Mosquito magnets

My wife claims that I only bring her along on tropical vacations to lure the mosquitoes away from me.

She is, to put it bluntly, a mosquito magnet.  If there's an outdoor party, and there is a single lonely mosquito anywhere within a five-mile radius, it will find her.  Worse still, she has a bad allergic reaction to bites; being bitten leaves her itching for days.

Bad combo, that.

I, on the other hand, barely get bothered at all.  The same strange dichotomy got passed to our kids; our older son doesn't seem to get bitten much.  On the other hand, we took a family vacation to Belize when our boys were twelve and fifteen, and I saw our younger son was sitting on his bed one evening examining his legs.  I asked him what he was doing.

Turned out he was counting mosquito bites.  He lost count at around forty.

[Image licensed under the Creative Commons User:Ngari.norway, Mosquito bite4, CC BY-SA 3.0]

The contention that many have, of some people being more attractive to mosquitoes than others, was just demonstrated conclusively in a paper last week in the journal Cell, by a team led by Leslie Vosshall of the Howard Hughes Medical Institute.  What Vosshall and her team did was to have volunteers wear nylon stockings on their arms for six hours, allowing the fabric to pick up any chemicals the person was secreting in their sweat and skin oils.  The nylons were then cut up into squares, and the pieces presented to hungry Aedes aegyptii mosquitoes.

The results were unequivocal.  One subject, #33, had an attractiveness to mosquitoes over a hundred times greater than the least attractive subjects, #19 and #28.

What seems to set apart people like poor #33 is the particular cocktail of carboxylic acids in their skin oils.  Carboxylic acids are small organic molecules characterized by having a carboxyl group -- a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl (-OH) group -- and include such familiar compounds as amino acids and fatty acids.  It turns out that of the hundreds of different kinds of carboxylic acids, each person produces different ones in different amounts -- and this "scent" (not that you or I would notice the difference) is what determines who is a mosquito magnet, and who largely gets left alone.

A little discouraging, though, is their other finding; that this chemical signature is relatively resistant to changes in diet and grooming habits.  None of the contentions you might have heard -- eating foods rich in B vitamins, using unscented soaps and shampoos, and so on -- seemed to make any difference.  The people who were mosquito attractors stayed that way throughout the course of the experiment, regardless what they ate and what cosmetic products they used.

While this study might eventually lead to better repellents, at the moment, we're kind of stuck where we were.  The best mosquito repellent is DEET (diethyltoluamide), which has a pretty good track record for safety, although (as I found out when I was in Ecuador) dissolves plastics.  (Fortunately, the only thing damaged was a ball-point pen; I discovered this when I applied some mosquito repellent, picked up the pen, and it promptly stuck to my hand.)  Some other products, like Avon's "Skin So Soft," seem to have some effect but aren't nearly as reliable as DEET.  

Maybe if Vosshall and her team can pinpoint exactly which carboxylic acids are causing the problem, they could find some kind of repellent that would work by blocking them or breaking them down.  I know my wife would appreciate it.  It's late October in upstate New York, and the eight mosquitoes still left alive around here are still waiting by our back door for one last chance to bite her.

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The walk of life

There are countless different actions we take every day that we do so automatically we're hardly even aware of how complex they are.

Take, for example, walking.  Walking takes the coordination of dozens of muscles, each of which has to contract and relax in exactly the right sequence to propel us forward and adjust for irregularities of the terrain we're navigating.  To avoid falling, we need to keep our center of gravity over our base of support, which is aided by adjustments in posture and such counterbalancing movements as swinging the arms.  But in order to do that we have to keep track of proprioception -- our sense of where our bodies are -- which is accomplished by a whole array of sense organs, including vision, the tactile sensors in the skin, and the semicircular canals -- the balance organs in the inner ear, which work a little like a carpenter's level.

And all of those -- the sense organs that keep track of what's going on and the muscles that use that information to contract and relax at the right times -- are linked by an astonishingly complex set of nerve relays and circuits coordinated by our brains.

All of that, just to get up and walk across the room.

