“The discovery is quite extraordinary,” said Denis Fournier, an ant biologist at the Université Libre de Bruxelles who was not involved in the research. Pointing to the ants’ novel form of reproduction, he added, “gives another glimpse of what nature is capable of inventing.”
A quick refresher from your sex-ed class: Normally, an embryo — from humans to simple multicellular animals — develops after a sperm fertilizes an egg. That single, fused cell divides to form an organism made up of genetically identical cells. Tear out almost any cell from your body, and you’ll find the same DNA as any other cell.
But yellow crazy ants — or at least, the males — are different.
Instead of mixing together, the genetic material from the queen’s egg and her mate’s sperm does not mix during the formation of a new male. Instead, both female and male ants contribute DNA-laden nuclei, which repeatedly start replicating separately. These develop into cells, which are then bound into an embryo.
As a result, the body of the male yellow crazy ant is not made up of cells containing the same set of DNA. Instead of male ants, the two cell lines each have their own distinct genetic lineage – one from the queen and the other from her mate. The queen and female workers of the species, in contrast, form from regular sperm-egg fusions.
“It’s exciting to be at the frontier of knowledge,” Zoom, an evolutionary biologist at the University of Mainz in Germany and lead author of the paper, said in the interview.
After studying plenty of other species, Darras added, “This is by far the most bizarre system I’ve ever worked with.”
A male yellow crazy ant represents what scientists call a chimera, or a single organism with two sets of genetically distinct cells. The name comes from a Greek mythological creature that is part lion, part goat and part serpent.
Scientists have found a handful of chimeras in nature, both in humans and other species, which sometimes result in people or animals with two different colored eyes. But most chimerism usually arises from rare developmental events, such as when one embryo absorbs another in the womb.
Scientists have known for some time that the sex life of ants is strange. Queens of some species clone themselves. Other types of ants have no males at all. And yet some ant species are thought to have four sexes.
Benjamin Oldroyd, an emeritus professor of behavioral genetics at the University of Sydney who was not involved in the paper, said he had attempted to list the reproductive systems of ants and related species, “both real and imagined.”
“But every time I’ve written a list like this, it’s proven that truth is stranger than fiction,” he said. “I never envisioned a species where males would be a mixture of cells from two lineages and that one lineage would be used to make sperm. I can only describe this as ‘crazy ant sex’ beyond my imagination.
Scientists have counted the number of ants in the world. The figure is so big, it is ‘unimaginable’.
Yet even in the crazy world of ants, the yellow crazy ant stood before this discovery.
The species is one of the worst insect invaders, moving through island ecosystems from Hawaii to Zanzibar. Supercolonies of these frenzied insects spray acid to subdue prey — Perhaps most notably, destroying red land crabs on Christmas Island in the Indian Ocean. Crazy ants have been listed by the International Union for Conservation of Nature “100 of the World’s Worst Invasive Alien Species.”
The yellow crazy ant’s peculiar way of reproduction may give it an edge as an invader. By carrying two separate genetic lineages, males may reduce the chance of inbreeding, even if only a few arrive on the island.
But Daras cautioned that much more work is needed to explore these questions. “At this point, it’s speculative,” Doras said. This yellow crazy ant study, he added, was about 15 years in the making.
“I imagine writers still have a lot to discover and tell us about the yellow crazy ant,” Fournier said.
Whatever caused the ants to develop this unusual reproductive system, Darras and his team write that ants are breaking a “fundamental law of biological inheritance” with a “reproductive mode unknown to science” until now.
Darras points out that the vast majority of ants are not studied. “I wouldn’t be surprised if we discover something similar in other species.”
Rockefeller University professor Daniel Kronauer points out that there are some ironclad rules in biology. “Fundamental laws are something for physics. Biology is like a collection of exceptions,” he said.
But he added, “This is a very interesting exception.”