Researchers have discovered a weird birth phenomenon in Iberian harvester ants. The queen gave birth to ants of two different species. The mystery surrounding a missing ant species was instrumental in the discovery of this bizarre reproductive feature. Data show that Iberian harvester ants, or Messor ibericus, produce hybrid workers by reproducing with another species of harvester ants, known as Messor structor. These ants are native to the Mediterranean region.
However, there’s a catch. The Iberian harvester ant colony found in the Italian island of Sicily was about 1,000 kilometers (621 miles) away from the nearest known Messor structor population. According to Jonathan Romiguier, a senior researcher at France’s University of Montpellier and senior author, he had a suspicion about the unusual trait of this species, and this paradox led him to investigate further.
His team studied more than 120 ant populations across Europe. Over the course of five years, they conducted laboratory experiments and sequenced the genomes of hundreds of ants. Then they arrived at the stage where they found out that eggs from a single queen gave birth to two distinct species of ant, one hairy and one almost hairless.
Researchers also discovered that eggs in Iberian harvester ant queens develop differently according to their requirements. It depends on whether they need mates to produce queens in the future or hybrid worker ants, which comprise 99% of the colony.
Messor structor and Messor ibericus belonged to the same species 5 million years ago. The two species continued to live in close proximity in Europe even after they split.
At some point, millions of years ago, Iberian ant queens lost their capacity to produce their own worker ants, which are female. Researchers haven’t yet discovered how this happened, but this event led the queens to mate with Messor structor ants, creating a hybrid workforce.
“We suspect it stems from an evolutionary conflict between queens and larvae, where a so-called ‘selfish’ genetic element skews larval development toward becoming queens to ensure its transmission to the next generation (since queens reproduce, while workers are largely sterile),” Romiguier wrote in an email.
Iberian harvester ant queens have been observed tracking down males of a different species, a phenomenon known as sperm parasitism. However, this was time-consuming, so Iberian harvester ants took a different approach. They cloned the sperm of Messor structor ants, a process known as sexual domestication. Scientists haven’t observed this phenomenon in any other animal. Gradually, these ants started to exercise control over the reproduction of these males, exploiting them in the wild. The domestication of males became possible by means of cloning a male just from the sperm of a different ant species. This eliminated the necessity to live in the same geographical area, as they maintained a lineage of Messor structor ants within their nest. This new mode of reproduction has been named xenoparous. Xeno means “alien”, while parous means “produce”. This is the first instance of xenoparity, which is the ability to pass on another species’ genome through its own eggs.
Researchers sequenced the genome of the ants and discovered that only “pure” Iberian harvester ants were queens and males that can mate to produce future queens. Hybrid female workers were produced from Iberian harvester ant eggs fertilized with Messor structor sperm.
Scientists explored how the Iberian harvester ants were able to produce Messor structor ants. They found that the queens cloned the male’s genetic material and stored it in their own bodies. The queen can also erase her own nuclear DNA and produce an offspring that has the sperm’s DNA. These males differ from Messor structor males produced from Messor structor queens, and their mitochondria contain DNA from the Iberian harvester ant. However, this is less than 0.01% of the genetic material. These offspring are actual clones as they are almost identical genetically to their fathers. A clone genome can heap up some mutations and become different from the original clone, over millions of generations. Cloning generally means copying of nuclear DNA.
The research team housed Iberian harvester ants in artificial nests in their lab. They kept tabs on them for two years, and directly observed the birth of two different species of males with varying genomes from a single queen. Two Messor structor males were hairless, while three Messor ibericus had hair on their bodies.
Future plans involve gaining insight into the cellular mechanisms that drive the cross-species cloning performed by Iberian harvester ant queens.
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