A lizard that breathes underwater

by Greg Mayer

This beats eating and swimming underwater: Lindsey Swierk, of SUNY Binghamton, reports, in the latest issue of Herpetological Review, that Anolis aquaticus can breathe underwater! Here’s a video she posted at Anole Annals:

The lizard, of course, is not breathing water; rather, it is breathing air that is trapped around it’s body, which it then visibly exhales in a bubble, and then “rebreathes”. I could not tell from how far around the body air was being drawn to the nostrils, but it seems to include at least the head. The longest she has seen them stay down is 16 minutes. It has long been noticed that air can be trapped around an anole’s body when it’s placed in water, and I’ve wondered whether that air might enable an anole to float longer or higher in the water (perhaps aiding “occasional transport”). But Lindsey has placed these casual observations on a much firmer basis, and recorded, for the first time to my knowledge, that the lizards are breathing; that’s something I never suspected. She proposes a “scuba tank” explanation for the behavior– that the lizard is getting oxygen from the recycled air.

Many species of anoles, both on the main and on the islands, are semiaquatic; aquaticus occurs in Costa Rica and Panama, and the ones filmed were in southern Costa Rica. These semiaquatic anoles inhabit the vegetation alongside streams, and jump into the water when approached. As Lindsey notes, it is an effective anti-predator behavior. Many times I have seen anoles of these species flee from my approach into the water; I think I may once have seen aquaticus myself, in southern Costa Rica.

h/t: Matthew, Thom Sanger

Swierk, L. 2019. Anolis  aquaticus (= Norops aquaticus)  (Water Anole). Underwater breathing. Herpetological Review 50:134-135. pdf; jump to p. 27


  1. Raskos
    Posted April 5, 2019 at 4:13 pm | Permalink

    This principle – gas exchange through the limit of the bubble surrounding the organism – is used by diving beetles and probably other aquatic insects. And I recall a diving spider that spins sort of a fixed diving bell attached to underwater vegetation and fills it full of air by repeatedly diving and entering it with a coat of air held on by its pelage. The diving bell is eventually filled with air and gas exchange through the surface tension membrane keeps it relatively fresh.

  2. Posted April 5, 2019 at 4:19 pm | Permalink

    Thanks. Very interesting and see how it could shake up people

  3. gravelinspector-Aidan
    Posted April 5, 2019 at 4:52 pm | Permalink

    She proposes a “scuba tank” explanation for the behavior– that the lizard is getting oxygen from the recycled air.

    That works – rebreather counter-lungs are standard personal equipment for over-water helicopter operations in the North Sea and Grand Banks, though not elsewhere TTBOMK. As part of basic training, and every 2 years afterwards, you have to be able to demonstrate ability to use them, upside down, in the mock-up of a submerged fuselage for a minute.
    But there are limitations. Mass balance for the chemistry of respiration will gradually replace the oxygen content with CO2. Typical exhaled breath contains about 6% v/v of CO2 while surface fresh air contains 21% O2 ; tidal volume for typical lungs is approximately a litre ; so depending on the volume of your counter lung you can calculate the endurance in breaths. Having more than about 2 kg of buoyancy (2 litres) has a bad effect on people’s ability to get out of overturned airframes (you have to swim down from any air pocket, to exit the window frames ; many people find this disorienting), so you get around 6 breaths before you get severe respiratory distress.
    You go through this training “dry” until you’ve learned what “respiratory distress” feels like, and can manage your breathing to meet the 2 minutes pass/fail criterion. If you fail, you don’t get a refund for the training course. Many people find this stressful, particularly if they’re self-funders, though not as stressful as a real crash. That makes the training more realistic. And more profitable.
    Then you do it again “wet”.

    The UK systems were self-filled (you take a big breath immediately before the water goes over your head, and fill the counter-lung with that, then release your harness and attempt to exit the fuselage) ; the Norwegian and Canadian systems incorporated a 4l STP air cylinder on a wet-blow valve.

