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Genetically diverse ant colonies raise more offspring

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Ant colonies with a higher degree of genetic diversity thrive better than those made up of individuals with more similar genetic backgrounds. This is the conclusion of an experimental study in which researchers compared different colonies of the common black ant with each other. “We assume that increased diversity leads to a more efficient distribution of tasks by workers, leading to an improvement in the overall performance of a colony”, explained Dr Romain Libbrecht of the Johannes Gutenberg University in Mainz (JGU), who led the study. It seems that colonies in which the ants differ more from each other raise more larvae to maturity than colonies made up of closely related individuals. The results of this study may explain why unusual phenomena, such as queens fertilized more than once and colonies with several queens simultaneously, may have evolved in some insect societies. This happens not only in ants, but also in many different species of eusocial insects.

Eusocial insects are often genetically closely related to each other

In the animal kingdom, genetic kinship plays a central role in the evolution of altruistic behavior. In the case of social insects, such as ants, bees and wasps, the workers forgo their own reproduction to help raise the brood produced by the queens. This reproductive division of labor has evolved in a context of close genetic kinship, as queens are usually impregnated by a single male and all subsequent offspring are the result of this mating. “The colonies of most eusocial insect species are characterized by close genetic similarity, possibly because this facilitates collaboration,” Libbrecht stressed.

There are other strategies as well. For example, a queen bee can mate with up to 20 drones, while a single Argentine ant nest (Linepithema humile) can hold up to 60 queens. “However, there is a price to pay if you go for greater genetic diversity. Under certain circumstances, queens may be at greater risk when mating with multiple males, and there may also be more conflict. between the workers, ”said Libbrecht. However, since such strategies were favored by natural selection, there must be certain advantages associated with them. Over the past 20 years, evolutionary biologists have tried to demonstrate the benefits of genetic diversity.

“We decided to take a different approach to identify how increased genetic diversity confers benefits on insect societies,” said Libbrecht, head of the JGU research group on reproduction, nutrition and behavior in insects. insect societies. He and his team launched an experimental study in which they manipulated the labor force of black ant (Lasius niger) colonies. This species is widely distributed throughout central Europe and can be found in city gardens, on balconies, in fields and at the edges of forests. Normally, a colony will only have one queen which usually mates with a single male, so all offspring share a very similar genetic makeup. Libbrecht and his team collected ants in the area around Mainz and divided them into two groups: one group consisted of ants gathered in one colony, the other group consisted of ants gathered in three different colonies. “What we did was collect pupae because the queens would not have accepted the foreign adult worker ants,” Libbrecht explained. Lead author of the article, Marina Psalti, added: “This means that the worker ants that emerged from the pupae in our test colonies were not related to their queens at all. This was necessary to rule out any effects. maternal potential. “

Ant colonies with higher genetic diversity produce more larvae

What Libbrecht’s team of evolutionary biologists observed is that greater diversity among workers resulted in improved larval production. There was no difference in the number of eggs produced by the two groups. “This meant that by starting from the same number of eggs, the group with more diversity among the workers was able to raise more larvae.” According to Libbrecht, under natural conditions a small colony can be very vulnerable at the founding stage and its ability to establish itself depends on how quickly a good number of worker ants can be added.

The reason why colonies made up of various ants perform better may be because they have a better division of labor. “Some workers would be better able to take care of the larvae, which need to be fed and cared for. Other workers might be more adept at finding food. Therefore, we show that the diversity within a colony offers advantages in terms of the choice of ants. tasks, ”Libbrecht summed up the findings.

Reference:
Psalti MN, Gohlke D, Libbrecht R. Experimental increase in worker diversity benefits brood production in ants. BMC Evol. Biol. 2021; 21 (1): 163. doi: 10.1186 / s12862-021-01890-x

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