Illustrated by Perry Shirley.

Stopping starfish virus ‘almost impossible’

By John Upton

Nearly 18 months into the worst marine epizootic that humanity has ever seen, scientists appear to have found the cause of death. A virus is being blamed for the mass die-off of starfish along North America’s western coastline. Sickened sea stars grow lethargic and their limbs start to curl. Next comes lesions and the shedding of limbs. The body deflates, then melts into puddles of slime and bone-like ossicles. More than a million starfish, coming from at least 20 species, have succumbed. Some local populations of the keystone predators, whose hunting prowess keep populations of plant grazers in check, have been decimated.

Hopes that the new diagnosis will usher forward a cure, however, are about as low as the deep-sea habitat of a brisingida.

Research described Sunday in Proceedings of the National Academy of Sciences blames the heretofore mysterious deaths on a densovirus — a type of virus that typically plagues crabs, shrimp and other invertebrates. The scientists gave the pathogen the name ‘sea star-associated densovirus,’ or SSaDV.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

The scientists discovered that loads of the densovirus were higher in sick starfish collected from the wild than in asymptomatic specimens. They also found that exposing lab starfish to the germ “consistently” induced the hallmark symptoms of sea-star wasting disease, while exposing specimens to heat-killed viruses remained healthy.

When the scientists turned their attention to ethanol-preserved sea stars collected as early as 1923, they discovered that the disease has been infecting starfish since at least 1942.

So why would it suddenly turn into such an ecosystem-rattling problem?

That’s just how viruses roll.

“This is the case for many viruses, including HIV and Ebola, which were present in populations since at least the 1930s but only became epidemics in the 1970s and 80s,” said Ian Hewson, an associate professor in Cornell University’s microbiology department, the leader of the recent research.

Perhaps the virus chanced upon a powerful genetic mutation. An improvement to the way it builds capsids, which are shells that protect viruses during their extracellular ventures, might explain its virulence boost.

Perhaps the manifest changes underway in the ocean, where pollution, carbon dioxide and heat are piling up, has weakened the victims’ natural defenses.

The scientists can’t say, yet, which of these factors is to blame. But they do note that large populations of starfish jammed into small habitats appear to be more vulnerable to outbreaks.

They point to a booming sunflower seastar population prior to the first large outbreak.

“We speculate that the current disease event has been exacerbated by an overpopulation of adult sea stars in the Salish Sea immediately prior to the current disease event,” Hewson said. “The Salish Sea was indeed the first population in which the disease was seen; it was noted in June 2013 on the Olympic coast. The first mass mortality occurred in the Vancouver region shortly thereafter.”

That suggests that preventing sea star populations from booming might help protect against future outbreaks. Given that it’s not clear why the Salish Sea population boomed, that’s a daunting task.

Assuming the scientists have accurately identified the cause of the wasting disease, how else could the discovery be used to squelch the current outbreak?

The answer to that question will not fill you with joy.

Infected mottled stars from Washington. Photo by Ian Hewson.
Infected mottled stars from Washington. Photo by Ian Hewson.

“Protecting sea stars in nature from an established pathogen, like the virus seen here, is almost impossible,” Hewson said.

Because the virus is so geographically widespread, Hewson said it would be unfeasible and impractical to remove and protect healthy sea stars. “Likewise, inoculating stars against the virus to build resistance would also not be feasible on a large scale,” he said.

Still, the benefits of finally finding the cause of the disease shouldn’t be understated. “The identification of the causative agent of sea star wasting disease enables accurate diagnosis and more effective management,” said University of Washington professor Carolyn Friedman, one of the new study’s coauthors.

For cheerier sea star times, let’s all tune out of reality for just a moment, and tune into the uninfected antics of Patrick — SpongeBob SquarePants’s friend .

Slug End of Road 2 bis

Where did all the bugs go?

By John Upton

Ever noticed that your car’s windshield is smattered with fewer bugs after long country drives than used to be the case? That’s good news for gas-station squeegee duties — but it’s foul news for the planet.

The world’s bug populations are crashing faster than a swarm of mosquitoes into a backwater bug zapper. And that has reverberating yet little-understood consequences for the species and ecosystems that rely on insects for food, pollination, pest control, nutrient cycling, and decomposition.

