Seventeen Year Itch

Back in 1996, Bill Clinton was still in his first term of office, Charles and Diana agreed to divorce, the Unabomber was apprehended, and Ella Fitzgerald died. That year I hadn’t even dreamed of moving permanently to North America: I was living in Yorkshire where mad cow disease was seizing the headlines in England. While so much history has flowed through newspaper presses since then, Brood II cicadas were all the while secretly sucking at tree roots waiting for the calendar to flip over to 2013.

I encountered the brood a couple of weeks ago at a rest area on the I-64 west of Richmond.  The first thing travelers noticed after stepping out of their cars was a chirping racket coming from every direction. I had heard the sound only once before when a 13-year brood of cicadas was emerging near home in 2011. This year it is the turn of the 17-year ensemble to sing.cicada on grass

For a few weeks every 17 years local residents have sleepless nights. The noise can be as loud as a passing truck, and at 90 decibels reaches a level at which the Occupational and Safety Administration warns we should not be exposed to for more than 8 hours a day to avoid hearing damage. Not being respecters of regulations, male cicadas chirp round the clock.

They are among the great wonders of the insect world, but not only because they have one of the longest life cycles. The question that intrigues me more is how they manage to coordinate mass emergence.  When ground temperatures rise above 64 °F (18 °C) in the Year of the Brood, the fossorial cicada nymphs start to burrow upwards, breaking the surface first at the southern edge of their range (North Carolina) and progressively towards northern limits (Connecticut).  Soon there are incalculable billions above ground, more than a million per acre, but during intervening years you are unlikely to see any at all.  So precise is their timing that local residents can plan when to be on vacation in 2030 during the next big pulse.

They look scary and are the biggest of their kind. They are an inch-and-a-half long with bulging red eyes, orange wing veins and leg stripes, and through their transparent wings you can see a black cigar-shaped body.  They look like bugs in zoot suits and were given the marvelous scientific name, Magicicada septendecim.

I was a member of a naturalist group heading for a wildlife center in the Blue Ridge, but the cicadas in the car park – not you would think the most auspicious place to watch wildlife – were the most memorable sights of the day. They were thought to be a bad omen by superstitious early colonists, who assumed (wrongly) that they were the same as locusts in the Bible which warned in the Book of Revelation: “Then from the smoke came locusts on the earth …” I guess that every seventeen (or thirteen years) there were particularly fiery sermons from the pulpit about the seven last plagues of Armageddon.

For all their fearsome appearance, they are harmless insects. They don’t bite or sting, nor do they eat vegetation as true locusts do. They can cause minor tree damage from “flagging” (browning) during nest-building, but are generally rather beneficial. Soon after mating and egg-laying the adults die, providing food for critters and fertilizing the soil. The only remaining cicadas are immature “instar larvae” hatched from eggs. These nymphs fall from the tree canopy to the ground where those that avoid predation burrow underground to find juicy roots to suck on … and on … and on until the calendar turns.

For the most part, the distribution of 17-year broods and 13-year broods don’t overlap, although they evolved from a common stock a few million years ago.  Today there are 15 broods in North America, twelve with 17-year cycles and three with 13-year, and you will not find them anywhere else.  Of the 3,000 species of cicada worldwide, only seven have periodical behavior.

Burrows and shells from which cicadas emerged in the car park
Burrows and shells from which cicadas emerged in the car park

We watched hordes of them lumbering up tree trunks and walls; we saw many flying unsteadily like old flying boats, often crashing into branches or to the ground where robins were waiting to pounce. For a small bird, a cicada is hamburger-sized (and probably just as nutritious), so the eaters were soon sated. Everywhere across the hard-trodden ground there were holes, about ten to the square yard and a little larger than earthworms make. These were the burrows from which cicadas had recently emerged, and scattered close by were the transparent brown shells (exuvia) which they had worn for so many years underground. They gave us a spectacle I may never see or hear again.

The greatest enigmas are how they know the time, and why coordinate their emergence instead of being independent like most insects. We know of genes that regulate daily cycles in animals, but I can’t understand how molecules make a 17-year timer. And if cicada nymphs were synchronizing eruption by communicating with each other underground, it stumps my imagination.  Perhaps it serves to overwhelm the appetites of predators so that at least some survive to breed, although that theory is controversial. A similar explanation has been offered for mast seeding of long-lived plants. Last year was a mast year for oaks, with acorns lying so thick in our yard that every step sounded like walking on cornflakes.  But mast years are unpredictable – they can be consecutive or after long gaps – whereas cicada years can be written into almanacs for years, even centuries, ahead.cicada on blue

There are few pat answers in nature and the life sciences. That was frustrating when I was a student preparing for exams, but now I think the mysteries are far more wonderful than the facts.

