time when corals were biding their time in their soft-bodied phase instead.

But while this new discovery is cause for hope, it should not be cause for complacency. Even though the corals themselves may persist in another guise, the vast diversity of species that depend on them may go for good if their reefs disappear.

More about corals: 
Bleached corals recover in the wake of hurricanes
Hope for corals – swapping algae improves tolerance to global warming

More about the effects of climate change: 
Icebergs are hotspots for life
When the heat is on, male dragons become female
Climate change responsible for decline of Costa Rican amphibians and reptiles

Reference:  Fine and Tchenov. 2007. Scleractinian coral species survive and recover from decalcification. Science 315: 1811.

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Shark-hunting harms animals at bottom of the food chain

Overfishing has disproportionately reduces the numbers of the ocean’s ‘apex predators’ and large sharks are disappearing particularly fast. Their absence allows their prey to flourish and the consequences of that can be disastrous for animals at the bottom of the food chain, and the humans that depend on them.

On the surface, plummeting populations of sharks do not seem like much cause for concern for humans or, for that matter, other sea life. But this simple viewpoint relies on splitting animals into two groups – predators and prey.

The sand tiger shark - one of the victims of overfishing.In practice, this distinction is far too crude. Too put it bluntly, there are predators and there are predators. Those at the top kill those in the middle, and stop them in turn, from killing those at the bottom. As the old saying goes, the enemy of my enemy is my friend.

The rise in shark fishing is mainly driven by a growing market for their fins. Sharks’ fins soup is a delicacy in China, which is utterly ludicrous given that the fins themselves are tasteless and merely add texture.

China’s strong economy has put this expensive treat in the range of the expanding middle classes and the world’s sharks are paying the price for it.

Ransom Myers from Dalhousie University, Halifax, decided to study the effects of declining shark numbers by analysing a uniquely comprehensive shark census taken over the last 30 years on the American eastern seaboard.

In these waters, several shark species have all but vanished since 1972, including 99% of the bull, dusky and smooth hammerhead populations.

And because fishing expeditions tend to catch larger individuals, the average size of the survivors has plummeted. Mighty animals like the tiger and black-tip sharks are now up to half as long as they used to be.

The hammerhead shark helps to control numbers of bottom-dwelling predators like rays and skates.Unsuprisingly, as the sharks declined, their prey benefited. Great sharks mainly hunt smaller predators, including their close relatives skates, rays, and indeed, smaller sharks, whose numbers surged in their absence.

The cownose ray, for example, is now ten times more common than it was in the mid-70s.

And here’s where the domino effects begin.

It turns out that large sharks inadvertently carry out a sort of protection racket for animals at the bottom of the food chain.By taking out the mid-level predators, they prevented these lesser hunters from decimating stocks of small fish and invertebrates.

The cownose ray feeds mainly on shellfish like scallops, clams and oysters. In the 80s, their small numbers made little dent on the local scallop population which sustained the economies and stomachs of local seaside towns.

In 1996, the ray explosion started to spell the end for the scallops. By 2004, the local North Carolina scallop fisheries which had thrived for centuries were forced to close and remain closed to this day. Little did the locals imagine that the disappearance of dangerous sharks from their waters could have such strongly felt economic consequences.

The ludicrous demand for shark’s fin soup will wreak irrevocable damage on oceanic ecosystems.This is far from an isolated incident. In Ariake Sound off Japan, shark fishing is particularly intense, and a booming population of long-headed eagle rays has decimated shellfish populations just like their cownose cousins in the Atlantic.

This is one of the first times that the removal of apex predators has been so thoroughly studied in the ocean. On land, the consequences are well-known.

Just last year, Australian scientists found that in some areas, persecution of the local top dog – the dingo – has allowed introduced predators like cats and rats to kill off up to two thirds of ground-dwelling mammal species.

As for the great sharks, the responsibility for preserving these great animals lies with the only predators they themselves face – the fishermen who kill them, and the Asian restaurant-goers who create the demand for their fins.

Surely, the price of irrevocably altering an ecosystem is too high to pay for the right to eat textured soup?

Reference: Myers, Baum, Shepherd, Powers & Peterson. 2007. Cascading effects of the loss of apex predatory sharks from a coastal ocean. Science 315: 1846-1850.

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Related posts on conservation and introduced animals:

The fox and the island: an Aleutian fable
Farmed salmon decimate wild populations by exposing them to parasites
Attack of the killer mice – introduced rodents eat seabird chicks alive

Christmas special – Virgin birth by Komodo dragons

A virgin birth is a key part of the Christmas story. Now, scientists have found that two Komodo dragons in English zoos have done the same. This ability helps dragon populations to recover in the wild, but it may push the remaining few closer to extinction.

