In the clutches of the Iberian Harvester Ant queens, another male species, the Builder Harvester Ant, emerges. These males are responsible for siring all the workers in the colony.

“This assertion appears utterly unbelievable, akin to the impossible,” remarks Jonathan Romiguier from the University of Montpellier, France. Nonetheless, he has confirmed its validity.

Romiguier’s curiosity was piqued by the Iberian harvester ants (Messor ibericus) after he discovered that all the workers were hybrids. About half of their DNA aligned with that of the builder harvester ant (Messor structor).

The most plausible explanation is that the queen of M. ibericus mated with a male of M. structor. This occurrence is seen in other ant species. The reasons remain unclear, but two main theories have emerged. One is that hybrids of closely related species could benefit from what’s known as hybrid vigor, where various genes can compensate for each other’s deficiencies.

Another theory suggests this may address a peculiar challenge faced by M. ibericus and several other harvester ant species: whenever M. ibericus queens mate with males of their own species, all offspring become queens. This might stem from a genetic tendency to secure their lineage, but it becomes detrimental for colonies that need worker ants for survival. Breeding with another species may provide a solution.

However, M. ibericus colonies are widespread across various Mediterranean locales, unlike M. structor colonies, which are exclusive to Sicily. Nonetheless, Romiguier and his team encountered peculiar, hairless males of M. structor within an M. ibericus nest. So, where did they originate?

The genetic examination of these unusual males yielded perplexing insights. A tiny segment of the mitochondrial DNA—passed solely from the mother—indicated that these males derive from the M. ibericus queen.

This hinted that the eggs produced by the queen of M. ibericus could encompass males of a different species. To verify this theory, Romiguier brought several M. ibericus colonies into his lab. “Under laboratory conditions, it’s nearly impossible to find a male,” he comments. “We maintained about 50 colonies and observed one male for two years without success. Then, fortune smiled upon us.”

From three M. structor males born in the lab, the evidence was undeniable: the queen of M. ibericus produced males from both species. The only explanation for this phenomenon is that the queen ant cloned M. structor males using stored sperm in specialized organs called spermathecae. The resulting eggs were almost entirely devoid of M. ibericus DNA, except for its mitochondrial component.

This also clarifies the origin of M. structor sperm: by producing two types of males, the queen guarantees that her daughters who evolve into queens can mate with both male types. The females use M. ibericus sperm to generate new queens, while M. structor sperm is utilized for hybrid workers and new male ants.

There are notable instances from other species—including ants, mollusks, and stick insects—where female eggs are manipulated by male sperm from different species, leading to the elimination of egg DNA and the production of unrelated individuals. However, this scenario mainly benefits males. This is the sole known instance where both male and female offspring from distinct species rely on each other for reproduction.

“The queen of M. ibericus is entirely dependent on her cloned males. Without them, she cannot produce workers,” states Romiguier. Moreover, the clones of M. structor need the males of M. ibericus for rearing workers and sustaining their colonies—there is no sign that they mate exclusively within their species.

While these findings may seem far-fetched, they have garnered the support of other specialists. “The researchers conducted thorough investigations into these ants,” comments Nathan Law from the University of Sydney. “Their results robustly affirm their conclusions.”

He speculates that cloned males could accumulate harmful genetic mutations that may not be purged over time due to the lack of interbreeding with other strains. “Eventually, this system may start to decline, especially as environmental conditions shift.”

Romiguier agrees that this exceptional situation might eventually lead to collapse. Yet, at present, it appears that M. ibericus and M. structor have navigated their relationship with ingenious adaptability, propelling their expansion throughout the Mediterranean, while M. structor colonies have not established themselves elsewhere.

Insects and Ecosystem Expedition Safari: Sri Lanka

A voyage into the depths of Sri Lanka’s vast biodiversity through a unique entomology and ecosystem-centered expedition.