Next Post: Baby’s first picture

Cardinal robes

As winter marches towards spring, two male northern cardinals have set up territories in our yard, keeping an eye on their mates but not getting along with each other.  They watch, emblazoned against a blue sky, from a favorite perch in bare trees. Catching sight of each other they ‘see red’, puffing up scarlet robes which get more brilliant as the breeding season approaches.

Why does red stand above all others, sometimes a sign of menace, sometimes a symbol of courage, and often expressing the power of joy and passion?

Cardinal
Cardinal in our yard

Red brake lights, red stop lights, red London buses, red light district, red planet, Redcoats, Red Army, red flags, cardinal bishops, Coca-Cola … the list goes on.  A color so intense it seems to sear the back our brain, where circuits originating in the red cone receptors of the retina are processed in the visual cortex. Would red convey a smaller emotional charge if blood was blue or fire green?

There’s nothing in a color beyond a wavelength – apart from how the brain perceives it. Hot peppers come in green as well as red, and red letter days and red herrings are fairly benign! Most mammals lack the red cone, seeing gray instead, but they are capable of as much passion as any primate or bird that has full color vision.  Bulls charge at a waving ‘gray’ flag.

To ask how a bird gets as hot as a cardinal is like asking for a Just So story – How the leopard got his spots … How the camel got his hump? Well, it’s the diet, dum-dum, because everyone knows, “We are what we eat.”  And looking around the yard, there is ostensible evidence everywhere.  Holly and Nandina bushes tempt hungry birds with dangling crimson berries.  But wait, biologists seldom answer a simple question with a straightforward story. Most of the intensity in these berries is from anthocyanin pigments which are not absorbed intact into the bloodstream. If berries are not wholly responsible, perhaps birds get their color from something else in their diet – like insects.  Errh … not the cactus juice-sucking insects that gave us cochineal for the pantry and for dyeing the tunics of Redcoat officers.

Most old sayings become threadbare in the light of research, and with a few exceptions there is no simple relationship between what we eat and how we look because of the rumbling process of metabolism going on inside.  Otherwise some of us would look like … well, I leave that to your imagination.

Nandina
Nandina

What then lends cardinals their color – and to so many wonders in nature, from fall leaves to appetizing vegetables?  Bugs Bunny would say that carrots are a good place to begin nibbling:

“Oh, carrots are divine, you get a dozen for a dime …”

Nearly two hundred years ago, a German student, one Heinrich Wickenroder, extracted from carrot juice a “yellow fatty oil with carotin” which dissolved in ether but not in water.  He won praise from his professors who thought it might fend off gut parasites, which were rampant in those days and still all too common in domesticated animals and wildlife.  Over time, his discovery expanded into a family of related molecules from plants, called carotenoids, including lycopene, lutein, and beta-carotene, which is the precursor of vitamin A. If I was asked to score my favorite molecules, carotenoids would be in the top ten beside DNA and chlorophyll.

Carotenoids are needed for photosynthesis, so they are almost ubiquitous in the plant kingdom, from whence we satisfy our own needs.  They prevent blindness, promote fertility, inhibit cancer, block oxidation, boost immunity, and make dandies of our avian friends in the yard.  I love the biological symmetry: carotenoids make plumage conspicuous in birds and give the power of vision so their mates and rivals recognize it and we can enjoy it (in fact, vitamin A is only responsible for the rod cells). Because we can’t make these virtuous molecules in our bodies but have to absorb them from our diet, the food police keep heaping more fruit and veg on our plates.

Northern cardinals obtain their supply from an omnivorous diet of berries, seeds, and insects, while American goldfinches subsist on strictly vegetarian fare.  When Cornell ornithologists reduced red carotenoids in the diet, cardinals grew pale, and goldfinches turned orange when yellow carotenoids were deficient. But changing diets didn’t go as far as switching their colors because the gut is wise to the vagaries of nature (and researchers) by converting one type of molecule to another.  It’s obvious that diet alone can’t explain everything because female cardinals eating the same food are so much drabber than males.  It takes testosterone to make a male hot.

