Red Fire Ant Social Structure Associated With Newly Discovered 'Social Chromosome"

A ‘social chromosome’ has been discovered in the genome of some fire ants that helps to explain why some colonies of the ants are home to two or more queens while some are intolerant of more than one. The researchers think that this discovery may help in the development of new pest control methods.


The extremely-invasive red fire ants typically live in one of two very distinct colony types. Either there is only one queen and no tolerance for more, or there are far more, some colonies contain hundreds of queens.

It’s been something of a mystery until now what creates this sharp divide in behavior. live in two different types of colonies: some colonies strictly have a single queen while other colonies contain hundreds of queens. But while investigating this, researchers “discovered that this difference in social organisation is determined by a chromosome that carries one of two variants of a ‘supergene’ containing more than 600 genes.”

“The two variants, B and b, differ in structure but have evolved similarly to the X and Y chromosomes that determine the sex of humans. If the worker fire ants in a colony carry exclusively the B variant, they will accept a single BB queen, but a colony that includes worker fire ants with the b variant will accept multiple Bb queens. The scientists analysed the genomes of more than 500 red fire ants to understand this phenomenon.”

“This was a very surprising discovery — similar differences in chromosomal structure are linked to wing patterns in butterflies and to cancer in humans but this is the first supergene ever identified that determines social behaviour,” explains co-author Dr Yannick Wurm, from Queen Mary’s School of Biological and Chemical Sciences.

“We now understand that chromosomal variants determine social form in the fire ant and it’s possible that special chromosomes also determine fundamental traits such as behaviour in other species.”

“During the reproductive season, young winged queens from both types of colonies emerge for their mating flights and are fertilised by males. Young queens destined to establish their own single-queen colonies disperse far and wide. This social form is highly successful at invading new territories. The other young queens join existing multiple-queen colonies close to their maternal colony. The multiple queens cooperating in such colonies are able to produce more workers than are found in a single-queen colony. This makes multiple queen colonies the more successful social form in busy environments.”

The red fire ant is an invasive species throughout much of the southern United States, and spreading throughout the rest of the country rather rapidly. They are famous for their “painful sting in South America where they are a native species, and in many other parts of the world where their aggressiveness and high population density have made them an invasive pest. They were accidentally introduced to the Southern USA in the 1930s and have since spread to many warm parts of the world including China and Australia. Efforts at controlling their spread have largely been unsuccessful, as indicated by the species Latin name, Solenopsis invicta, meaning “the invincible.”

Dr. Wurm added, “Our discovery could help in developing novel pest control strategies. For example, a pesticide could artificially deactivate the genes in the social chromosome and induce social anarchy within the colony.”

Such a pesticide could have serious downsides though, as most of the pesticides currently used to control the species do. Attempting to control the ants through the use of pesticides also seems likely to be a very ineffective and destructive undertaking when you consider the past attempts. The previous eradication attempts with pesticides actually helped their spread, by killing off the less-hardy native ant species. And the pesticide in question, Mirex, also killed off large numbers of birds, though at the time the loss of birds was blamed on the ants…

As far as the ants effect on native fauna goes, research has shown that in just the last 70 years many species of lizards gave adapted to the presence of the species by growing longer legs and behaving differently.

The new research was just published January 16th in the journal Nature.

Source: Queen Mary University of London

Image Credits: Red Fire Ant via Wikimedia Commons

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