Frog-attacking fungus flourished before mass extinctions

Mountain yellow legged frogs of the Sierra Nevada might join the list of species that have disappeared due to the fungal pathogen B.d. / Flickr: USFWS Pacific Southwest Region

By John Upton

Scientists had never encountered anything like it.

Discovered in the late 1990s by researchers trying to figure out why frog populations were disappearing around the world, Batrachochytrium dendrobatidis, or B.d., has already wiped out perhaps 200 to 300 amphibian species. It has shaken ecosystems, starving birds and other frog eaters and allowing insects to run rampant.

“We have something the world has never seen before,” Vance Vredenburg, a biology professor at San Francisco State University who specializes in amphibians, told me earlier this year. “It’s jumping from species to species to species.”

The recent discovery that chytrid was present in New England in the 1960s, three decades before the disease’s effects were noticed, points to the alarming possibility that the die-offs are the result of worldwide environmental degradation.

B.d. is a type of chytrid — a member of the most primitive division of fungus: Chytridiomycota. Toadstools, molds and all of the other forms of fungus evolved from chytridiomycotes. Chytridiomycotes today are the smallest and simplest type of fungus, but these wily grandfathers still pack one helluva punch.

Before a frog is infected, it is hunted down by swarms of tiny chytrid zoopores that propel themselves through the water by flapping their tail-like flagella. The pathogen changes shape and burrows into the frog’s skin, which it consumes while it creates more zoospores, causing the frog to grow more layers. Many species can tolerate the parasites at low doses, but once a frog’s skin is infected with enough of the fungus it will go into cardiac arrest, its electrolyte levels thrown out of balance and its tiny heart stopped. (Weirdly, some species, including the American bullfrog, appear completely immune.)

“We find literally hundreds, and tens of thousands — I’ve seen it myself — dead animals on the shorelines of lakes,” Vredenburg said.

Research led by University of California, Berkeley ecologist Jamie Voyles helped explain how the fungus kills. What’s less clear is why it apparently started to cull amphibians all around the world at about the same time.

B.d. under a microscope / Flickr: AJC1

Kathryn Richards-Hrdlicka, a doctoral candidate at the Yale School of Forestry and Environmental Studies, took samples from 10 species of amphibians preserved in formalin at the Peabody Museum of Natural History. She reported Tuesday in the journal Methods in Ecology and Evolution that the fungus was infecting frogs in New England as long ago as 1968, the year in which one of the oldest of the studied specimens was collected.

“It’s possible dieoffs did happen back then and no one noticed, although die-hard herpetologists around here tell me someone would have noticed,” Richards-Hrdlicka told me. “I think it’s possible that when B.d. came to New England, it may have wiped out the more susceptible lineages or gene pools and what we’re left with today are those gene-pool winners.  That may explain why I can pick up 10 frogs here and three to four of them will be infected, with light zoospore loads, and show no signs of infection.”

Alternatively, rampant world trade could have brought two chytrid strains into contact that merged to spawn a super pathogen, as other B.d. researchers have hypothesized.

But Richards-Hrdlicka also said that the changing environmental conditions facing all species around the world right now might simply make frogs more vulnerable to the chytrid than they were in the past.

And there’s the rub. When frogs were disappearing without explanation in the 1990s, many speculated that the chordata class amphibia was acting like a canary in a coal mine, dying off before other types of animals because they are so sensitive to their environment.

The discovery of B.d. muted that suspicion, but now we know that B.d. was present long before these prominent collapses. Previous studies showed it was lurking in Africa in the 1930s.

Fungus is the great decomposer. When animals and plants are stressed, their defenses weaken and they can be eaten alive by fungus, which treats its prey as though it is dead flesh awaiting decomposition. So perhaps the mystery of the disappearing frogs really can be traced back to just about everything that is out of whack with our environment: Climate change, pesticides, habitat loss, water diversions, water degradation, air pollution, you name it.

Scientists had never encountered anything like B.d.

Until 2006.

That’s when bats in a cave in New York started dropping dead from white nose syndrome. Since then, the disease, which is caused by a type of soil fungus that chews through the mammals’ wings, has spread rapidly west, killing an estimated 7 million hibernating bats in just six years.