According to Christian lore, Mary gave birth to baby Jesus without ever having had sex with Joseph. A biologist might describe this with the unwieldy word ‘parthenogenesis’, the Greek version of the more familiar term ‘virgin birth’(‘parthenos’ means virgin, and ‘genesis’ means birth.)

The New Testament aside, shunning fertilisation and giving birth to young through parthenogenesis is rare among higher animals, occurring in only one in every thousand species. Nonetheless, in a few short weeks, eight more virgin births are expected in the English town of Chester. The mother is called Flora, and she is a komodo dragon.

The Komodo dragon - world's largest lizard and virgin motherKomodo dragons are an endangered species in their island homes of Indonesia. Fifty-two zoos around the world co-operate in a dedicated breeding programme that aim to boost the natural populations of these largest of lizards.

In Europe, only two female dragons, both living in England, are sexually mature. One of these, Flora, lives at Chester Zoo where she has laid a clutch of 25 eggs despite never having been kept with a male.

Three of Flora’s eggs tragically collapsed while they were being incubated, but this provided Phillip Watts and colleagues from the University of Liverpool to trace their origins. They analysed the genetic make-up of the lost eggs using genetic fingerprinting and found that their genomes matched those of their mothers.

Children born through sex have two copies of every gene, one inherited from their father and one from their mother. But in the case of Flora’s babies, all of their genes were identical, suggesting that they all came from Flora alone.

Komodo dragon hatches after virgin birthWatts found a similar situation in London Zoo, where a late female called Sungai had given birth to four healthy dragon-lings (see left, image courtesy of Ian Stephen/Nature), over two years after she lost contact with a male.

Scientists had suspected that the babies were the result of sperm that Sungai had stored during that time, but genetic tests confirmed that she was the sole parent.

This double-sighting of parthenogenesis in Komodo dragons suggests that this unusual strategy is not so unusual in these lizards. It could even be used to help populations weather hard times.

Komodo dragons have Z and W chromosomes, rather than our Xs and Ys and in their case, it is the ones with a matching pair who are males (ZZ or WW), and the ones with a dual set who are females (WZ). As a result, parthenogenetic dragons are always male and when populations dwindle, they can kick-start numbers by mating with their own mothers.

This strategy could cause large problems for conservationists. By causing all an individual’s gene pairs to be identical, parthenogenesis achieves what inbreeding usually takes generations to do.

In rare cases, it could help struggling populations to recover, but if dragon numbers become so small that parthenogenesis becomes the norm, reduced genetic diversity could push the species further towards extinction

Zoos need to take heed as well. Females are usually kept apart from males, who are transferred between zoos to act as reptilian studs. This reduces the risk of aggression on the part of the larger males, but it could lead to a excessive number of virgin births.

Clearly, the key to saving this magnificent animal is more research into how best to account for its new-found ability, and breed a healthy diverse population.

More about animal sex and reproduction: 
Butterflies evolve resistance to male-killing bacteria in record time 
When the heat is on, male dragons become females
Chimerism, or How a marmoset’s sperm is really his brother’s
Aphids get superpowers through sex

Reference:  Watts, Buley, Sanderson, Boardman, Ciofi & Gibson. 2006. Nature 444: 1021-1022.

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Farmed salmon decimate wild populations by exposing them to parasites

Salmon migrations serve to protect newly hatched youngsters from the parasites that afflict their parents. But salmon farms undermine this protection and jeopardise wild stocks by exposing young salmon to large numbers of parasitic sea lice.

The next time you buy salmon from your local supermarket, think about the hidden costs in each succulent fillet. Compared to wild fish, farmed salmon is far less likely to burden your wallet. But by buying it, you may be placing a much larger burden on the environment. Fish stocks around the world are declining due to over-fishing and ‘aquaculture’ – the farming of fish – was originally thought to help. But farming brings with it a host of ecological problems.

Wild salmon suffer fewer parasites than their farmed cousins. If the farmed fish are meat-eaters, as salmon are, they must be fed on the proteins and oils of wild fish, which does nothing to alleviate the stress on wild populations. Domesticated farmed fish are also genetically different to their free counterparts, and escapees risk spreading their genes and replacing local genetic diversity.

But the biggest and most immediate problem may be to do with the spread of parasites. Large, crowded and trapped animal populations are an easy target for parasites, and salmon farms are no exception. Farmed salmon are often infested with sea lice, parasitic relatives of prawns and shrimp, that cause direct damage, starve their host and increase vulnerability to disease. But the real problem comes when infected farmed salmon pass their parasites onto wild fish.

Martin Krkošek and colleagues from the University of Alberta believe that salmon farming may be disrupting behaviour that evolved in salmon to protect their young from parasites.

