All posts by John Upton

Why don’t we measure biodiversity?

By John Upton

Vast resources are plowed into measuring the metrics associated with global warming. Calculations reveal that American and European greenhouse gas emissions are falling while China’s are rising, and that more carbon dioxide is being pumped out worldwide every year than had been the case the year before. We know that carbon dioxide levels passed a record-breaking 400 parts-per-million point in May, well above the preindustrial level of 280 ppm, before dipping in line with normal seasonal fluctuations — that knowledge is courtesy of air monitoring in Hawaii and the findings of ice-core studies. And gravity-measuring satellites are used to estimate the rate at which glaciers are melting — revealing that despite harboring just 1 percent of the world’s land ice, these thawing rivers of ice are responsible for 29 percent of the rise of sea levels.

The results of these measurements don’t just keep us awake at night. They help policy-makers target efforts to reduce emissions and to prepare communities for changes in the climate.

But what about biodiversity?

Although the world is rallying around efforts to come to terms with its climate problem (even if not enough is being done to actually solve that problem), it is failing to measure the alarming decline of biodiversity, which by one recent estimate has fallen 30 percent in 40 years. It is not investing the resources needed to track the genetic stockpile contained in the cells of plants, animals, mushrooms and other forms of life as forests are bulldozed, rivers are diverted and acidifying oceans are overfished.

Every time a species or a jungle is lost, and every time environmental tumult helps generalists (such as ring-billed gulls) outcompete specialists (such as piping plovers), the world loses some of its genetic code. That code is critically important. It can help an ecosystem weather changes in the, well, in the weather, which is happening now more than ever in human history. It can help sustain a myriad of complex food chains that underpin the very functioning of the natural world. And it can present humans with chemical compounds that prove useful as new drugs or foods.

If we are to get a handle on the specifics of the biodiversity crisis, which we must do if we are to effectively manage the problem, then more scientists need to be trained and employed and provided with the resources needed to advance their fields.

Aware of the problem of falling biodiversity, the United Nations last year formed the Intergovernmental Platform on Biodiversity and Ecosystem Service. The group is structured a bit like the Intergovernmental Panel on Climate Changeits primary function is to review, assess, synthesize and share information about biodiversity with policy makers.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

The group held meetings in Malaysia this week to discuss two main topics: the measurement and assessment of genetic and biological resources; and the calculation of the value of key ecosystem services.

The conclusion: The world just isn’t doing enough to measure biodiversity.

“Of the estimated 10.8 million species on land and in the oceans, less than 2 million have been scientifically described,” IPBES chairman Zakri Abdul Hamid, science advisor to Malaysia’s prime minister, said in a statement published Wednesday at the end of the three days of talks. “If we don’t know what species there are out there, we don’t know what niche they fill in a healthy ecosystem or perhaps in remedying some human condition.” More from the statement:

Most world nations – unanimously committed to protecting biodiversity – nevertheless cannot measure and assess their genetic and biological resources, nor the value of key ecosystem services nature provides to them, international experts from 72 countries warned today.

In addition to taxonomists, nations lack economists able to put a value on the water purification, storm protection and other services of nature, which would inform trade-off choices in development planning. And fewer still deploy social scientists to estimate nature’s non-economic (e.g. cultural) values, or to find ways to effect needed changes in human attitudes and behaviour.

“There’s an old saying: We measure what we treasure. Unfortunately, though we profess to treasure biodiversity, most nations have yet to devote adequate resources to properly measure and assess it along with the value of ecosystem services,” Zakri said. “Correcting that is a priority assignment from the world community to IPBES.”

Human infections are dead ends for valley fever fungus

By John Upton

People infected with two closely-related species of fungi are dying in growing numbers in the American southwest. The Coccidioides spores are blown with dust into lungs, where they can trigger a painful and sometimes-deadly condition known as valley fever.

But any cocci that ends up in a human has hit a dead end. It will not reproduce to spawn a new generation.

That’s because of the lifecycle adopted by these varieties of cocci after evolving with the rodents that share their desert home. The coccis’ ancient ancestors lived and dined on plants. Then they evolved to feast instead on the rotting flesh of dead animals. Now they have evolved to live inside a living mammal, sometimes waiting for years for the host to die so they can pounce and quickly consume the fresh kill.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

Mammals whose immune systems can’t control the fungus may die quickly. But as I explain in Vice’s Motherboard blog, most animals that are infected with cocci develop few symptoms — and those symptoms are normally short-lived:

Normally, [the Cocci] eek out lives as filaments called hyphae. The hyphae live in the soil and produce spores, a lucky few of which get sniffed into the lungs of desert rodents. The spores balloon in size inside the host, forming spherules. The mammal immune system kicks quickly into gear at this point, building walls around the spherules, containing them and developing immunity against further attacks.