The reason the topic of locomotion comes up is a paper a couple of weeks ago in Current Biology describing a single-celled protist called Euplotes eurystomus that has fourteen leg-like appendages -- and is able to walk.

The scientists studying Euplotes found that the appendages had thirty-two different configurations, which they called"gait states," and that somehow, the little creature was keeping track of which sequence of gait states allowed for the most efficient walking.  It turned out that the internal scaffolding of the cell, made of hollow threads called microtubules, created cross-links from each appendage to the others.  The amount of tension in the microtubules allows the organism to coordinate the movement of all fourteen appendages.

"The fact that Euplotes' appendages are moving from one state to another in a non-random way means this system is like a rudimentary computer," said Wallace Marshall, of the University of California - San Francisco, who co-authored the paper.

Euplotes eurystomus [Image from Larson & Marshall, UCSF]

All of this puts me in mind of the idea of irreducible complexity -- that there are structures in living organisms that would not work if all the parts hadn't been created all at the same time.  It's a favorite salvo of the young-Earth creationists and proponents of intelligent design.  The battle cry usually goes something like, "One percent of an eye isn't good for anything."  Richard Dawkins does a brilliant takedown of this entire argument in his tour-de-force exposition of the evolutionary model The Blind Watchmaker, in which he demonstrates that "one percent of an eye" -- a simple, light-sensing patch -- is indeed better than nothing, and that once you have that one percent, incremental gains in acuity can lead to the complex eyes now found in the animal kingdom.  (More fascinating still, the ability to sense light is such a powerful evolutionary driver that this process may have occurred, independently, dozens of times in different lineages.  For a wonderful overview of the evolution of eyes, check out this article from 2017 in the journal Nature.)

So locomotion, like vision, isn't irreducibly complex at all.  It's complex, yes; but hardly irreducible, because a single-celled organism is able to use chemical reactions and a network of microtubules to accomplish something very much like walking.  Our ability to coordinate motion has a history going back billions of years, during which time it has evolved into an action so complicated and intricate it's a damn good thing we don't have to keep track of it consciously.

Think about that next time you move your muscles.

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The ancestral worm

I live only a few miles from the tallest waterfall in the eastern half of North America, which is not Niagara Falls but Taughannock Falls.

Taughannock (for non-locals, pronounced ta-GAN-uck) Falls is sixty-six meters tall, ten meters higher than Niagara.  It is way narrower than Niagara, and has a far smaller water volume even when it gets rainy around here, but hey, a record is a record.

All that gray rock you see surrounding the narrow thread of the waterfall is Devonian-age shale and limestone, sedimentary rocks deposited about four hundred million years ago when this whole area was at the floor of a shallow sea.  Taughannock Creek has gradually cut its way through the layers of rock, creating a hanging valley at the top of one of the gorges this area is known for -- and exposing literally millions of fossils.

Some of the most common fossils you can find in Taughannock Gorge are brachiopods, shelled animals that look to the untrained eye a bit like a clam.  They're only distantly related to mollusks, however -- the internal structure would make that immediately apparent.  Even the shells show the difference, if you know what to look for.  The easiest way to tell is that bivalve (mollusk) shells are symmetrical across the hinge line, and brachiopods are not.  (Whereas brachiopods are symmetrical across the midline of the shell, and most bivalves aren't.)

Syringothyris texta, an extinct Devonian brachiopod [Image is in the Public Domain]

Although incredibly common as fossils -- I know a couple of places where you can fill your pockets with brachiopod fossils in under fifteen minutes -- they're quite rare as living animals today.  They got hit hard by the Permian-Triassic Extinction (what didn't?) and never really recovered.  There are about thirty thousand species of brachiopods known to the fossil record, of which only a little fewer than four hundred have survived to the day.  Those survivors aren't common anywhere.  They're mainly deep marine species, animals none of us are going to run into on a daily basis.

But that low modern diversity belies what a dominant group they were back before the End Permian Event wiped out an estimated 96% of life on Earth.  Along with trilobites, they were one of the commonest life forms in the planet's oceans before the "Great Dying" of 252 million years ago destroyed them.

