Hot Boys, Cool Girls, and the Fate of a Living Fossil

Imagine if the sex of your unborn offspring was determined by the climate you lived in while pregnant. Vacation in Cabo? Guaranteed son. Visiting the Northern lights? You’re having a daughter. This method of sex determination would play havoc with human sex ratios: countries like India and China, already on the verge of sex-ratio breakdown would become even more male-dominated, while Canada and the Scandinavian countries would swing towards a female majority (and given the general state of the world when men have been in charge, that’s a fairly appealing thought).

But sadly that’s not how sex determination works in humans — instead it’s a 50-50 chance based on whether the sperm fastest to the egg carries a male chromosome or a female chromosome. However, it is how sex is determined in lizards and crocodiles,[1] which might prove to be a bit of a problem as the worlds climate changes for the warmer.

When mating season comes, and reptile hormones are all in a tizzy, males donate a packet of sperm to a female, which is stored in her cloaca (how romantic). She then uses this sperm to fertilize eggs, and bury them in a nest for incubation. Lizard moms manipulate the sex ratio of their offspring by choosing where to build a nest: if they want more females, they will build a deeper nest in cooler areas — if they want sons, they build a shallow nest in warm habitats.

A doting mom.

A doting Nile crocodile mom.

Why exactly this method of sex determination has evolved is up for debate. Some research indicates that it may be the ancestral state for all amniote vertebrates (animals which lay eggs on land), dating back around 300 million years. It may continue to exist in lizards, crocodiles, and turtles because it is adaptively neutral — that is, it doesn’t necessary convey a great evolutionary advantage, but it also isn’t disadvantageous.

Other scientists argue that temperature-dependent sex determination (TSD) ensures that regardless of the climate or seasonal conditions, the sex best able to cope will hatch. For example, the spotted skink in Tasmania uses TSD: cool incubation temperatures lead to male offspring, and warm incubation temperatures lead to female offspring. In order for newborn female skinks to survive winter, they need ample amounts of time to grow during the summer. Having a brood of female skinks late in the breeding season is a bad idea: they won’t have time to grow, and will likely die over winter, meaning a wasted breeding season for mum. However, because of TSD, this doesn’t happen – females hatch only early in the summer, when temperatures are warm. As the average temperature cools down in mid- and late-summer, any egg laid hatch as males. No matter what time a clutch of eggs is laid, TSD makes sure that the sex that appears is the one best able to survive.

The Tasman spotted skink. Credit: Parks and Wildlife, Tasmania

The Tasman spotted skink. Credit: Parks and Wildlife, Tasmania

Unfortunately, this can backfire if the climate moves out of the ranges in which that behaviour has evolved to be adaptive (the evolutionary trap that also affects sea turtle behaviour — a behaviour that was previously beneficial becomes negative in light of recent, rapid changes). That’s the possible fate facing the tuatara.

The tuatara is a New Zealand reptile that looks like a lizard, but isn’t. Instead, it is the only living member of an ancient order of reptiles, the Rhynochocephalia, which reached its peak 200 million years ago. Anatomically, they are the most unspecialized amniote, and researchers think they may be good models for understanding the behaviour of dinosaurs. They don’t reach sexual maturity until they’re 20, and can live until well over 100. For millennia they were widespread across New Zealand, until the introduction of rats and cats as invasive predators led to a dramatic decline in their numbers, and eventually extirpation from the main islands. Currently, the tuatara survives in relic populations on the small islands of New Zealand which have never been colonized by predatory mammals.

Looks like a lizard...but isn't.

Looks like a lizard…but isn’t.

But even if it can survive the rats, cats, and minuscule gene pool, climate change might get it. Tuatara sex is determined by temperature — warm temperatures lead to males, cool temperatures to females. Like in other TSD species, to some degree the effect of air temperature can be mitigated by changing nest depth. Digging a deeper nest can, in theory, counter-balance increased solar radiation or air temperature to maintain a balanced sex ratio. Unfortunately, the islands of New Zealand that the tuatara inhabit don’t have a soil base deep enough to allow that sort of digging (plus, tuatara arms are pretty stubby, they’d be hard-pressed to dig a deep nest).

Which means that the tuatara might be in trouble. Researchers predict that, if global climate change proceeds according to schedule, by 2080 tuatara’s will be laying nests consisting entirely of male eggs. This might be great for a fantasy football league, but isn’t quite so good when it comes to species survival.

A tuatara, disturbed by the possibility of living only with other males.

A tuatara, disturbed by the possibility of living only with other males.

Active intervention by humans might help. Tuatara’s can be translocated to islands with cooler climates. Or, as has been done with sea turtles, volunteers can move nests — reburying them in shadier locations, or at lower depths. But without that help, one of the last living fossils could very well go extinct.

Sources

Mitchell, N. J, M. R Kearney, N. J Nelson, and W. P Porter. “Predicting the Fate of a Living Fossil: How Will Global Warming Affect Sex Determination and Hatching Phenology in Tuatara?” Proceedings of the Royal Society B: Biological Sciences 275, no. 1648 (October 7, 2008): 2185–2193. doi:10.1098/rspb.2008.0438.

Refsnider, J. M., B. L. Bodensteiner, J. L. Reneker, and F. J. Janzen. “Nest Depth May Not Compensate for Sex Ratio Skews Caused by Climate Change in Turtles: Nest Depth and Turtle Sex Ratios.” Animal Conservation 16, no. 5 (October 2013): 481–490. doi:10.1111/acv.12034.


[1] Also turtles, but they’ve got it flipped the other way: high temperatures lead to females, and low temperatures to males. Just to confuse biologists even further, some species have found a third way. Temperature extremes (high or low) lead to female dominated nests, while mid-range temperatures lead to male dominated nests.

Credit: Houston Zoo Blogs.

The Secret Superpower of the World’s Cutest Animal

Venom is generally thought to be the property of snakes, lizards, and various creepy-crawlies. But they don’t have exclusive rights, and mammals are not to be outdone. Some members of our hairy brethren have also shown a propensity for envenomating the unlucky. These would-be poisoners include the American shrew, the Haitian solenodon, and the most famous venomous mammal, the platypus.

The Haitian solenodon is a curious looking critter.

The Haitian solenodon is a curious looking critter. Credit: Eladio Fernandez

The playtpus, and other venomous mammals, are a little weird looking – weird enough that their poisonous bites (or elbow spurs, for the platypus) don’t seem too out of character. But the other venomous mammal? The new kid on the block? It’s not odd-looking – in fact, it’s probably the cutest animal on the entire planet: the slow loris.

Credit: Houston Zoo Blogs.

Credit: Houston Zoo Blogs.

Slow lorises are a collection of primate species that live in South East Asia. Currently, there are eight recognized species (up from one not too long ago), and the number will likely increase again as more research is done on them. They are a comparatively old genus of primate, related to lemurs and galagos (the adorable weirdos of the Primate order). They’re nocturnal, mostly solitary, and move (slowly) through the trees of tropical rainforests, and increasingly, fields of crops, feeding on insects and generally minding their own business.

They’re not monkeys, and will be sad if you call them monkeys, so please don’t.

Do you know what else makes slow lorises sad? Captivity.

Do you know what else makes slow lorises sad? Captivity.

