Social parasitism

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In biology, social parasitism is a special form of parasitism . Social parasitism is defined as the relationship between two animal species in which a eusocial species with a sterile worker caste (or a species that has lost its worker caste secondarily) takes advantage of the social system of other, likewise eusocial species. Social parasites are extraordinarily specialized species that typically manage to exploit the rich but heavily guarded resources of a colony of eusocial creatures through mimicry or other forms of camouflage . Social parasitism occurs mainly in hymenoptera .

Occurrence

Several hundred species of ants are known around the world that have developed into social parasites of other ants, and it is assumed that there are a few more hundred species that have the potential to take this evolutionary path. There are also many known cases of social parasitism in bees and wasps . In this context, it is very astonishing that this form of parasitism in termites has hardly been observed at all, although this group of animals with very many eusocial species occurs in large parts of the world.

Social parasitism in ants

The following sections deal exclusively with social parasitism in ants, as this is where it is most diverse and has been best researched. The first three categories are to be distinguished from the others because they are probably the most strongly derived form of social parasitism in evolution (Wilson definitions).

So far 54 species are known in Central Europe , which occur either temporarily or permanently as a social parasitic. That is 35% of all known species, of which 15% spend their entire life cycle as parasites. What is very astonishing is that social parasitism seems to be much more common in temperate latitudes. Only half as many cases are known from the tropics , even though around 97% of all known ant species occur there. The following theories were put forward to explain this phenomenon (according to Seifert):

  • A cool climate offers more favorable conditions to penetrate a host colony, as the workers are inhibited in their aggressiveness and speed of movement.
  • The ant communities of the tropics are incredibly diverse and very fragmented. Since social parasitism is likely to be tied to a specific species in its development, the species-poorer ant fauna of the northern hemisphere, with its partially quite homogeneous populations , offers better adaptation conditions for the parasitic species.
  • Polygynous species are common in the temperate latitudes . This makes it easier for related species to invade, as the acceptance of young queens in polygynous colonies must be higher to ensure polygyny.

Inquilism: permanent social parasitism

Teleutomyrmex schneideri

The classic example of perfect social parasitism is Teleutomyrmex schneideri ( Greek: "the last ant" ), a species of ant that was discovered by Heinrich Kutter in the middle of the 20th century . This extraordinary parasite occurs exclusively as a lodger of two ant species, Tetramorium caespitum and Tetramorium impurum , in the French and Swiss Alps. In T. schneideri no worker castes can be observed, so there are only queens and males. The parasite is completely dependent on the workers in the host colony. Most of the time it lives ectoparasitic on the backs of its hosts . In the course of tribal history, however, this extreme form of adaptation resulted in the body appearing stunted compared to other species (for example, the chitin shell is thin and unpigmented, and only liquid food can be consumed).

Dulosis: slavery

Some species of ants have become dependent on workers of other species. The parasitic ant species goes on veritable raids in order to attack the ant nests of other species and to carry off the brood. After returning home to their own nest, the captured eggs and pupae are taken care of by already enslaved female workers and raised to serve as slaves themselves. The slave-keeping ant species is so physiologically adapted to the predatory way of life that it could not survive without the robbed workers. Dulosis occurs in the Amazon ant ( Polyergus rufescens ) and members of the Formica sanguinea group (can also be found in Germany).

Temporary social parasitism

The social parasite only uses the host nest to establish a colony. The newly mated queen of the parasitic species finds a host colony and ensures "adoption", either through compulsive submission of the workers or through forms of appeasement. The original landlord queen is then killed by the intruder or "converted" workers. Little by little, the nest turns into a mixed colony until it finally becomes a colony of the parasite queen and her offspring due to the extinction of the last host worker. Temporary social parasitism occurs in Europe, for example, in all real wood ants, i.e. in Formica species of the subgenus Formica sensu stricto .

