A bat with a stupendously long tongue

New species of mammals aren’t found very often, but if one is, chances are it will be a bat.  Bats are secretive, often nocturnal, and numerous.  With more than 1200 species in the order Chiroptera, they represent 20% of all mammalian species (red in the pie chart below); the only bigger order is the rodents:

In 2005 a new species of bat was discovered in the cloud forests of Ecuador (perhaps reader Lou Jost has seen this one):  Anoura fistulata, otherwise known as the tube-lipped nectar bat. (The short paper describing it, by Nathan Muchhala et al., is free for download here, and the reference is at the bottom of this post.)  As National Geographic News reported last week, its unusual method of feeding—inserting an absurdly long tongue into flowers and lapping up the nectar—has just been filmed for the first time.

What is unusual about the bat is that its tongue is longer than its body!

The creature is only about two inches (five centimeters) long, but its tongue is nearly three and a half inches (nine centimeters) long—one and a half times longer than the bat’s body.

When not collecting nectar from the Centropogon nigricans flower, the bat’s tongue is retracted and stored in the animal’s rib cage.

That’s the longest tongue relative to its body size of any mammal, even longer than that of Gene Simmons! Just as a comparison (no griping, readers), if my own tongue were of similar relative size, it would be eight and a half feet long.

A. fistulata is distinguished from other species in the genus by having a lower lip that is elongated, extends further than the upper lip, and is rolled into a tube covered with papillae.  And of course there’s that tongue. Both of these features are shown in the figure below, taken from the paper.

Fig. 2 from Muchhala et al. Lip morphology of Anoura fistulata. A) Lateral view of noseleaf, lip, and partially extended tongue with papillae; and B)
dorsal view of noseleaf and lip.

But of course what we want to see is how they use that tongue. This was filmed just recently by a National Geographic crew.  As their article reports:

In the new high-def video—which aired Sunday as part of the National Geographic Channel’s Untamed Americas documentary series—the bat is shown feeding on the wing. (The Channel and National Geographic News are affiliated within the National Geographic Society.)

“These bats can hover,” said biologist Nathan Muchhala, who helped discover the species in an Andean cloud forest. “They’re like hummingbirds in that sense.”

In a close-up, the animal’s tongue slithers, snakelike, down the flower’s long neck. When the tongue reaches the pool of sweet nectar at the bottom, the tip transforms, becoming suddenly prickly as hairlike structures called papillae extend outward.

“Just before the bat retracts the tongue, the [papillae] stick straight out sideways,” said Muchhala, of the University of Nebraska-Lincoln. “That maximizes the surface area, allowing it to act like a mop and sop up as much nectar as possible.”

Here’s the video, which shows the bat hovering like a hummingbird (this, by the way, is an example of “convergent evolution,” since these bats and hummingbirds independently evolved nectar feeding, long tongues, and hovering):

The narration is very good here: I love the line “necessity is the mother of evoluiton.”

As National Geographic reports, getting that video was no easy matter:

To get the super-tongue footage, National Geographic filmmakers flew to Ecuador, where Muchhala and his team were waiting with a bat they’d already netted. Filming took place in a special tent, in which the bat could freely fly and feed. To make the tongue visible to the camera, a small hole was cut at the base of the flower. “They put the camera behind the hole and got that amazing close-up shot,” Muchhala said. At first, the bats were bothered by the humans and the bright lights in the tent and would not approach the flower to feed, but they eventually adjusted.”They actually get so used to it that after a while,” Muchhala said, “you come into the tent and they come up to you and will land on your hand looking for nectar.”

The long tongue was first discovered before they knew anything about the bat’s ecology, but, like Darwin’s orchid and its pollinating moth, a long tongue in a nectar-feeding bat implies a flower with a long corolla tube. Muchhala published another paper in 2006 (reference below) verifying this and giving a diagram showing how the bat’s tongue is retracted into its abdomen with special muscles:

Dietary studies of Anoura in four reserves on the eastern and western slopes of the Andes confirm this prediction. During 129 nights of mist-netting in 2003–05, I captured 46 A. geoffroyi, 38 A. caudifer, and 21 A. fistulata, and identified the pollen on their fur and in their faeces. Pollen from Centropogon nigricans, which has corollas 8–9 cm long, was carried only by A. fistulata (Fig. 1d), as might be expected, given that other Anoura could not reach this flower’s nectar. During 55 hours of nocturnal and diurnal videotaping of 12 flowers of C. nigricans, ten bats were the only visitors. This observation, combined with the finding that A. fistulata was the only bat visitor, supports the conclusion that A. fistulata is the only pollinator of this plant.