What brings all this up is a paper in Current Biology last week describing a fossil found in China that is a good candidate for the common ancestor of brachiopods and the two other groups of lophophorates -- phoronid (horseshoe) worms and bryozoans (moss animals).  Once again, looks are deceiving; these three groups of animals bear little superficial similarity.  The horseshoe worms are sedentary animals that live in U-shaped tubes, and bryozoans are tiny colonial species that look a bit like miniature corals.  But they are alike in internal structure, and all three have a lophophore, a tube-like feeding structure surrounded with tentacles.  And this newly-discovered species, the early Cambrian Wulfengella, looks like it's the right animal in the right place at the right time to be the ancestor of all three groups.

Artist's reconstruction of Wulfengella [Image courtesy of Robert Nicholls, Paleocreations.com]

All of this just goes to show how non-intuitive relationships can be.  Wulfengella doesn't look on first glance anything like any of the three groups it's suppose to be the ancestor to, but its fine structure gives away its kinship.  And it once again highlights how much everything -- the biodiversity, the terrain, the continents themselves -- have changed throughout Earth's history.  We only think things are static because our lives are so short; on the grander scale, the current configurations of the planet will last the blink of an eye.  If you'll indulge me quoting one more time the words of one of my favorite poems, from the eloquent mind of Alfred Lord Tennyson, because I can't think of a better way to close this post:

There rolls the wave where grew the tree.

O Earth, what changes hast thou seen?

There where the long road roars has been

The stillness of the central sea.

The hills are shadows, and they flow

From form to form, and nothing stands --

They melt like mists, the solid lands --

Like clouds, they shape themselves, and go.

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A hostile beauty

William Shatner, of Star Trek fame, wrote some profoundly moving words in his book Boldly Go, about his experience riding into space on Jeff Bezos's Blue Origin shuttle:

I love the mystery of the universe.  I love all the questions that have come to us over thousands of years of exploration and hypotheses.  Stars exploding years ago, their light traveling to us years later; black holes absorbing energy; satellites showing us entire galaxies in areas thought to be devoid of matter entirely… all of that has thrilled me for years… but when I looked in the opposite direction, into space, there was no mystery, no majestic awe to behold... all I saw was death.

I saw a cold, dark, black emptiness.  It was unlike any blackness you can see or feel on Earth.  It was deep, enveloping, all-encompassing.  I turned back toward the light of home.  I could see the curvature of Earth, the beige of the desert, the white of the clouds and the blue of the sky.  It was life.  Nurturing, sustaining, life.  Mother Earth.  Gaia.  And I was leaving her.

Everything I had thought was wrong.  Everything I had expected to see was wrong.

I had thought that going into space would be the ultimate catharsis of that connection I had been looking for between all living things—that being up there would be the next beautiful step to understanding the harmony of the universe.  In the film Contact, when Jodie Foster’s character goes to space and looks out into the heavens, she lets out an astonished whisper, "They should’ve sent a poet."  I had a different experience, because I discovered that the beauty isn’t out there, it’s down here, with all of us.

He's right in one sense; the vast majority of the universe is intrinsically hostile to life.  It's why I've always found the Strong Anthropic Principle a little funny.  The Strong Anthropic Principle claims that the physical constants which are, as far as we currently understand, not derivable from anything else -- such as the strength of the four fundamental forces, the masses of the subatomic particles, the speed of light, the fine structure constant, and so on -- were set with those values in order to make the universe accommodate matter and energy as we know it, and ultimately, life.  The words they use are "fine tuned."  If any of those constants were even a little bit different, life would be impossible.

Typically, the argument progresses from "fine tuning" to "implies a fine tuner" to "implies God."

This whole line of thought, though, ignores three things.  First, of course we live in a universe that has the physical constants set such that life is possible; if they weren't, we wouldn't be here to discuss the matter.  (This is called the Weak Anthropic Principle.)  Second, when I said those constants are not derivable from anything else, you should place the emphasis on the phrase that came before it; as far as we currently understand.  It may be that physicists will eventually find a Grand Unified Theory showing that some -- perhaps all -- of the physical constants are what they are because of a single fundamental principle stating that they aren't arbitrary after all, that they couldn't have any other values.

