Pink, pink, gold

When I was in Ecuador in 2019, I was blown away by its natural beauty.  The cloud forests of the mid-altitude Andes are, far and away, the most beautiful place I've ever been, and I've been lucky enough to see a lot of beautiful places.  Combine that with the lovely climate and the friendliness of the people, and it puts the highlands of Ecuador on the very short list of places I'd happily move to permanently.

What brought me there were the birds.  It's a tiny country, but is home to 1,656 species of birds -- about one-sixth of the ten-thousand-odd species found worldwide.  Most strikingly, it has 132 different species of hummingbirds.  Where I live, in upstate New York, we have only one -- the Ruby-throated Hummingbird (Archilochus colubris) -- but there, they have an incredible diversity within that one group.  Because each species is dependent on particular flowers for their food source, some of them have extremely restricted ranges, often narrow bands of terrain at exactly the right climate and altitude to support the growth of that specific plant.  You go a few hundred meters up or downhill, and you've moved out of the range where that species lives -- and into the range of an entirely different one.

The most striking thing about the hummingbirds is their iridescence.  My favorite one, and in the top five coolest birds I've ever seen, is the Violet-tailed Sylph (Aglaiocercus coelestis):

[Image licensed under the Creative Commons Andy Morffew from Itchen Abbas, Hampshire, UK, Violet-tailed Sylph (33882323008), CC BY 2.0]

What's most fascinating about birds like this one is that the feathers' stunning colors aren't only due to pigments.  A pigment is a chemical that appears colored to our eyes because its molecular structure allows it to absorb some frequencies of light and reflect others; the chlorophyll in plants, for example, looks green because it preferentially absorbs light in the red and blue-violet regions of the spectrum, and reflects the green light back to our eyes.  Hummingbirds have some true pigments, but a lot of their most striking colors are produced by interference -- on close analysis, you find that the fibers of the feathers are actually transparent, but when light strikes them they act a bit like a prism, breaking up white light into its constituent colors.  Because of the spacing of the fibers, some of those wavelengths interfere destructively (the wavelengths cancel each other out) and some interfere constructively (they superpose and are reinforced).  The spacing of the fibers determines what color the feathers appear to be.  This is why if you look at the electric blue/purple tail of the Violet-tailed Sylph from the side, it looks jet black -- your eyes are at the wrong angle to see the refracted and reflected light.  Look at it face-on, and suddenly the iridescent colors shine out.

So the overall color of the bird comes from an interplay between whatever true pigments it has in its feathers, and the kind of interference you get from the spacing of the transparent fibers.  This is why when you recombine these features through hybridization, you can get interesting and unexpected results -- as some scientists from Chicago's Field Museum found out recently.

Working in Peru's Cordillera Azul National Park, on the eastern slopes of the Andes, ornithologist John Bates discovered what he'd thought was a new species in the genus Heliodoxa, one with a glittering gold throat.  He was in for a shock, though, when the team found out through genetic analysis that it was a hybrid of two different Heliodoxa species -- H. branickii and H. gularis -- both of which have bright pink throats.

"It's a little like cooking: if you mix salt and water, you kind of know what you're gonna get, but mixing two complex recipes together might give more unpredictable results," said Chad Eliason, who co-authored the study.  "This hybrid is a mix of two complex recipes for a feather from its two parent species...  There's more than one way to make magenta with iridescence.  The parent species each have their own way of making magenta, which is, I think, why you can have this nonlinear or surprising outcome when you mix together those two recipes for producing a feather color."

The gold-throated bird apparently isn't a one-off, as more in-depth study found that it didn't have an even split of genes from H. branickii and H. gularis.  It seems like one of its ancestors was a true half-and-half hybrid, but that hybrid bird then "back-crossed" to H. branickii at least once, leaving it with more H. branickii genes.  All of which once again calls into question our standard model of species being little cubbyholes with impermeable walls.  The textbook definition of species -- "a morphologically-distinct population which can interbreed and produce fertile offspring" -- is unquestionably the most flimsy definition in all of biology, and admits of hundreds of exceptions (either morphologically-identical individuals which cannot interbreed, or morphologically-distinct ones that hybridize easily, like the Heliodoxa hummingbirds just discovered in Peru).

In any case, the discovery of this hybrid is fascinating.  You have to wonder how many more of them there are out there.  The fact that its discovery ties together the physics of light, genetics, and evolution is kind of amazing.  Just further emphasizes that if you're interested in science, you will never, ever be bored.

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The birds and the bees and the flowers and the trees

One of the most fascinating aspects of evolution, and one of the least appreciated (outside of the biology-nerd community, anyhow), is how insects and flowering plants have coevolved.

