These Male Ants Have Two Separate Sets of DNA

A genetic condition called chimerism may have helped yellow crazy ants become a dominating invasive species, a new study suggests

seven ants picking up food
Yellow crazy ants (Anoplolepis gracilipes) CSIRO via Wikimedia Commons under CC BY 3.0

Most male yellow crazy ants have two distinct sets of DNA in their bodies, a new study published last week in Science finds. The ants display a genetic condition called chimerism, named for the mythical chimera that has body parts from various creatures. In a similar way, researchers suggest that different body parts in these male ants can have different sets of genetic material.

This unusual trait may have helped the insects become one of the world’s most successful invasive species. The ants are the first known species for which chimerism is required to create fertile males, Science News’ McKenzie Prillaman reports. 

“It’s exciting to be at the frontier of knowledge,” Hugo Darras, an evolutionary biologist at the University of Mainz in Germany who led the research, tells the Washington Post’s Dino Grandoni. “This is by far the most bizarre system I’ve ever worked with.”

Most animals, including humans, form when a sperm fuses with an egg, creating a cell called a zygote that contains DNA from both parents. The zygote then divides, eventually forming an organism with mostly the same genetic material throughout its body. In wasps, bees and ants, however, males generally are born from unfertilized eggs and therefore contain only genetic information from their mother. Females are born from fertilized eggs, and their cells contain a set of chromosomes from each parent—also called diploidy.

But previous research found that yellow crazy ants didn’t seem to follow these trends—males appeared to have two different copies of genes, just like the females. Yet, “it didn’t make any sense that all males in this species would be diploid,” because diploid male ants are usually sterile, Darras tells Science News. “Nobody had any explanation.”

To find out more about the insect’s unusual genetics, Darras and his colleagues collected more than 600 yellow crazy ants from East and Southeast Asia and extracted DNA from their cells. They found that cells in the bodies of female worker ants were identical and contained chromosomes from both the mother and father.

Males also had genetic material from both parents—the difference, however, was that each cell contained only genetic material from just one parent. That’s because, the researchers write, the males are formed from a sperm and egg that never fuse together. In this way, chimerism may benefit the ants by helping them avoid inbreeding, since the males carry two lineages that don’t mix.

“There were lots of crazy hypotheses to explain what was happening in these ants, but none was as crazy as the one we discovered,” Darras tells New Scientist’s Christa Lesté-Lasserre. 

Yellow crazy ants are aggressive, acid-spraying insects that have successfully colonized much of the tropics, reshaping entire ecosystems and outcompeting native species. They’ve been so damaging that the International Union for Conservation of Nature placed them on a list of the world’s 100 worst invasive species, per the Wet Tropics Management Authority.

These ants aren’t the only animals to be chimeras—mice, rabbits, cats and even humans have chimerism in some cases. In humans, it occurs when a fraternal twin embryo absorbs its sibling. 

“This is a very special system,” evolutionary biologist Guojie Zhang of Zhejiang University in China, who was not involved in the research, tells Science News. “The question would be how frequently this system can be observed in other ant lineages.”

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