    You can, I’m sure, do the same sort of calculations for the lizards. Given the general coolness of water, and the poikilothermy of most small non-avian diapsids, 16 minutes doesn’t seem unreasonable. The volume of the “bubble” must be several times the tidal volume. Of course, since you can’t reason with the lizards, you’d have a job finding the limits under the oversight of an Ethics Committee.

    • rickflick
      Posted April 5, 2019 at 9:13 pm | Permalink

      I’d settle for a tank of Nitrox.

  4. Torbjörn Larsson
    Posted April 5, 2019 at 5:04 pm | Permalink

    Ah, it became a paper, nice! I believe I saw a similar video a few months back – this was much more instructive.

    ADDED: A search revealed that video material has been on the net st least since December [ https://www.iflscience.com/plants-and-animals/video-captures-the-bizarre-way-this-lizard-has-evolved-to-breathe-underwater/ ]. “However, Swierk is quick to caution that her work is in its infancy, and she is simply reporting on a “cool observation”. No study has been published on the topic, although a short natural history observation will be published in the March issue of Herpetological Review. Nevertheless, she believes her work could eventually lead to a better understanding of how evolution has led to multiple solutions to the same problem – how species remain underwater for long periods of time.”

  5. Hugh Spencer
    Posted April 5, 2019 at 5:13 pm | Permalink

    It’s all to do with diffusion of oxygen into the bubble of air trapped underwater – as the animal uses the O2 the differential partial pressure causes O2 to diffuse into the bubble – thus replenishing it. For a good full explanation see Ekert 5th edition, p 559.

    • Posted April 6, 2019 at 12:21 pm | Permalink

      Thank you for the explanation! I thought that the animals could use only the oxygen originally brought down in the bubble.

  6. ThyroidPlanet
    Posted April 5, 2019 at 5:16 pm | Permalink

    I remember that fascinating video – I’m glad it was published!

  7. Posted April 5, 2019 at 5:36 pm | Permalink

    Reblogged this on The Logical Place.

  8. loren russell
    Posted April 5, 2019 at 6:45 pm | Permalink

    There’s a particularly elegant version of the gas-exchange “bubble” known as plastron respiration. It’s been demonstrated in a number of aquatic arthropods, and perhaps best studied in the riffle beetles [family Elmidae] which are benthic, many in fast-running streams with high oxygen content. The plastron is a surface surrounding the insect’s spiracles which densely covered with very short, hydrophobic-surfaced hairs, preventing water from reaching the underlying surface, and so generating an air bubble, even against an atmosphere or more of water pressure.

  9. Heather Hastie
    Posted April 5, 2019 at 7:16 pm | Permalink

    Very cool!

    I reckon I’ve got it beat though. NZ has an insect that hides from predators underwater for up to ten minutes – the Tusked Weta.

    There’s BBC video of it doing just that on this post: https://www.heatherhastie.com/tusked-weta-versus-foraging-pig/

    • Posted April 6, 2019 at 7:50 am | Permalink

      The lizards have been observed to stay down for 16 minutes, and the longest one came up after being disturbed.


      • Heather Hastie
        Posted April 6, 2019 at 10:57 pm | Permalink


  10. CAS
    Posted April 6, 2019 at 2:20 pm | Permalink

    She proposes a “scuba tank” explanation for the behavior– that the lizard is getting oxygen from the recycled air.

    I notice the bubble popping up gets smaller over time. If the lizard produced skin secretions coating the air-water interface around its body, this might be a true rebreather that removes CO2 (such as used in fancy dive equipment). This could result if CO2 were much more soluble in the coating than O2. In fact, CO2 is much more soluble in many liquids than O2.

    • CAS
      Posted April 6, 2019 at 2:31 pm | Permalink

      Also, CO2 is generally poisonous to air breathers, so removal would greatly enhance the dive time.

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