Coevolution occurs when two different species (or groups of species) reciprocally affect each other's evolutionary changes.  A commonly-cited example is the pair made up of cheetahs and impalas; the fastest cheetahs get more food than the slowest, and the slowest impalas get turned into food more than the fastest, so each species has a tendency to get faster and faster (at least until other considerations, like the limitations of physiology, kick in).  This specific type of coevolution is sometimes called an evolutionary arms race, and can occur not only with speed but with issues like toxicity (in the species being eaten) and toxin tolerance (in the species doing the eating).

The coevolutionary relationship between flowering plants and insects is a curious one.  Certainly, there are insects that eat (and damage, sometimes fatally) plants; witness the gypsy moths that this year have shredded trees in our part of New York state.  Fortunately for our apple and cherry trees and other susceptible species, most trees attacked by gypsy moths survive defoliation and are able to put out another set of leaves once the moths' caterpillars are gone, and because the moths are a "boom-and-bust" species, they seldom mount a serious infestation like this year's more than once a decade or so.

But there's a "nicer" side to coevolution between insects and flowering plants, and that has to do with pollination.  We all learned in elementary school how bees and butterflies pollinate flowers, but it's more complicated than that; insects and plants have in some senses opposite interests in pollination.  For insects, the more different species of flowers they can visit, the more potential nectar sources they can access; but that's actively bad for flowers, because if a bee visits (for example) a rose and then a clover blossom, any pollen transferred does the plant no good at all because the two species aren't cross-fertile.  That pollen is "wasted," from the plant's perspective.

A species peony from the Caucasus Mountains, Paeonia mlokosewitschii -- nicknamed "Molly-the Witch" because most people can't pronounce "mlokosewitschii" -- primarily pollinated by ants and wasps  [photo taken this spring in the author's garden]

Plants have adopted a variety of strategies for coping with this.  Some, such as wind-pollinated plants (oaks, maples, willows, grasses, and many others) produce huge amounts of pollen, because they don't have a carrier to bring it from one flower to the next, and much of the pollen never reaches its target.  (This is why wind-pollinated plants like ragweed are primary culprits in pollen allergies.)  The same thing is true of plants that are visited by many different kinds of pollinators, and for the same reasons.

But the other approach is specialization.  If a flower has a shape that fits the mouthparts of only one species of pollinator, the pollen picked up is almost certainly going to be transferred to a flower of the same species.  In stable ecosystems, like rainforests, there are flowers and pollinators that have coevolved together so long that both are completely dependent on the other -- the pollinator's mouthparts don't fit any other flower species, and the flower's shape isn't compatible with any other pollinator's mouthparts.

Anna's Hummingbird (Calypte anna) visiting Crocosmia flowers in San Francisco, California [Image licensed under the Creative Commons Brocken Inaglory, Humming flowers, CC BY-SA 3.0]

As my evolutionary biology professor put it, this strategy works great until it doesn't.  Specialists get hit hardest by ecological change -- all that has to happen is for one of the pair to decline sharply, and the other collapses as well.  Their specialization leaves them with few options if the situation shifts.

The topic comes up because of a paper this week in Biological Reviews that looks at plant species which try to do both at once -- attract various species of pollinators (increasing the likelihood that pollen gets widely distributed, and mitigating the damage if one species of pollinator disappears) while encouraging those pollinators to feed exclusively on the flowers of that species only (decreasing the likelihood that the pollen will be transferred to a flower of an unrelated species).

A trio of researchers -- Kazuharu Ohashi (of the University of Tsukuba), Andreas Jürgens (of Technishe Universität Darmstadt), and James Thompson (of the University of Toronto) found that this complicated "hedging your bets" strategy is more common than anyone realized.  Some of the solutions the plants happen on are positively inspired; the goat willow (Salix caprea) has evolved to be pollinated by two different pollinators, bees and moths -- and the flowers actually change scents, producing one set of esters (chemicals associated with floral fragrance) during the day, and a different one at night, to attract their diurnal and nocturnal visitors most efficiently.  Cardinal shrub (Weigela spp.) flowers change scent as they age -- young flowers have fragrances attracting bees and butterflies, older ones attracting species like drone flies.

"[Y]ou'd expect that flowers would mostly be visited by one particular group of pollinators," said study lead author Kazuharu Ohashi, in an interview with Science Daily.  "But flowers often host many different visitors at the same time and flowers appear to meet the needs of multiple visitors.  The question we wanted to answer is how this happens in nature... Most flowers are ecologically generalized and the assumption to date has been that this is a suboptimal solution.  But our findings suggest that interactions with multiple animals can actually be optimized by minimizing trade-offs in various ways, and such evolutionary processes may have enriched the diversity of flowers."

Evolution is more subtle than a lot of us realize, happening on solutions to ecological problems that nearly defy belief.  The bucket orchid of South America (Coryanthes spp.) has a flower with a complex "trap" that only appeals to one species of bee -- and is so convoluted that when I explained its function to my biology students, I had to assure them more than once that I wasn't making it all up to fool the gullible.  The strategies vary dramatically from species to species, but always fall back to that tried-and-true rule -- evolution is the "law of whatever works."