A Science paper dealing with the planet’s sixth great extinction, underway since 1500, warns that invertebrate species are faring even worse than vertebrates. Two-thirds of monitored bug populations have declined by an average of 45 percent. Their habitat is being destroyed, and they are being drenched with agricultural insecticides.

The July 25 paper was penned by an international team of researchers led by Stanford University’s Rodolfo Dirzo following an exhaustive literature review. The following chart from the paper shows the  percentage of species of insects in the orders ColeopteraHymenopteraLepidoptera, and Odonata that have declined by as much as 40 percent (shown in dark red) during just the past four decades.

bugs-declines-bThe next chart also includes data on Orthoptera, which includes grasshoppers and crickets.

bugs-declines-aVertebrate populations, meanwhile, have fallen by an average of a quarter, the researchers found. The largest of these species are faring the worst.

vertebrate-declines“In the past 500 years, humans have triggered a wave of extinction, threat, and local population declines that may be comparable in both rate and magnitude with the five previous mass extinctions of Earth’s history,” the researchers wrote in the paper. “This recent pulse of animal loss, hereafter referred to as the Anthropocene defaunation, is not only a conspicuous consequence of human impacts on the planet but also a primary driver of global environmental change in its own right.”

The problem of creepy-crawly declines could be worse than anybody realizes. Unlike charismatic mammals, very few invertebrate species, including lowly centipedes, slugs, spiders, and worms, come under the trained eyes of scientists or conservationists. Fewer than 1 percent of the 1.4 million described species of invertebrates have been assessed for threats by the International Union for Conservation of Nature, which maintains the Red List of Threatened Species. Of those few species that have been assessed, 40 percent were found to be threatened.

Lepidoptera, which includes butterflies, moths, and of course their caterpillar larval stages, are the best studied and monitored order of insects, and evidence suggests that their abundance has fallen by 35 percent worldwide. Lepidopteran species richness is nearly 8 times greater in undisturbed sites than in developed areas, and abundance appears to be 60 percent higher on average in near-pristine environments than elsewhere.

As bad as that might be, it appears that these plant-munchers, which metamorphose into nectar-sucking plant pollinators, are faring far better than lesser-studied orders of insects.

bugs-decline-c

Snails and their shell-less terrestrial gastropod mollusk cousins, the slugs, by sticky contrast, are among the least-well studied. These species may seem like mere pests to many gardeners, but they help break down organic material and they provide food for larger animals. Grasping how slug and snail populations are coping with the defaunation of the Anthropocene relies right now on little more than educated guesswork.

“We mentioned slugs as a point of reference regarding the fact that many groups of invertebrates have been very poorly studied in rigorous, quantitative ways and over long, consistent periods,” Dirzo told us.

Illustrated by Perry Shirley

“Given the fact that at least some species of terrestrial mollusks seem to do well in disturbed areas, I suspect several of them might not be so severely impacted and might be thriving,” Dirzo said. Then again, he added, “given their strong dependence on moist, relatively mild-to-cool habitats, climate disruption might have a strong, negative impact on them.”

Illustrated by Perry Shirley.

Wolverine wipeout

By John Upton

A warming world means a melting cryosphere, which is bad news for species that have evolved to thrive on ice and in snow. Polar bears made depressing history in 2008 when they became the first species to be listed under the U.S. Endangered Species Act solely because of threats from climate change. These sea ice-dwelling carnivores had appeared poised, until Tuesday, to be joined in their global warming-induced regulatory infamy by snow-burrowing wolverines.

Wolverines resemble small bears with bushy tails. They are also known as mountain devils, gluttons, caracajou, and skunk bears. They are the largest member of Mustelidae — a carniverous family of mammals that includes otters, badgers, weasels, and ferrets.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

While polar bears are a highly visible species, wolverines are enchantingly difficult to spot. This is despite their inhabitation of a broad swath of the Arctic that includes northern portions of Europe, Asia, and North America.  In North America, most the populations inhabit Canada and Alaska, although several hundred individuals are estimated to live in the contiguous U.S., mostly in the northern Rocky Mountains. These populations have recently been growing, yet fears over the future of snow in the Lower 48 had federal officials considering adding wolverines to the list of threatened species. On Tuesday, the U.S. Fish & Wildlife Service ruled against the proposed wolverine listing.

