A parasitic ant is a type of ant that exploits the social structure of another ant species for its own survival and reproduction. The most common types of parasitic ants infiltrate a colony of a closely related species by using pheromones identical to those of the colony's workers to avoid conflict and blend in. The parasite lays eggs alongside existing ones for the host colony's worker ants to raise and nurture as their own. Other parasitic ants transport the host colony's pupae and larvae back to the parasite's colony, where the brood will be raised as their own. The host brood that were transported are unable to differentiate between the parasites and their own colony, and serve as worker ants for the parasites. The earliest parasitic ants most likely evolved 16 million years ago as temporary social parasites (ants that infiltrate a colony and kill the host queen). Parasites usually cause harmful effects to the target colony and can inhibit the colony's growth and development. In some cases parasites have been observed to evolve their anatomy to reflect that of their target species, which causes them to remain undetected inside a colony for the majority of their lifespans. The parasites may also experience social parasitic syndrome, causing changes to their anatomy adapted for parasitism. Social parasitic syndrome has been identified in the genera Acromyrmex and Pseudoatta.
Species and characteristics Of the more than 12,000 species of ants, around 230 are considered parasites. The genus Formica contains many parasitic species, with over half of its 172 species confirmed or suspected to be parasites. Other genera – such as Acromyrmex (leafcutter) ants and Myrmica red ants – also show parasitic behaviors. Typical ant colonies have at least three castes: queens, workers and drones (males). Some species also have a fourth caste of soldiers who defend the colony. However, some socially parasitic ant species have developed a separate pseudo-caste of mutated worker ants that exhibit queen-like phenotypes (visual attributes). The mutated ants contain a mutated supergene (a cluster of related genes within a chromosome) that allows them to develop traits such as wings, larger eyes and ovaries (a reproductive organ in queen ants). The mutated ants are capable of reproduction.
Features Parasitic ant species can evolve over time to reflect the preferred host species. Rather than becoming visually homogeneous, such as matching their host's colors, they instead evolve similar anatomical shapes and features to blend in with the hosts through touch. The parasitic queen's features are also significantly altered, with the vast majority of species' queens shrunken to at least 35% of a normal queen's size. The pheromones of parasitic ants are also altered to reflect those of the host species through a process known as rubbing. The parasite uses its mandible to attach itself to a host ant and cover its own body with the host's pheromones. The host usually responds aggressively to the parasite's mandibles. This is done so as to obtain the host's cuticular hydrocarbon profile, which is a collection of chemicals specific to each individual colony, and is used for identification among colony members. Covering themselves with the host's profile can make the parasite indistinguishable from host workers. This is done to minimize any potential conflict while the host colony is being entered. The species Formicoxenus provancheri (shampoo ant) uses a slightly different method of imitating pheromones, in which they use their glossae (tongue-like structures) to obtain the host's pheromones, then use it to cover themselves.
Phylogeny Parasitism in ants likely first arose around 16 million years ago in the form of temporary social parasites. Entomologists disagree on the exact origins of specific parasites, but do observe that many parasitic ants are closely related to the species they parasitize, following Emery's rule. Inquiline parasitism (ants living inside the nest of a host) has evolved at least 40 separate times in ants, all within the formicoid clade. There are primarily 6 ant subfamilies that evolved inquilinism at around the same time period. Temporary social parasitism has evolved at least 60 times in multiple ant species, marked by the parasites losing the ability to form their own colonies, instead relying on taking over existing colonies of other species. Most groups of parasitic ants are monophyletic.
Social parasitic syndrome Social parasitic syndrome is a series of changes that can occur in parasitic ant species during their transformation towards exploitative behaviors. It is usually marked by the loss of a worker caste, shrinkage of body structures and overall size, broadening of the petioles, and a reduction in mandible size. Queen ants affected by the syndrome contain a mutated supergene on chromosome 13, which causes increased egg production, altered metabolism and significantly shrunken bodies. The supergene is a collection of 200 individual genes that contribute to the syndrome's effects. The supergene is rarely not passed down to future generations. Affected queens have a similar visual appearance in size and structure to workers of their own or closely related species, with the exception of having wings. The syndrome has been identified in species of the genera Pseudoatta and Acromyrmex. After inheriting the supergene and being affected by the syndrome, the ants are no longer able to independently survive without exploiting a host colony, making them obligate parasites.
Methods There are several methods that parasitic ants use to exploit other colonies. A common method observed involves a parasitic queen ant infiltrating a colony and killing the existing queen, so as to become accepted by the hosts as a permanent member of the colony. Most parasites (excluding inquiline ants) eventually kill the host queen by either attacking the queen or killing off the workers who care for her. Some ants also utilize slave raids to transport host eggs back to their own colony to raise as their own.
Slaver ants
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