Third, as Shatner points out, most of the universe -- even most of the Earth, honestly -- is pretty fucking hostile to life as it is.

But I question his statement that this makes the universe any less beautiful.  I was in Iceland this summer and got to see an erupting volcano -- the whole nine yards, with jets of orange lava fountaining up and cascading down the side of the cinder cone.  I could feel the heat on my face from where I stood, about a hundred meters away; much closer, and my skin would have blistered.  The sulfur fumes were only made tolerable by the fact that it was a windy day.  The hillside beneath my feet was vibrating, the air filled with a roar like thunder.  Standing there, I was in no doubt at all about my own frailty.

It was also incredibly, devastatingly beautiful.

I was thinking about the beauty of the universe -- as unquestionably inimical as it is to our kind -- when I saw images from the Hubble Space Telescope of the Cat's Eye Nebula, along with a visualization of what it would look like close up, created by a team led by Ryan Clairemont of Stanford University:

The spirals are thought to be caused by two stars in the center of the nebula orbiting around each other, each emitting a pair of plasma jets that have been twisted by the stars' motion in the fashion of the jets of water sprayed from a spinning garden sprinkler.  But whatever the cause of the pattern, I was immediately struck by its awe-inspiring beauty.

I've never been to space, and I don't mean to gainsay Shatner's experience.  But I find the vast immensity of space to be beautiful even though I know my own existence in it is all but insignificant.  I can look up at the autumn constellations, as I did last night -- Perseus and Andromeda, Pegasus and Pisces and Aquarius -- and appreciate the beauty of those stars glittering in the night sky from the warm safety of my home planet.  Maybe some of them have planets harboring their own frail, fragile life forms, who just like us are dependent on the searing fires of their host stars to survive, and just like us look up into the night sky with awe and wonder.

Frightening?  Sure.  Dangerous, savage, unpredictable?  Undeniable.

But also deeply, overwhelmingly beautiful.

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Jurassic rainbow

Regular readers of Skeptophilia might recall that about a year ago, paleontologists announced the discovery of a bird fossil from northeastern China that had a long, pennant-like tail -- and that from the extraordinary state of preservation, they were able to determine that the outer tail feathers had been gray, and the inner ones jet black.

Determining feather, hair, and skin color of prehistoric animals is remarkably tricky; the pigments in those structures break down rapidly when the animal's body decomposes, and the structures themselves are fragile and rarely fossilize.  The result is that when artists do reconstructions of what these animals may have looked like, they base those features on analogies to modern animals.  This is why in old books on dinosaurs, they were always pictured as having greenish or brownish scaly skin, like the lizards they were thought to resemble, even though dinosaurs are way more closely related to modern birds than they are to modern lizards.  (To be fair, even the paleontologists didn't know that until fairly recently, so the artists were doing their best with what was known at the time.)

But it does mean that if we were to get in the TARDIS and go back to the Mesozoic Era, we'd be in for a lot of surprises about what the wildlife looked like back then.  Take, for example, the late Jurassic Period fossil found by a farmer in China that contained the nearly-complete skeleton of a birdlike dinosaur.  Here's the fossil itself:

What's remarkable about this fossil is that the feathers were so well-preserved that paleontologists were able to get a close look at the melanocytes -- the pigment-containing cells -- and from the arrangement and layering of those cells, they determined that the dinosaur's head feathers were arrayed like a rainbow, similar to modern hummingbirds, sunbirds, and trogons.

So here's the current reconstruction of what this species looked like:

[Reconstruction by artist Velizar Simeonovski, of The Field Museum]

Kind of different from the drab-colored overgrown iguanas from Land of the Lost, isn't it?