Slow lorises have been in the news recently, thanks to singer Rihanna’s ill-informed decision to pose for a photo with one in Thailand, and then post it on Instagram (which led to the arrest of the people smuggling them, so that’s a happy ending for everyone who isn’t going to a Thai jail now). Prior to that, slow lorises were probably best known for that YouTube video of a loris being ‘tickled’. I’m not going to link to it, because that guy doesn’t really need anymore attention, but if you watch it, you should know that the loris isn’t raising its arms because it wants to be tickled – it’s raising its arms as a defense mechanism.

Now, as far as a defense mechanism goes, surrendering is not necessarily a winning strategy in the “red in tooth-and-claw” natural kingdom. But the slow loris has a trump card – its not raising its arms to surrender, but to access its venom glands.

In the wild, this sort of behaviour generally just gets you eaten.

In the wild, this sort of behaviour generally just gets you eaten…

On the arms of a slow loris, about where you’d get a bicep tattoo (if you were that sort of person), there are venom glands. These glands secrete Part A of the slow lorises venom. But there are problems with your body constantly leaking venom – for example, it makes cuddling difficult. So for the venom to become active, slow lorises mix it with their saliva (Part B). By licking the glands on their arms, slow lorises activate the venom, giving themselves a toxic bite.

...unless you have venomous armpits. Credit: Helga Schulze, in Krane et al 2003.

…unless you have venomous armpits. Credit: Helga Schulze, in Krane et al 2003.

And it can be a nasty bite, for such an adorable little animal. There has been at least one reported human death from a slow loris bite, and even if you don’t die, it is going to swell, pus, bleed, fester, and hurt for a long time. Which serves you right for trying to harass them. When smugglers catch slow lorises for the pet trade, they surgically remove the teeth to prevent bites to the  privileged idiots who illegally buy the animals later on.

The venom serves a number of purposes. It is strong enough to kill small prey, although loris teeth likely do that just as well. During the mating season, male lorises fight violently for access to females, and use their venomous bite to cause serious damage to one another. But again, their teeth would get the job done just as well. Producing venom is energetically-expensive, and would be difficult to favour evolutionarily without it providing a major survival or reproductive advantage at some point in a lorises lifetime. And if there’s one advantage a slow loris is always looking for, its how to not be eaten.

No, it's not trying to seduce you. It's loading up on venom (which you can see glistening around the nose). Credit: Anna Nekaris

No, it’s not trying to seduce you. It’s loading up on venom (which you can see glistening around the nose). Credit: Anna Nekaris

Lorises are small, slow, and vulnerable to many predators. They prefer to avoid confrontation, but that’s not always possible. So when travelling through the forest, the lorises will coat their fur in a layer of venom by licking themselves all over. Predators can smell the venom-wash, and are encouraged to find something else to eat. It’s so effective that slow lorises can saunter casually past the baleful glare of a jungle cat or a sunbear without fear – something that all tiny herbivores wish they could pull off with such aplomb. Rather than being an offensive weapon, the venom of a slow loris is defensive in function.

On the other hand, they shouldn’t get too cocky. While cats and bears shy away from the scent of slow loris venom, orangutans – another predator of lorises – seem to treat it like a healthy dollop of hot sauce on-top of a cute little appetizer. Sometimes even the cutest animal in the world can’t catch a break.

Oops. Credit: Madeleine Hardus.

Oops. Credit: Madeleine Hardus.

Featured photo by Houston Zoo Blogs

References

Dufton, Mark J. “Venomous Mammals.” Pharmacology & Therapeutics 53, no. 2 (1992): 199–215.

Klotz, John H., Stephen A. Klotz, and Jacob L. Pinnas. “Animal Bites and Stings with Anaphylactic Potential.” The Journal of Emergency Medicine 36, no. 2 (February 2009): 148–156. doi:10.1016/j.jemermed.2007.06.018.

Nekaris, Anne-Isola, Richard S Moore, Johanna Rode, and Bryan G Fry. “Mad, Bad and Dangerous to Know: The Biochemistry, Ecology and Evolution of Slow Loris Venom.” Journal of Venomous Animals and Toxins Including Tropical Diseases 19, no. 1 (2013): 21. doi:10.1186/1678-9199-19-21.

Whittington, C. M., A. T. Papenfuss, P. Bansal, A. M. Torres, E. S.W. Wong, J. E. Deakin, T. Graves, et al. “Defensins and the Convergent Evolution of Platypus and Reptile Venom Genes.” Genome Research 18, no. 6 (May 7, 2008): 986–994. doi:10.1101/gr.7149808.

honeybee

Decoding the Honey Bee’s Dance

The careful insect ‘midst his works I view,
Now from the flowers exhaust the fragrant dew,
With golden treasures load his little thighs,
And steer his distant journey through the skies.

– John Gay, Rural Sports (canto I, l. 82)

In the summer of 1944, as World War 2 reached its climax, one man in the German country-side was turning his eyes away from the shattered world of men and looking towards a more orderly universe: that of the honey bee. Dr Karl von Frisch was an Austrian zoologist. Originally trained as a medical doctor, he found his true calling in animal behaviour. (I also went to university thinking I’d be a doctor, and somehow stumbled into animal behaviour – but the similarities end there). He basically invented the field of ethology (studying animal behaviour), and went on to win a Nobel Prize in 1973, all through the study of the humble honeybee.

Von Frisch had been studying the behaviour of honeybees for over 20 years, his fascination beginning as a post-doctorate student in 1914. At that time, received wisdom held that bees and other insects were simple creatures with poorly developed senses – colourblind automatons that buzzed to and fro in a random, endless search for flowers. von Frisch, rightfully, thought this idea was nonsense: “the bright colours of flowers,” he noted, “can be understood only as an adaptation to color-sensitive visitors.” So, following in the footsteps of all good iconoclasts, von Frisch decided to upend conventional wisdom.

Using a series of elegant experiments, von Frisch set out to prove that honeybees had colour vision – and he accidentally stumbled on to far more. First, von Frisch acquired a beehive with a glass wall, enabling him to observe the activity of the bees within the hive. Then, he captured a number of foraging bees and marked them with paint so that he could tell them apart. He then trained those foraging bees to associate a specific colour – blue – with the presence of food. The forager bees quickly learned to search only food bowls associated with the colour blue, and to ignore food bowls placed on grey or black pieces of paper. This proved that honey bees had some ability to differentiate between colours – and later, using the same methods von Frisch proved that bees can also differentiate red and yellow (completely unsurprising to anyone who has stood in a field of wild flowers).

But von Frisch noticed something else. When his scout bees found a blue dish full of nectar, they would return to the hive. After a short time, entire groups of foraging bees would leave the hive, and head directly for the blue dish – often in a group without the original scout bee. Somehow, the original bee was communicating to the rest of the hive – she was able to tell the rest of the group exactly where they would find food. Somehow, the bees were speaking with one another.

He observed the scout bees as they returned from their foraging expeditions. How did they act when they entered the hive? He found that upon returning to the hive, the foraging bee appears to dance:

“The foraging bee…begins to perform a kind of “round dance”. On the part of the comb where she is sitting she starts whirling around in a narrow circle, constantly changing her direction, turning now right, now left, dancing clockwise and anti-clockwise, in quick succession, describing between one and two circles in each direction. This dance is performed among the thickest bustle of the hive. What makes it so particularly striking and attractive is the way it infects the surrounding bees; those sitting next to the dancer start tripping after her, always trying to keep their outstretched feelers on close contact with the tip of her abdomen….They take part in each of her manoeuvrings so that the dancer herself, in her mad wheeling movements, appears to carry behind her a perpetual comet’s tail of bees.”