Specialization on one species of pollinator is exceedingly rare in angiosperms, and C. nigricans is the only example known in flowers pollinated by bats. After the initial evolution of a glossal tube, the extreme tongue length of A. fistulata probably coevolved with long flowers such as those of C. nigricans. In an example of convergent evolution, pangolins (scaly anteaters) also have a glossal tube; despite their different diets, ant-eating and nectar-feeding animals face similar evolutionary pressures for highly protrusible tongues, and pangolins and A. fistulata have independently converged on a similar solution.

Part of rom the Muchhala paper in Nature: c, Ventral view of A. fistulata, showing tongue (pink), glossal tube and tongue retractor muscle (blue), and skeletal elements (white). d, Anoura fistulata pollinating the specialized flower of Centropogon nigricans; because of the long corolla, only A. fistulata can reach its nectar. (Fig. 1a, M. Cooper; Fig. 1d, N. M.)

LOL!

How did this evolve? Well, of course we’re not sure, but, as Muchhala (2006) suggests, it could be a form of “coevolution,” in which the bat evolved its long tongue in concert with the flower evolving its long corolla tube.  A flower that is already being pollinated by bats (and whose nectar is being nommed) might accrue a reproductive advantage by making the nectar a little bit more inaccessible—a little farther away from the opening. That forces the bat to press its head up against the flower, ensuring a better contact between bat and flower (the pollen is carried between flowers on the bat’s head).  And if the flower tube gets longer, that then gives an advantage to bats who have a longer tongue, since those individuals will be better at getting the nectar, and hence will be better fed and leave more offspring.  And so tongue and flower, spurred on by each other’s evolution, mutually elongate.

True “coevolution” occurs when two species act as selective forces for each other, so that they evolve in concert. The word is often misused to imply one species adapting to another, as in certain forms of mimicry, but true coevolution involves reciprocal evolutionary adjustments between a pair of species.  Although it’s probably common in nature, we don’t have a lot of good examples.

Will this system evolve until the flower gets three-foot nectar tubes and bats have three-foot tongues? Probably not. There’s a limit to how far this type of coevolution can proceed, presumably imposed by the evolutionary costs of making longer corolla tubes or producing longer tongues.  For the same reason, the very long tails of male African widowbirds don’t become ten feet long, for although females prefer longer tails than males actually have, at some point the added sexual benefits of having a longer, more attractive tail are outweighed by the loss in fitness such a tail confers (it could, for example, seriously impede the male’s ability to fly).

There are no new evolutionary principles demonstrated by this example, but it’s nevertheless thrilling, for it shows us another unexpected way that natural selection has worked, producing adaptations that seem a priori inconceivable.

_______________

Muchhala, N., P. Mena, and L. Albuja. 2005. A new species of Anoura (Chiroptera: Phyllostomidae) from the Ecuadorian Andes. J. Mammalogy 86:457-461.

Muchhala, N. 2006.  Nectar bat stows huge tongue in its rib cage. Nature 444:701-702. [Isn’t that a terse and informative title? Hemingway could have written it.]

29 Comments

  1. RWO
    Posted June 17, 2012 at 6:29 am | Permalink

    I barely passed sophomore high school biology, and I could always look this up on the internet, but since JC is a biologist and he is right here: it is news to me that all bats do not exist solely on insect fare. Of the 140 or so bat species, how many feed solely on insects, and are there other food sources for bats besides insects and this flower? I have read of some North American bat species that are suffering recent population declines from uncertain (chemical agricultural by-products, climate change) causes. Is this bat, and other remote-location bat species, known to face recent imminent survival threats?

    • Posted June 17, 2012 at 7:54 am | Permalink

      I’ll put my two cents worth in here since I live in nectar-feeding bat territory. In southern Arizona, the Mexican long-nosed bat and Mexican long-tongued bat (both endangered) are the sole pollinators for several species of Agave, particularly A. palmeri which has flowers that are adapted to the bats (tubular, though not very long, and thickened at the tip to withstand repeated encounters with a rather large, heavy, and clumsy flying mammal). The bats are probably best known for pollinating saguaros, though in that case insects help too, since the flowers attract many bees and butterflies.
      Agaves attract insects and hummingbirds, but only the bats appear to be successful pollinators. If there are no bats, the plants don’t set seeds, though in a very wet year they might reproduce asexually and produce bulbils (tiny leaf rosettes). Some agaves regularly produce bulbils and some do both.
      Some agave photos:
      http://www.mineralarts.com/cactus/bigagave.html

      Nectar feeding bats are guests or pests (depending on your point of view) at hummingbird feeders. Their tongues won’t fit through the holes, but they knock the feeder until the liquid splashes out, and lap it up on the fly. You can see them flying with their tongues hanging out. They don’t hover, and if you’re moving around the feeder while they’re flying, you’re likely to get slapped by a wing. A few bats can drain a quart of liquid within an hour.