Wolverines breed more slowly than most mammals, making them especially vulnerable to breeding disruptions. Once a female reaches the age of three, she normally becomes pregnant every year — but most pregnancies are strategically aborted. That’s because it can take two years or more for the wolverine to forage enough carrion, fruits, and berries, and to hunt enough small animals and insects, to build up the energy reserves needed to raise a litter.

Once she is ready to rear a litter, the female adopts a very specific denning strategy — one that will make it difficult for the species to survive in the parts of its territories where snow becomes history. The wolverines dig their dens in deep snow, forming living spaces around logs and rocks that include tunnels, runways, and bedsites. There has never been a record of a wolverine denning in anything other than excavated snow. And whenever such a cave starts to melt, the wolverine mother abandons it.

“We have determined that habitat loss due to increasing temperatures and reduced late spring snowpack due to climate change is likely to have a significant negative population-level impact on wolverine populations in the contiguous United States,” U.S. Fish & Wildlife Service officials wrote in the proposal to list those populations as threatened.

“In the future, wolverine habitat is likely to be reduced to the point that the wolverine in the contiguous United States is in danger of extinction.”

At least one senior FWS official had been pushing the agency to reject the proposal, arguing that it relies too much on “speculation” about the future effects of climate change. The agency announced on Tuesday that scientists know “too little about the ecology of the wolverine” to list it as threatened or endangered at this time. The ruling “does not close door on this issue,” one official said.

It was this focus on uncertainties that was already making scientists who served on a panel that advised the government on the proposal hot under the collar.

“Myself and the other climate scientists on the panel are disappointed that they’re focusing on the uncertainty, and appear to be ignoring the aspects of science that are much more certain,” said Tim Link, a hydrology professor at the University of Idaho.

Wolverines and polar bears certainly aren’t the only species that will feel the heat as global temperatures rise. Dozens of species of coral might be added to the endangered species list because of the combined effects of disease, warming ocean temperatures, and ocean acidification. Like global warming, ocean acidification is caused by carbon dioxide pollution, which is produced by fossil fuel burning and by deforestation.

“From the history of the Endangered Species Act, if you look at the 1,500-plus species that have been listed, the overwhelming majority have not been listed because of climate change,” said Mike Senator, an attorney with the Defenders of Wildlife, which had been pressuring the government to list wolverines under the Act.

“It’s been the loss of habitat and other threats — but that’s not entirely surprising, given that climate change has been recognized as a relatively recent issue. We certainly expect that we’ll see more species listed, at least in part, because of climate change.”

Illustrated by Perry Shirley

Ocean reserves help with acidification

By John Upton

Our power plants and cars have pumped so much carbon dioxide into the atmosphere that the oceans are becoming more acidic. Something like a quarter of our carbon dioxide pollution dissolves into the seas, where it reacts with water:

CO2 (aq) + H2\leftrightarrow H2CO3 \leftrightarrow HCO3 + H+ \leftrightarrow CO32− + 2 H+

Those leftover hydrogen ions at the right of the equation add up. The hydrogen ion concentration at the surface of the world’s oceans has increased by 26 percent since pre-industrial times, leading to a pH decline of 0.1. That might not sound like much, but it has been enough to kill off billions of farmed shellfish and punch holes in the shells of wild sea snails.

Illustrated by Perry Shirley
Illustrated by Perry Shirley

Shellfish and corals are especially vulnerable to ocean acidification because they rely on calcium carbonate to make their shells and skeletons. Ocean acidification increases concentrations of bicarbonate ions while decreasing concentrations of carbonate ions — and these animals need calcium carbonate to produce their protective body parts.

Fish, meanwhile, are thought to be suffering neurological effects of acidifying oceans, while vast mats of algae are expected to flourish.

The good news is that populations of animals naturally adapt to changes in their environments — and evolutionary changes to help some species cope with ocean acidification are already underway. The bad news is that changes in oceanic pH levels might be happening too quickly for animals to adapt, threatening scores of marine species with extinction.

I asked Ryan Kelly, an assistant professor at the University of Washington’s School of Marine and Environmental Affairs, and a coauthor of a recent BioScience paper about acidification that I wrote about for Pacific Standard, whether we could do anything to help species accelerate the rate with which they evolve needed adaptations.

“‘Accelerating’ species’ evolutionary adaptations to acidification would mean either tweaking the heritability of traits — and it’s unclear whether this is desirable, or how to do it; or increasing the strength of selection — which would mean making the selective impacts of acidification worse than they already are,” Kelly said. “So I’m thinking that, in an evolutionary sense, you don’t want to accelerate adaptation.”