It’s when the immune system fails to contain these spherules that the fungus can propagate throughout its victim, sometimes with deadly consequences. As an infected rodent dies, collapsing into the desert, the cocci burst out of suspended animation and unleash streamers of hyphae that eat the rotting meat. As the fungus feasts, hyphae and spores slip back into the soil, ready to start the cycle all over again.

Humans don’t slip into the desert sands when we die. We are embalmed or cremated, making any infection a waste of time for the fungus and, in some cases, a waste of life for humanity. “If a cocci spore gets into a human, it has made a big mistake,” John Taylor, a University of California at Berkeley mycologist, told me. “It’s unlikely to ever become adapted to living in humans.”

Black-backed woodpeckers would face extinction without wildfires

By John Upton

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

This summer has been a tinder-dry scorcher in the American West, where climate change is being blamed for a horror fire season. Mountain snow is melting earlier nowadays and summers are getting hotter — and that perilous partnership is fueling a steady surge in the frequency and size of the region’s wildfires.

The infernos kill firefighters, destroy homes and damage public infrastructure.

But it’s worth remembering that fires are healthy and regenerative phenomena in many ecosystems — including those in the West.

Blazes clear out water-hogging undergrowth and provide blank slates upon which timberlands can grow anew, boosting forest biodiversity. Rugged pods that encase the seeds of some specialized plants open after fire, sowing the genesis of the next generation in fertile fields wiped clean of competitors.

It’s not just plants that have evolved to rely on fire. Woodpeckers, for example, can flourish in its wake. The black-backed woodpecker has a particularly specialized diet that leaves it dependent upon the charred aftermath of wildfires. The species feasts on the wood-boring beetles that proliferate in burned trees following blazes in Western American mountain-ranges.

Rim Fire
The aftermath of the Rim Fire, the fourth-largest wildfire in Californian history, photographed near Yosemite National Park in early September by San Francisco journalist Chris Roberts.

But us humans are not as fond of fire as are the beetles or the woodpeckers that hunt them. Public policy dictates that fires should be avoided and, if that fails, confronted without compromise. The practice of preemptively thinning out forests to reduce fire impacts, and the logging of forests after they burn, have both taken heavy tolls on the black-backed woodpeckers.

Populations of these birds have been harmed so severely by public policies of wildfire suppression that the federal government is reviewing whether genetically distinct populations in two regions should be added to its list of endangered species.

“This is the first time in the history of the Endangered Species Act that the government has initiated steps to protect a wildlife species that depends upon stands of fire-killed trees,” Chad Hanson, an ecologist with Earth Island Institute, said when the U.S. Fish & Wildlife Service announced the review in June.

A clean-up following the Rim Fire, making it more difficult for black-backed woodpeckers to inhabit this area. Photo by Mike McMillan of the U.S. Forest Service.
A clean-up following the Rim Fire, making it more difficult for black-backed woodpeckers to inhabit this area. Photo by Mike McMillan of the U.S. Forest Service.

Hanson coauthored research published in May in The Open Forest Science Journal that showed just how severely one of those two populations of woodpeckers, which lives in the Sierra Nevada and southern Cascade ranges of California and Oregon, has been affected by humanity’s wont to battle fire. Hanson and his colleague, Dennis Odion, obtained data from the government and from their own observations which they used to model the effects of typical wildfire suppression policies in the Sierra on the species’ habitat.

“A scenario based on thinning 20 percent of mature forests over a 20-year period, and post-fire logging in 33 percent of potential habitat created by fire, reduced the amount of primary habitat after 27 years to 30 percent of the amount that would occur without these treatments,” the scientists wrote in the paper.

“Our results indicate that conserving the distinct population of black-backed woodpeckers in the southern Cascades and Sierra Nevada and the biodiversity for which they are an indicator will require that more unthinned area be burned by wildfires and protected after fire as critical habitat.”