The species, christened Caihong juji from the Mandarin words meaning "big rainbow crest," adds another ornate member to the late Jurassic and early Cretaceous fauna of what is now northern China.  And keep in mind that we only know about the ones that left behind good fossils -- probably less than one percent of the total species around at the time.  As wonderful as it is, our knowledge of the biodiversity of prehistory is analogous to a future zoologist trying to reconstruct our modern ecosystems from the remains of a sparrow, a cat, a raccoon, a deer, a grass snake, and a handful of leaves from random plants.

I think my comment about being "in for a lot of surprises" if we went back then is a significant understatement.

Even so, this is a pretty amazing achievement.  Astonishing that we can figure out what Caihong juji looked like from some impressions in a rock.  And it gives us a fresh look at a long-lost world -- but one that was undoubtedly as rainbow-hued and iridescent as our own.

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Nonlocal and unreal

This year, the Nobel Prize in Physics went to three scientists who have proven beyond a shadow of a doubt that our common-sense perception of how the universe works is very, very far off from the reality.

What that reality actually is remains to be seen.

John Clauser, Alain Aspect, and Anton Zeilinger were the recipients of the award this year "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science."  Their experiments established a mind-boggling fact: the universe is not locally real.

What that means, in non-technical language, is harder to pin down.  In physics, the concept of locality has to do with the fact that information transfer has a speed limit -- the speed of light.  If an event occurs at one point in space, then that event can only affect another point in space if it's nearby enough that light has enough time to travel between one and the other.  Reality means that an object's properties are independent of observation; it's a hard-science version of the time-honored question, "if a tree falls in the forest, and no one is there, does it make a sound?"

While the "locality" piece isn't perhaps something that impacts us on a daily basis -- light travels so fast that on the scales we usually deal with, it may as well be instantaneous -- "reality" certainly does.  Even the physicists balked for decades against the hints they were getting that locality and reality were on shaky ground.  No less a luminary than Albert Einstein said, "Do you really believe that the Moon is not there when you are not looking at it?"  But ever since Northern Irish physicist John Stewart Bell first proposed that there was something at the heart of quantum mechanics that called local reality into question, way back in 1962, the loopholes for avoiding that bizarre conclusion have been closing one by one.

The heart of the problem lies with entanglement.  The idea here is that you can create a pair of particles such that you know if one has a particular property (such as a spin axis pointing up) the other will have the opposite property (spin axis pointing down).  So far, nothing too weird about that.  It's no odder than putting each of a pair of gloves into a sealed box, and handing a box to your friend; if when your friend opens his box, he finds a left-handed glove, you automatically know your box must contain the right-handed one.  The system was set up that way.

But what Bell implied was that this wasn't the case.  The gloves were neither right nor left until you opened one of the boxes; if your friend did that, and observed a left-handed glove, the glove in your box "sensed that" (whatever the hell that means!) and instantaneously became right-handed, regardless of how far apart they were at the time.  The measurement process somehow created the state of the system, even if the parts of it were separated by a distance too great for light to cross.

For a long time, the prevailing approach amongst physicists was just to pretend it wasn't happening, an approach David Mermin summed up as "shut up and calculate."  Perhaps there were "hidden variables" that made some sort of locally real explanation account for the strange phenomenon of entanglement; using our analogy, that the gloves were what they were even though they hadn't been observed yet, no superluminal communication necessary.  And for a while, they kind of got away with it.  But with a series of ingenious experiments, Clauser, Aspect, and Zeilinger conclusively showed that there are no hidden variables; the universe, it seems, is not locally real.

What exactly is happening is another matter.  The three recipients of this year's Nobel Prize in Physics have shown that what John Stewart Bell proposed sixty years ago is spot-on correct, as crazy as it sounds.  There is something about the process of observation that does lock the observed object into a particular state faster than should be possible; Schrödinger's long-suffering cat seems to be not a wild metaphor but how the universe actually works.

I find this whole thing fascinating but a little overwhelming.  It's hard to imagine how our physical surroundings can behave in a manner so completely opposite to our common-sense notions.  But Clauser, Aspect, and Zeilinger have demonstrated conclusively that they do -- and it lies with the rest of the physics community to tell us laypeople exactly what that means.

