Unusual flora from a distant Pacific isle unveil fresh perspectives on a significant ecological dilemma: how disparate and often hostile partners can establish persistent mutualistic alliances with the same host.
Researchers investigating ant plants in Fiji have uncovered one method by which a host plant can maintain harmony among inhabitants that might otherwise harm one another. By providing distinct chambers within an enlarging tuber — each chamber with an entryway from the exterior but no link to neighboring chambers — the Squamellaria plant averts clashes among the various ant species that nourish it and inhabit it. The recent findings from Washington University in St. Louis and Durham University in the UK were published on July 10 in Science.
“Our research indicates that compartmentalization is one answer,” stated Guillaume Chomicki from Durham, the lead author of the study. “The significance of compartmentalization is evident from the lethal disputes triggered when the barrier between separate ant species residing in adjoining compartments is removed.”
“However, it’s not for the benefit of the ants that these plants have developed those compartments — it’s actually for their own sake. The more ants reside within a tuber, the greater the nutrient acquisition for the plant,” he explained.
“Dried Squamellaria tubers — along with similar tubers, many of which have remained in herbaria or collections since at least the 1880s — never provided the insights that Guillaume managed to uncover in the field,” remarked Susanne S. Renner, a biologist at WashU and senior author of the study. “Two key factors are required: observing and identifying the ants, and comprehending that the tubers encompass completely distinct compartments with separate entrances to the outside, akin to a condo complex.”
In biological terms, a symbiotic relationship, or symbiosis, is a close and enduring interaction between two different species. When this relationship is mutually advantageous, it is termed mutualism. Numerous symbioses include one host species that possesses several mutualist partners. Nevertheless, theory postulates that unrelated partners can result in destabilizing conflict due to competition for host resources.
In the situation of Squamellaria, Chomicki and Renner have previously documented how certain specialized ants actively cultivate Squamellaria — by planting its seeds and enriching the seedlings with their droppings — and subsequently nesting within the domatia (hollow chambers) that develop on each plant shortly after the expansion of its cotyledons. Only after the ants place a seed into a fissure in the bark can Squamellaria commence germination.
This farming behavior is vital to the plant’s survival, as it is an epiphyte that grows on the branches of rainforest trees and lacks any other method to establish itself in the rainforest canopy. Back in 2014, during a field expedition high amidst the treetops of Waisali Rainforest Reserve, Chomicki retrieved a Squamellaria that unveiled an even more intricate set of interactions.
“When I dissected this plant (Squamellaria wilkinsonii), which had a domatium measuring about 8 inches in diameter, I was astonished to find two ant colonies inhabiting it,” he recalled. “My initial thought was parabiosis, a specific type of symbiotic relationship where two ant species nest together. However, the nests were entirely separate, which was perplexing.”
This observation sparked his new investigation with Renner. Together, they outline a series of experiments designed to explore how the plant allows multiple species of ants to coexist within its hollow chambers — starting with observing the effects of removing the internal walls.
“Removing the partition walls between two ‘apartments’ with a dissecting knife — thus placing different ant colonies in direct physical contact — resulted in an immediate conflict where workers fought to the death,” Chomicki noted.
The researchers measured the frequency of conflicts among ant workers of the relevant species during a 25-minute period following the removal of the partition walls. They recorded significant worker fatalities in both ant colonies that previously occupied separate compartments.
As long as compartmentalization is preserved, various symbiont species can co-exist harmoniously, but the experimental removal of compartment walls leads to fatal conflicts. (Video: G. Chomicki and S. Renner)
The latest research involved feeding experiments that confirmed the plants were gaining nutritional advantages from the diverse ant species residing within their compartments. The study also employed computed-tomography scanning, a method infrequently utilized in plant studies. “The scanning was crucial in revealing the compartmentalization of the domatia,” Renner commented. “Merely dissecting domatia does not clarify which chambers are interconnected and which ones are isolated. This revelation emerged when developing 3D models from the CT scan data.”
The findings expose a mechanism for conflict reduction that enables hosts to benefit from the presence of multiple, unrelated symbionts, according to Renner and Chomicki.
“What is distinctive about Squamellaria is that we can observe directly what theory has long speculated — that unrelated partners would clash due to competition for host resources,” Renner stated. “Yet here we also discover a straightforward, remarkably effective evolutionary tactic to alleviate these disputes: compartmentalization. Thus, despite being unique, the Squamellaria-ant relationships shed light on a longstanding, general concern in the ecology and evolution of species interactions.”
Chomicki G, Metzler D, Naikatini A, Renner SS. Compartmentalization reduces conflict in multipartner plant-insect symbioses. Science. July 10, 2025. DOI: 10.1126/science.adu8429.
The article Condo-style living helps keep the peace inside these ant plants was first published on The Source.