Is there anything that we can do?

“What you do want to do, in order to protect marine ecosystems as we know them, is to preserve the adaptive capacity of the species that make up those ecosystems. That means preserving the genetic diversity that exists within those species, so that when the selective pressures of acidification happen, there will be some variability in those species’ responses. When there’s no genetic diversity, you get no variability in response to selective pressure, and natural selection and evolution doesn’t really work.”

Which means that we need to expand and improve the globe’s network of marine reserves, banning fishing in some places, and giving species the best possible shot of surviving the storm of acidity that’s building around them.

“From a conservation perspective, measures that preserve existing genetic diversity safeguard the adaptive capacity of species and ecosystems. This means working to maintain large population sizes and not fragmenting habitats, which are common conservation measures.”

As U.S. Secretary of State John Kerry led workshops last month dealing with ocean acidification and other ocean health issues, President Barack Obama’s administration proposed sweeping expansions of marine reserves surrounding remote Pacific Ocean atolls. The move would limit fishing for tuna and other species, helping to protect top predators that are critical for ecosystem health, while also protecting smaller species that are killed as bycatch.

“This is an important step in trying to maintain the health of this region and, as a result, the surrounding areas in the Pacific,” said Lance Morgan, president of Marine Conservation Institute. “It will give us more resilience into the future. We’ll have to replicate this and do more work in other areas as well, but it is an important step.”

Meanwhile, the National Oceanic and Atmospheric Administration is planning to expand the boundaries of Gulf of the Farallones National Marine Sanctuary and Cordell Bank National Marine Sanctuary, both of which lie off the West Coast, where strong upwelling leads to especially severe rates of ocean acidification. Meanwhile, Kiribati recently announced that it would close an area the size of California to fishing to help wildlife recover.

Ocean acidification is not a major consideration in the creation of marine reserves, but it’s a growing threat against which the reserves can help populations of wildlife evolve natural defenses.

emu and ostrich

How are emus related to ostriches?

By John Upton

Which came first — the chicken or the egg?

It’s inside an egg that genes combine to code for an individual, so we’re going to go with ‘the egg.’ Next question, please.

Which came first — the ostrich or the emu?

Looking at pictures of these flightless birds, you’d be forgiven for mistaking them for kissing cousins. They’re both swift-footed birds with buns of feathers hitched high — alluring outfits that show off their slender legs and necks.

emu and ostrich
Illustrated by Perry Shirley.

But they’re not as closely related as they might at first seem.

Ostriches and emus are both ratites — members of a group of large flightless birds endemic to the Southern Hemisphere. Ratites were all thought to have descended from a common ancestor; examples of what scientists dub vicariance biogeography, or convergent evolution, in which members of once-conjoined populations become geographically separated, such as through the geological manifestation of a new river, gulf, or mountain, and then pursue their own evolutionary trajectories. In the case of ratites, they were thought to have gone their separate ways following the bust-up of Gondwana, from where their presumed ancestor was thought to have hailed.

Just a decade ago, in his book The Ancestor’s Tale: A Pilgrimage to the Dawn of Evolution, famed biologist and writer Richard Dawkins described ratites as a “truly natural” group. “Ostriches, emus, cassowaries, rheas, kiwis, moas and elephant birds really are more closely related to each other than they are to any other birds,” he wrote. “And their shared ancestor was flightless too.”

Dawkins’ statement reflected leading science from the time. But advances in molecular phylogenetics have since revealed the folly of longheld assumptions about ratite evolution. The apparent similarities between different species of ratites are now thought to have been the consequence of convergent evolution — the independent evolution of similar features by different species in far-flung places that inhabit similar ecological niches.

It seems that flightlessness just makes sense in the right environments. Research in recent years has revealed that selection pressures independently pushed the forebears of today’s ratites to shrink their wings, bloat their bodies, flatten their sternums, and evacuate the skies.

