Can Ants Reproduce Without a Queen?

Ant colonies typically rely on a queen to lay eggs and sustain the population. However, in some species, worker ants can assume reproductive roles when a colony loses its queen. This ability affects colony survival and genetic diversity, shedding light on their complex social structures and evolutionary adaptations.

Conditions That Lead to Queenless Colonies

The stability of an ant colony depends on the presence of a reproductive queen, but various factors can lead to queen loss, disrupting colony structure. Predation is a major threat, as queens, with their limited mobility, are often targeted. In species where queens forage or defend the nest, their exposure to predators like birds, amphibians, and rival ants increases. Parasitic organisms, such as fungi from the Ophiocordyceps genus, can also kill queens, further destabilizing colonies.

Internal colony dynamics contribute to queen loss as well. In polygynous species, where multiple queens coexist, competition often leads to aggressive interactions, sometimes ending in the death or expulsion of weaker queens. This phenomenon, known as queen execution, is common in species like Formica sanguinea, where workers regulate colony size by eliminating queens. In monogynous colonies, where only one queen exists, natural aging reduces reproductive output. If workers fail to rear a replacement, the colony declines.

Environmental stressors further threaten queens. Habitat destruction, pesticide exposure, and climate fluctuations can disrupt colony stability. Deforestation and urbanization fragment habitats, making it harder for queens to establish nests or find mates. Insecticides, such as neonicotinoids, impair queen fertility and longevity, leading to colony collapse. Studies published in Science show that chronic exposure to these chemicals reduces egg-laying capacity, accelerating population decline.

Types of Reproduction in Worker Ants

When a colony loses its queen, workers in certain species can reproduce. Though they lack fully developed reproductive organs, some can lay eggs and, in rare cases, produce viable offspring. The mechanisms vary across species and include gamergate reproduction, parthenogenesis, and the laying of unfertilized eggs.

Gamergates

In some species, specific workers known as gamergates develop functional ovaries and reproduce. These individuals can mate and lay fertilized eggs, effectively replacing the queen. This occurs in Harpegnathos saltator, an Indian jumping ant species where workers battle for dominance after the queen’s death. Victors undergo physiological changes, including ovarian activation and increased longevity, sustaining the colony. Research in Proceedings of the Royal Society B (2021) found that gamergates experience hormonal shifts, particularly in juvenile hormone levels, regulating their reproductive capacity. Unlike queens, gamergates mate within the nest, ensuring genetic continuity. This strategy is beneficial in environments where founding new colonies is difficult, allowing the existing colony to persist.

Parthenogenesis

Some ants reproduce through parthenogenesis, a form of asexual reproduction where eggs develop without fertilization. In Cataglyphis cursor, a desert ant species, workers generate female offspring through automictic parthenogenesis, a process restoring diploidy. A Current Biology (2018) study found that this allows colonies to persist without mating. However, parthenogenesis reduces genetic diversity, making colonies more vulnerable to environmental stress and disease. Despite this limitation, it provides a short-term survival strategy, particularly in isolated or resource-scarce habitats.

Laying Unfertilized Eggs

In many species, worker ants lay unfertilized eggs that develop into males through haplodiploidy, the sex determination system in Hymenoptera. While this does not produce worker replacements, it influences colony dynamics. In Dinoponera quadriceps, workers lay trophic eggs, non-viable eggs consumed by nestmates for nutrition. In species like Aphaenogaster cockerelli, workers produce viable male offspring, which later mate with queens from other colonies. A Molecular Ecology (2020) study found that worker-produced males contribute to gene flow, maintaining genetic exchange despite queen loss. Though this strategy does not ensure long-term colony survival, it supports reproductive cycles and potential colony establishment.

Genetic Implications in Worker-Produced Offspring

When workers reproduce, colony genetics shift, affecting long-term viability. Unlike queens, which mate with multiple males to maximize genetic diversity, worker reproduction results in a restricted gene pool. Workers typically produce haploid males from unfertilized eggs, reducing genetic recombination. This limitation weakens colony resilience and adaptability.

In species relying on worker reproduction, repeated transmission of similar genetic material can lead to an accumulation of harmful mutations. Studies on Cataglyphis ants show that automictic parthenogenesis increases homozygosity, raising the risk of recessive genetic defects. This genetic bottleneck effect can make colonies more vulnerable to disease and resource shortages by limiting physiological and behavioral adaptations.

Worker reproduction also alters colony dynamics. In a queen-right colony, workers are more closely related to their sisters than to their own offspring, reinforcing cooperation. When workers begin reproducing, kin selection pressures shift, sometimes leading to intracolony conflict. Research on Dinoponera ants has documented aggressive interactions among reproductive workers competing for dominance. This competition disrupts cooperative brood care and reduces colony efficiency, particularly in species where multiple workers attempt to establish reproductive hierarchies.