Scientists discover new colony structure of fire ants that evolved in one species before spreading to others

Scientists at Queen Mary University of London have discovered a new form of ant society is spreading across species. They found that after the new social form evolved in one species, a “social supergene” with the instructions for the new social form spread to other species. This spread took place through hybridization, ie breeding between ants of different species. This unlikely event creates an alternative way of life, making the ants more successful than if they had only the original social form.

Red fire ants originally only had colonies with one queen. The team previously found that about a million years ago, a new social form emerged in which colonies could have dozens of queens. One version of a large portion of the chromosome, called the “social supergene,” contains the genetic information needed to make workers accept more than one queen. The new research, published today in nature communicationanalyzed the entire genomes or instruction sets of 365 male fire ants to investigate the evolution of the social supergene, and found that the same version of this chromosome is present in multiple fire ant species.

Transfer of large amounts of genetic information between species is rare due to genetic incompatibilities. In this case, however, the advantages of having multiple queens outweigh the incompatibilities, and the genetic material repeatedly spread to other species from the one source species in which this new social form evolved. The multi-queen social form has advantages in different situations. For example, a colony with multiple queens will have more workers and thus may outnumber a colony with only one queen. In addition, if there is a flood, a colony with multiple queens is less likely to become queenless.

dr. Yannick Wurm, Reader in Evolutionary Genomics and Bioinformatics at Queen Mary University of London and a fellow of the Alan Turing Institute, said: “This research reveals how evolutionary innovations can spread across species. It also shows how evolution works at the level of DNA and chromosomes.

“It was incredibly surprising to find that other species could acquire a new form of social organization through hybridization. The supergene region that creates multi-queen colonies is a large piece of chromosome containing hundreds of genes. The many parts of a genome evolve to work on sophisticated ways together, suddenly making a mix with different versions of many genes from a different species complicated and quite rare.

“Instead of carrying out additional queens as in a single-queen colony, the new version of the supergene leads workers to accept multiple queens. After extensively studying the history of the supergene and the new social form, we next want to identifying which genes or parts of the supergene region lead to these behavioral changes. This will also help fill more gaps in our understanding of evolutionary processes.”

Rodrigo Pracana, a lead author of the study, also at Queen Mary University of London, added: “Our study shows how detailed analysis of large numbers of wild animals can provide surprising new insight into how evolution works.”

Queen Mary’s team was previously one of the first in the world to apply large-scale DNA sequencing approaches to wild insects — enabling them to discover one of the first known supergenes.

Red fire ants are native to South America and are notorious for their painful sting. One of these species is known in many other parts of the world, where its aggressiveness and high population density have made it an invasive pest. Attempts to control the spread of this species have largely failed, as evidenced by its Latin name, Solenopsis invictameaning ‘the invincible’.

The research was supported by the Leibniz Institute for the Analysis of Biodiversity Change, where Dr. Eckart Stolle assisted as part of Queen Mary’s team before continuing this work at the Leibniz Institute.

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Materials supplied by Queen Mary University of London. Note: Content is editable for style and length.

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