Several years ago, University of Florida researchers used BUCKy software to analyze the genomes of various birds, and found that the ratite family tree includes a surprising cousin — tinamous, an order of grouse-resembling birds from Central and South America. These birds spend much of their lives on the ground, but many of the species are perfectly capable of flying. The tanimous were found to be more closely related to emus then they were to ostriches, providing further evidence of the independent evolution of flightlessness in different ratites. The findings were published in the journal Systematic Biology:

(Credit: Systematic Biology)
(Credit: Systematic Biology)

“The independent evidence we obtained provided strong corroboration of the hypothesis that nonostrich paleognaths form a clade,” wrote the three scientists involved with the research in their paper. “This sharply alters our understanding of the evolutionary history of the flightless ratites by providing support for multiple losses of flight. It remains possible there was a single loss of flight early in paleognath history followed by a regain of flight in tinamous, but this is unlikely because the loss of flight appears to be a relatively easy transition for birds whereas the loss followed by the regain of flight has never been documented. The hypothesis that flight has been lost multiple times in the ratites suggests that some of the most distinctive morphological characters in ratites arose through convergent evolution.”

We asked one of the authors of the paper, Edward Braun, an associate professor in the university’s biology department, how this information and similar analyses could help answer our question. Which species is older — the emu or the ostrich?

Braun said that’s a tough question to answer; but he suggested a couple of alternatives, which he then answered.

“One valid question is, ‘When did ostriches start looking like ostriches, and when did emus start looking like emus?'” Braun said. “I suspect that, if the question is asked that way, the answer is, ‘About the same length of time.'”

“On the other hand, another way of asking the question is, ‘When did ostriches separate from other extant birds, relative to emus?’ The answer to that is clear. Ostriches have no close relatives. Ostriches separated from other birds a long time ago; probably in the Paleocene [66 to 56 million years ago], since there are middle Eocene fossils that are probably now extinct parts of the ostrich lineage. Emus are more closely related to rheas, kiwis, and quite close to cassowaries.”

Enjoy this fun video of emus and an ostrich playing with a motorized ball, which helps to reveal differences in the appearances of the species:

bilby

Easter Bilby protects Australia’s outback

By John Upton

Some Australian kids don’t believe in the Easter Bunny.

The clutches of chocolate and colored eggs hidden in the yards and living rooms of environmentally-aware households Down Under are deposited, through orifice unknown, by the Easter Bilby.

Browse the easter sweets selection in just about any Australian store right now and you’ll find foil-wrapped chocolate icons of the adorable outback-dwelling marsupials.

Rabbits are ravenous, fast-breeding, and destructive pests in Australia, where they were introduced by hunters and graziers during the 19th Century. The bare rabbit-resembling bilby, on the other hand, is a native Australian species that’s vulnerable to extinction. Celebrating the Easter Bilby helps Australian kids learn about the ecological importance of native mammals — while avoiding the awkward passions for invasive counterparts that the Easter Bunny can imbue.

bilby
Illustrated by Perry Shirley.

The beauty of the bilby lies in its relationship with Australia’s fragile, old, and nutrient-poor land. It digs through arid and semi-arid soils, bioturbing them, improving water drainage and reducing flooding and erosion. The digging helps spread seeds. It creates microhabitats for bugs and fungi. It turns over soils and helps with nutrient cycling.

From the Mammal Review paper by P. A. Fleming et al.
Mammal Review

The effect of native Australian diggers, such as bilbies, echidnas, and wombats, is “increased plant vigour and resilience, increased biodiversity and consequently improved ecosystem functioning,” scientists wrote in a Mammal Review paper published last year.

But Australian ecosystems have been ravaged during the past two centuries by introduced species, including rabbits, pigs, and camels, and by land clearing. The native diggers are hunted by introduced cats and foxes. Those pressures have helped push half of the nation’s digging mammals toward extinction, the researchers concluded following an exhaustive review of scientific literature. “[T]he loss of digging mammals has contributed to the deterioration of ecosystems,” they wrote.

Rabbits dig as well — but they apparently do not dig deep enough to produce the same benefits as bilbies. Previous research has shown that digging bilbies foster 80 percent more seedlings than do digging rabbits.

“When bilbies, bandicoots, and bettongs dig for food, their diggings are deep, roughly-conical pits which penetrate deep into the soil layers,” Murdoch University wildlife biologist Trish Fleming, one of the coauthors of the Mammal Review paper, told Wonk on the Wildlife.

“Rabbits dig shallower pits, which disturb a large area of the top soil layers. This would expose the soil to drying out, which means it’s less suitable for soil microorganisms or for new seeds.”