The following table was lifted from the paper. It compares the amount of black-backed woodpecker habitat available within a study area following 27 years of simulated fire suppression policies:

woodpeckers and fire

And this photograph of an acorn placed in the trunk of a Rim Fire-charred pine is an endearing reminder that wildlife perseveres following fire. Wild Equity Institute founder Brent Plater tells me it might have been put there by a squirrel or a scrub jay — but that it was most likely the handiwork of an acorn woodpecker. “Caching acorns in tree cavities is what they do for a living,” he said.

Photo by Chris Roberts
Photo by Chris Roberts

These chicks puke at predators

By John Upton

When Eurasian rollers forage for insect prey for their young, they’re not just on a quest for nourishing fat and protein. They’re fossicking through an ecological armory for chemical weapons.

Some plants produce toxins to deter herbivores. Some insects that eat those plants use those plant toxins for their own defense. Eurasian roller chicks use the plant toxins from those insects to produce a pungent orange liquid — an unsavory concoction that scientists have concluded is used as a defense against predators.

A team of Spanish researchers found that Eurasian roller nestlings vomited when they picked them up, but not when they approached the young birds, talked to them or gently prodded them. “This fact suggests that the vomit might be produced in response to some kind of predators that actively grasp and move prey during the predation event such as snakes, rats and mustelids, which are common predators of hole-nesting species as rollers,” the scientists wrote in a paper published in the journal PLOS ONE.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

The researchers collected the puke and smeared some of it on pieces of chicken, which they offered (with the smeared side hidden) to 25 dogs alongside a similar chunk of poultry smeared only with water. Some of the mutts strangely showed no appetite for chicken whatsoever. But 18 of the 20 dogs with a hankering for hen opted first for the untreated meat, indicating that the smell is off-putting for a predator. Most of those 18 dogs subsequently wolfed down the vomit-smeared chicken, but six of them left it entirely alone.

“One could wonder about the nestling advantage of this defence,” the scientists wrote. “Kin selection is a possible answer to that question because a predator that finds the first nestling of a brood of five to be distasteful may leave alive the others.”

From where do the chicks get the hydroxybenzoic and hydroxycinnamic acids, phenolic acids and psoralen needed to produce their unpalatable puke?

The scientists matched these compounds to toxins produced by plants to deter animals from feeding on them. Many insects have developed an immunity to such toxins, and some use the plants’ toxins to defend themselves. That’s the case for many of the grasshoppers upon which the rollers prey, and the scientists believe that the chicks are, in turn, purloining the poisons from the grasshoppers to defend themselves.

But that’s not all — the scientists think that the parent birds might also be hunting for more-poisonous insects, such as centipedes, that most other birds would never touch.

“Grasshoppers are the main prey that rollers hunt to feed their nestlings,” they wrote. “Furthermore, rollers feed their offspring with a large share of poisonous arthropods that are avoided by most of the other sympatric insectivorous birds. This suggests that rollers are resistant to these toxic substances and could have the ability to sequester chemicals from their protected prey to defend themselves.”

An adult Eurasian roller.
An adult Eurasian roller in Kazakhstan. Photo by Ken and Nyetta.

Research: Bat-killing fungus arrived from afar

By John Upton

A ripple of bat deaths has grown since 2006 to become millions of Chiroptera deep, stretching out from its New York epicenter into five Canadian provinces and west at least as far as Missouri. The latest state to be affected was Minnesota, where infected bats were discovered in two parks.

The dead bats were all members of species that hibernate — and they succumbed to white nose syndrome. The disease is caused by a fungus that eats away at their wings and faces.

Little brown bats are among the worst affected. These adorably tiny bats were common throughout Eastern America as little as a decade ago, sucking down mosquitoes and other pests during their nocturnal maunders. Now the species appears to be on the verge of being listed as federally endangered.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

Mammals appear to have developed high body temperatures to help stave off infections of fungi. But hibernating bats have a chink in that armor: When they hibernate, their body temperatures plummet. And when most bats hibernate, they huddle together, which helps the fungal infection spread through the slumbering colony.

What caused this fast-moving fungus to suddenly begin attacking bats? Did it go rogue, evolving from a soil eater into a devourer of bat flesh? Or is it an invasive species that arrived from some far-flung place?

A pair of Wisconsin-based U.S. Forest Service scientists studied the DNA of the disease along with that of more than a dozen species of other fungi found growing in bat caves in the eastern U.S. What they found, first and foremost, was that the pathogen was not quite what everybody thought it was.