The scout bee whirls in circles; her infectious energy sends waves of excitement through the beehive, notifying them that the scout has found food somewhere near the hive. This “round dance”, coupled with the scent of a specific flower trapped in the leg-hairs of the scout bee, alerts the hive to the proximity and type of food available. Other bees then leave the hive, and search the immediate area to find the food source. von Frisch had proved that bees were more complex than anyone (except probably beekeepers) had previously thought, but future research would have to wait. The aftermath of WWI, the crippling effects of the Treaty of Versailles, the rise of Nazi Germany, and the onset of WWII meant that Karl von Frisch would be kept away from his beloved bees for nearly 20 years.

And then, in 1944, they were reunited.

Years later, during his Nobel prize speech, von Frisch said of his younger self, “in 1923,…I believed I knew the language of the bees.” He went on to ruefully acknowledge, “the most beautiful part had escaped [him].” During his early experiments on honeybee behaviour, von Frisch had always kept the experimental food sources close to the hives – within 50m. This time, he tried something different. Setting the food sources hundreds of metres away from the hive, he was astonished to see “the recruits immediately started foraging at that great distance.” von Frisch wondered, “could they possess a signal for distance?”

He began a series of experiments, moving the experimental food sources incrementally further away from the hive. von Frisch found that the ‘round dance’ was used up to 50m. Within a 50m radius of the hive, honeybees communicated the location of food sources by dancing in a circle. But when the food source was moved outside that radius, the bees communicated in a different way – the ‘waggle dance’.

Within a short distance of a hive, honeybees don’t need to be given explicit directions to locate a food source. They’ll find it relatively quickly just by searching the area. But when the distance increases, random searching becomes too inefficient. In discovering the ‘waggle dance’, von Frisch discovered how honeybees give pinpoint locations to distant food sources, and forever changed our understanding of the complexities of insect behaviour.

The waggle dance works like this. A foraging bee returns to the hive, and takes its place in the centre of the honeycomb. Other, eager bees, gather around it. The foraging bee then begins to move in a figure-eight pattern. It moves through the straight part of the figure eight waggling its tail, and then peels off to the left or right to complete the figure eight, before cycling again through the waggling straight phase. Each completed figure eight is called a ‘circuit’, and an individual dance is composed of between 1 and 100 circuits. Each of these two phases, the tail waggling straight phase, and the completing the figure eight’s circles, gives different information to the other bees.

The tail-waggling phase tells the other bees in the hives how far away the food source is. The further away the food source, the more slowly the bee travels through the straight phase. von Frisch said that, “for distances from 200 to 4500m, they increase from about 0.5 second to 4.5 second.” The intensity of the waggling also tells the other bees something – a more frantic waggle indicates a more bountiful food source.

The dancing bee’s movement through the circles of the figure eight tells the other bees what direction to search in. The bee arranges itself along the central vertical axis of the hive, facing directly upward the middle of the hive. If the figure eight is evenly placed across this axis, then the food source is directly in-line with the position of the sun outside. As the bee tilts the figure eight away from the central axis, it indicates that the food source is similarly displaced from the position of the sun. The angle of difference between the figure eight and the central axis of the hive is the same as the angle of difference between the sun and the direction of the food source.

This requires a degree of trigonometry I am almost certainly incapable of doing, and I like to think I’m cleverer than a bee.

But honeybees are capable of something even more remarkable. The sun, obviously, changes position throughout the course of the day. And it takes a foraging bee quite some time to get back to the hive – especially if it has found a food source four kilometres away. The sun may have changed position by the time the foraging bee starts dancing, which would lead it sharing an incorrect direction.

Luckily, bees are better dancers and better mathematicians than most of us. They account for the movement of the sun, and adjust the angle of their dance accordingly to maintain the correct direction. This is about the equivalent of a human in Calgary shaking their ass and running in a circle to tell someone how to get to the McDonalds in Lethbridge. Try that next time someone asks you for directions, and see how far you get.

Originally posted at other-nations.com

Featured image by flickr user Scott Kinmartin

Glyptodon_(Riha2000)

The Weird World of Prehistoric Mammals

Scientifically inclined children tend to fall into one of two camps: space or dinosaurs (with some outliers appearing in the maternally-disapproved areas of ‘bugs’ and ‘reptiles’). They’re either hanging models of the solar system in their room and building model rockets, or digging in the dirt and insisting every oddly coloured rock is a newly discovered fossil animal. They’re reciting the names of Saturn’s major moons, in declining order of their orbital period,[1] at the dinner table, or etching long Latin names into their desks[2] (and, somehow, still only getting 7/10 on spelling tests).

I was undoubtedly a dinosaur kid. Space held no interest for me, but I developed (and still quietly nurture) dreams of paleontology. The release of Jurassic Park surely helped this, as did growing up near the badlands of Alberta and visiting the premier dinosaur museum on the planet – the Royal Tyrell Museum. I would stump around in dry, dusty riverbeds in the hot prairie summer imagining that every crack in the mud, or every exposed cliff face, held a footprint or a rib bone – or better yet, a raptor claw – just waiting to be discovered

jp

Then I grew up, and travelled to Africa for the first time, and learned that living animals could be just as weird and wonderful as the extinct ones[3]. Except, not quite. Living animals can be strange looking. And the dinosaurs, of course, were sublime. But one group of underrepresented animals transcends them all in their bizarre otherworldliness – the failed experiments of the early Cenozoic Era.

The Cenozoic Era is the span of geologic time extending from 68 million years ago through the present day, beginning with the extinction of the dinosaurs. Colloquially (at least, as colloquially as geologic eras can be known), it’s called the Age of Mammals. The standard narrative (though currently up for debate) is that the extinction of the dinosaurs opened up new ecological niches for mammals to exploit. In the absence of big, scary lizards, mammals were able to take over the world.

This "feathered dinosaur" thing has really done some damage to their credibility as terrible lizards. From  Godefroit, Demuynck, Dyke, Hu, Escuillié & Claeys, 2013.

This “feathered dinosaur” thing has really done some damage to their credibility as terrible lizards. From Godefroit, Demuynck, Dyke, Hu, Escuillié & Claeys, 2013.

This early, rapid evolution of mammal species led to a whole lot of tinkering. Not all of it was successful, but much of it was spectacular. In no particular order, here are some of the strangest of evolution’s early experiments in mammals.

1. The Dawn Horse

Let’s start small. Contemporary horses range in side from the small (and faintly ridiculous) miniature horse, to the tall, sturdy draught horses that stand about 6 ft. But the ancestor of the horse makes even a miniature horse look like a giant. The earliest Equid, Eohippus validus, stood a mere 12-18 inches high. A newborn baby would tower over it. Presumably, the ancestors of squirrels rode it.