Then there’s the wee issue of rabbit plagues. Looking out across an affected Australian farm, the land can appear as if it is moving.

“Rabbits feed on soft shoots of plants, and then will dig up any vegetation within reach, including the roots and bark off trees.  In plague numbers, they wipe out any living plant material.  There are expanses of productive lands which have never recovered from plagues of rabbits,” Fleming said.

So go and get stuffed with caramel, Easter Rabbit. Aussies don’t need your type sniffing about in their gardens.

peacock

Here comes the peacockstepper

By John Upton

What’s hotter than a cutie in decadent clothes?

A cutie in decadent clothes — who can dance like no one is watching.

Sexual selection is a term coined by Charles Darwin to explain why some species have developed elaborately ornamental feathers and antlers — appendages that help woo mates. In humans, it has been argued that sexual selection pressures gave rise to facial hair and ample bosoms.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

The elaborate trains of peacocks are among the most classical examples of sexual selection. During breeding time, peahens will visit areas where peacocks vie for their attention with spectacular dances. The peacocks raise their trains in a semicircle and whip them around, sometimes leaning them over the judging peahen. They shake their tail feathers and perform a jig with their feet.

A peahen readied for an eye-tracking experiment. Photo by Jessica Yorzinski.
A peahen readied for an eye-tracking experiment. Photo by Jessica Yorzinski.

A team of researchers set out to try to figure out just what actually interests the peahens during these spectacular courtship displays. They trained captive peahens to wear a patch over one eye and an infrared eye-tracker on the other. Then they watched while peacocks wooed their ridiculously-attired subjects inside black-plastic enclosures that minimized distractions.

After analyzing the footage and data, the scientists realized something surprising. The peahens weren’t looking at the tops of the brightly colored feathers. They were watching the peacocks’ lower regions.

“Based on the scanpath of where the females are looking, you can see that their gaze is focused on the lower train — that is, the lower feathers as well as the legs,” Jessica Yorzinski, an evolutionary biologist who studies animal communication, told Wonk on the Wildlife.

what-peahens-watch

“The peahens may be assessing the width or symmetry of the peacock’s lower train and this could indirectly tell the peahens about the quality of that potential mate,” Yorzinski said. “For example, it’s possible that peacocks with more symmetrical trains produce peachicks that are healthier.”

So what’s the point of having such long and elaborate feathers if peahens are so interested in peacocks’ lower bodies? Yorzinski and fellow researchers explain their theory in a recent paper published in The Journal of Experimental Biology:

Even though we found that the peahens were primarily assessing the lower train, the upper train of the peacock may play an important role in courtship as a long-distance attraction signal in dense vegetation.

In The Descent of Man and Selection in Relation to Sex, published in 1871 (which the researchers awesomely cite in their paper), Darwin noted that peahens can appear coy and uninterested in males, despite the elaborate mating displays. Yorzinski and her colleagues helped explain this phenomenon by discovering that peahens spend more than two-thirds of their time scanning the environment for predators and the like, even as a beautiful peacock dances in front of them.

It’s nice to watch a beautiful dancer, but, from a peahen’s perspective, there’s not much point in finding an idyllically cute male if they’re going to be eaten before they get the chance to mate with them.

Illustrated by Perry Shirley.

Why fish need wood

By John Upton

Trees don’t just provide habitat for arboreal and terrestrial creatures — dead trees that have toppled over in shallow waters are critical for aquatic wildlife. Woody habitat in lake littoral zones provides shelter for fish. It also supports the growth of algae and the like, which are eaten by herbivorous fish and other critters.

As the globe warms and as aquifers are sucked dry, lake levels in many parts of the world are falling. And as a lake’s water level drops, semi-submerged trees that ring the lake’s shallows can be left high-and-dry. That can decimate fish populations — harming birds and other species that feed on them.

“Reduced lake levels generally decrease littoral habitat, which is critical to aquatic food webs,” wrote University of Wisconsin researchers in a recent paper published by the Canadian Journal of Fisheries and Aquatic Sciences. “Fishes across all trophic levels are known to rely heavily on littoral food sources, with littoral zones supporting 65% of the consumption by lentic fish communities and 57% of their body carbon.”

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

The scientists sampled fish from 2000 until 2005 and again from 2007 to 2009 in Wisconsin’s Little Rock Lake, which is in the Great Lakes region. Declining water levels in the Great Lakes, which is Earth’s largest body of fresh surface water, are a major worry for scientists.

