Ants avoid reproductive competition with close relatives

Co-operation is a key innovation in evolution, from evolution of genomes and multicellular organisms to insect societies, such as ants and honeybees to human societies. Crucially, any co-operation is stable only when conflicts among group members are kept at bay. Researchers from the Universities of Oulu and Helsinki in Finland investigated how ant queens balance competition and cooperation.
Images of black ants, worker and queen Photo: Lotta Sundström.

In ant societies, it’s not only the queens and workers who cooperate, but it is also common for several queens to share a nest and reproduce together. Such queen unions inevitably harbour conflicts among the queens over how they share reproduction. As in any cooperative situation, conflicts and competition among participants threaten to undermine the common good.

How do co-breeding queens then find a balance between increasing their own reproductive success and avoiding harmful competition within the group? A study in the black ant Formica fusca, whose nests often house multiple queens, suggests that relatedness between co-breeders matters. In the study, researchers showed that when queens were experimentally exposed to odours from a nestmate queen, a competitor, they ramped up their own reproduction, especially if the odour came from a highly fecund nestmate. However, if the odours came from a queen who was a close relative they did the opposite and laid fewer eggs.

“We knew from earlier studies that workers of this species, Formica fusca, are particularly good at recognizing their relatives, so it was interesting to see that queens have such abilities as well”, says Professor Heikki Helanterä from the University of Oulu. “Societies with multiple queens are common in ants, but in other ant species similarly accurate recognition has not been observed – usually ants discriminate between members of their own society and outsiders, but within societies discrimination is absent”.

Such fine-tuning of reproduction may help groups of close relatives avoid reproductive competition and coordinate their efforts to increase their joint success.

The new findings shed light on the social evolution of ants, which produces different changes and adaptations in individuals. The social evolution of ants and social conflicts are also linked to the environment outside the nest, where rapid environmental change affects the survival of the species. Research is being conducted to determine whether or not - and how - the individual changes produced by social evolution contribute to species survival in a changing environment.

The research article was published in February 2023 in the journal Behavioral Ecology: Heikki Helanterä, Martina Ozan, Liselotte Sundström, Relatedness modulates reproductive competition among queens in ant societies with multiple queens, Behavioral Ecology, 2023; https://doi.org/10.1093/beheco/arad004

Last updated: 26.6.2023