Credit:

Credit: Henrich Harder

2. Glyptodon

Armadillos are strange. I think that’s a fairly uncontroversial thing to say. They’re small, nearly blind mammals best known for their leathery shell, which cartoons have taught us allow them to roll into little balls to protect them from predators, or to be used as balls in a game of croquet. The contemporary armadillo can be used for this purpose[4] because they’re relatively small. But their ancestor, Glyptodon, was a different story altogether. The ancestral armadillo Glyptodon was nearly 12 ft. long, and weighed up to 2 tons – it was the size of a VW Beetle (and far, far cooler). Rather than using it for croquet, early humans hunted it – and then used its protective shell as a house.

Glyptodon_(Riha2000)

Credit: Pavel Riha

3. Amebelodon

Elephant tusks serve a number of purposes: part weapon, part tool, and part method of bothering your older siblings. Learning to use them properly takes time, but when correctly utilized, tusks are a key part of an elephant’s survival strategy. When elephants lose tusks, to disease, fighting, or old age, their chance of surviving the next dry season decreases significantly. So they’re useful now, in their current form. But it took some tinkering to get there – and some tusks were created more equal than others.

Amebelodon was a member of the gomphotheres, a lineage of primitive mammal that eventually led to elephants. Like elephants, they were large bodied, terrestrial herbivores. And, like elephants, they had tusks. But Amebelodon took things to extremes. It had two upper tusks, like an elephant, but on its lower jaw (which is tuskless in elephants), Amebelodon had two long, flattened teeth, which gives it its name, the shovel-tusked gomphothere.

Fossil evidence from the shovels indicates that they were probably used in the same way as elephant tusks. But unlike the elephant, which is a noble, proud animal[5], Amebelodon was simply too silly looking to be allowed to live, and natural selection weeded it out.

That mouth is more than a little frightening.

That mouth is more than a little frightening.

4. Megatherium

What are the largest land mammals to ever live? Elephants? Check. Mammoths? Sort-of elephants, but I’ll give you a half mark. Whales? You didn’t read the question. Sloths?

Now we’re talking.

Sloths today are known as beloved members of childhood films, stars of viral videos, and the butt of jokes. But one genus of sloth, Megatherium, once ruled the Earth (or at least South America). Megatherium, the giant ground sloth, was the size of an elephant, and probably the largest species existing in its time. It dwelt on the ground, and lived in groups. While probably herbivorous, some renegade paleontologists have suggested it might have been at least partially carnivorous, and able to chase saber-toothed cats off their kills. In case you needed fuel for nightmares, hopefully that helps: a pack-living, elephant-sized carnivorous ground sloth.

I kind-of wish this one still existed.

megatherium

5. The Terror Bird

This seems like a cheat, because it’s not a mammal, but it’s only a half-cheat. The Terror Bird, or Phorusrhacos, was an 8 ft. tall, 300 lb., carnivorous bird. It couldn’t fly, but hardly needed to. It ran down small (child-sized) mammals, grabbed them in its taloned feet, and then smashed them into the ground until they died.

As for why it’s only a half-cheat: the story goes that the paleontologist who discovered it assumed, based on its size, that it must’ve been a mammal, and gave it the name Phorusrhacos – which lacks the ending traditionally ascribed to bird names. “Terror Bird” is much catchier, anyways.

The terror bird, proud owner of one of the greatest names in the animal kingdom.

The terror bird, proud owner of one of the greatest names in the animal kingdom.


[1] For the curious: Iapetus, Titan, Rhea, Dione, Tethys, Enceladus, and Mimas.

[2] ‘Micropachycephalosaurus’ currently holding the dubious honour of longest dinosaur name.

[3] Have you ever really looked at an elephant? Or a giraffe? Those things are weird.

[4] No they can’t, please don’t try.

[5] Ignore what I said earlier about them looking weird.

redwood

The Life and Death of the Largest Tree in the World

“The redwoods, once seen, leave a mark or create a vision that stays with you always. No one has ever successfully painted or photographed a redwood tree. The feeling they produce is not transferable. From them comes silence and awe. It’s not only their unbelievable stature, nor the color which seems to shift and vary under your eyes, no, they are not like any trees we know, they are ambassadors from another time.”

– John Steinbeck, Travels with Charley: In Search of America

On March 24th, 1991, in Humboldt Redwoods State Park, California, a tremendous crash rent the quiet spring air. Park rangers over a mile away feared the worst. Had a train derailed? The rail bridge over the Eel River had seen better days, and most of the tracks were in need of repair. Rangers, park stuff, and curious onlookers rushed to the site of the noise. The bridge was intact, and there was no sign of a derailed train. But just south of the river a giant had fallen. The Dyerville Giant, a California coast redwood, and probably the largest tree in the world, had reached the end of its life.

The Dyerville Giant had been having a bad week. It was the rainy season, and the soil in the forest was saturated with water, creating a shifting, roiling, muddy base for the tree to stand in. The shallow root system it used to anchor itself in the ground was becoming exposed, and the winds whipping around its canopy – 370 ft above the forest floor – pulled and pushed 24 hours a day. A smaller tree had given up a few days earlier, crashing to the forest floor, but not before knocking other trees into precarious positions, like a gigantic domino. One of those dominos was left teetering ominously towards the Dyerville Giant. On March 24th, the leaning tree fell, and took the giant down with it.

The scene of the fallen giant must have looked, as well as sounded, like a train wreck. The shockwave created by the impact had disturbed the forest up to four hundred feet away, and splattered mud and debris nearly three storeys high on the trunks of surrounding trees. In the blink of an eye, the largest tree in the world was down. At the time it fell, the Dyerville Giant was 372 ft tall – far taller than the Statute of Liberty (a petite 150 feet), and taller even than Niagara Falls. It was of another age, at least 1600 years old when it fell. When the Dyerville Giant was a seedling, pushing its way through the soil for the first time, the Visigoths were sacking Rome, and the Roman Empire was beginning its final decline.

As a sapling (at 65 ft, a tall sapling), while it struggled for light and nutrients in a forest crowded with taller relatives, Liu Yan was establishing the Han Dynasty in China, and a Hindu philosopher in India was writing the Kama Sutra. Every year, if growing conditions were right, it grew up to another six feet. It grew steadily through the years, as kingdoms of men appeared, expanded, grew corrupt, and fell apart. Great works of literature were written and lost. Art was produced, and burned. The Dyerville Giant stretched inexorably upwards.

In the 1860s, as the newly created country of America sought to tame the wildness of the American West, for the first time in its life the Dyerville Giant faced a threat other than wind and fire. Settlers in California quickly established the value of the coast redwood. The wood is light but strong, and resists decay. Its red sheen is beautiful, and perhaps most importantly, the wood doesn’t catch fire easily. In 1863, the Pacific Lumber Company was created, and its owners, A. W. McPherson and Henry Wetherbee purchased 6,000 acres of good redwood forest at $1.25 an acre. By 1882, the PLC was the largest employer in the area, and solely responsible for the growth and development of towns springing up all along the valleys of Northern California. By 1895, McPherson and Wetherbee had sold a controlling share in the company to a Detroit millionaire named Simon J. Murphy. The Murphy family would steward the Pacific Lumber Company for the next 100 years, and demonstrate a rare sense of ethical corporate management.

