Recent research has revealed a fascinating and unusual survival strategy in Iberian harvester ants that challenges conventional biological understanding. The queens of these ants possess the remarkable ability to produce eggs that develop into two distinct ant species. This unexpected reproductive trait emerged during a study aimed at uncovering the mystery surrounding a missing ant species.
A dedicated research team discovered that Iberian harvester ants, scientifically known as Messor ibericus, were producing hybrid worker ants by mating with another harvester ant species, Messor structor, in the Mediterranean region. However, a significant question arose: the Italian island of Sicily, where the colony was identified, is approximately 1,000 kilometers (621 miles) away from the nearest known population of Messor structor. Jonathan Romiguier, a senior researcher from France’s University of Montpellier and the lead author of a study published on September 3 in the journal Nature, expressed his intrigue: “We had a strong suspicion that something was very unusual about this species, but to be honest, we were far from imagining just how unusual it really was.”
To investigate this paradox, the research team studied over 120 ant populations across Europe. They sequenced the genomes of hundreds of ants and conducted laboratory experiments over five years. Their efforts led to a groundbreaking discovery: a single queen could lay eggs that developed into two different species of ants—one hairy and one almost hairless. The findings indicate that the eggs of the Iberian harvester queens develop in different ways based on the queen's need for future mates to produce new queens or a workforce composed mainly of hybrid ants, which constitute 99% of the colony.
This revelation is reshaping our understanding of ant reproduction. It illustrates that ants can produce individuals of another species as part of their life cycle. Jessica Purcell, an assistant professor in the Department of Entomology at the University of California, Riverside, noted that harvester ants collect seeds from various plants, creating unique vegetation patterns around their nests. She acknowledged her previous encounters with Iberian harvester ants while studying other ant species in Italy.
According to the study, Messor ibericus and Messor structor share a common ancestry, having diverged over 5 million years ago. Despite their separation, both species continued to inhabit the same geographical areas in Europe. In certain regions, such as eastern France, they still coexist. It is believed that Iberian harvester ant queens lost the ability to produce their own female worker ants at some point in their evolutionary journey, prompting them to mate with nearby populations of Messor structor to create hybrid workers. Romiguier explained that this evolutionary conflict between queens and larvae could lead to a situation where a “selfish” genetic element influences larval development toward becoming queens, thus securing its transmission to future generations.
This dependency on Messor structor for survival led to a fascinating reproductive strategy known as sperm parasitism, where Iberian harvester ants sought out males from another species. Instead of the traditional mating process, they began to clone the sperm of Messor structor males, a phenomenon referred to as sexual domestication. Romiguier likened this process to humanity's domestication of livestock, allowing these ants to gain control over the reproduction of males they initially exploited in the wild.
Through this innovative strategy, Iberian harvester ants managed to maintain a lineage of cloned male Messor structor ants within their colonies. This development eliminated the necessity for geographic proximity to another species, allowing for the widespread establishment of hybrid worker ants throughout the Mediterranean region. The study introduces the concept of xenoparous reproduction—defined as the ability to propagate another species’ genome through one’s own eggs. Romiguier emphasized that this discovery marks the first time the evolution of xenoparity has been documented beyond the ant species.
By sequencing the genome of these ants, researchers discovered that the only “pure” Iberian harvester ants are the queens and males capable of mating to produce future queens. Other eggs fertilized with Messor structor sperm resulted in hybrid female workers. When the team investigated how these queens produced Messor structor ants, they found that the queens could clone the male’s genetic material from sperm stored within their bodies, effectively removing their own nuclear DNA during the process.
In a remarkable laboratory experiment, researchers observed the birth of two distinct species of males from a single queen. The males that hatched from Messor structor were hairless, while those from Messor ibericus had hair, a key characteristic for differentiating species in ants. The team plans to investigate the specific cellular mechanisms that allow for this cross-species cloning. Romiguier noted, “Currently, we know that the mother’s genetic material is removed from the ovum at some point, leaving only the genetic material of the foreign male in the embryo.”
The implications of this study extend beyond just understanding ant reproduction. Researchers are eager to explore the cloning process in greater detail, which could offer insights into artificial cloning in other species. Dr. Jacobus J. Boomsma, an expert in ecology and evolution, remarked on the study’s significance, emphasizing that the traits evolved in these ants are adaptations driven by natural selection. The hybrid workers provide a competitive edge, enabling Iberian harvester ants to expand their range significantly.
As the investigation into Iberian harvester ants continues, researchers are excited about the potential discoveries that lie ahead. Purcell highlighted the novelty of this reproductive strategy and the myriad mysteries yet to be unraveled, eagerly anticipating the next steps in Romiguier's research journey.