During the monitoring period, drought led to a decline in water levels of a little more than a meter. That left three quarters of the lake’s woody habitat stranded on land. The following graphs from the paper show the close relationship between water levels and woody habitat:

lake-level

The sampling results painted a picture of an ecosystem in steep decline — a decline that the scientists linked to the loss of soggy wood.

Things got so bad during the drought that the scientists’ minnow traps started to come up empty.

“The rapid decline of the perch population was associated with the loss of available CWH [coarse woody habitat],” the paper states. “Perch first failed to appear in a trapping event in 2005, after only a 10% loss of CWH. No perch were detected in 2008 or 2009 after 58% and 72% of the available CWH had been stranded from the littoral zone.”

The loss of the perch was blamed on the declining water levels, with changed temperature and oxygen levels potentially contributing. A loss of food was also stated as a potential factor. As was the loss of spawning habitat and loss of shelter from predators due to the disappearance of woody habitat.

“Previous research has suggested the potential for predator–prey encounter rates to increase with reduced CWH, which would result in intense bass predation on perch. … [T]he severe depletion of the perch population might have been exacerbated by the relatively high densities of bass in Little Rock South, which initially increased with reduced lake level.”

Eventually, though, the largemouth bass were found to grow more slowly as the lake’s water level fell.

The study’s lead author, Jereme Gaeta, tells Wonk on the Wildlife that the findings have implications for a warming planet.

“Future climate projections are uncertain, but we generally expect evaporation to outpace precipitation in many regions such as northern Wisconsin,” Gaeta said. “Our research shows that loss of littoral habitat can change not only the way fishes interact but also change fish community and food web structure.”

To help protect aquatic communities from the loss of littoral woody habitat, the paper recommends manually placing dead trees in lakes — something scientists call tree drops.

“Potential preventative measures when lake levels drop are limited. Our best options are to protect and restore natural shorelines to ensure future inputs of woody structure are possible and, when water levels begin to drop, add trees to deeper waters or steeper shorelines,” Gaeta said.

Little Rock Lake
This photograph from the paper shows wood stranded above Little Rock Lake’s shoreline as water levels declined.
Illustrated by Perry Shirley.

Heterokaryosis hypothesis: Could it help feed the world?

By John Upton

As scientists have started to figure out what a mycorrhizal fungus really is, they’ve discovered that it might be a really fun guy.

I mean, ahem. They’ve discovered that it might really be fungi.

Genetic sequencing is revealing surprising secrets of arbuscular mycorrhizae. The discoveries are casting doubt on notions of fungal individuality and offering new ways of boosting the amount of food that’s grown the world over.

Mycorrhizal fungi, aka myco, are soil dwellers that forage for water and nutrients, which they exchange for sugars produced by photsynthesizing plants. As I explained recently in Grist, they cool the globe and boost crop yields.

Research during the past decade suggests that what many of us would assume was a single myco fungus might actually be lots of mini fungi bits — genetically diverse nuclei that live and work together inside what we would logically perceive to be a fungus. There, the nuclei collaborate to create long mycelia and hyphae that stretch from root to root, delivering water and nutrients up to the plants, and passing carbon from the plants down into the soil.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

This proposed blend of different nuclei is called the heterokaryosis hypothesis (a heterokaryon is a cell containing genetically diverse nuclei) — and it’s highly controversial. A recently flurry of papers has concluded that it is flat-out wrong, but those findings have been criticized by scientists who subscribe to the hypothesis.

If correct, the hypothesis could help scientists solve a couple of longtime fungal mysteries.

For one thing, it could help explain how and why mycelia from seemingly different fungi fuse together as they snake through the soil.

It could also explain how these types of fungi reproduce. Molecular evidence tells us that the fungi exchange genes, which suggests that they are mating. But scientists have never been able to figure out quite how they’re doing it. The heterokaryosis hypothesis suggests it’s the nuclei within each fungus that are breeding. It appears that they are migrating through fusions between the hollow mycelia.

“Why this heterokaryosis thing is so important,” said Ian Sanders, a professor of evolutionary biology at the University of Lausanne, “is because — I believe — we can use these genetic differences among the nuclei to create fungi that make plants grow better.”

