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Ant supercolony

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Exceptionally large ant colony
Large anthill in South Tyrol

An ant supercolony is an exceptionally large ant colony, consisting of a high number of spatially separated but socially connected nests of a single ant species (meaning that the colony is polydomous), spread over a large area without territorial borders. Supercolonies are typically polygynous, containing many egg-laying females (queens or gynes). Workers and queens from different nests within the same supercolony can freely move among the nests, and all workers cooperate indiscriminately with each other in collecting food and care of the brood, and show no apparent mutual aggressive behavior.

As long as suitable unoccupied space with sufficient resources is available, supercolonies expand continuously through budding, as queens together with some workers migrate over short distances and establish a new connected nest. The supercolony can also expand over long distances through jump-dispersal, potentially ranging between continents. Jump-dispersal usually occurs unintentionally through human-mediated transport. A striking example of an ant species forming supercolonies across continents is the Argentine ant (Linepithema humile). The also highly invasive red imported fire ant (Solenopsis invicta) and Solenopsis geminata additionally use classic mating flights, thus using three primary modes of dispersal. Out of some 14,000 described ant species, supercolonialism is found in less than 1% of all ants.

In general, ants that form supercolonies are invasive and harmful in the non-native environments. While not all supercolonial species are invasive and not all invasive ants are dominant, supercolonies are usually associated with invasive populations. Some invasive species are known to form supercolonies in their native habitat as well. In their native range, relatively small supercolonies are observed, whereas they are much larger, dominant and a threat for ecological diversity in their invasive range. Exceptions of species that form supercolonies without being invasive are mainly found in the genus Formica.

Although supercolonies are mainly observed in relatively few ant species, similar unicolonial populations are also found in some species of the termite genus Reticulitermes.

Unicoloniality versus supercoloniality

Large trail of ants

Initially, it was hypothesized that unicoloniality is a characteristic of certain ant species in which all workers of that species are amicable, whatever their nest of origin. So, all members of the species would accept each other, irrespective of the nest of origin and irrespective of the distance between the nests. In contrast, multicoloniality is the common characteristic of ants to show all colonies being aggressive to each other, including different colonies of the same species. A supercolony would be a large aggregation of nests of a species that normally would exhibit multicoloniality, but in the case of a supercolony has all workers from all connected nests being non-aggressive to each other. The Argentine ant (Linepithema humile), forming megacolonies of spatially separate nests, was thought to be a perfect example of unicoloniality, never exhibiting multicoloniality.

Giraud et al. (2002), however, discovered that L. humile also forms supercolonies that are aggressive to each other, so unicoloniality turned out to be limited. They hypothesized that the difference between supercoloniality and unicoloniality is not clear-cut, but that they are rather points on a continuum between two extremes: multicoloniality with all colonies generally being aggressive to each other, contrasted with unicoloniality with absolute absence of aggression between colonies, and supercoloniality somewhere in between.

Therefore, Pedersen et al. (2006) redefined supercoloniality and unicoloniality as follows:

Supercolony: A colony that contains such a large number of nests that direct cooperative interactions are impossible between individuals in distant nests. There are no behavioral boundaries (aggression) within the supercolony.
Unicolonial: A unicolonial species is one that can form supercolonies. A unicolonial population consists of one or several supercolonies.

They suggest that the success of invasive ants such as L. humile stem from the ecological conditions in the introduced range that allow to dramatically extend the dimension of supercolonies, rather than from a shift in social organization in the invaded habitat.

Supercolonies in termites

Although supercolonies are mainly observed in relatively few ant species, similar unicolonial populations are also found in some species of the termite genus Reticulitermes.

In France, a supercolony of the invasive termite species Reticulitermes urbis was observed, covering about seven hectares, similar to an ant supercolony. Invasive unicolonial metapopulations of Reticulitermes flavipes in Toronto, Canada are described in 2012. They can cover tens of kilometers, number hundreds of thousands or millions of individuals and show lack of intercolony aggression. Especially in urban habitats they form area-wide supercolonies.

Examples

Species known to form supercolonies are: (see also the list on AntWiki)

Formica

A supercolony of Formica obscuripes in the US state of Oregon, consisting of more than 200 nests and an estimated population of 56 million individuals was described in 1997.

The Ishikari supercolony of Formica yessensis on Hokkaido, Japan comprise estimated more than 45,000 nests, more than 300,000,000 workers and more than 1,000,000 queens.