Red grouse are hardly that.  A game bird looking like a large cardinal in the open heather would soon end in a vixen’s den or on a Scottish table. But the males have a small red comb, a token that performs the same service as the cardinal’s feathers.  Since grouse are plagued by roundworms and ticks, ornithologists wondered whether treating the males with anti-helminthic drugs could improve their breeding performance as well as their overall health. They did.  After ridding them of parasites, the birds absorbed more vitamins from their food which, in turn, increased the color intensity of their combs.  The little red flag on their heads was more attractive to the hens, who thought they would make healthier partners.  Female cardinals get the same message. They can’t be hoodwinked by a frail male because carotenoids painting the breasts of males bursting with blushing pride make honest birds of them.

Next Post: A Death Observed

A Dog’s Dinner

Banana Joe stole the show!

No, not the LA radio presenter, I mean the affenpinscher from Attleboro who won Best in Show last week at the Westminster Dog Show in NYC.

I’m not a pooch person, prefer big mushy dogs, but Joe the affenpischer who looks like a cross between a toy and a monkey is easy to love. And a monkey dog he is (ein Affe, a monkey). Like monkeys, Joe and our Golden enjoy a banana, which is not so surprising if you consider it is a perfectly natural food for their cousins – wolf packs in Minnesota and Alaska.  Erhh!

We changed their dietary preferences after the first wolf cub was adopted by a human family.  I ought to pause to correct myself because dogs can’t express preferences any more than I could as a London schoolboy. It is only a slight exaggeration to say that we were served Dickensian gruel for school lunch. I remember peering through the kitchen window at the cooks watching over steaming vats of bubble and squeak made from yesterday’s left-overs and stirring custard thick as tar but not so smooth. It was ‘Hobson’s choice’, or, in other words, no choice at all, just as it has always been for our dogs.

Until the food industry realized there was a canine market, most dogs had to make-do with human left-overs, living hopefully for a bone flung their way with a morsel of meat on it.  As members of the Order Carnivora, their ancestors enjoyed a high protein diet before they were domesticated around 10,000 years ago (some put it earlier). Neolithic people were then switching from hunting and gathering to agriculture, growing various cereal crops in the Old World, sweet potato, corn and beans in the New, and – yes – bananas in New Guinea.  Growing-their-own enabled them to form settlements with greater food security, and afterwards their diet became much richer in starch. So did the dogs’.

A new study of whole genome resequencing shows what an impact this change had on canine genetics. There are not as many genetic differences between dogs and wolves as you might think from their manner and appearance, but significant differences were found between genes involved in brain function and the digestion of starchy and fatty foods.  It seems that a genetic bottleneck occurred in the early prehistory of domestication. Animals with gene variants that favored compliant behavior and efficient starch digestion squeezed through, and those survivors became the founders of modern dogs. The wild-type wolf genes disappeared because dogs lacking genes that were better adapted to the new life were either kicked out for bad behavior or didn’t thrive on the new diet. Lying at your fireside is an example of how we sculpt the evolution of species.

Lilah
Lilah’s turn

Now to sweeter talk. Sweet is one of our five senses of tastes, but long before we celebrated it by inventing confectionary it was probably beneficial for distinguishing between good and bad food. Since wolves will occasionally eat vegetable matter it’s not surprising that they share the same sweet taste receptor gene, Tas1r2, as ourselves, and dogs inherited it from them.  Other mammals can taste sweetness too – raccoons and of course bears – but not all. Cats can’t taste it because their Tas1r2 is pseudogenized (meaning it doesn’t function), and likewise in sea lions, otters, dolphins, and hyenas.  Since they are flesh-eaters that swallow their food whole there’s no time for tasting and therefore no point in having a sweet taste receptor. But biologists who love to tell a commonsense story are often embarrassed by an ugly fact that threatens a beautiful theory. We might expect a species that sips its food to have a well-developed sense of taste, but apparently vampire bats don’t have a sweet tooth in their heads.

Now back to bananas and Banana. Our dog, Lilah, has a more discerning palate than her owner because she turns her nose up at green bananas which are just full of starch but she will happily chomp on yellow ones in which much of the starch has been converted to sugar.  We throw away overripe bananas but, given the chance, she will gorge on them knowing they have the most sugar.  The French clearly know their bananas too because their grocery stores have premium prices on fruit with brown skins.  Belle banane.

Banana Joe deserved a better reward. He was taken to a swanky Manhattan restaurant where he was served filet mignon to celebrate victory. I expect he was glad to leave starch behind for a day if only to prove he is still a card-carrying carnivore.

Next Post: Cardinal robes