      “Specialization on one species of pollinator is exceedingly rare in angiosperms.”

      I’m not sure how “exceedingly rare” is quantified here, but some of the examples that do exist are quite well known: Peniocereus greggii (American night-blooming cereus cactus) is pollinated by the White-Lined Sphynx moth. Yuccas each have their own species of moth that lives in the flower and pollinates it. There are several desert plants with tubular red flowers, such as ocotillo and chuparosa, that are pollinated only by hummingbirds. Etc.

      On environmental dangers to bats: Western U.S. bats face destruction of habitat due to development, loss of food supply due to desertification (ranching and agriculture), and loss of water due to all those things. One bright spot is that several species like to live in old mineshafts, of which there are millions in the West. Several Federal agencies are now filling in the more dangerous shafts (those near urban areas or hiking trails etc.) but the shafts are surveyed for bats first, and those with bats are not filled in, but fitted with special gates to allow the bats in and keep humans out.

      Bats in the eastern U.S. are vulnerable to White Nose Disease, a recently-discovered fungal infection. It affects hibernating bats but cannot tolerate high temperatures:
      http://en.wikipedia.org/wiki/White_nose_syndrome

    • Notagod
      Posted June 17, 2012 at 8:31 am | Permalink

      As stated by Dr. Coyne above there are more than 1200 bat species, your estimate of 140 species is an order of magnitude lower than the actual count.

      For food, from wikipedia:

      The majority of food consumed by bats includes insects, fruits and flower nectar, vertebrates and blood.[53] Almost three-fourths of the world’s bats are insect eaters. Insects consumed by bats include both aerial and ground-dwelling insects. Each bat is typically able to consume one-third of its body weight in insects each night, and several hundred insects in a few hours. This means a group of one thousand bats could eat four tons of insects each year. If bats were to become extinct, the insect population is calculated to reach an alarmingly high number.

      You can find a lot of information about bats at batcon.org,
      Bat Conservation International

      • RWO
        Posted June 17, 2012 at 12:42 pm | Permalink

        Thanks for the replies. I knew JC provided a number for bat species in the post text, and I’m not sure why I pulled 140 out of my ying-yang instead of just re-reading to find the answer. Batcon.org is appreciated. Bats, bees, amphibians, sea life, the synergistic chain — I don’t see a way out of awful times dead ahead.

  2. Torbjörn Larsson, OM
    Posted June 17, 2012 at 7:03 am | Permalink

    Very good narrative, so good in fact that I should revisit my choice of not watching nature videos anymore. With the exception of Attenborough, I found the recurring anthropomorphic narrative tedious.

    I love the line “necessity is the mother of evoluiton.”

    As long as we do personal preferences, I don’t mean to nitpick each and every narrative meme, but as a perspective I still find that irritatingly suggesting a false analogy. Something along the line of “flying is the mother of gravitation”.

    It is all right if we embrace the context, and it isn’t as in-your-face erroneous as some. But it could perhaps be put more faithfully. “Survival is a mother of evolution”? “Good living is a mother of evolution”? (Seeing that relatively bad living, say low fecundity, is also a driver, I guess I can’t drop “a” for “the”.)

    Okay, maybe I am just nitpicky. :-/

    • Chris
      Posted June 17, 2012 at 7:05 am | Permalink

      heh, snap! (see 3)

  3. Chris
    Posted June 17, 2012 at 7:04 am | Permalink

    Thanks for a great article Jerry but I have to disagree about the script. Necessity is exactly *not* the mother of evolution and this kind of creationistic cart-before-the-horse way of describing evolution is in no small measure responsible for people’s skepticism and misunderstanding of the subject. Necessity implies a designer or some kind of decision-making process in order to get ‘fitter’.

    The final phrase of the piece where he says that the flower simply wouldn’t exist unless the bat was there also smacks of a creationistic outlook. How fortunate that the creator made a bat with a long tongue that fits so precisely!

    Does the film go on to discuss the possible evolutionary pathways or does it just leave it at the miraculous?

  4. MAUCH
    Posted June 17, 2012 at 7:06 am | Permalink

    Why evolution is true! Only through adaptive speciation would these two organism have this symbiosis. I can’t imagine god going to all this trouble.

    • Posted June 17, 2012 at 10:29 am | Permalink

      I’ve always thought that if God had created everything, no adaptation would be necessary. Everyone would get along, nobody would eat each other, and the pink unicorns would graze happily beside the winged lions.

