Pleometrosis

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In the case of pleometrosis (also: pleometrosis) several ant queens or queens of other social hymenoptera (very rarely also termites ) establish a state together . Eggs are laid together and the brood is cared for together. Even if a pleometrotic foundation is known in a number of species, it occurs relatively rarely in nature. Pleometrosis is often, but not always, associated with the presence of several fertile and egg-laying sex animals in a colony (called polygyny).

The opposite, i.e. that a queen alone and independently of other queens founds a new state, is known as haplometrosis (or haplometrosis). This is often associated with only one queen per colony, called monogyny.

Occurrence

A new nest can be founded by pleometrosis by related queens (usually sisters, from the same mother nest), but also by unrelated individuals of the same species. This cooperation in nesting occurs in ants in the subfamilies Myrmicinae (e.g. genera Solenopsis , Messor , Acromyrmex ), Dolichoderinae (e.g. genera Azteca , Iridomyrmex ) and Formicinae ( e.g. genera Myrmecocystus , Lasius , Camponotus , Formica , Oecophylla ). All species in question are territorial , both older colonies fight against new foundations on their territory, as well as different neighboring new foundations fight one another. This gives colonies an enormous advantage if they manage to increase the number of workers very quickly at the very beginning. This can be achieved more easily through the cooperation of several young queens. Almost all pleometrotic species establish new colonies claustral , i. H. the queens lock themselves up together in a chamber that they do not leave to forage. The advantage for the individual queens is reversed as soon as the new colony is safely established. As soon as there are enough workers, the young queens often fight among themselves until only one is left. In these cases a pleometrotic foundation is associated with a monogynous colony.

Due to the increased number of eggs, the colony starts with more (and larger) workers, so that losses are less significant. In addition, the nest opens earlier, which means that they can eat earlier and the queens lose less weight. While with polygynous species (such as Myrmica rubra ) pleometrosis only brings advantages for the emerging colony, with monogynous species monogyny must first be established through elimination struggles.

Problem with monogynous species

In most cases, the queens of monogynous species start fighting shortly after the first workers hatch at the latest. In a few species (e.g. Myrmecocystus mimicus) the aggression only comes from the workers. This fight can mean serious injuries or even death for the surviving queen. Instead of fighting, it can happen that the queens of some species ( Lasius flavus , Camponotus ligniperda ) flee to other nest areas, which leads to the creation of an olygyny . Several queens live in different nest areas and are accepted by the workers.

Optimal number

However, there is an optimum in the number of founding queens. In the case of Myrmecocystus mimicus and Messor pergandei , for example, it was shown that the most eggs were laid and the mortality rate was lowest in a group size of three to four queens. The reason for this has not yet been adequately clarified, but is presumably an increased risk of disease and the fact that rival queens eat the "opposing" eggs.

literature

Individual evidence

  1. ^ Giorgina Bernasconi & Joan E. Strassmann (1999): Cooperation among unrelated individuals: the ant foundress case. Trends in Ecology and Evolution 14 (12): 477-482.
  2. ^ SW Rissing, GB Pollock (1991): An experimental analysis of pleometrotic advantage in the desert seed-harvester ant Messor pergandei (Hymenoptera; Formicidae). Insectes Sociaux 38 (2): 205-211. doi : 10.1007 / BF01240970