Xenobiosis

Here one species lives in the walls or chambers of the other's nest and roams freely among its hosts. It receives food, often through regurgitation , yet the brood is kept separate.

Lestobiosis

A few smaller species of ants, mostly belonging to the genus Solenopsis or related genera, wait in the nest walls of other ant or termite structures and penetrate their hosts' nest chambers to steal food and / or rob the brood. Some species of Carebara in Africa and tropical Asia build their nests in the walls of termite mounds and likely live off the inhabitants or their brood.

Cleptobiosis

Some smaller species of ants build nests near larger ones and take food or brood from the host colony. A species of Crematogaster has even been described in India , waiting in wait for a Holcomyrmex species, laden with preyed food, heading home to rob them in a moment of threat from other enemies. This behavior is obviously not an individual achievement, but is carried out systematically by the parasitic colony.

In the south of the United States of America workers were the type Conomyrma pyramica observed gathering up the dead insects from a Pogonomyrmex had been disposed of colony (including Pogonomyrmex -Leichen).

Plesiobiosis

Social parasitism is only rudimentary. Different species of ants build their nests close together, but hardly bother each other, unless their nest chambers are accidentally broken open, then fighting and nest robbery can occur.

Social parasitism in wasps

In principle there are three forms of social parasitism in wasps :

  • Parasitoid attack. The female wasp attacks another species of wasp, paralyzes it, and lays its eggs in it. The immobile victim then serves as food for the larvae.
  • Labor parasitism . A female is specifically looking for a victim who has already been paralyzed by another species of wasp, digs herself into the brood chamber, eats the parasitoid's eggs and lays her own eggs. This form is not very common.
  • Replacement of the queen. The parasitic female invades a social species wasp nest and kills the queen to take her place. This phenomenon seems to be equally common in wasps and ants. For example, two of the sixteen Vespula species found in North America are permanent social parasites.

Social parasitism in bees and bumblebees

Social parasitism is also a widespread phenomenon in bees. It occurs in the families of the Halictidae, Anthophoridae, Megachilidae, and Apidae. The parasitic bee species typically penetrates the nest chamber and lays an egg in one of the many brood chambers. The rapidly growing larva then passively displaces the original inhabitant or even actively kills them with the mandibles, which are very early in some species . In rare cases, the victim is eaten. In contrast to the wasps, bees are not known to have a parasitoid lifestyle, as they very rarely feed on animal protein.

A species of bee ( Lestrimelitta limao ) is known from Argentina , which undertakes veritable raids against bees of the genus Melipona and Trigona . It is primarily a matter of capturing food supplies that are stored in the goiter in order to create them in their own colony. During the attack, the attacker secreted a strong lime-like smell from her mandibular glands . This pheromone, identified as citral , obviously heats up the workers, so that they leave the hive. It has already been observed that L. limoa occupied the conquered nest and annexed it as a colony of its own (similar to the dulosis in ants).

Social parasitism in bumblebees is a direct result of the aggressive organization of their colonies and has been fairly well researched. In some species of the genus Bombus , the queens try to invade foreign nests and kill the founding queen in order to take her place. In such cases, the founding queen and her court often defend themselves to the point of death. Multiple invasions often occur in succession. In one extreme case, 20 dead B. terrestris were found in one colony . Temporary social parasitism and even equilism have also been detected in Bombus .

Termite social parasitism

As already mentioned, social parasitism is almost non-existent in termites . In comparison to the Hymenoptera , a rather weak form occurs here, which is most closely comparable to the xenobiosis in ants. Species from three orders have been observed, Ahamitermes , Incolitermes and Termes, in which behavior is recognizable that could be described as nest parasitism. The members of these species live in the walls of other termite colonies and feed on the paper mache-like structure. This approach causes not inconsiderable problems in the host colony, as it can damage the highly efficient ventilation system. A very special case of social parasitism caused by an ant species has already been mentioned above under 'Lestobiosis'.

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