“That’s really similar,” Vredenburg said.

Arctic trees could heat the planet

By John Upton

Trees and shrubs suck water up from the earth and into their leaves through super-thin straws in their trunks called xylem. When sunlight hits a leaf, it causes some of that water to evaporate, which in turn draws more water up from the roots through the xylem. This solar powered plumbing system keeps plants hydrated, allowing them to combine carbon dioxide from the atmosphere with water from the soil to create sugars essential for their growth. This process of photosynthesis also releases waste oxygen, which is breathed by animals and fungi.

Tundra swans migrate north to breed in Arctic tundras / Flickr: chiptape

But the system starts to fall apart when temperatures drop below freezing and the water turns to ice. Some plants produce antifreeze, and some have evolved to seize on short growing seasons when melted water is briefly available, but most simply cannot survive in the Arctic or Antarctic. Either the frozen water is too rigid to move through the xylem, or water freezes and thaws inside the plant, creating deadly bubbles that wreck its insides.

That’s the main reason that tundras are so barren — water in the soil is often locked up as ice that is useless to most plants, especially to tall trees.

As tundras heat up and ice wanes, forests are blooming in new places. Logically, one would expect these new and expanded forests to slow climate change by sucking up the atmosphere’s burgeoning carbon dioxide supplies and turning them back into oxygen.

But a new study published in the journal Climate Nature Change suggests that such logic might not prevail. That’s because the soils of tundras are home to vast reservoirs of carbon that could be stirred up and spewed back into the atmosphere by the return of the forests.

The researchers compared carbon levels in the heathlands of tundras in northern Sweden with those in nearby birch forests, which are replacing the heath as Earth heats up. They discovered that the amount of carbon stored in the low-lying heath vegetation and in the soil beneath it exceeded the amount stored in the forests’ plants and soil.

“Counterintuitively,” the researchers wrote in the paper, “increased plant growth in the European Arctic could result in C (carbon) being released to the atmosphere, accelerating climate change.”

To explain this counterintuitive result, the researchers found that frenetic plant activity in birch forests during the summer growing season triggered the decomposition of old organic matter in the soil, causing the ecosystem to leak more carbon than it captured.

Lead researcher Iain Hartley, a geography lecturer at the University of Exeter, warned that more studies are needed in a wide range of Arctic environments to determine whether expanding forests will indeed exacerbate global warming. (Unlike many other arctic tundra environments, those studied by the researchers lacked a permafrost.) But the findings point to that as a major risk.

“At the moment, the results are relevant to a particular change in vegetation,” Hartley told me in an email. “There is a lot of further study required to try and work out how carbon storage will change as forest colonises tundra in different areas of the Arctic.”

Our ape brethren — some kill, some love

By John Upton

Five to seven million years ago, as the climate cooled around them, our ancestors began to shy away from some of their hitherto ilk. The forefathers of ourselves and of the neanderthals stopped sleeping with the foremothers of the bonobos and the chimpanzees, and vice versa. We went our separate evolutionary ways.

A female bonobo. All she needs is love. / Flickr: Princess Stand in the Rain

While wanderlust scattered our predecessors around the world, the other apes remained exclusively in Africa. Some 2 million years ago, the African landscape was cleaved by a new cascade — the Congo River. Unable to cross this vast waterway, the other apes split into two species. The bonobos lived on the river’s south; the chimpanzees to its north.

With the extinction of the neanderthals 30,000 years ago, these two species of apes became our closest relatives. We share 98.7 percent of our genes with each of these species. Bonobos and chimps, meanwhile, share 99.6 percent of their genome with each other.

But those tiny genetic divergences belie dramatic differences in behavior that developed as the bonobos and chimps evolved into independent species.

A male chimpanzee. Natural born killer. / Flickr: Rickydavid

The chimpanzees developed and refined the darkest sides of the human character. They rape, they murder, they form gangs and posses that fight deadly battles.

The bonobos, meanwhile, came to adopt our make-love-not-war traits. They frolic and revel in merrymaking from the time they are babies until they die. They live in peaceful matriarchal societies. And they freely sleep with multiple partners to bond and have fun — including with same-sex partners.

