A blister on their nose allows them to breathe underwater: some American anole lizards use an amazing concept for diving, report biologists. A bladder “sticks” to its water-repellent cuticle in the snout area, which rises and falls when you breathe in and out. A gas exchange takes place, which enables the animals to dive for up to 18 minutes, according to the test results.
How can you get oxygen for a certain period of time underwater without gills? Take as deep a breath as possible and hold your breath – that is our method. Some animals like marine mammals or turtles do it in a similar way – they are just much more efficient than we are. In arthropods, however, there is another concept: some aquatic beetles, spider species and even a bizarre diving fly take an air bubble with them under the surface of the water. You breathe in and out of this supply – a concept known as rebreathing. Technical diving equipment for humans is also based on this principle.
“However, rebreathing was not previously considered as a possible natural mechanism for underwater breathing in vertebrates,” says Luke Mahler of the University of Toronto. But as part of their study, he and his colleagues were now able to clearly demonstrate this technology in certain representatives of the anole lizards. These are semi-aquatic species of these small reptiles that are found in Central and South America. It was known that they can gather food underwater and, especially in danger, literally dive down. The study was based on observations made by co-author Lindsey Swierk from Binghamton University: She was able to show that the Anolis aquaticus from Costa Rica forms a blister in the area of the snout underwater, suggesting a function in breathing.
What’s up with these bubbles?
The researchers have now devoted a more detailed study to this phenomenon. “We were able to prove that the semi-aquatic anoles exhale air into this bubble that sticks to their skin. Then the lizards pull the air back in – that’s why we refer to this concept as ‘rebreathing’ based on diving technology, ”says first author Chris Boccia from the University of Toronto. To confirm that the anoles actually use the air in the bladder to breathe, the scientists carried out analyzes of the gas during dives in their test animals. They found that the oxygen content in the bladders decreased significantly over time, which documents the consumption by the animals.
But is the Anolis aquaticus a bizarre exception? As part of their study, the scientists now also targeted other types of semi-aquatic anoles and were able to demonstrate that all of them used the technique of rebreathing, although some species are only distantly related to one another. “Our work shows that this strategy has repeatedly developed with anoles, which use aquatic habitats.” A basis for this was probably the fundamentally water-repellent properties of the skin of these lizards: It is hydrophobic, so that rain, for example, can easily roll off. When diving, however, the effect leads to air cushions on the surface. The researchers explain that the concept with the blister on the nose evolved from this.
Like a kind of second lung?
The researchers suspect that the process of inflating and retracting the bladder may provide some additional benefits for animal divers’ care. First of all, the movement of air presumably improves absorption in the animals’ respiratory organs. The bladder could also help release excess carbon dioxide from the exhaled air into the surrounding water. Conversely, oxygen could also diffuse from the water into the air supply via the bubble surface and thus increase its capacities, the researchers suspect. Thus the bladder would have the same function as a second lung. The researchers now want to clarify the details of the processes through further investigations.
“This work enriches our knowledge of the amazingly creative concepts with which organisms master the challenges in their environment. That is interesting in itself, but discoveries like these could also inspire technical solutions, ”emphasizes Boccia. “There is still no concrete approach to implementing the anole rebreathing system. But maybe it is worth thinking about possible applications in diving, for example, ”says the scientist.
Source: University of Toronto, specialist article: Current Biology, doi: 10.1016 / j.cub.2021.04.040