      The reality of evolution is much more interesting and awe inspiring. Life for life’s sake! Not toys to amuse a “God” invented by control freaks who conceive of a Supreme Being as an immortal toddler in a Fisher Price universe.

  5. Notagod
    Posted June 17, 2012 at 7:26 am | Permalink

    Your presentation is very good, the narration in the video not as good in my opinion. The narration seemed a bit over dramatized to me. As an example, the narration states, beginning at 2:34, that this bat is the sole pollinator and without “him” the flower simply wouldn’t exist. But, if the bat had a shorter tongue the flower would still exist wouldn’t it? Wouldn’t the flower, maybe, just be shorter? To exist in their current configurations the bat needs the flower just as much as the flower needs the bat.

    • whyevolutionistrue
      Posted June 17, 2012 at 7:35 am | Permalink

      Yes, yes, I disliked that sentence as well, but I can’t review every word of a documentary. I took it to mean that the flower in the present form couldn’t exist without the selection pressure imposed by the bat. Another way to construe it is to say that the flower did exist before the bat, and had another pollinator as well, but elongated so much (perhaps because bats were the main pollinator) that it could no longer be pollinated by anything else, and so would go extinct without the bat.

      As for necessity being the mother of evolution, that’s clearly not creationist since it mentions evolution. Remember that this is simply wordplay on the American phrase, “Necessity is the mother of INVENTION.” One could also construe it as the increasing length of corolla tubes provides a strong selective impetus for the evolution of long bat tongues, and vice versa.

      But this is all nitpicking, really. The story is what is interesting.

      • Notagod
        Posted June 17, 2012 at 9:38 am | Permalink

        Much better now. It is a bit harsh of me to expect the narrator to attend to all the angles in such a short clip. For some reason or other my brain just didn’t pick up the likely intended meaning that you have described.

        The narration might have been improved by replacing “would not exist” with “would go extint.” However, yes, with your explanation in mind my complaint is reduced to a nitpick. I’m almost sure though, that it was an honest complaint at the time I made it. 😉

  6. Posted June 17, 2012 at 7:39 am | Permalink

    Excellent video, and amazing work by Nathan (part of a much larger study of his on the evolution of pollination syndromes in Centropogon, Burmeistera, and relatives). I haven’t seen this bat, at least not knowingly, but I have often seen long-tongued bats coming to hummingbird feeders at night here in Ecuador. How do they find the feeders?

    • Nathan Muchhala
      Posted June 17, 2012 at 9:51 am | Permalink

      Hi Lou! Thats a really interesting question, how do they find the feeders? Theres no odor – I’m sure they learn from copying eachother, but did the first bats learn from copying hummingbirds at dusk? Incidentally this just recently swept through Ecuador, I think in the past 4 years (correct me if you know different), but no preserves used to have problems with sugar-water dissappearing at night and now this is happening from Rio Guajalito to Tapichalaca…

      • Posted June 17, 2012 at 4:27 pm | Permalink

        Tucson has had bats at hummingbird feeders for years, though it seems to be more common now than a decade ago. Our bats typically visit between the first quarter and full moon, when there is plenty of light just after dark, which suggests that they may be following the hummingbirds. My other theory is that for a few years, agaves were popular ornamental plants in the city and were widely planted in yards, creating a substantial population of “tame” agaves (the Tucson basin is too low for any of the native species to grow there naturally). The flowers aren’t usually scented but the stalks are so tall that I assume the bats can see them. The bats may also be drawn to artificial but permanent water sources such as golf course ponds and swimming pools, which offer another opportunity for them to encounter hummingbird feeders.
        For Tucson it may also mean that native food sources are growing scarce. Development has destroyed hundreds of square miles in the last decade, the desert grassland “agave country” where the bats live is becoming desertified by a combination of man-made and natural causes, and interest in landscaping with native plants (or plants in general) has plummeted in the last five years. People aren’t planting anything in new yards, and in older yards they aren’t replacing dead plants, or are cutting everything down to make room to park their pickup trucks. My yard, with its agaves, yuccas, cacti, and young native oaks and other trees, is becoming more of an anomaly every year. But our agaves get pollinated and our hummingbird feeders get drained by the “succubi”, whatever the reason.

      • Posted June 17, 2012 at 7:36 pm | Permalink

        Hi Nate, nice to be in touch again, and nice to see your work featured here! What an interesting idea that maybe this is a “cultural advance” by the bats, communicated by example. It would take some careful work to prove it, though. I remember first seeing this phenomenon in Tinalandia on the west slope, back in the days when I was working as a bird guide, which must have been at least ten years ago, maybe more. When you say “recent”, what timespan are you thinking?