The genetic differences and similarities between the three ape species were announced this week in the journal Nature by an international team of scientists after they sequenced a bonobo’s genome for the first time. Human and chimpanzee genomes were sequenced previously.

But the new genetic data doesn’t reveal why the two sides of the human character are divided so dramatically between our two closest relatives. The researchers speculate that our shared ancestor may have exhibited the entire spectrum of behaviors, just like us.

“Chimpanzees and bonobos each possess certain characteristics that are more similar to human traits than they are to one another’s,” the researchers wrote in the paper. “No parsimonious reconstruction of the social structure and behavioural patterns of the common ancestor of humans, chimpanzees and bonobos is therefore possible. That ancestor may in fact have possessed a mosaic of features, including those now seen in bonobo, chimpanzee and human.”

The Congo River is the world’s deepest river. Flickr / United Nations Photo

Was Azaria Chamberlain killed by a native or invasive dog?

By John Upton

Australia’s legal system exonerated Lindy Chamberlain of infanticide this week, again, 32 years after a dingo ran off with her baby. A basis of the prosecution was always the notion that dingoes don’t eat babies. Ergo, prosecutors argued, the mother’s nightmare story was fabricated to cover up her own hideous deed while camping at Uluru.

A dingo at Fraser Island, Queensland, where a four-year old girl was attacked in 2007, helping confirm that dingoes are capable of attacking kids. Flickr: ogwen

Perhaps Chamberlain’s legal nightmare could have been avoided if the powers that be had listened more closely to the Pitjantjatjara people. The traditional stewards of the land where two-month old Azaria was hunted down know dingoes well. They reportedly never doubted that a dingo was capable of such ferocity. Similar attacks since have shown they were right.

The seclusive canines remain a mystery to most people. Scientists cannot even agree on whether the predators should be considered a native species in Australia. That’s because they were introduced several thousand years ago by seafarers sweeping south through Asia.

Those who argue that dingoes are a native species point out that they have struck an ecological balance with the environment.

University of New South Wales researchers set up a test they thought would reveal whether dingoes should be considered native. They monitored the activity of rabbit-like bandicoots in suburban backyards, some of which were home to pet dogs and some of which were not. Because the nocturnal bandicoots avoided yards that contained dogs during the day, they concluded that the creatures have evolved to instinctively identify the threat posed by dogs through thousands of years of dingo interactions. That suggests to them that dingoes have become a native species.

“The logical criterion for determining native status of a long-term alien species must be once its native enemies are no longer naïve,” the scientists, Alexandra Carthey and Peter Banks, wrote in a January paper published in the journal PLoS ONE. “Our study suggests that these bandicoots may no longer be naïve towards dogs.”

On the other hand, the foreign and invasive nature of the species in Australia is also clear.

When dingoes arrived, they did what invasive predators do best: They chewed through the wildlife and condemned native species to extinction. Their arrival coincided with the extirpation from mainland Australia of the thylacine, a dog-like predator that’s better known as the Tasmanian Tiger. The species survived in Tasmania, an island that remained inaccessible to the dingoes, until the 20th century when the last sad specimen died in a zoo.

Thylacines were Australia’s largest predators until the dingoes arrived. Recent research by scientists at the University of New South Wales and the University of Sydney revealed that the female thylacines of mainland Australia were considerably smaller than the dingos, making them vulnerable to direct predation by the continent crashers.

The dueling species also differed in a way that highlights dingoes’ alienness. Like almost all other native Australian mammals, thylacines were marsupials. (The other native Australian mammals are monotremes — egg-laying echidnas and platypuses.) Marsupials give birth shortly after conception and rear their young on a teat in a pouch. Dingoes, on the other hand, are placental mammals. If dingoes are to be considered a native species, then they are the continent’s only native placental mammal.

Dingoes can be found nowhere in the world other than in Australia. They have evolved into a distinct subspecies of the grey wolf, although that distinction is blurred by interbreeding with pet and feral dogs brought by more recent European settlement.

So if dingoes aren’t native to Australia, then they can be considered native to nowhere. They are either a native Australian species or a homeless wolf on a milleniums-long walkabout.

