When nature rewards cannibalism – EL PAÍS

A mantis, photographed in the Ukraine. DPA via Europa Press (DPA via Europa Press) Vinegar fly larvae feed on decomposing plant matter, but if you leave them without food, they abandon the vegetarian diet and turn to cannibalism. This new lifestyle is not easy for an insect that is not a priori adapted to be a predator. Breaking through the tough cuticle of an insect and penetrating inside requires some pretty powerful teeth. Therefore, by the time they reach the third and final larval stage, those that have been feeding on their mates have 20% more teeth than herbivores, making them supercannibals. Apparently all larvae have a potential cannibal inside them from the start, ready to come out if need be. One last ace up the sleeve. Supercannibals do not occur only in invertebrates, but also among amphibians. Tiger salamander tadpoles normally feed on small aquatic invertebrates, but can develop a larger, toothed head form that is cannibalistic. One study showed that physical friction between these tadpoles is necessary for cannibals to develop. These conditions occur when the tadpoles grow in a space with a high density of individuals. But if both fly larvae and tadpoles have the potential to become supercannibals, why don’t they always do so? For any animal, cannibalism is rarely the first choice. Eating someone of your own species carries several risks. For starters, disease transmission. Pathogens such as parasites or viruses have their favorite species, so if a cannibal eats an infected partner, it is more likely that it will spread. In contrast, it is less common for pathogens to cross from one species to another. Let us remember the example of mad cow disease, caused by an infectious protein that damages the brain of these cattle. Feed used as food was prepared using the remains of animals, including cattle and sheep. The cows were eating infected cows. When a population of animals grows too large and is unsustainable, cannibalism can be an adaptation to survive. Clashes in nature between animals of the same species are frequent, but rarely end in death. For the participants in a duel, it is too risky to go that far. However, when the ultimate goal is to eat the opponent, the fight inevitably has to go to the end. Jay Rosenheim, an entomologist at the University of California, recounts in an article for Science magazine that he once observed two female praying mantises having a fight. He saw how one female ate the leg of the other, but somehow the crippled one managed to win and ended up killing her aggressor. Finally, it is possible that a cannibal ends up eating his relatives or even his children by mistake, which is not ideal for the transmission of genes. There is a species of bedbug, Geocoris pallens, whose females are unable to differentiate between their own eggs and those of others. In one experiment, scientists prepared containers divided in half by a mesh. On one side they placed a solitary bedbug and on the other they left it empty or put more female bedbugs. With the net dividing the plaque, the solitary bug couldn’t blend in with the rest, but it could detect their presence. They remained in the containers for 24 hours, which was enough time to lay eggs. When the solitary bug did not detect other females, it ate practically no eggs, but if only one bug was on the other side, it could cannibalize more than 30% of its offspring. The mere detection of other females activated the ingestion of eggs because, supposedly, if there are other females around, the probability of consuming the clutch itself decreases. Hunger and population control All these disadvantages maintain the balance against cannibalism, but in certain circumstances, taking certain risks can be worth it and the balance tips the other way. As we’ve seen with fruit fly larvae, being starving helps a lot. The same thing happens to the larvae of another insect. In one study, scientists at Tanta University in Egypt found that octopamine triggered cannibalism in mosquito larvae. This is a hormone involved in the control of hunger and aggressiveness. When scientists administered it to the larvae, they turned them into cannibals. On the contrary, if they blocked the receptors for octopamine in their brain, the scientists were able to eliminate this behavior. Some living beings, who benefit from the cannibalism of others, actively promote it so that the balance tips in their favor. There are plants, such as the tomato, that in the face of a threat modify the chemistry of their leaves, causing them to lose nutritional quality. As a consequence, the caterpillars that feed on them begin to eat each other and the garden is filled with cannibals, who also transmit more diseases. Thus, the tomato plant manages to control the population of caterpillars and conserve much more of its leaves. From a human point of view, cannibalism seems an aberrant and immoral behavior, but in nature it is necessary because it contributes to the balance of ecosystems. . This is what a recently published review in the journal Science defends. When a population of animals grows more than necessary and the high density of its individuals is unsustainable, cannibalism can be one more adaptation of the species to survive. Better to eat each other than to end up all starving to death. Therefore, ecologists see cannibalism as a regulating and healing force. Some scientists even propose that there may be cases of animals in which eating part of their own offspring is a type of parental care. For example, there are fish that live in a small pond. It could happen that, when all the pups were born, there would not be enough oxygen for all of them and they would die of suffocation. By eating a few eggs before they hatch, the parents avert catastrophe. What might seem like a paradox at first makes sense in the eyes of evolution and survival. Nature is neither kind nor cruel, it simply exists, which is no small thing.You can follow MATERIA on Facebook, Twitter and Instagram, or sign up here to receive our weekly newsletter.50% discountSubscribe to continue readingRead without limits