Scientists have called the disease Geomycetes destructans since it was identified in 2009. But the recent research, described in the journal Fungal Biology, indicates that the fungus is actually a member of the genus Pseudogymnoascus. Hence, it has been reclassified P. destructans.

Of the other species of Pseudogymnoascus fungi sampled in the studied hibernacula, the scientists reported that none were closely related to P. destructans. That’s significant, because it suggests that white-nose syndrome arrived in New York from some other part of the world, perhaps on the shoes of a traveler or shipped in as a few spores with freight.

Researcher Andrew Minnis said the study is part of a wider effort to find a way to protect bats from the fungus. “Once key elements of this [fungus] species’ biology, including mechanisms of pathogenicity, are identified, it will be possible to target them,” he said.

Once it was realized that many related fungi were present in bat caves, but weren’t killing bats, “thoughts arose that these species could be used for comparative purposes — to understand why P. destructans is different,” he said. Following the findings from this study, “further and more informed comparative work can now be performed.”

Confirmed and suspected white-nose syndrome cases. Map updated August, 2013 by the U.S. government.
Confirmed and suspected white-nose syndrome cases. Map updated August, 2013 by the U.S. government.

Dutch gulls eat their young on Sundays

By John Upton

The durations of days and years are calibrated by celestial turntables: The spinning of the Earth and its arcing around the sun. Humans and wildlife alike live out rituals according to daily and annual schedules.

But the seven-day week is a human construct. It’s an arbitrary chunk of time that cocoons timetables of work and rest, of television programming and soccer practice. Whenever you see wildlife falling into a weekly routine, you can be confident it’s the result of a human influence.

A weekly schedule plays out among European herring gulls and lesser black-backed gulls nesting in the dunes of the Dutch island of Texel. And it’s a macabre one.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

A chick being reared in these dunes may dread Sunday more than a young atheist dreads their mandatory church outings. It’s on Sundays that adult gulls are most likely to cannibalize the young. Saturdays are also popular chick-eating days among the Texel gulls, though not to the same extent as is the case on Sundays.

Sometimes the gulls eat their own chicks — or their own eggs. But more often they steal the unattended young of other birds, in some instances to be shared with their own hungry broods.

That’s not the only weekly pattern that marine ornithologist Kees Camphuysen has discovered during his studies on the island. Chicks tend to grow in spurts during the week, then their growth slows down over the weekends.

The Royal Netherlands Institute for Sea Research scientist thinks he knows what’s going on. He contends that it’s the weekly patterns of the region’s beamtrawlers and shrimpers that are driving the hebdomadal trends.

“[A] very strong weekly pattern in fleet size occurred, with high numbers of boats at sea Monday through Thursday, a much reduced number (mostly homeward bound) on Friday, and near to nothing on Saturdays and Sundays,” he wrote in his Ph.D. thesis.

The Texel Dunes gulls feast on the by-caught scraps of the fishing fleet, trailing the boats to scavenge protein for themselves and for their growing chicks. But when this supply of human surplus dries up over the weekends, the chicks’ growth rates slow, and hunger can drive the birds to cannibalism.

“Only commercial fisheries have a periodicity that can explain the strong, cyclic synchronisation in chick growth,” Camphuysen wrote. “Chick cannibalism rates were a mirror image of the rhythmic cycle in growth increments.”

The following series of photographs was published in Camphuysen’s Ph.D. thesis, showing an attack on an unattended chick by a bird from a nearby nest. The attacking gull can be seen sharing the kill with its own chick. If you would prefer to not see an adorable lesser black-backed gull chick being pecked to death and gutted by its own kind, then stop scrolling now.

cannibal-gull-in-action

Guppies father fry after they die

By John Upton

You have to be quite the stud to sire a clutch of ankle-biters long after you’ve croaked it.

Yet that’s just what male members of many species of animals can do. And with apologies to any ghostly egos of dead dads of the animal world, the reality is that these feats are not to their credit.

Females of some species of crabs, salamanders, turtles, lizards, bats and fish can store sperm inside their bodies, which they use to fertilize their eggs many months or even a year or more after they have mated. That means that males can father offspring long after they are dead.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

One such species is the Trinidadian guppy. Female guppies live much longer lives than do male guppies, but the longevity of the sperm when stored inside special ovarian receptacles can make up for the difference.