So there's something to think about when you're working in your garden.  The birds and the bees and the flowers and the trees are a lot more complicated and interconnected than they may seem.  Many of the sophisticated mechanisms they use to assure survival and reproduction are only coming to light now -- and papers like Ohashi et al. give us a new lens into how beautiful and intricate the natural world is.

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Most people define the word culture in human terms.  Language, music, laws, religion, and so on.

There is culture among other animals, however, perhaps less complex but just as fascinating.  Monkeys teach their young how to use tools.  Songbirds learn their songs from adults, they're not born knowing them -- and much like human language, if the song isn't learned during a critical window as they grow, then never become fluent.

Whales, parrots, crows, wolves... all have traditions handed down from previous generations and taught to the young.

All, therefore, have culture.

In Becoming Wild: How Animal Cultures Raise Families, Create Beauty, and Achieve Peace, ecologist and science writer Carl Safina will give you a lens into the cultures of non-human species that will leave you breathless -- and convinced that perhaps the divide between human and non-human isn't as deep and unbridgeable as it seems.  It's a beautiful, fascinating, and preconceived-notion-challenging book.  You'll never hear a coyote, see a crow fly past, or look at your pet dog the same way again.

[Note: if you purchase this book from the image/link below, part of the proceeds goes to support Skeptophilia!]

Saturday science shorts

Because I am totally disheartened by the news, frustrated by the lack of critical thinking everywhere I look, and also because my blender exploded when I was making breakfast this morning and splattered orange juice and half-processed fruit over every square inch of the kitchen including myself, I am retreating to my happy place, namely: cool stuff in science news.

Let's start with a story from astronomy about something that is a near-obsession with me; the possibility of life on other planets.  This particular research involves the star system TRAPPIST-1, discovered last year and found to have not one, not two, but seven planets, three of which are in the so-called "Goldilocks Zone" (where the temperature is juuuuust right for water to be in liquid form).  Of course, that doesn't guarantee that water's there, just that if it was, it would be liquid, which scientists surmise would be a pretty good indicator of the likelihood of the probability of hosting life.

Now, researchers have found that all of the TRAPPIST-1 planets do have water -- in some cases, up to five percent of their mass.  So the three in the habitable zone might well be water-worlds.  All of which reminds me of the planet Kamino from The Phantom Menace, which otherwise was a dreadful movie, but I have to admit reluctantly that this part was cool.

Here's what we know about the TRAPPIST-1 system, although keep in mind that the illustrations of the planets are artists' renditions of what they might look like:

[image courtesy of NASA/JPL]

So that's pretty wicked cool.  The difficulty, of course, is that even if they did host life, it'd be hard to see that if the inhabitants had not advanced technologically to the point that they were sending out signals.  But even that hurdle might not be insurmountable -- as I wrote in a post a couple of weeks ago, astronomers are now trying to figure out if life is present on an exoplanet by the composition of its atmosphere.

Then, from the realm of biology, we have a study elucidating how those tiny jet fighters of the avian world -- hummingbirds -- maneuver as well as they do.

A group led by Roslyn Dakin and Paolo Segre of the Smithsonian Conservation Biology Institute of Ottawa examined hundreds of hours of high-speed video of hummingbirds in flight, looking at twenty-five different species and examining how they do their amazing aerobatics, including pivoting while in flight, hovering, and moving in an arc so narrow that it almost defies belief.  

The research took them to remote places in Panama, Costa Rica, and my favorite country of Ecuador -- the tiny nation that is host to 250 different species of hummingbirds, including the preternaturally beautiful Violet-tailed Sylph (Aglaiocercus coelestis):

Where I live, we have a paltry one species, albeit a beautiful one -- the Ruby-throated Hummingbird.  So it's no wonder the researchers decided to head south.

Another hummingbird researcher, Christopher Clark of the University of California-Riverside, has said that the new study is like moving from analyzing individual gestures of a ballerina to looking at how the moves fit together.  "Now," Clark says, "we're putting together the entire dance."

Last, some scientists at the University of Zurich have for the first time been able to see new neurons being formed in the brains of embryonic mice.  

Starting out by tagging 63 neural stem cells in the hippocampus, Sebastian Jessberger and his team were able to watch as the neurons grew outward and formed connections (synapses) with neighboring neurons.  What was most intriguing was that some of the new neurons had short lives -- perhaps acting as scaffolding for the developing brain and then self-destructing (undergoing apoptosis) when their task was complete.

Amongst these tagged cells, the red ones are the newest, orange next, and continuing through yellow and green (the oldest cells).

What is most exciting about this is that being mammals, it's expected that the knitting together of the embryonic human brain probably proceeds in a very similar fashion.  So what Jessberger et al. are doing might well inform us regarding how our own neural systems form.

So there you have it -- three cool new developments in the world of science.  Which has cheered me up considerably.  That's a good thing, considering the fact that now I have to go clean my kitchen, which I'm definitely not looking forward to.