The relationships between different living things continue to be one of the main topics of study in science. Specifically, the mutualism has been extensively studied and, currently, truly surprising cases of animal mutualism continue to appear.
In this article on our site we will explain the definition of mutualism in biology, the types that exist and we will also see some examples. Find out everything about this form of relationship between animals.
What is mutualism?
Mutualism is a type of symbiotic relationship. In this relationship, two individuals of different species benefit from the relationship between them, obtaining something (food, shelter, etc.) that they could not obtain without the presence of the other species. It is important not to confuse mutualism with symbiosis. The difference between mutualism and symbiosis is that mutualism is a type of symbiosis between two individuals.
It is quite possible that every organism on planet Earth is in some way associated with at least one other organism from a different species. In addition, it seems that this type of relationship has been key in the history of evolution, for example, the origin of the eukaryotic cell, the appearance of plants on the earth's surface or the diversification of angiosperms or flowering plants.
The costs of mutualism
Mutualism was originally thought to be an altruistic action on the part of organisms. Nowadays it is known that this is not the case, and that the fact of taking from another something that one cannot manufacture or obtain oneself, has costs.
This is the case of flowers that produce nectar to attract insects, so that the pollen adheres to the animal and is dispersedAnother example is that of plants with fleshy fruits in which frugivorous animals take the fruit and disperse the seeds after passing through their digestive tract. For plants, creating a fruit is a considerable expenditure of energy that benefits them directly.
Despite this, studying and getting meaningful results about how big the costs are for an individual is a difficult task. The important thing is that at the species level and at the evolutionary level, mutualism is a favorable strategy.
Types of mutualism
To better classify and understand the different mutualism relationships in biology, these relationships have been classified into several groups:
- Obligated mutualism and facultative mutualism: within mutualistic organisms there is a range in which a population can be obligate mutualistic and without the presence of the other species cannot fulfill its vital functions, and facultative mutualists, which can survive without interacting with the other mutualist.
- Trophic Mutualism: In this type of mutualism, the individuals involved obtain or degrade the nutrients and ions they need to live. Normally, in this type of mutualism, the organisms involved are, on the one hand, a heterotrophic animal and, on the other, an autotrophic organism. We should not confuse mutualism and commensalism. In commensalism, one of the organisms obtains benefits and the other obtains absolutely nothing from the relationship.
- Defensive mutualism: Defensive mutualism occurs when one of the individuals involved obtains some reward (food or shelter) through the defense of the other species that forms mutualism.
- Dispersive Mutualism: this mutualism is that which occurs between animal and plant species, so that the animal species obtains food and the plant the dispersion of its pollen, seeds or fruits.
Examples of mutualism
Within the different mutualistic relationships there may be species that are obligate mutualists and species that are facultative mutualists. It may even happen that during one stage there is obligatory mutualism and during another it is optional. The rest of the mutualisms (trophic, defensive or dispersive) can be obligate or facultative, depending on the relationship:
Mutualism between leafcutter ants and fungi
Leaf-cutter ants do not feed directly on the plants they forage, instead create orchards in their nests where they lay the cut leaves and on these they place the micelo of a fungus, which will feed on the leaf. Once the fungus grows, the ants feed on the fruiting bodies of these. This relationship is an example of trophic mutualism
Mutualism between rumen and ruminant microorganisms
Another clear example of trophic mutualism is that of ruminant herbivores. These animals feed mainly on grass. This type of food is extremely rich in cellulose, a type of polysaccharide impossible for ruminants to degrade without the collaboration of certain beings. Microorganisms housed in the rumen degrade the cellulose walls of plants, obtaining nutrients and releasing other nutrients that can be assimilated by ruminant mammals. This type of relationship is a obligatory mutualism, both ruminants and rumen bacteria cannot live without each other.
Mutualism between termini and actinobacteria
The termites, to increase the immune level of the termite mound, build nests with their own feces. These bundles, when solidified, have a cardboard appearance that allows the proliferation of actinobacteria. These bacteria act as a barrier against the proliferation of fungi Thus, the termites obtain protection and the bacteria feed, so we are faced with a case ofdefensive mutualism
Mutualism between ants and aphids
Some ants feed on the sugary juices expelled by aphids. While the aphids are feeding on the sap of the plants, the ants are drinking the sugary juice. If any predator tries to bother the aphids, the ants will not hesitate to defend the aphids, their main food source. It is a case of defensive mutualism.
Mutualism between frugivorous animals and plants
The relationship between frugivorous animals and the plants they feed on is so strong that, according to several studies, since some of these animals have become extinct or have reduced their numbers, the fruits of the plants have reduced in size.
Frugivorous animals select the most fleshy and striking fruits so there is a selection of the best fruits by these animals. In the absence of animals, plants do not develop such large fruits or, if they do, no animal will be interested in it, so there will be no positive pressure for that fruit to be a tree in the future.
In addition, some plants, to develop large fruits, need a partial pruning of those fruits. The dispersive mutualism is really necessary not only for those species involved, but also for the ecosystem.