Researchers introduced a population of lab-reared guppies into a pond beneath a waterfall in Trinidad’s Lower LaLaja. They fastidiously monitored each of the fish as the population grew, studying the Poecilia soap opera dramas of who was mating with who.

The scientists discovered that many guppy fry were fathered by fish that had died generations prior to their births. Within eight months of research, around one quarter of the guppies being born (described as “new recruits” in the following graph) were being fathered by dead males.

Lo ́pez-Sepulcre A, Gordon SP, Paterson IG, Bentzen P, Reznick DN. 2013 Beyond lifetime reproductive success: the posthumous reproductive dynamics of male Trinidadian guppies. Proc R Soc B 280: 20131116.
Lo ́pez-Sepulcre A, Gordon SP, Paterson IG, Bentzen P, Reznick DN. 2013 Beyond lifetime reproductive success: the posthumous reproductive dynamics
of male Trinidadian guppies. Proc R Soc B 280: 20131116.

“Clearly, posthumous reproduction has important fitness consequences for males, as it allows them to expand their reproductive lifespan to equal that of females,” the scientists wrote in a paper, published this month in the journal Proceedings of the Royal Society B. “[L]ong-term sperm storage by females can also buffer the loss of genetic variation in organisms where females outlive males, enabling males represented in stored sperm to reproduce, even after death.”

How birds avoid cuckoos

By John Upton

One of nature’s more ridiculous sights is that of a pair of adult birds rearing an oversized cuckoo chick.

Cuckoos are members of a large family of birds, some of which have done away with chick rearing, instead depositing their eggs in the nests of other species. This is called brood parasitism.

The parasitized birds rear the cuckoo chick as if it were their own, even as it grows to dwarf them in size — and as it pushes any other chicks from the nest to certain death.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

(Ever noticed a dead chick beneath a tree and wondered how it fell out? Next time look up for a nest, and wonder whether a cuckoo is being raised therein.)

It seems that the the parental compulsion to raise young is so strong that the parasitized birds remain blind to the possibility that the brood contains none of their own DNA.

While many bird species remain oblivious to what would seem to be obvious signs that they are raising an unrelated chick, selection pressure has of course led to the evolution of some defenses against brood parasites.

Scientists compared defensive strategies developed by barn swallows living in China with those in Europe and found that they developed different defenses.

In Europe, martins and barn swallows, which seem to be better than some similar species at avoiding cuckoos, prefer to build their nests indoors. That’s where cuckoos are less likely to strike; they prefer open areas and avoid human habitation.

“Suitable cuckoo hosts breeding close to human habitation enjoy a selective advantage from breeding indoors,” the researchers wrote in a paper published in the journal Behavioral Ecology and Sociobiology. “These findings suggest that birds benefit from association with humans in terms of reduce risk of parasitism.”

The scientists say it’s harder for the barn swallows to build nests indoors in China. There, they have developed an alternative trick that’s largely lacking among their European counterparts: A Chinese barn swallow will often recognize a cuckoo egg. So when a cuckoo egg shows up in its nest, it will toss it over the side.

“These findings suggest that barn swallows in China have gained egg rejection behavior because they cannot avoid parasitism when breeding outdoors.”

Watch a Reed warbler feed a much larger cuckoo chick:

Mosquitoes hunt us by our smell, then zero in on our heat

By John Upton

The Zzzz–zzZZZzzz–zzZZ sound that a mosquito makes while you’re trying to sleep isn’t the random modulation of a directionless insect. It’s the sound of a predator carefully circling its prey, smelling body odors and reading body heat, planning its strike.

Blood-hungry mosquitoes are females, on the desperate hunt for protein with which they can manufacture eggs. They repeat their hunt several times, making them dangerous vectors of disease. Their eggs will be laid in standing water before the female buzzes the last buzz of a short life as an airborne adult. Between the egg and adult stage comes the larvae, commonly known as mosquito wrigglers.

To find their prey, the female mosquito hones in on our smell. As they close in on their prey, they scan our body heat to help direct their strike.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

That’s the conclusion of Dutch researchers, who set up a small wind tunnel with 3D tracking equipment and conducted experiments with hungry week-old female specimens of Anopheles gambiae, an African mosquito that hunts human blood and can transmit malaria. For some of the tests, the researchers placed a used sock at one end of the wind tunnel to gauge how they responded to human smell. In others, they placed a heat element at the end, set to 34°c to mimic the temperature of a human. Other tests involved using neither the sock nor the heat; and others used both. The researchers studied how the mosquitoes zeroed in on a specific point at the end of the wind tunnel under the different conditions.