Newborn salmon are especially vulnerable to parasitesSalmon are known for their massive and demanding migrations in order to mate and lay eggs. Because of these treks, the young salmon enter the ocean several months before the adults and their parasite passengers return. In this way, the youngsters gain precious months’ respite from infections during which they can develop unhindered. It’s the same strategy that human parents use when they move to the country to raise their children in safer surroundings.

But this safe period is shattered if the ocean is crammed with lice-ridden farmed populations. Across the North Atlantic from Canada to Norway, wild juveniles are being infested with sea lice. The farms are providing the lice with new routes for infecting even more hosts, and the young salmon are not ready for them.

To adults, sea lice are irritating but tolerable, but to the much smaller young, carrying more than two lice is always lethal. Not only do they take up valuable nutrients the juveniles need to grow but they make them more vulnerable to predators and weaken their immune systems.

Krkošek analysed data on salmon and lice populations off the western coast of Canada and revealed disturbing trends. The lice were decimating many local populations of salmon, killing up to 95% of juveniles in some regions.

As aquaculture continues to spread, this study provides us with a harsh reality check and consumers around the world have the power to reverse the trend by protesting with their money. Choosing wild fish over farmed varieties sends a message to the fishing industry that the benefits of buying cheaper fish are outweighed by the costs to wild populations.

Hope for corals – swapping algae improves tolerance to global warming

Corals are under severe threat from climate change as higher temperatures cause them to lose the algae that provide them with energy. But salvation may come in the form of a newly discovered ability of corals to swap their algal partners with strains that can take the heat.

Among all of the world’s animals, the two which have built the largest settlements could not be more different. The champions, humans, are intelligent and mobile, rapidly adapting to new conditions with technology and ever-changing strategies. In contrast, the runners-up, corals, seem unchanging and immobile, spending their lives ensconced in their impressive but stationary reefs. But it now seems that corals may have to adapt quickly in the face of looming extinction, ironically, brought about by humans.

Coral reefs are a haven for wildlifeCorals are hugely successful animals. Their reefs have endured across millions of years and today, they cover an area of 280,000 square kilometres, larger than the entire United Kingdom. Their success depends on a partnership with a group of algae called zooxanthellae. Over a million of these lodgers can live in a single cubic centimetre of coral, and they provide their landlords with both colour and energy through photosynthesis.

Despite their benefits, the algae are expensive to maintain. During periods of environmental stress, the corals eject them to make ends meet, losing their colour in the process. These ‘bleached’ corals (below) are free to regain their partners at easier times, but if conditions don’t improve, they die.

Bleached and damaged coral

This is the doom that they now face as global warming threatens to send oceanic temperatures soaring to record levels. The existence of the corals and the biological riches they support is under severe threat. But new research from by Ray Berkelmans and colleagues at the Australian Institute of Marine Science shows that some corals may be able to buy themselves some extra time by swapping their algal partners.

There are 8 different lineages of zooxanthellae (labelled A to H) and it is becoming increasingly clear that how a coral reacts to its environment depends on which of these groups it harbours. In particular, corals with group D algae seem to be particularly good at dealing with high temperatures, and this might prove to be their salvation.

Berkelmans tested this idea by transplanting 22 colonies of the stony coral (Acropora millipora) from a cool inshore reef on the eastern coast of Australia, to a warmer bay about 400 miles away. The colonies contained group C algae, and within half a year, they had all bleached and seven had died. But a few months later, about half of them had recovered and regained their colour. Every single survivor had replaced their partners with those from group D.

Further experiments revealed that the corals’ ability to tolerate temperature was based almost entirely on their choice of partners, with their own biochemistry had no detectable effect. In this partnership, the algae proved to be the weakest link. The key difference between the various groups lies in the membranes of their chloroplasts – their in-house photosynthesis factories. Those that can take the heat have membranes that are stable across a larger range of temperatures.

It isn’t clear from this study alone whether the ability to evict less hardy tenants is widespread among coral species, or even among other populations of stony coral. Even if it is, it may not be enough. Berkelmans found that corals that made the swap could tolerate temperatures about 1-1.5°C higher. With the temperatures of the world’s oceans set to increase beyond that, the corals are living on borrowed time.

We can only hope that this newly discovered ability of corals to rapidly adapt to environmental change gives us enough time to curb carbon emissions and halt climate change.

More about corals: 
Bleached corals recover in the wake of hurricanes
Corals survive acid oceans by switching to soft-bodied mode

More about the effects of climate change: 
Icebergs are hotspots for life
When the heat is on, male dragons become female
Climate change responsible for decline of Costa Rican amphibians and reptiles
Reference: Berkelmans & van Oppen. 2006. Proc Biol Sci 273: 2305-2312.

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