Biological marvels of flight

August 18, 2022 • 12:00 pm

I’ve finished reading Richard Dawkins’s new book Flights of Fancy: Defying gravity by Design and Evolution, and quite enjoyed it, for it incorporates many of the principles he’s emphasized in his books—the gene’s-eye view, coevolution, arms races, step-by-step adaptive evolution, evolutionary convergence, and so on—into a discussion about a single adaptation, flight. Well, not a single adaptation, since he discusses gliding animals like flying squirrels and flying fish, the true flight of animals like birds and bats, and the “flying” of pollen via their insect vectors or of seeds via dispersal mechanisms.

And the “design” in the title refers to a convergence between what natural selection has done to facilitate aerial movement and how humans through deliberate design have mimicked many of nature’s contrivances in aircraft.

One of the pleasures of the book is discovering odd but fascinating bits of flight-related natural history that show us the power and “cleverness” of natural selection. Her are two examples he discusses.

The first is the Javan cucumber, Alsomitra macrocarpa, found on the tropical islands of East Asia. It disperses its seeds from a gourd that disgorges remarkable gliding seeds with two wings that look like this:

From Wikipedia:

The seed or samara of this species is unusual in having two flat bracts extending either side of the seed to form a wing-like shape with the seed embedded along one long edge and the wings angled slightly back from it. As the seed ripens the wings dry and the long edge furthest from the seed curls slightly upwards. When ripe, the seed drops off and its aerodynamic form allows it to glide away from the tree. The wing spans some 13 cm and can glide for great distances. The seed moves through the air like a butterfly in flight — it gains height, stalls, dips and accelerates, once again producing lift, a process termed phugoid oscillation. In the past it was often found on the decks of ships at sea.

You can see that dipping and stalling in the second video below.

By the way, Richard has a great discussion about why it’s adaptive for plants to disperse their seeds. If your parents are growing in a good place, why send them many meters away to a place that might not be as good? But you can read about that yourself.

The remarkable aspects of these seeds is how far they glide, ensuring that many of them find themselves well away from their parent. Here are two videos, one from Attenborough, showing the phenomenon.  These features are certainly evolved as adaptive for the plant.

The Attenborough introduction:

. . . and a video from YouTube showing the remarkable gliding power of these seeds, which resemble plantlike albatrosses in their ability to glide very far without flapping:

This next one is remarkable. I’ve taught about “pseudocopulation”, a trait that some orchids use to spread their pollen using wasps as surrogate genitalia. There are many orchids that resemble female wasps, and randy males try to copulate with them. (Some of these “wasp orchids” even produce pheromones resembling those of female wasps.)

The “intent” of the orchid (I’m speaking in evolutionary jargon, of course) is to affix its pollen sacs, or pollinia, onto the wasp. After a fruitless attempt at copulation, the wasp, with a sac of pollen stuck to its body, eventually makes its way to another orchid, tries to bonk it, and transfers the pollinia to the female’s stigma, effecting fertilization.  (These wasp-mimicking orchids almost never produce nectar to lure the insects; they save their energy and just act sexy.)

One remarkable orchid that tricks wasps this way is the “hammer orchid“; or rather orchids, as there are ten species in the genus Drakaea found in western Australia. A wasp, lured by a part of the flower that looks like a female wasp (it also smells like one), lands on that bit and tries to copulate with it. (The Attenborough video below shows the similarity between flower and female wasp.) At some point, the female-mimicking part of the flower folds over, hammering the male wasp against the pollinia. The pollen sticks to its body, and fertilization is halfway there.  The act is completed when the frustrated wasp tries copulating with a different orchid, and the hammer then puts the pollina in contact with the stigma.

Females of these species are wingless (see below) and the orchid has evolved (unknowingly, of course) to look like them. The resemblance is facilitated by the female wasps’ habit of hanging atop a step to lure the males, which is just what the orchid does.

Note that only males can pollinate these orchids (or any wasp-mimicking orchid), so the flower potentially loses half its pollinators. But since females can’t pollinate anyway, being wingless, it’s not that big a loss. What puzzles is me is why the wasp nevertheless persists trying to copulate with the flower. If it ever learned not to waste its time, the flower would go extinct.

Have a look. There are even more remarkable tactics that orchids use to fertilize each other, but I’ll save those for later.

13 thoughts on “Biological marvels of flight

  1. I am just an amateur but here is my guess about one reason trees prefer to spread their seeds elsewhere. If they only shed them nearby and there was some kind of
    disease or adverse change in their environment, all the seeds would perish.However, by spreading seeds randomly they hedge the risk of extinction because some of these
    distant seeds might avoid the disease and flourish. Staying strictly local is like extreme specialization, which is risky. Taking a chance makes sense. Humans explore new habitats, possibly for the same reason. Expand your options if possible. Possibly related is this: why do nectar-seeking insects fly from one bush to another rather than staying on one bush for a longer period of time where there may be lots more flowers in one place? Maybe this is because they need to locate other sources of that nectar in case the original one dies or is extirpated? So they get a map of their environment that has more information that they need and they can consult this map if one place becomes inhospitable or denuded. Any other ideas?

