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Thibaud Monnin, a researcher
at the Laboratoire Fonctionnement et évolution des systèmes
écologiques (Workings and Evolution of Ecological Systems Laboratory,
CNRS - Université Paris VI -ENS)(1), has shown
that a complex mechanism regulates reproduction in Dinoponera quadriceps
queenless ants. The reproductive female or “gamergate” of the
colony uses a chemical signal to trigger an attack on any ant that attempts
to take her place. This research, conducted in collaboration with a team
from the University of Sheffield (2), is published in
Nature (3).
About one hundred species of ants do not have queens. In such species
(4), all of the female workers have the capacity to mate
and to reproduce, in strong contrast with species having queens (5),
in which the female workers are morphologically incapable of mating, and
in which only the queens can reproduce. In Dinoponera quadriceps
queenless ants, major conflict develops between the workers in any one
colony: there is only one reproductive female worker, the gamergate, and
every female worker would be better off if they became the gamergate.
The workers are organized in a dominance hierarchy. The gamergate is at
the top of the hierarchy. Immediately below her come a few dominant workers
who could become gamergates by taking the place of the current gamergate.
The other female workers are dominated, and can never reproduce.
When a pretender dominant worker challenges the gamergate, the gamergate
marks the pretender chemically, thereby inducing the dominated workers
to immobilize the pretender by biting her legs and antennae and holding
on to them for several hours, or even several days, until the pretender
ceases to threaten the gamergate. Only the gamergate produces the chemical
signal, which is smeared on with the sting. The dominated workers co-operate
with the gamergate because they thereby increase their indirect reproduction.
The research also shows that the dominated individuals, often neglected
in animal society research, play a major role in this species. The dominated
female workers cannot become reproductive, but, to some extent, they choose
the reproductive female. The dominated females generally help the reproductive
female, but if she is old or in poor health, they may help the dominant
pretender. They then immobilize the old gamergate, thereby enabling the
young dominant female to establish herself as the new gamergate.
Notes:
(1) The Génétique-Populations-Socialité
(Genetics-Populations-Sociality) team studies evolution of reproduction
from the standpoint of genetics, of individual reproduction strategies,
and of communications: http://www.biologie.ens.fr/fr/ecologie/genetique.html
(2) Department of Animal and Plant Sciences:
http://www.shef.ac.uk/aps/
(3) Reference: Pretender punishment induced by chemical
signalling in a queenless ant, Thibaud Monnin, Francis Ratnieks, Graeme
Jones, Richard Beard, Nature, September 5, 2002.
(4) Queenless ants represent 1% of ant species.
(5) Queens and workers are morphologically different.
Queens are larger and have wings.
Researcher
contact:
Thibaud Monnin
Laboratoire Fonctionnement et évolution des systèmes écologiques
(CNRS - Université Paris VI -ENS)
tel: +33 1 44 27 32 94,
thibaud.monnin@snv.jussieu.fr
Press contact:
Carine Noël
Tel : +33 1 44 96 49 88
e-mail : carine.noel@cnrs-dir.fr
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