At the beginning of the 1900s, cosmopolitan Americans in San Francisco, New York, and Chicago, were developing the first idea of a conservation ethic, focused on preserving some of the wildness of the American frontier. As a young country, America had a love-hate relationship with its untamed parts. The boundless forest and unexplored mountain ranges both mesmerized and frightened Americans. For pioneers, the wildness was an ugly thing to be tamed and controlled, but latter generations recognized that America’s wildness could be what established it as a unique country all of its own. Let Europe have its cathedrals and ruins, America’s forests would be its cathedrals; its mountains would be castles.

In 1917, the Save-the-Redwoods League travelled from San Francisco to Humboldt County to witness the majesty of the redwood forests. Amazed by what they saw, the League raised money and in 1921, Humboldt Redwoods State Park was established. Other companies might have seen this as an infringement, but Pacific Lumber worked with the conservationists. It both sold, and donated, land to the League for far less than it would have been made if they had cut the trees down. In the 1950s, Pacific Lumber pioneered the idea of selective logging and sustainable yield – rather than clear-cutting; they cut down only mature trees, allowing young trees to continue growing. The bulk of today’s Humboldt State Park is made up of the Pacific Lumber Company’s holdings.

It was at this time that the Dyerville Giant got its name. Dyerville had been a small town at the confluence of the North and South forks of the Eel River, just north of the giant. In the 1920s it was the site of the park headquarters, and beginning in the 1930s also the site of a Civilian Conservation Camp, established as part of the New Deal. The fortunes of the small community ebbed and flowed over the next 40 years, but its fate was decided decisively in 1964, when the Eel River overflowed its banks and swept the town downstream. Dyerville was never rebuilt, but the giant tree in the area gained a name, and today a plaque and a picnic area commemorate the former town site. By the time it was named, the growth of the giant had slowed considerably, and its height was estimated at around 360 feet.

On September 30, 1985, after a week of aggressive stock purchases, Pacific Lumber was taken over by Charles Hurwitz and Maxxam Inc., of Texas. Following the completion of the hostile takeover, the Murphy family resigned, and PLC took on a vastly different form. Hurwitz and Maxxam immediately reinstated clear-cutting. Environmental activists were outraged, and in 1990 Maxxam and the redwoods became a boiling point for protest. In an embarrassing collusion between government and industry, the FBI tried hard to label the protest group, Earth First!, a terrorist organization (a label that has remained largely successful). Protests continued against Maxxam’s clear-cutting for over a decade, to little effect. Eventually, karma had enough and stepped in – Pacific Lumber filed for bankruptcy. In twenty short-years, Hurwitz and Maxxam’s aggressive and unsustainable forestry had undone the Pacific Lumber’s reputation and dismantled the company that the Murphy family worked so hard to build.

The Dyerville Giant, of course, wasn’t around to see the end of Pacific Lumber. It fell in 1991, during the angriest years of the protest. It will lie where it fell for another 400 years, slowly decaying and returning its nutrients to the soil. While it decomposes, it will provide a home for over 4000 species of birds, plants, fungi, insects and animals – a diverse ecosystem in its own right, and essentially ensuring that the Dyerville Giant will live forever. As Edward Munch wrote, “From my rotting body, flowers shall grow and I am in them and that is eternity.”

Originally posted at other-nations.com

Featured image by: Craig Wolf

seaturtle

“It’s a Trap!” – Evolution in a Human-Altered World

Imagine you’re a member of a species who fate has placed not particularly high on the food chain. Maybe you’re not the quickest, or the brightest; or maybe you just taste good. Regardless of the reason, that dietary position – one of “prey species” – is going to affect your behaviour and evolutionary history. Maybe you’ve grown small and solitary, so you can creep quietly through the night and avoid detection. Or, maybe you’ve taken to living in the trees to avoid ground-dwelling predators.

But these patterns of behaviour come with trade-offs. If you live in the trees, for example, you might reproduce slowly and have long periods of time in between each additional offspring – baby animals require a good deal of attention if you live in the trees, or else they’re liable to fall out. One offspring at a time might be the most you can handle. On the ground you could raise kids more quickly – they’re less likely to hurt themselves, so require less attention. But the predators rule the ground, so you’re forced to stay in the trees.

Tree climbing is hard.

Tree climbing is hard.

However, if the predators disappear – for example, if they’re killed or chased away by humans – you may be able to move to the ground, and raise your children there. You’ll gradually adapt to a ground-living lifestyle, and your kids will raise grand-children on the ground. But what happens if the predators return? In that case, you’re stuck: your lifestyle requires that you live on the ground, in a human-altered environment, but when the situation changes, you’re lifestyle suddenly needs an adjustment you may not be capable of making. You’re trapped.

In the soul-destroying jargon of scientific writing, an evolutionary trap occurs when a formerly adaptive strategy becomes maladaptive in the face of human-induced environmental change. In English, it means that something that was good for you suddenly becomes bad, because of a change that humans initiated. Evolutionary traps occur when human behaviour accidentally reroutes an animal’s behaviour away from something good, and towards something harmful to itself.

For an example, consider sea turtles. Sea turtles spend the majority of their long lives as nomadic wanderers in the open ocean, but for reproduction. Female sea turtles drag their not-insignificant bulk out of the forgiving water, and bury their eggs in sandy beaches throughout the tropics. Then they return to the ocean, to let their offspring fend for themselves (remind your ungrateful children of this when they demand an increased allowance – at least you didn’t abandon them on a cold, damp beach). When the baby sea turtles hatch, they have one goal: get to the water. To do this, they follow simple, evolved behavioural cues called ‘Darwinian algorithms’. The simplest is “move towards the light”. This basic rule ensures they dig up, out of the sand, rather than down. Once on the surface on a moonlit night, it ensures they move towards the reflective surface of the ocean water. A basic rule that has served baby sea turtles well for millions of years.

Sea turtle deathtrap. Credit:  raredelights.com

Sea turtle deathtrap. Credit: raredelights.com

Until humans discovered electricity and a penchant for beachfront property. Now the sea turtles simple rule backfires, and baby sea turtles hatching at night don’t run towards the ocean, but instead towards the halogen lights of beachside tennis courts and condos and all-night liquor stores. After a hatching, the owners of those properties wake in the morning to find the bodies of baby sea turtles on their doorsteps, dead from exhaustion after a fruitless attempt to find the ocean. The manufactured light of humans overpowers the natural light of the moon, and reroutes the turtles into an evolutionary trap.

That’s one (particularly gruesome) example, but there are more. Grassland birds are predisposed to build nests in open plains. But farm pastures look similar to those plains, and birds that build nests in pastureland are in for a rude surprise when the mechanical harvester comes calling. Manatee’s prefer to winter in warm water – and have recently enjoyed over-wintering near the run-off of coastal power plants, where effluent increases the water temperature. Besides probably being unhealthy, they die of cold if the power plant shuts down for any reason.

Hard to criticize him for swimming in effluent in cold weather. I mean, Canadians go to Arizona in winter - that's basically the same thing. Credit: cruisenaplesflorida.com

Hard to criticize him for swimming in effluent in cold weather. I mean, Canadians go to Arizona in winter – that’s basically the same thing. Credit: cruisenaplesflorida.com

Humans, too, are not immune to an evolutionary trap. For many thousands of years, we have inhabited a world characterized by constant scarcity – particularly food scarcity. Fat, sugar, and salt, were rare and necessary commodities. Because of their rarity, we evolved a craving for these foods – ensuring that we would rarely turn them down if they were available, in order to stockpile resources for the next scarce period.