        That new red Burmeistera is waiting for you here, hope you come visit one of these days. We (EcoMinga) built a scientific station in the Rio Zunac that you are welcome to use.

        • Posted June 17, 2012 at 7:40 pm | Permalink

          Oops, I see you said in the past four years. Definitely it has been going on longer than that. But it is not conspicuous when it happens–Tinalandia was unusual in that the dining area had feeders adjacent to it, so the bats were visible during dinner. At Tapichalaca, it would be harder to notice if bats were visiting. Maybe it had been going on there earlier, and nobody noticed.

  7. Thanny
    Posted June 17, 2012 at 8:34 am | Permalink

    You say co-evolution, I say arms race. It’s not predator-prey, but still adversarial.

    • whyevolutionistrue
      Posted June 17, 2012 at 8:39 am | Permalink

      What’s so adversarial about it? The bat is helping the flower reproduce; the flower is giving food to the bat. In my book that’s known as a mutualism.

      • Gregory Kusnick
        Posted June 17, 2012 at 10:03 am | Permalink

        Well, presumably the orchid wants to minimize the nectar reward per pollination, while the bat wants to maximize it.

        • Achrachno
          Posted June 17, 2012 at 10:15 am | Permalink

          Minor point: the plant is not an orchid but a Lobelia relative –quite distantly related. I don’t know if we could say it’s converging on an orchid-like form, but they’re both bilaterally symmetrical and some species of each might be playing versions of the same pollination game.

          • Gregory Kusnick
            Posted June 17, 2012 at 10:27 am | Permalink

            Yeah, I realized that about two seconds after I clicked Post.

      • Thanny
        Posted June 17, 2012 at 10:51 am | Permalink

        The flower is forcing the bat to invest resources in a gigantic tongue, while the bat is no doubt enforcing a minimum amount of provided nectar. If it were simple mutualism, the flower wouldn’t need to enforce pollen gathering by getting longer and longer, all the while providing enough nectar to make it worth it for the bat.

        The number of unpollinated dead-end flowers and starved bats over the course of their evolution was surely not small.

        Consider milkweed and monarch butterflies by analogy. The milkweed depends on the butterflies for pollination, and the butterfly larvae on the milkweed for food. Yet the plants and caterpillars go through deadly combat every season.

        I guess my point is, mutual dependance between two species is not a warm and fuzzy love story. More often than not, it’s two species trying to exploit each other, and somehow striking a balance where both benefit. I have no doubt that many other such relationships over evolutionary time developed and ended when one side or the other succeeded too well at the exploitation.

        • Achrachno
          Posted June 17, 2012 at 5:58 pm | Permalink

          I don’t think monarchs are effective pollinators of milkweeds. It requires a strong bee to pull the pollen sacs out of the little slots in the central column. Monarchs just use milkweeds as a larval food source — and they swipe a bit of nectar. If milkweeds had feelings, they’d probably not like monarchs at all.

      • Old Rasputin
        Posted June 17, 2012 at 8:37 pm | Permalink

        “In my book that’s known as…”

        It’s not often that one gets to hear that phrase used in a simultaneously figurative and literal sense.

        One of these days I need to write a book just so I can get away with word play of this order.

  8. Mary Gnusader Canada
    Posted June 17, 2012 at 8:38 am | Permalink

    Amazing view. This stuff is so interesting. Thanks for posting and explaining the evolutionary processes involved.

  9. Gregory Kusnick
    Posted June 17, 2012 at 9:58 am | Permalink

    Just as a comparison (no griping, readers), if my own tongue were of similar relative size, it would be eight and a half feet long.

    Nothing to gripe about this time, since you’re directly comparing length to length, which is always valid regardless of scale.

  10. Andrew Sinnott
    Posted June 18, 2012 at 1:39 am | Permalink

    This is bloody interesting, I’m a big fan of bats and loved reading this article. I would say one thing with regards to your comment on convergence. The engineer/biomechanic in me says the bat isn’t truly hovering. From what I can see in the video the wing movement couldn’t produce the uplift on the back stroke. To hover, a hummingbird flaps its wings in a figure of eight motion so that it inverts on the back stroke producing uplift, and the bat’s wing position is never inverted. I would say this bat is supporting itself on the flower as it drinks with a less forceful forward flight, or something of that ilk. This suggests that the flower would also have to have evolved some structural integrity as well as the deep neck, to effectively support the bat and deposit the pollen. I would also guess that with this supporting mechanism, true hovering probably won’t evolve in this bat as it’s just too energetically demanding.


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