May 19 news, according to foreign media reports, this may be the most unexpected journey of life. Biologists from a 2012 Southeast Asian expedition to East Timor discovered that a hooked blind snake had burrowed out of a very unexpected place: the butt of an ordinary Asian toad.
Mark O'Shea from the University of Wolverhampton in the United Kingdom and colleagues stumbled upon this unusual event when they found a rock underneath. It is the first record ever recorded of a prey that has ever been swallowed, a toad and a hook-blind snake that survives in its digestive tract.
O'Shea said: "It's very surprising that vertebrates with lungs were able to pass through the digestive tract unharmed and survive.
Illustration: Hooked blind snake
Admittedly, some larvae and small marine invertebrates can pass through the entire digestive tract of carnivores unharmed. However, once in the mouth of an animal, larger prey may be chewed to death. Even if they somehow dodged this doom, they would be squeezed in the throat of the predator.
Even if you avoid this disaster, you will face greater problems. Most prey are unable to fend off stomach acid in predators, and the deep lack of oxygen inside the digestive system is another huge challenge.
However, for prey devoured by toads or birds, the chances of survival may be a little higher. These animals often push food behind their throats before swallowing, which may increase the probability that the devoured person will safely pass through the predator's digestive system.
This helps explain a poisonous amphibian, where the salamander with a rough outer skin can tolerate being swallowed by frogs. Once inside the frog's belly, the salamander kills the frog with a toxin before it is secreted and digested. The salamander will then crawl out of the frog's mouth.
Illustration: A salamander with a rough appearance
But in O'Shea's discovery, the hook-blind snake did not kill the toad, but passed through the toad's dark and narrow intestines, thus retreating completely.
Compared to most species, the hooked blind snake seems to be better suited for this dark journey. Its slender body is only a few millimeters wide and can pass effortlessly through small holes and crevices. Therefore, it is not difficult for a hooked blind snake to pass through the narrow digestive tract of the toad.
O'Shea believes that the ground hook blind snake crossed the toad's intestines on its own, rather than simply moving passively through intestinal muscle contractions.
And the toad's dietary habits also make the journey of the hook blind snake easier. In the hours before swallowing the snake, the toad may not have ingested other foods, meaning the path through the intestines was clearly recognizable. If this is the case, the hook-blind snake will crawl through the toad's intestines for a shorter time and correspondingly reduce the exposure time in the digestive juices.
In any case, the skin of the hook-blind snake may be the biggest barrier to life. The hook-blind snake has rough skin, and to help the blind snake move on land, it is not only closely connected but also layered, which can prevent the erosion of the toad's gastric juice to the greatest extent.
In addition, the biggest problem that the hook blind snake needs to face is prolonged lack of oxygen. Due to the small size of the hook-blind snake, it requires less air than many animals. But lack of oxygen is still a big problem. O'Shea said: "Theoretically, the time it takes for a hooked blind snake to pass through the intestine will determine whether it survives or not. ”
Pictured: Japanese white-eyed bird
Researchers don't know exactly how long it takes the snake to pass through the toad's intestines. But although they watched it drill out of the toad alive, it died after about five hours.
Although no detailed examination was conducted, the researchers believe that the hooked blind snake may have died from complications caused by lack of oxygen. O'Shea said: "We can't imagine any other factor that would kill it. ”
Snails may be better off than hooked blind snakes in the same situation because they can survive in an oxygen-starved environment.
In a study published in 2011, Shinichiro Wada of Tohoku University in Japan and colleagues fed the Japanese white-eyed bird a small ground snail, Tornatellides boeningi, to see if the snails could pass through the bird's digestive system intact. About 15 percent of the snails survived, passing through the entire digestive tract for anywhere from 20 to 120 minutes. This study proves for the first time that snails can avoid being digested. "Snails can pass through the digestive tract in a short period of time by not being completely exposed to digestive juices." Tian Yuan ichiro said.
Illustration: Common shellfish
Snails are able to resist digestion probably because their hard shell provides natural armor. But Tanichiro and his colleagues found that snail size is also the key to survival. They examined the shell of the surviving snail, about 2.5 millimeters wide, and was able to remain intact after passing through the digestive tract. The shells of larger snails are usually divided into several pieces. The researchers believe that snails may also produce mucus to ward off the acidic environment of the digestive tract, but this idea still needs to be validated.
Occasionally, however, large snails can pass through the digestive tract unharmed. Jasna Simonova of Charles University in Prague, Czech Republic, found that snails up to 17 mm in diameter sometimes come out alive from the digestive tracts of various birds. These larger snails are digested without harm.
Another unexpected type of gut traveler is a creature called Caenorhabditis elegans. Hinrich Schulenburg and his team from Kiel University in Germany found nematodes in the intestines of slugs collected in northern Germany. Later, they were surprised to find that there were also live nematodes in the slug's feces.
Schulenburg said: "These nematodes seem to have been eaten by slugs, and it is surprising that the slugs originally had an organ in their bodies for grinding and ingesting food, which should have killed the nematodes." "We also don't know how they survive in acidic conditions." According to the researchers, other types of nematodes have also been found in slugs and earthworms, which are also able to pass through the digestive tract unharmed.
