‘Sexual Parasite’ Ant Queens Enslave Other Species to Create Cloned Hybrid Workers

Alt heds: Queen Ants Spawn Cloned Ant Workers From a Different Species / These ‘Sexual Parasite’ Queen Ants Spawn Workers From a Different Ant Species / These ‘Sexual Parasite’ Queen Ants Breed an Army of Hybrid Ant Workers 

Ant life can be brutal^[1]. And the queens that rule over each colony are suitably ruthless—even bending the rules of biology a little to create their own armies of hybrid clones to do their bidding.

In a Nature^[2] paper published September 3, researchers describe how queen Iberian harvester ants (Messor ibericus) are able to spawn offspring from an entirely different ant species. The reason why is that the queens appear to keep their own reserves of sperm from males of another harvester ant species, Messor structor, cloning them using the males’ sperm to produce a supply of hybridized workers to handle the grunt work around the colony.

“It was first nearly a joke to explain the weird results we first had, something like, ‘Queens producing two different species? No, that’s ridiculous,’” Jonathan Romiguier^[3], senior study author and an evolutionary biologist at the University of Montpellier in France, told Gizmodo. It was only after a long process of analyzing genetic data that the “joke” became a “serious hypothesis,” he said.

An uncanny reunion

M. ibericus and M. structor can co-exist but are genetically separate, having diverged from each other over five million years ago—around the time that humans and chimpanzees diverged^[4]. So it was confusing for Romiguier and his colleagues to find a sprinkle of M. structor ants living inside an Iberian harvester ant colony. These weren’t strays from another colony, as there weren’t any M. structor colonies in the vicinity that the researchers knew of.

To investigate why the other harvester ants were there, the researchers conducted a genomic analysis of the ants, and monitored 65 Iberian harvester ant colonies in the lab. The big genetic reveal unfolded rather progressively, Romiguier said, and then when a lab-based colony’s queen gave birth to two male ants of different species, the team realized that their “joke” hypothesis was real.

As they suspected, the rogue ants carried genuine M. structor DNA, with the exception of their mitochondria—which they would’ve inherited from their mother^[5], aka, the queen. This, the researchers note, demonstrates an unprecedented case of “sexual domestication.”

A stranger among familiar faces

What’s more, when the researchers put these clones into an ordinary M. structor colony, they were perceived as invaders and killed. Rominguier thinks this may be because the clones’ pheromones appeared to be that of the M. ibericus. That would have sent a warning signal for the ordinary M. structor ants that the clones, despite looking exactly like them, were intruders to be ousted, he explained.

“It’s an absolutely fantastic, bizarre story of a system that allows things to happen that seem almost unimaginable,” Jacobus Boomsma, an evolutionary biologist at the University of Copenhagen who did not participate in the study, told Nature News^[6].

“It’s no doubt a weird and wonderful discovery, shedding light on the importance of hybridization as a source of innovation in biology and reminding us to be open to the unexpected,” Jessica Purcell, an entomologist at the University of California in Riverside not involved in the study, wrote in an accompanying News & Views^[7].

“It basically breaks many assumptions we had about what a species is, and how we should define it,” Rominguier said. ”M. ibericus colonies are one of the most complex colonial lifeforms known so far, as they can produce the greatest diversity of individuals, differing in terms of sexes, castes, and species, each with a dedicated role within a cohesive reproductive unit.”