That worked well, until we created a world that (for some of us) never has a scarce period. In that case, the insatiable cravings for fat and sugar and salt backfire, creating an evolutionary trap that some biologists argue may be one of the causes of the West’s obesity epidemic.

Traps can be escaped. Following a rash of sea turtle deaths in Florida, a lights out policy began to be advocated, mandating that beachfront lighting be turned off or dimmed at night during egg-laying season. It remains to be seen, however, if we can escape the trap that we’ve caught ourselves in.

Featured photo: redbubble.com

References

Schlaepfer et al. 2002. Ecological and evolutionary traps. TREE 17: 474-480.

orchids_rainforest_1_cuipo

The Harmattan: Part II

Contrary to popular belief, true rainforest is not a tangled, fetid mass of clinging vines and threatening shadows. It doesn’t require a machete and a sense of determination to traverse (though it’s best to watch your step – the snakes camouflage well, and don’t always flee from intruders). Instead, rainforests are cathedrals.

Tall, ancient trees buttressed with tremendous roots shape the architecture of the forest, and overhead the canopy seals out light and sound. The floor of a rainforest can be a surprisingly cool and quiet place, like a monastery cloister in the silent hours before matins. Small breaks in the overhead branches allow shy rays of light. The trees dilute the sun’s tropical power, until only dapples glaze the forest flower – more beautiful than the shapes cast by any stained glass window.

But unlike a cathedral, where life occurs mostly on the stone floors and in musty hallways and uncomfortable pews, life in the rainforest flees the depths and stretches to the sky. Vines and lianas wrap crawl towards light. Monkeys leap from branch to branch 30m above the ground, and hummingbirds zip through the canopy, dodging branches at super-human speeds.

At the top of the forest, in the highest level of the canopy – the emergents – flowers grow. Orchids wrap their roots around the sturdy branches of trees, and unfold their petals to capture sun and rain. Orchids are epiphytes. They grow on trees or rocks, but do not parasitize their hosts. This allows them to grow in places inaccessible to other plants – for instance, 45m above the forest floor – but it is a lifestyle that brings its own set of challenges.

High above the forest floor, orchids can gather water and sunlight, but they are otherwise divorced from the nutrient cycle – they cannot access the circle of growth, death, and decay that infuses the soil with endlessly recycled nutrients. To acquire the nutrients necessary for growth, orchids in the Amazonian rainforest rely on a more fickle source – they rely on the harmattan.

The harmattan can deposit as much as 190kg per hectare of mineral rich dust every year – it is nature’s own fertilizer. Over the course of a year, hundreds of millions of tons of dust are carted around the world. Much of this dust is dumped in the Amazon basin, where it fuels rainforest growth on a massive scale. Looking back through the geological record, palaeontologists and geologists noticed something interesting: fluctuations in rainfall over North Africa correlate closely with the expansion and contraction of the rainforest. High rainfall in North Africa leads to less dust being tossed around the world by the harmattan, and a shrinking in the rainforest; periods of drought in the Sahel cause more dust to be carried to the Amazon, and an increase in rainforest size.

For a long time, this theory relied on climate modeling and inference from the geologic record. The trace minerals deposited in dust plumes are difficult to measure, requiring elaborate and expensive laboratory techniques (I know – I once tried to measure the trace levels of iron in seawater, it was a frustrating experience. But then, I’m a mediocre chemist). However, advances in technology have allowed scientists to collect dust deposited in the Amazon and compare it with North African soil – the two are virtually identical.

If that’s not enough for you, the harmattan sometimes brings life in more direct ways. In 1994, researchers in the Caribbean made a curious discovery – a new species of grasshopper. Or at least, new to the Caribbean. It was well known in its home territory – North Africa. Caught in the harmattan, the grasshopper had been carried across the Atlantic. Despite its stressful week, it lived. Tough little buggers.

The harmattan brings both life and death. It’s dust triggers toxic blooms in the ocean, while at the same time fuelling rainforest growth. The dust of North Africa is a finite resource – researchers estimate that the harmattan will deposit nutrients for another 1,000 years. After that, it’s difficult to tell what will happen. The Amazon may shrink, as it has in historical times, but Florida’s beaches will be safe for swimmers.

The driest landmass on Earth fuels the growth of the planet’s lushest rainforests. Without the desert, the rainforest would die. Two massive ecosystems, separated by an ocean, are intimately connected. Changes in one reverberate around the world to affect the other. The harmattan is a powerful reminder of the interconnectedness of life on Earth.

Neil Griffin

Featured photo from blog.cupio.org

Literature Cited

Bristow CS, N Drake and S Armitage. 2009. Deflation in the dustiest place on Earth: The Bodele Depression, Chad. Geomorphology 105: 50-58.

Bristow CS, KA Hudson-Edwards, A Chappell. 2010. Fertilizing the Amazon and equatorial Atlantic with West African dust. Geophys. Res. Let. 37

Garrison et al. 2003. African and Asian Dust: From Desert Soils to Coral Reefs. Bioscience 53.

Stoorvogel JJ, N Van Breemen and BH Jassen. 1997. The nutrient input by Harmattan dust to a forest ecosystem in Cote d’Ivoire, Africa. Biogeochemistry 37: 145-157.

Swap R, M Garstang, S Greco, R Talbot and P Kallberg. 1992. Saharan dust in the Amazon Basin. Tellus 44B: 133-149.

Prospero, JM. 1996. Saharan Dust Transport Over the North Atlantic Ocean and Mediterranean: An Overview, in The Impact of Desert Dust Across the Mediterranean. Editors: S Guerzoni and R Chester. Kluwer Academic Publishers: Nowell, USA.

harmattan-pic

The Harmattan: Part I

The Harmattan: The Winds of Life and Death, Part I

On Thursday January 17th, 2013, the residents of Siesta Key, Florida woke to an unpleasant sight. Dead fish in the thousands were washing up on the beach, vomited from the sea on the incoming tide. The fish were killed; victims of a red tide. Red tides are the colloquial name given to a phenomenon called algal blooms, rapid, explosive growths of toxic algae which float in slimy mats across large expanses of the ocean. Algal blooms kill fish and other marine wildlife by clogging their gills with slimy muck and asphyxiating them, by sucking all of the available oxygen from the water column, and by releasing toxic chemicals. They’re not much better for humans – causing respiratory problems if the water is swam in, and even death if people consume contaminated shellfish. Red tides are a recurrent nightmare for ocean-front communities throughout the Caribbean and up and down the East Coast. They cause severe economic damage by shutting down tourism and fisheries for months at a time.

Most algae grow at low densities because they cannot acquire the necessary nutrients to grow faster. They live a tenuous existence, constrained by the emptiness of the ocean. But like an oxygen starved fire, they need only a spark to burst into uncontrollable life. For algae, that spark is iron. The growth of algae is constrained by a lack of iron. Iron is rare in the open ocean – most biologically available iron comes from dust and soil blown into the sea. That happens regularly, but its not usually enough for algae to take advantage of, so they’re said to be iron-limited. But occasionally, a massive influx of iron – like opening the door on a backdraft – causes an explosive growth of algae which leads to a bloom. The source of those periodic iron influxes is an unlikely one. The spark which causes algal blooms in North American comes from many thousands of miles away, deep in the Sahara Desert. It is one of the greatest shows of primal force and power found anywhere on Earth, capable of influencing weather on a global scale. It is the harmattan.