The team was also surprised to find that not only juvenile nematodes were able to survive through the digestive tract of predators, but so did adult nematodes. Because the larvae have a tough outer layer, we can think that this will protect them during the crossing, and they will tolerate harsh environments more than adult nematodes. "It's still a conundrum," Schulenburg noted, noting that nematodes often seem to survive through the digestive system of predators, which never last more than a day in slugs.
Illustration: Caenorhabditis elegans
Gut travel is rare for terrestrial organisms, but seems to be more common in aquatic environments. Casper van Leeuwen of Utrecht University in the Netherlands and colleagues found that some adult aquatic snails are still able to survive after passing through the digestive tract of wild ducks. A female species of shrimp can also survive in the intestines of white sucker fish, while some mussels can safely pass through the body of the anemone.
Van Leeuwen and his team speculate that the characteristics of living in humid environments may help invertebrates stay active in predators' bodies. On the other hand, the characteristics of the digestive system of predators also contribute to the survival of these predators. For example, some birds digest quickly, which also helps to quickly pass through the digestive system of what they ingest, and some of them may be too late to be processed.
Throughout the biological world, travel through the predator's digestive system seems to be fairly common, allowing some small and weak creatures to survive briefly in the predator's body. In this way, some species use predators as their means of transportation, enabling themselves to migrate over long distances.
The snail observed by Tadamoto ichiro and his team seems to be like this. They found these snails not only on Hahajima Island, one of Japan's Ogasawara Islands, but also on neighboring islands. The study found that the distribution of these co-species snails seems to indicate that snails have wings and can migrate between different islands.
This gene migration between snail populations can be explained by the theory of gastrointestinal survival. Tagenichiro's team found that the locally ubiquitous Japanese white-eyed bird is the main carrier of snail gene migration.
"These results suggest that snails can be spread by birds that prey on them," Tagenichiro noted. In addition, they witnessed that as long as a snail can safely pass through a bird's digestive system, it means that snails can continue to form a new population in a new place.
Schulenburg suspects that nematodes may also be able to use slugs as free buses to get themselves from one place to another. Another possibility is that the slugs' guts themselves have a lot of appeal to nematodes: they may use the slugs' gut bacteria as their food source.
In 2014, Jan-Jakob Laux and a research team at the University of Hamburg in Germany documented the first case of insects relying on predators to travel long distances. They suspect that eggs from the aquatic leaf beetle Macroplea mutica are spread by mallards because the eggs are able to pass through the mallard's digestive system unharmed. It is reported that due to the slow movement of this insect, its geographical distribution in the Gubei region has always been a mystery.
However, for the hook-blind snake mentioned at the beginning of the article, its passage through the toad's digestive system is most likely an accident. O'Shea believes that the toad mistook the hooked blind snake for its prey, the earthworm. He said: "I'm sure the toad doesn't know it's a vertebrate that it's swallowing. It thought it was just a shiny worm. ”
It is not uncommon for toads to swallow a hooked blind snake, but rarely can a full body retreat with a hooked blind snake. However, the hook-blind snake may rely on the owls' digestive tract to "travel around".
Studies have reported that hooked blind snakes have been found in owls' lairs. Exactly how they appeared there is unclear. But some researchers say the hook-blind snake climbed the tree to eat invertebrates that lived in nest debris. Another study suggests that owls bring them to their nests as food for their chicks.
Although O'Shea does not doubt the climbing ability of the hooked blind snake, the probability that it must first find the owl's nest, or arrive by chance, is too small. It is also difficult for an owl to feed a hooked blind snake to a chick: the snake will curl up when touched, and may fall into the depths of the nest.
O'Shea said: "I think these hook-blind snakes are more likely to have passed through the intestines of owls. Like toads, owls often devour their prey without chewing.
If predators unknowingly ingest live animals, what are the health effects? For example, intestinal parasites usually enter animals along with food and water and then survive in the intestines. Schulenburg believes that the nematodes he found in the intestines of slugs (C. Schulenburg) elegans) is actually quite possibly a parasite. "If that's the case, it's exciting," he said. "I think it's possible."
Some nematodes are true parasites, while others can switch between different ways of living independently and living parasitically. Caenorhabditis elegans is considered non-parasitic, but the evidence suggests that it can also be a parasite, providing humans with an example of how animals evolved into parasites.
Schulenburg said: "It will be a perfect system for studying adaptation and molecular mechanisms, and it is exciting to know what kind of characteristic organisms are needed to live as parasites as parasites. "As one of the simplest animals with a nervous system, nematodes are often used in all kinds of research.
Tadamoto also believes that the parasite may be involved in the interaction between snails and birds. He found that parasitic flatworms live in many land snails, and he thinks birds may be the ultimate hosts for these flatworms. Tagenichiro deduces that the flatworm may have used the snail as its Trojan horse to enter the intestines of the mallard. "I'm working on the relationship," Tadagenichiro noted.
However, digestive tract travelers such as these can not only exploit predators for their own benefit, they can also have a positive impact on predators. Schulenburg believes that by ingesting bacteria from the intestines of slugs, Caenorhabditis elegans is beneficial to the microbial communities in the intestines of predators. "Some organisms that feed on bacteria help increase the diversity of the gut microbial community," he said.
However, the hook-blind snake may have little effect on the toad that eats it, except that it gives the toad the strange sensation of foreign bodies moving in the stomach and intestines. "The toad seems awkward," O'Shea noted. After all, a snake had burrowed out of its ass.
Source of this article: NetEase Science Man