    1. Each flower only produces a tiny drop of nectar, and it takes some time for it to produce more. Given that bees and wasps are incredibly fast and efficient, they would soon tap out an entire bush if they stayed with just one, and would then spend valuable time waiting. They get more by just moving on to a different bush.

    2. I think it is more that you cannot grow up in the shade of a parent. Many plant pathogens & diseases are spread by insects, or wind, so disease is hard to avoid. Perhaps though its daughter plants would find better soil or water conditions by dispersing. non-flyers use animals & birds such as jays.

      1. There’s also an enormous root system right under the tree. I’ve heard estimates to be something like the volume of the top branches or more.

        1. That’s the rule of thumb I was taught, for estimating how far to space out trees when thinning an (artificial) plantation which hadn’t been thinned for about 50 years after being planted in the interwar reforestation flush. Lots of horribly unstable trees whose interfering root systems would rip out when the trunk was pushed over by the wind, or by the impact of another tree which wasn’t falling in the direction the thinner (the chain-saw man) intended.

  2. Well, that’s a great guess, and you’re right. It all rests on the fact that environments are unpredictable over both the short and long term. So it’s always better to have at least some form of dispersal available. Good job!

    1. Does the risk of inbreeding also play a role? If their offspring grow up right next to them, when they reproduce, their proximity increases the likelihood of a back-cross. Could this be a factor?

  3. (These wasp-mimicking orchids almost never produce nectar to lure the insects; they save their energy and just act sexy.)

    Stinger teasers.

  4. Very good! In the different kinds of flying organisms, we see how the challenge of flight is always solved by re-purposing what they already have. Vertebrates fly with their front legs. Insects with modified gills (at least that is apparently the case, as they are descended from Crustaceans). And there is the amazing flying squid that glides with webbed arms and fins on the mantle.

  5. Watching the Javan cucumber, Alsomitra macrocarpa seed glide, dive, swoop in the breeze it seemed a pity the seed didn’t have a nervous system that allowed “enjoyment” “euphoria” as in, those crazy people who jump off cliffs in wingsuits must experience. After that whimsical thought I landed with a hard cold facts about human constructed powered flight.
    After listening to a BBC report and reading `others about climate change and the aviation contribution to it in the form of Jet A1 fuel admission it appears, unlike the US, aircraft flights to the UK & Europe for one single flight can crisscross around countries as they fly under control of multiple flight control towers (not to mention, political considerations) wasting time burning fuel. The report claims (now I’m trying to remember here) but it was quite a significant amount of fuel emissions could be saved annually just by allowing commercial aircraft to fly direct, airport to airport (frecking makes sense!)
    It is part of a no small amount of aviation1 fuel burnt globally “the sector is responsible for about 2.5% of global carbon emissions and equivalent to the release of more than 900m metric tons of CO2 annually just prior to the Covid-19 pandemic” Posted on November 29, 2021 by Frontiers Science Communications in Climate Action.
    AND this type of action getting back to the point of the post,
    “The scientists found that taking better advantage of the winds would have saved around 200 kilometres worth of fuel per flight on average, adding up to a total reduction of 6.7 million kilograms of carbon dioxide emissions across the winter period. The average fuel saving per flight was 1.7% when flying west to New York and 2.5% when flying east to London.”
    January 25, 2021 Source: University of Reading
    how dumb are we!

    1. it appears, unlike the US, aircraft flights to the UK & Europe for one single flight can crisscross around countries as they fly under control of multiple flight control towers (not to mention, political considerations) wasting time burning fuel

      (My emphasis).
      By coincidence, this morning’s trash TV selection included the glorious tale of Avianca flight 052 who arrived in American ATC space with about 2 hours of fuel in reserve, and through a combination of bad weather, confused communication in the ATC system and confused communication between the ATC and the plane, ran out of fuel attempting to land at JFK. 73 dead.
      You don’t need multiple borders to get fscked-up ATC instructions. I remember one flight, entirely within UK airspace, where the ATC were telling us that we had 2 minutes to make the run from the strand line, around the city limits and get onto the runway, or the airport was going to shut down for the night and leave us with an extra 130-odd miles to fly to Edinburgh.
      Yes, aviation is a small, but significant and growing, part of human CO2 emissions. Corollary : if you choose to have children, don’t expect them to be going to beautiful, “unspoiled” parts of the world for a holiday. They won’t be able to afford the carbon emissions taxes, even if the “unspoiled” target is still “unspoiled”.
      Second corollary : aviation fuel should be taxed the same way that land-(surface-)vehicle fuel is taxed. That’d combat aviation emissions, for a decade or several.

      1. I can only go on what these reports said and can only add that we need to get smarter and as quick as we can for the reason you have stated, tourism, etc. E.g. some Scandinavian countries are dropping short-haul flights if they are adequately serviced by rail.
        Covid knocked the airline industry around and here in NZ, Air NZ has cancelled thousands of flights into the future, simply because they can’t service them with no staff. It was a shambles and travellers are worried about their long term booked flights.
        Air NZ tested and are using some Biofuel to supplement jet fuel and others are doing similar things. Science has a big role to play I suspect with our tanning and frolicking, I want to be there and do that dispositions.

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