Lawrence Durrell, in his novels The Alexandria Quartet, provides a vivid description of the harmattan:

Before sunrise the skies of the desert turned brown as buckram, and then slowly darkened, swelling like a bruise and at least releasing the outlines of cloud, giant octaves of ochre which massed up from the Delta like the drift of ashes under a volcano. The city has shuttered itself tightly, as if against a gale. A few gusts of air and a thin sour rain are the forerunners of the darkness which blots out the light of the sky. And now unseen in the darkness of shuttered rooms the sand is invading everything, appearing as if by magic in clothes long locked away, books, pictures and teaspoons. In the locks of doors, beneath fingernails. The harsh sobbing air dries the membranes of throats and noses, and makes eyes raw with the configurations of conjunctivitis. Clouds of dried blood walk the streets like prophecies; the sand is settling into the sea like powder into the curls of a stale wig. 

Michael Ondaatje, in The English Patient, adds another:

Travelling alone the ground like a flood. Blasting off paint, throwing down telephone poles, transporting stones and statue heads. The harmattan blows across the Sahara filled with red dust, dust as fire, as flour, entering and coagulating in the locks of rifles. Mariners called this red wind the “sea of darkness.” Red sand fogs out of the Sahara were deposited as far north as Cornwall and Devon, producing showers of mud so great this was also mistaken for blood. 

In Arabic it is called the kamsin, meaning 50, because it blows for 50 days. The Tuareg, blue-veiled nomads of the Sahara are the ones who call it harmattan, poetically The Hot Wind of the Desert, but more literally, just “evil thing.” In the more staid realm of meteorology, it is a West African Trade Wind, originating in the Sahara near Lake Chad. But that’s hardly exciting.

The harmattan is the troubled offspring of two major wind systems which clash over North Africa: moist tropical winds blowing up from the equator, and cooler, subtropical winds coming down from the north. In winter these two fronts collide at the southern edge of the Sahara, the Sahel, and the harmattan is born – a powerful, spinning “extratropical cyclone” that blows north and west across the desert.

To say it stirs up sandstorms is an understatement. A member of the French Foreign Legion once wrote that the harmattan travels, “as a mist or fog of dust as fine as flour, filling the eyes, the lungs, the pores of the skin and nose.” It is a hot, dry wind which blows incessantly for months. Humidity can drop as low as 10%; all of the moisture is sucked from the air, causing spontaneous nose bleeds. Visibility is minimal. The sand creeps everywhere, and cities shut down – their people hidden behind windows and walls as the mercury climbs to 50 degrees C. In 1927, the harmattan derailed a train in Algeria. In 1999, it decimated a grove of date palms at an oasis in Mali. Without the life-giving sustenance of the trees, the community was abandoned within a week.

But the harmattan is too powerful to be contained to just one continent. The violent convective winds that swirl through the Sahara jettison thousands of kilograms of dust and sand kilometres into the atmosphere, where they are grabbed by high altitude winds and whisked out to sea.

Of course, and as is always the case, Darwin noticed it first. On January 16th, 1833, the HMS Beagle was travelling passed Santiago, the largest island of Cape Verde (an island republic a short hope from Africa’s west coast). In his journals, Darwin wrote that, “the atmosphere was so hazy that the visible atmosphere was only mile distant.” Owing to the direction of the wind, he surmised that, “the dust probably came from the coast of Africa”. The novelty of the ocean dust wore off quickly, as the constant whirl of sand grains infiltrated every nook and cranny of the Beagle, and damaged the delicate compasses and sextants on which the sailors relied.

Caught in tropospheric air currents, dust from the harmattan takes a week to cross the Atlantic, before depositing as a silty shower in North and South America. One estimate says that as much as 20% of the soil on the eastern seaboard has its origins in North Africa. The iron-rich dust of the desert bleeds into the ocean half a world away, where it triggers toxic algal blooms. Along with dust, the winds carry microbes and fungal spores across the ocean, which are linked to the decline of coral reefs in the Caribbean. Humans can be harmed more directly too – the winds carry fungal meningitis spores around the world. In North Africa, outbreaks of meningitis regularly follow in the wake of the harmattan.

But the harmattan doesn’t just bring death; it also brings life. Part II tomorrow.

Neil Griffin

Repost of an article originally written for other-nations.com

Feature photo credit: Aka Teraka, akateraka.wordpress.com

Literature Cited

Garrison et al. 2003. African and Asian Dust: From Desert Soils to Coral Reefs. Bioscience 53.

Herald-Tribune. “Red tide, fish kill reported at Sarasota beaches”, January 17th 2013.

Stoorvogel JJ, N Van Breemen and BH Jassen. 1997. The nutrient input by Harmattan dust to a forest ecosystem in Cote d’Ivoire, Africa. Biogeochemistry 37: 145-157.

Prospero, JM. 1996. Saharan Dust Transport Over the North Atlantic Ocean and Mediterranean: An Overview, in The Impact of Desert Dust Across the Mediterranean. Editors: S Guerzoni and R Chester. Kluwer Academic Publishers: Nowell, USA.

Ondaatje, M. 1993. The English Patient. Vintage Canada: Toronto, Canada.

de Villiers M, and S Hirtle. 2003. Sahara: A Natural History. McClelland and Stewart Ltd: Toronto, Canada.

ss_130410_cicada_invasion_01_ssfull

The Cicada – Nature’s Mathematician

A prime number is one (which is) measured by a unit alone.

– Euclid, Elements 

 In c. 300 BCE, the Greek philosopher Euclid wrote the thirteen books that made up his magnum opus, Elements, and so doomed nearly 2000 years of Western students to a math education they didn’t want and don’t understand. In Elements, Euclid laid out a collection of definitions, axioms, and mathematical proofs, as well as developing geometric algebra and spatial geometry. Following the invention of the printing press, it became the second most published book in the world (after the Bible).

Blame this guy for forcing you to learn math.

Blame this guy for forcing you to learn math.

If you didn’t understand most of that paragraph, that’s okay. We’ll take it easy on the math.

One of the definitions laid out by Euclid in Elements is that of ‘prime numbers’. A prime number is a number greater than one that is only divisible by one and itself. All other numbers are called ‘composite’ numbers. 1, 2, 3, 5, 7, 11, 13, 17, and 19 are prime numbers. 4, 6, 9, 12, 14, and 15 are composite numbers. There are infinitely many prime numbers, and no easy formula for determining them. For many years a number’s primality was determined by trial division, which is as slow as it sounds. Now computers can determine prime numbers (though outside of the esotericism of math, I’m not sure who cares).

But Euclid didn’t actually discover prime numbers (sorry, dude). Nature had already been making use of them for millions of years. For the real discoverers of prime numbers we have to turn to the animal kingdom – specifically, we have to look at cicadas.

Cicadas are a widespread family of insect, containing between 2500 and 3000 species. They’re moderately sized insects (averaging ~2 inches long) that mostly feed on sap, although they have a nasty looking proboscis that can do some damage if they mistake your arm for a tree. Cicada’s are most well known for the distinctive sound they making, a characteristic click-and-buzz song that forms the soundtrack of night throughout the tropics and subtropics.