The result?

Check out the following figures. Each row shows three views of the same wind tunnel experiments. The blue circles show the location of the plume of smell blown through the wind tunnel from the sock. The green lines track the mosquitoes approaching the end of the wind tunnel through the smell plume; red lines track the other mosquitoes. The target is at the center of the end of the tunnel.

mozzietracks“With heat alone, flights were … short and direct,” the scientists wrote in their paper, published in the online journal PLoS ONE. “The presence of human odor, in contrast, caused prolonged and highly convoluted flight patterns. The combination of odor+heat resulted in longer flights with more landings on the source than to either cue alone.”

So next time a mosquito is keeping you awake at night, don’t think of it as an idiot that’s buzzing mindlessly around your head. It’s just getting a good read on its prey before launching its strike.

Illustrated by Perry Shirley
Illustrated by Perry Shirley

A hungry red tide is a dangerous red tide

By John Upton

When fertilizer or sewage runs into a waterway, or when phosphorous and nitrogen rise up from the ocean depths, algae can converge and feast and mushroom on the buffet of growth-inducing nutrients.

But scientists have discovered that starving a poisonous red tide of its nutrient supply can trigger a very dangerous and counterintuitive response.

Red tides are freaky types of algae blooms. They often occur in the ocean or in salty bays, and they frequently produce poisons. Scientists prefer the term “harmful algal bloom,” since a red tide isn’t always red and it is most certainly not a tide.

Illustrated by Perry Shirley
Illustrated by Perry Shirley

The most common type of algae in Gulf of Mexico red tides is a dinoflagellate called Karenia brevis. The neurotoxin produced by these single-celled creatures help protect them from predation: Would-be hunters can die if they take a mouthful. But as the red tides break down, the poison escapes from the plankton cells and it can drift through the marine environment, poisoning it. The toxin can even spray into the air, aerosolized by crashing waves, where it can get into lungs and trigger serious ailments in people and other animals. The Floridian West Coast is often the worst affected.

Concentrations of the poison in each of the algae cells varies widely — from a mild 1 picogram per cell to a treacherous 68 picograms per cell. Needless to say, figuring out what causes a bloom to be especially poisonous would be valuable for public health officials.

Since Karenia brevis uses nutrients to grow, one may assume that starving them of phosphorous and nitrogen, such as by preventing fertilizer or sewage runoff into the Gulf, would protect the environment from their poisons.

But that’s only true up to a point. If you can keep nutrients out of the water, a bloom will not materialize, so there will be no danger of the waterway being poisoned by it. But if the nutrient supplies suddenly dry up, an existing bloom will switch into a defensive mode, stop growing and become very toxic.

The ecological theory to describe this response comes to us from botany. It is called the carbon:nutrient balance hypothesis.

North Carolina scientists grew samples of the dinoflagellate in water taken from the Gulf in a laboratory. Some samples were fed plenty of phosphorous, but others received very little. The scientists found that K. brevis strains living with limited phosphorous supplies produced 2.3 to 7.3 times more poison than did those that had plenty of phosphorous available.

“Because PbTxs [K. brevis brevetoxins] are potent anti-grazing compounds, this increased investment in PbTxs should enhance cellular survival during periods of nutrient-limited growth,” the scientists wrote in their paper, published last month in PLoS ONE.

The algae samples living without much phosphorous put their carbon to a defensive use, since it couldn’t be used as effectively for growth. The proportion of carbon that each cell used to produce poison as much as doubled when phosphorous was limited.

This is consistent with the carbon:nutrient balance hypothesis. When vegetation has lots of carbon and lots of nutrients available, it invests those building blocks of life into fast growth. But when nutrients, be they phosphorous or nitrogen, are in short supply, the carbon is put to a different use: Defense against predators.

It also helps explain some of the late season bursts in toxicity noticed in the red tides: They become poisonous after they have greedily slurped down the last of the available nutrients.

This research was limited to phosphorous. But previous research uncovered a similar red tide response when nitrogen was limited.

The discovery could help public health managers predict the potency of red tides in the Gulf of Mexico. By measuring the amount of phosphorous in the ecosystem, it could become possible to determine how dangerous the red tides will become.