Tapinoma

Three of the four species identified in the `Tapinoma nigerrimum complex´ are known as supercolonial: T. darioi, T. ibericum and T. magnum. Tapinoma nigerrimum is monodomous to moderately polydomous, multicolonial, and supercoloniality is unknown.

Tapinoma sessile lives in its natural habitat in small colonies. Invaded in urban areas, it exhibits extreme polygyny and polydomy and becomes a dominant invasive pest. Dependent on the season, the number of nests in the colony may alternately fuse into one or a few in winter and grow from spring, to reach maximum nest density in summer. Their early-season population growth is exponential. In general, T. sessile colonies move on a regular basis. They establish trails between nest and food resources, and to colonise new areas.

References

  1. ^ Supercolonies. AntWiki (July 2022 accessed)
  2. ^ Outnumbered: a new dominant ant species with genetically diverse supercolonies in Ethiopia. D.M. Sorger et al.; Insectes Sociaux no. 64, issue 1, Feb 2017 (full text). doi:10.1007/s00040-016-0524-9
  3. Success of Introduced Argentine Ants Tied to Reduced Genetic Variation. Kim McDonald, University of California, May 2000
  4. ^ Supercolonies of ants (Hymenoptera: Formicidae): ecological patterns, behavioural processes and their implications for social evolution. Heikki Helanterä, Myrmecol. News 32: 1-22, 2022. doi:10.25849/myrmecol.news_032:001 (open access, CC-BY)
  5. Patterns of spread in biological invasions dominated by long-distance jump dispersal: Insights from argentine ants. Andrew V. Suarez, David A. Holway, Ted J. Case, 2001 (full text); doi:10.1073/pnas.98.3.1095
  6. A risk analysis for fire ants in the Netherlands. Jinze Noordijk, EIS, Nov 2010. via
  7. ^ Reduced genetic variation and the success of an invasive species. Proc. Natl.Acad. Sci. USA no. 97, May 2000
    "We defined a supercolony as a group of nests among which intraspecific aggression was absent."
  8. ^ Evolution of supercolonies: The Argentine ants of southern Europe. Tatiana Giraud, Jes S. Pedersen, en Laurent Keller, 2002. Proceedings of the National Academy of Sciences 99: 6075-6079 (doi:10.1073/pnas.092694199). Publication
  9. Native supercolonies of unrelated individuals in the invasive Argentine ant. JS Pedersen et al., Evolution Vol 60, Issue 4, 2006 (full text). doi:10.1111/j.0014-3820.2006.tb01156.x
  10. Unicoloniality in Reticulitermes urbis: A novel feature in a potentially invasive termite species. Laurianne Leniaud et al., Bull. of Entomol. Res., Vol 99, Issue 1, 2008 (full text). doi:10.1017/S0007485308006032
  11. Genetic Evidence for Multiple Invasions of the Eastern Subterranean Termite Into Canada. Scaduto et al., Environl Entomol., Vol 41, Issue 6, 2012 (full article). doi:10.1603/EN12158
  12. ^ J. McIver, T. Torgersen and N. Cimon. A supercolony of the thatch ant Formica obscuripes Forel (Hymenoptera:Formicidae) from the Blue Mountains of Oregon. Northwest Science vol 71 issue 1, Feb 1997 (full-text)
  13. Nasty little yellow ant establishes first U.S. colonies in Fort Lauderdale. David Fleshler, Sun Sentinel, 2 Nov 2017 (archived)
  14. The Guianese population of the fire ant Solenopsis saevissima is unicolonial. Lenoir et al., Insect Science vol 23 issue 5, May 2015.
  15. ^ Four species within the supercolonial ants of the Tapinoma nigerrimum complex revealed by integrative taxonomy (Hymenoptera: Formicidae) Seifert et al., Myrmecological News, March 2017. Complete pdf (7,2 MB)
  16. ^ Seasonal polydomy in a polygynous supercolony of the odorous house ant, Tapinoma sessile. Grzegorz Buczkowski and Gary Bennett, Ecological Entomology vol 33 issue 6, Dec 2008; Summary on Researchgate.
    "The supercolony of T. sessile occupied a total of 90 different nesting sites Tapinoma sessile may be highly polygynous, polydomous, and can attain enormous population sizes, much like the invasive L. humile."
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