Cicadas live most of their life-cycle underground, as subterranean nymphs, buried in up to a foot of soil. They feed on juice extracted from plant roots, and go through multiple stages of development before they’re ready to breach the soil and make a bid for freedom. This development is a slow process, taking many years, but eventually they’re old enough to leave home. Cicada’s behaviour is triggered by soil temperature, so in the year when they are most developed, they wait for the sub-surface soil to reach 17°C, and then climb to the surface.

The life cycle of a cicada is..complex.

The life cycle of a cicada is..complex.

On the surface, they climb into a nearby tree, and then must sit for six days while waiting for their soft and squishy underground form to harden into a new, aerodynamic, hard exoskeleton. On the seventh day, they are able to fly. But only if they’ve survived that long. While they wait for six days, cicadas are vulnerable to just about everything: birds, reptiles, and any number of mammals. Trees filled with young cicadas are a buffet for predators. But the cicadas are not defenceless, and one brainy genus in particular, the Magicicada of North America, has evolved two ways to protect itself, both involving numbers (math can save your life).

First, the Magicicada satiate their environment. They don’t come out of the ground one-or-two nymphs at a time, they come out in a mass swarm – more than 1.5 million cicadas per acre. They coat trees, playgrounds, and houses, and for a few weeks make a deafening racket. The call of the male cicada is loud enough to damage a human’s hearing.

 

 

Imagine you are a cicada and you’ve studied probability. You know that every predator will eat five cicadas. If you appear in a small group of only 10 cicadas, you’re pretty much done for – even with only one predator, you have a 50% chance of being eaten. Two predators or more and you’re a goner for sure. But this individual risk decreases as the number of cicadas you travel with increases – if you appear in a group of 100 cicadas, your chance of being eaten is now only 5%. The larger the group, the lower the individual risk of being eaten. This dilution of risk is the same principle that drives schooling in fish, and herd living in zebras, antelope, and other plains-dwelling mammals.

(It also explains why it’s good reason to go hiking with friends, rather than alone.)

 

The clever dog food has satiated its predator.

The clever dog food has satiated its predator.

The second way Magicicada protect themselves is by exploiting the properties of prime numbers to confuse predators. Magicicada don’t come out of the ground every year – instead they emerge in intervals of 13 or 17 years. These, as you now know, are prime numbers. And there’s a good reason for cicada’s to cycle every 13 or 17 years.

Populations of animals naturally fluctuate. Usually these fluctuations follow predictable cycles based on the life history characteristics of the animals: how old they are before reproducing, how many offspring they have, and how long they live. The small mammals and birds that feed on cicadas fluctuate on 2 and 4-year cycles. That means that every 2 or 4 years there is a peak in the population of these predators – which is bad news for prey.

 

A traditional predator-prey cycle.

A traditional predator-prey cycle.

If a prey cycle and a predator cycle happen to line-up on top of one another, you get a period of ‘resonance’, where both predator and prey numbers are high. The large numbers of predators decimate the prey population, and do serious damage to its hopes of long-term survival.

By making use of prime number intervals, Magicicada avoid the possibility of resonance. 13 and 17-year cycles are not divisible by 2 or 4, so the Magicicada emergences will never coincide with a peak in predator population. If Magicicada used a 14 or 15-year cycle instead, non-prime numbers, then they would regularly emerge in years of high predator numbers. Natural selection decided that was a bad idea, and has pushed the cicadas towards prime number cycles instead. And it works: mathematical models show that if cicadas emerged in a non-prime year, they would face 2-5% higher predation. That doesn’t sound like a lot, but in the natural world the margin for error is often very slim, and an extra 5% per reproductive cycle reduction in cicada population could have long-term repercussions.

 

Knowing the complexity of their life cycle may make you appreciate them more. But maybe not.

Knowing the complexity of their life cycle may make you appreciate them more. But maybe not.

Euclid and his intellectual descendants may have argued and written about prime numbers first, but they weren’t the original discoverers. That honour goes to cicadas, nature’s mathematicians.

 

Neil Griffin

Note: This is repost, with some changes, from an older blog of mine (other-nations.com).

Featured image by Ron Edmond

Literature Cited

 

Campos PRA, de Oliveria VM, Giro R and DS Galvao. 2004. Emergence of prime numbers as the result of evolutionary strategy. Phys Rev Lett 93

Goles E, Schulz O, and M Markus. 2001. Prime number selection of cycles in a predator-prey model. Complexity 6:33-38.

 

How Home Decor Could Save Your Life (If You’re A Spider)

Like all artists, spiders spend the best parts of their lives working to create a vision that will be appreciated by only a few individuals. However, unlike other artists, a spiders work is also cleverly disguised deathtrap, where its unfortunate prey lies suspended and confused in midair, twitching frantically while it waits for sweet release.

Although come to think of it, I’ve seen the same sorts of behaviour in tourists lost in New York’s Museum of Modern Art.

Art claims another victim. Credit: Dan Hyde

Art claims another victim. Credit: Dan Hyde

Spider webs are breathtaking examples of artistry and complexity in the natural world (at least from a distance – when you walk into one in the woods, a web is somewhere between irritating and terrifying, depending on your arachnophobia). But spiders don’t stop at just the basic web – what’s a home without a few accoutrements, to add an individual taste?

Spiders decorate their webs with stabilimenta: silk decorations. Some of these decorations are rather pretty – for example, the complex geometric patterns of the Argiope spiders, which make the spider look as those it is sitting in the middle of a flower. Other decorations are slightly more macabre – for example, the wrapped and desiccated remains of yesterday’s dinner.

See? A pretty/frightening flower. Credit: austinbug.com

See? A pretty/frightening flower. Credit: austinbug.com

That may not exactly be the way you or I try to decorate our homes. (Although I suppose big game hunters mount the stuffed heads of their prey on walls). But for spiders (and perhaps for big game hunters), these silk decorations serve an important function: compensation.

Compensation?

Compensation?

Size matters if you’re a spider. Like Goldilocks and her misappropriated goods, when birds are searching for a spider to eat, they look for a spider that is just the right size. Spiders that are very small go unnoticed, while spiders that are large are too big to eat. Medium-size spiders are perfect for birds, which, conversely, makes being medium-sized a poor life choice for a spider.

Perched in the middle of carefully-spun stabilimenta, smaller spiders can create the illusion of being much larger – reducing the chances of becoming a bird’s midday snack.

"Oh these? Yeah, they're real. No big deal." Credit: Flickr user 'Chasingtheflow'

“Oh these? Yeah, they’re real. No big deal.” Credit: Flickr user ‘Chasingtheflow’

Size probably has a genetic component, and unfortunately for spiders (as for all of us), you can’t always choose what your parents give you – that receding hairline, poor eye-sight, or a penchant for storing fatty foods on your thighs. But technology lets us cope with our shoddy genes: hair plugs, contact lenses, and infomercial gym equipment.

Spiders use silk decorations as their own way of changing the odds – mom and dad combined to make you a bird-sized meal? Dress up your web to make your legs look longer. It’s cheaper than high heels. 

Neil Griffin

References

Bateman and Fleming. 2013. The influence of web silk decorations on fleeing behaviour of Florida orb weaver spiders, Argiope florida (Fabricius, 1775)(Aranaeidae). Can. J. Zool