Parasitic fungus may have emerged 18 million years before the ants with which it lives today
Analysis of 309 strains indicates that the genus Escovopsis emerged 56.9 million years ago, but only began interacting with today’s mutualistic ants 38 million years ago, challenging the theory that they all emerged at the same time.
image:
An ant (genus Atta) removes fragments of a fungus garden used to feed the colony. The insects’ cleaning behavior functions as a social immune system
view moreCredit: Quimi Vidaurre Montoya/IB-UNESP
A genus of fungi previously considered a parasite of fungi associated with ants may actually have much more complex ecological functions. According to a study published in the journal Communications Biology and supported by FAPESP, one piece of evidence is that they appeared 18 million years before the ants with which they are associated today.
The results are based on the analysis of 309 strains of the genus Escovopsis collected in eight countries in the Americas. By observing fragments of the genomes, morphological characteristics, geographic distribution, and phylogeny of the species – something like their evolutionary kinship – the researchers were able to determine the relationship with leafcutter ants over 38 million years. Escovopsis emerged 56.9 million years ago.
“Our main hypothesis is that they emerged associated with ancestral groups of fungus-growing ants and then began to coexist with the current leafcutter ants 38 million years ago. Another possibility is that they lived in a different context during those initial 18 million years, outside of their association with ants, as leaf colonizers or degrading organic matter, for example,” explains Quimi Vidaurre Montoya, the first author of the study. Vidaurre Montoya conducted the study as part of his postdoctoral research with a fellowship from FAPESP at the Institute of Biosciences of São Paulo State University (IB-UNESP) in Rio Claro, Brazil.
Leafcutter ants (subtribe Attina) cultivate fungi for food. According to a recent study by the group published in the journal Science in 2024, this mutualistic relationship is thought to have emerged 66 million years ago (read more at agencia.fapesp.br/52936).
“Our current work is on Escovopsis, a genus of fungi that isn’t cultivated by ants, but is present in the colonies of some species of farming ants and can kill some of their cultivars. Because of this, it’s portrayed as a ‘parasite,’ when in fact only one of 24 species is known to cause infection in the fungus cultivated by ants,” Montoya explains.
The study is part of a project supported by FAPESP through the FAPESP Research Program on Biodiversity Characterization, Conservation, Restoration, and Sustainable Use (BIOTA-FAPESP), coordinated by André Rodrigues, a professor at IB-UNESP and a researcher at the Center for Research on Biodiversity Dynamics and Climate Change (CBioClima), which is one of the Research, Innovation, and Dissemination Centers (RIDCs) supported by FAPESP.
Adaptations
The authors note that Escovopsis underwent morphological and physiological adaptations over evolutionary time, apparently to increase reproductive efficiency and adapt to life inside anthills. These changes mainly occurred in the vesicles that produce conidia, which are structures that perform asexual reproduction.
“The vesicles change from a globular shape in species closer to the common ancestor to a cylindrical shape in more recent species. These changes may have been responses to barriers imposed by the ants or their symbiotic fungi,” Montoya says.
Physiological data indicate that the growth rate, number of vesicles, and production and viability of conidia gradually increased as the genus diversified. Species with cylindrical vesicles may grow faster than those with globular structures. The thinner, elongated vesicles of more recent species produce considerably more viable conidia than older groups with globular vesicles.
“Apparently, there’s a coevolution between ants, symbiotic fungi, and Escovopsis. We don’t know if they evolved to become parasites or if they're opportunists that feed on debris and can eat what remains when the system as a whole collapses. But if it were a specialized virulent host, as part of the literature assumes, it would destroy the system regardless of whether it was in equilibrium or not,” Montoya says.
Little-known fungi
This study is an offshoot of broader work on the genus Escovopsis that began during Montoya’s doctoral studies. He received a scholarship from FAPESP to conduct research under the guidance of Rodrigues. Montoya also completed an internship at Emory University in the United States.
At the time, Montoya analyzed the two largest existing collections of these fungi: the IB-UNESP collection, which was collected and maintained by Rodrigues’s group, and the Emory collection, which was maintained by Professor Nicole Marie Gerardo, Montoya’s supervisor abroad.
One of the first results of that effort was the description of two new genera previously classified as Escovopsis. Two others discovered in that work are still in the process of being described. Montoya and Rodrigues also led the description of 13 new species of Escovopsis, with ten more in the process of being described.
“These fungi are still poorly understood from physiological and ecological points of view. Therefore, it’s premature to treat them all as parasites. Our studies suggest that they have other functions and can live in relative harmony in colonies,” Montoya believes.
According to the researcher, only the Escovopsis weberi species has been proven to cause infections in fungi cultivated by ants. Experiments by his group and others show that several strains did not kill the fungi in the presence of these insects.
In vitro experiments that support the claim of parasitism disregard the fact that the affected fungi rely on ants for protection. Therefore, evaluating the effect of Escovopsis on mutualistic fungi without ants and their hygiene behaviors, which act as a social immune system, would not make sense (read more at agencia.fapesp.br/54199).
“Some more virulent fungi are immediately removed by ants when inoculated into the colony. In experiments with Escovopsis, however, they don’t give it much importance,” the researcher says.
About São Paulo Research Foundation (FAPESP)
The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. You can learn more about FAPESP at www.fapesp.br/en and visit FAPESP news agency at www.agencia.fapesp.br/en to keep updated with the latest scientific breakthroughs FAPESP helps achieve through its many programs, awards and research centers. You may also subscribe to FAPESP news agency at http://agencia.fapesp.br/subscribe.
Journal
Communications Biology
Article Title
Digging into the evolutionary history of the fungus-growing-ant symbiont, Escovopsis (Hypocreaceae
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