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An ancient invasion

Just about anywhere you are in the world, you are confronted constantly with invasive species.

Some are so ubiquitous we've stopped even noticing them.  Here in the United States, for example, most lawn grasses are non-natives (including, amusingly, Kentucky bluegrass), as are dandelions, daisies, burdock, garlic mustard, multiflora rose, bush honeysuckle, and thistle.  None of our domesticated animals are native to North America, but neither are such ridiculously common creatures as house mice, the various species of rats, Japanese beetles, pigeons, starlings, house sparrows, and goldfish.  

It's tempting to lump all these species together and say "exotic = bad," but that's a vast, and inaccurate, oversimplification.  Some have clearly had devastating effects on native species; feral and owned-but-outdoor cats, for example, kill an estimated two billion birds a year in the United States alone.  (Yes, that's billion, not million.  Cats are responsible for more bird deaths than any other single cause.)  Other exotics have had far less impact; dandelions may be in every lawn in North America, for example, but they don't seem to do much in the way of outcompeting other species.  (And, as I said earlier, lawn grasses are exotics themselves anyhow.)

A lot of effort by environmental agencies has been put into eradication of exotics, to varying levels of success.  Rats and mice, for example, are generally a lost cause, given their fast reproductive rate and ability to survive on damn near any kind of food; but some isolated islands have done pretty well, most notably South Georgia, which wiped out their rat and mouse infestation in 2018 in order to save endangered birds that nest there.

The southeastern United States, however, has had almost zero success controlling kudzu, also called "mile-a-minute vine" because of its stupendous growth rate.  Introduced in 1876, and hailed as a source of browse for cattle and starch-rich roots that could be used in place of potatoes, the vine went on to cover trees, barns, and slow-moving individuals, and to this day blankets acres during its growing season.

Kudzu in Atlanta, Georgia [Image is in the Public Domain]

Where it gets interesting is the observation by one of my AP Environmental Science students a while back, who said, "But if you go back far enough, isn't everything exotic?"  It's a point well taken.  Species move around, and introductions happen by accident pretty much continuously.  (In fact, there's a whole mathematical model called island biogeography that has to do with the effects of such factors as island size and distance from the mainland on immigration rate and stable biodiversity.)  Our own deliberate and accidental introductions are only continuing a process that has been going on for a long time.

A very long time, to judge by the research of Ian Forsythe (of the University of Cincinnati) and Alycia Stigall (of the University of Tennessee - Knoxville).  They've been studying the "Richmondian Invasion" -- a sudden influx of new species into the shallow sea that covered what is now northern Kentucky, southwestern Ohio, and southeastern Indiana that occurred during the Late Ordovician, 450 million years ago.

The invasion was surprisingly rapid.  Due to exceptionally well-preserved strata, they were able to show that the new species were introduced from the north, as rising seas allowed them to cross what had been a low ridge of dry land, over only a few thousand years.  And what Forsythe and Stigall found was despite the magnitude of the invasion, and the speed with which it occurred, it didn't have very much effect on the recipient ecosystem's pre-existing species.

The reason, Forsythe and Stigall say, is that most of the invaders were low on the trophic ladder -- they were filter-feeders and grazers on phytoplankton.  It'd have been a different story if the invaders had been high-trophic-level predators.

All of this should inform our decisions on where to put our limited resources for environmental management.  High-impact, high-trophic-level invaders -- feral cats, rats, and the like -- are more critical to control than low-level herbivores like pigeons and house sparrows.  (It bears mention, though, that just being a herbivore doesn't mean "harmless;" here in the northeastern United States, whole forests of ash trees are being killed by the emerald ash borer, and farmers and viticulturists are rightly flipping out about the wildfire-spread of the spotted lanternfly.)

So it's a complex subject.  But it's fascinating that an analysis of an exotic invasion 450 million years ago might inform our decisions about how to manage exotics today.  Yet another indication of the value of pure research -- it can give us an angle on real-world problems that we wouldn't have arrived at otherwise.

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