Sanders has been involved with research in Colombia, where fungi have been developed that boosted cassava yields by one fifth while requiring less fertilizer. The research program is being expanded to Africa, where cassava, a root vegetable similar to a potato, is a dietary staple.

The breakthroughs relied on breeding techniques that took advantage of fungal heterokaryosis. More such breakthroughs would mean bigger yields of crops, more food, and less world hunger.

(Speaking of food, it’s worth noting that the heterokaryosis theory has nothing to do with mushrooms. There are two main types of mycorrhizae. Endomycorrhizae, which are the subject of this article, are arbuscular. They pierce the roots of plants with tiny vesicles and arbuscules, which are microscopic organs that helped both kingdoms of life adapt to life on land some 460 million years ago. It is the other type of mycorrhizae, ectomycorrhizae, the less common and less ancient union that engulfs roots without penetrating them, that produces mushrooms.)

Endomycorrhizae fungi infuse the roots of nine out of ten crop varieties, yet we know precious little about them. That’s largely because of complications inherent in trying to study an organism that’s intricately woven into the body of another; the result of nearly a half billion years of interdependent evolution.

The heterokaryosis hypothesis has its detractors. They point to research, such as this paper published this month in PLOS Genetics, in which nuclei sampled from a single fungus were nearly genetically identical. Supporters of the hypothesis point to findings from other research where vast genetic diversity appears to have been discovered. Sample sizes in some of the experiments have been very low, and just a few strains have been analyzed, making all of the results highly contentious.

One believer in the hypothesis is Toby Kiers, a mycological researcher at Vrije Universiteit Amsterdam. “It’s a neat concept, because even within an individual you’ve got individuals,” she said.

Kiers will begin lab experiments next month designed to help breed mycorrhizal strains that further boost crop yields. I highlighted the planned research in a recent magazine article about myco fungus in The Ascender:

[Kiers] has secured funding to watch mycelia squeeze through tiny mazes, peering at them through microscopes as they trade nutrients with plants for sugars under different conditions. The goal, she says, is to “study their decision-making skills.”

Kiers’s research will combine cutting-edge microscopy and mycology with old-fashioned breeding techniques in a bid to select the most useful fungal strains. “They’re quite easy to select on,” she said, “because there’s so much genetic variability — even within a single hyphae, within a single spore.”

Illustrated by Perry Shirley.

Global warming is changing how caterpillars eat

By John Upton

Animals can evolve to survive global warming by changing their behavior and by changing their bodies. Butterflies are particularly sensitive to climate change, and changes in their behavior have been well documented — most notably in their migration patterns and ranges. North American Butterfly Association president Jeffrey Glassberg recently told the Maryland Independent that climate change is affecting Rhopalocera on a vast scale. “There’s a whole suite of butterflies whose ranges are retreating,” he said. (Such changes are the subject of Flight Behavior, a novel by Barbara Kingsolver dealing with climate change.)

And now comes the first evidence that butterfly larvae are changing the internal workings of their bodies to help them cope with warming temperatures.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

University of North Carolina scientists studied the optimal feeding temperatures of Colias spp. caterpillars from California’s Sacramento Valley and Colorado’s Montrose Valley. The frequency of very hot days and nights at both sample sites have increased since the 1970s, when a similar study with the same caterpillar populations was conducted. Caterpillars feed best within specific temperature ranges, and the researchers discovered that the caterpillars have evolved to feed at higher temperatures. The results of the study were published in the journal Functional Ecology:

This study is among the first to show population changes in physiological performance in response to recent climate change, although previous theoretical work has predicted such changes. While previous work has highlighted adaptation to seasonal timing, specifically photoperiodic cues, our work suggests that rapid adaptation to changing thermal regimes may also be an essential mechanism.

I asked lead researcher Jessica Higgins whether she thinks that butterflies are among the first organisms to adapt their physiologies to warming conditions — or whether she thinks this was just the first time that such changes have been detected by scientists.

“I do think that other organisms may be adapting, but we can’t detect it because of the lack of good historical data,” Higgins said. “What made my experiment so unique was that I had this snapshot of caterpillar physiology back in the 1970s. I was able to compare my results with what they previously found and then correlate it with temperature. I think my study highlights that there can be adaption to physiological traits — not just changes in seasonality, which has been the main focus of previous adaptation-to-climate studies. “

Illustrated ecology news.