Either of which sounds like an appropriate description to me.

Uluru, a famous sandstone rock in the Northern Territory where baby Azaria was snatched in 1980 / Flickr: LKEM

Algae stole gene to unlock ice

By John Upton

Polar bears are spectacular inhabitants of sea ice, which is an inhospitable habitat that grows and retreats around the poles with the seasons. But something else lives on the harsh terrain that gets much less attention: Algae.

Algae combines ocean nutrients with energy from the sun to provide whales and other herbivores with a critical source of food, particularly in the early spring.

But how did algae come to survive such challenging conditions? Scientists looking for an answer to this question discovered that some evolutionary larceny was necessary before algae could move into the icy digs.

Effect of algal ice-binding proteins on ice / PLoS ONE

Ice-dwelling algae has a special tool that allows it to live in the uninviting climate. These algae ooze gelatinous ice-binding proteins known as extracellular polymeric substances. The proteins manipulate the salt content and pore structure of the ice as it grows around the algal bloom, making the teeth-chattering microclimate all the more accommodating.

Scientists analyzed the ice-binding proteins produced by three species of sea ice-dwelling algae and reported last month in the journal PLoS ONE that the structure of the proteins was “completely incongruent” with the evolution of algae. That strongly suggested that the genes for producing the proteins came from somewhere else.

Species can hijack genes from other wildlife through a number of processes that scientists call horizontal or lateral gene transfer. Viruses are sometimes involved, but not always.

The ice-binding proteins closely resembled proteins produced by bacteria, leading the researchers to conclude that the algae initially stole the gene from bacterial neighbors.

The scientists sampled similar proteins produced by bacterium at the bottom layer of Antarctic sea ice and discovered that nearly half of its amino acids matched those of the special proteins produced by nearby algae.

“Our results strongly suggest that the [ice-binding protein] genes of sea ice diatoms were acquired from bacteria, possibly in separate events,” concluded the researchers. “The acquisition of these genes was an essential factor in allowing the diatoms to expand their range to polar sea ice.”

Sea ice and some icebergs off eastern Greenland / NASA

Fungus thriving, worms waning, after BP oil spill

By John Upton

Fungus has a remarkable ability to thrive when the environment is stressed, allowing it to prey upon animals and plants when those forms of life are weakened. When the Permian period ended with a climate-changing bang 250 years ago, courtesy of volcanoes or perhaps a meteorite, soil fungus overwhelmed the world’s forests. Fungus diseases today are wiping out hundreds of species of frogs and millions of bats, not to mention entire forests.

New research shows that this mysterious kingdom of life is also thriving in the wake of the Deepwater Horizon oil spill.

Scientists studied microscopic life in polluted shoreline sands around Alabama. They compared their findings to the results of surveys taken before the spill and found a sharp reduction in the number and diversity of microscopic animals, replaced by a spike in fungus.

“Our data suggest considerable (hidden) initial impacts across Gulf beaches may be ongoing,” the researchers report in a June 6 paper in the journal PLoS ONE, “despite the disappearance of visible surface oil in the region.”

Tiny sediment-faring worms known as nematodes were heavily affected. Scores of different types of nematodes used to make their homes along the gulf’s floor and it shorelines. But the researchers discovered that these benthic communities are now hospitable for just a handful of nematode species, mostly scavengers and predators.

The fungus that has taken over the oily sand is dominated by species that have a knack for breaking down hydrocarbons. Fungus is the world’s great decomposer and perhaps things will return to normal after the gulf’s new microscopic rulers have converted BP’s disgusting mess into something a little more palatable for the displaced members of the animal kingdom.

Research results

Cross River gorillas caught on video

By John Upton

There are two species of gorillas — Eastern and Western, both of which live exclusively in Africa. Cross River gorillas are an extremely rare subspecies of the Western gorilla. Just 250 of the great apes are believed to live today.

In a world first, using a camera hidden in a tree, conservationists working in Cameroon’s Kagwene Gorilla Sanctuary shot video of eight of them traipsing down a jungle trail.

Wait or scroll through to the 38-second mark to watch one beat his chest and charge past the hidden camera in an apparent show of aggression and domination.

Illustrated ecology news.