A Queen That Produces Offspring of Two Different Species

In biology, it is almost a truism that the offspring produced by a species belong to that same species. Yet research on European harvester ants of the genus Messor has revealed a system that overturns this basic expectation. The study shows that queens of the Iberian harvester ant, Messor ibericus, can produce male offspring belonging to two different species during their lifetime. Moreover, they rely on sperm from another species, the harvester ant Messor structor, in order to produce their worker caste. In other words, a single queen can give birth to males of both M. ibericus and M. structor, while the workers are first-generation hybrids formed through cross-species reproduction.

This phenomenon is not a rare accident of hybridization. Instead, it represents a stable reproductive strategy that has become fixed through evolution. The researchers even introduced a new term for it: xenoparity. This concept describes a reproductive mode in which females produce individuals belonging to another species as part of their own life cycle.

Male of Messor ibericus (left) and male of Messor structor (right)（感謝Jonathan Romiguier, Yannick Juvé and Laurent Soldati提供）

At first glance the discovery seems almost science-fiction-like. To understand how it works, some background on ant genetics is useful. Queens and workers possess diploid genomes, meaning they carry two sets of chromosomes, whereas males are haploid and carry only a single set. For a long time, researchers were puzzled by genetic evidence suggesting extensive hybridization among these ants, even though the species involved rarely occur in the same regions of Europe.

Genomic analyses and controlled laboratory colonies eventually resolved the mystery. Worker ants in M. ibericus colonies display unusually high genetic diversity. Kinship analyses revealed that their maternal genes originate from M. ibericus, while their paternal genes come from M. structor. Without this cross-species cooperation, colonies cannot establish normal worker populations.

In addition to producing workers through hybridization, queens of M. ibericus can also lay eggs that develop into M. structor males within their own nests. In one experiment, researchers monitored a colony headed by a single queen for a year and a half. During that time they observed male offspring belonging to two species emerging from her eggs. The males with dense body hairs belonged to M. ibericus, while nearly hairless males belonged to M. structor. Yet the mitochondrial DNA of all of them still traced back to M. ibericus.

This outcome arises through a process known as androgenesis. In this form of development, the embryo retains only the paternal nuclear genome, while the maternal nuclear DNA is eliminated early in development. As a result, the male is genetically derived entirely from the father's lineage, despite developing inside an egg laid by a female of another species.

Consequently, three different types of males can be found within a colony of M. ibericus: males of its own species, M. structor males produced internally by the colony, and naturally occurring M. structor males originating from outside populations. These males perform different reproductive roles. Males of M. ibericus provide sperm that produces new queens, while M. structor males provide the sperm needed to generate hybrid workers. Through this division of labor, the queen maintains a large and stable worker society. In effect, the system resembles a form of biological domestication, in which another species is incorporated as a workforce within the colony’s life cycle.

A queen of Messor ibericus relies on males of different species to produce new queens or workers（圖片來源：Juvé Y et al. (2025)，採用 CC BY 4.0 授權）

Despite belonging to the same species, the M. structor males produced within M. ibericus colonies differ from their wild counterparts. Their genetic diversity is extremely low, resembling patterns seen in clonal or domesticated populations. Morphologically they appear smoother and less hairy than typical wild individuals, making them visibly distinct. Genetic evidence nevertheless still places them within the same species, although their unusual evolutionary situation has clearly shifted them away from their original state.

Through a mechanism known as sperm parasitism, M. ibericus evolved the ability to internally produce males of another species. In doing so, it effectively integrated M. structor into its own life cycle. Researchers have drawn parallels between this relationship and the ancient endosymbiosis that gave rise to mitochondria in eukaryotic cells. The paternal genetic lineage of M. structor has become permanently embedded within the reproductive cycle of M. ibericus, functioning almost like a colony-level equivalent of mitochondria. If M. structor were removed from the system, M. ibericus itself would no longer be able to survive.

Author: Shui-Ye You

Reference:

Juvé Y et al. (2025). One mother for two species via obligate cross-species cloning in ants. Nature.