MUTUAL AID
Insect-killing fungi find unexpected harmony in war
UMD study reveals that two strains of pathogenic fungi unexpectedly divide up insect victims rather than aggressively compete for resources.
University of Maryland
image:
Two strains of fungi (Ma549 and Mr2575) were grown together in a lab dish containing potato dextrose agar and specially modified to glow in different colors (red and green, respectively). This image depicts their colonization of the dish over a period of five days. Both fungal colonies grow to touch each other, but their method of growth differs. While Ma459 produces seed-like spores, Mr2575 extends thread-like structures called hyphae.
view moreCredit: University of Maryland, Raymond St. Leger
University of Maryland entomologists uncovered a unique relationship between two species of fungi known for their ability to invade, parasitize and kill insects efficiently. Instead of violently competing for the spoils of war, the two fungi peacefully cooperate and share their victims.
The findings, published in the journal Public Library of Science (PLOS) Pathogens on November 7, 2024, offer insight into some of the biggest evolutionary successes in nature’s history, according to study co-authors Raymond St. Leger, a Distinguished University Professor of Entomology, and entomology Ph.D. candidate Huiyu Sheng.
“It’s not survival of the fittest in the way we often think of. Sometimes, it’s the survival of those who can just get along,” St. Leger explained. “Rather than wiping each other out, these fungi apparently evolved sophisticated ways of coexisting—and we are just beginning to understand that balance.”
The study focused on two species of a fungal genus called Metarhizium, which can be found in soil around the world. Members of this fungal group protect plants from damaging abiotic stresses (such as drought or poor nutrients) and harmful insects.
“These microorganisms have been called keystone species because they play crucial roles in both plant health and natural insect population control,” St. Leger said. “Our findings may help explain their extraordinary success in ecosystems worldwide.”
Using advanced imaging techniques with fluorescent proteins that made the fungi glow red or green, the scientists observed how the fungi interacted when colonizing (infecting, spreading inside and eventually killing) insects. Rather than one strain dominating and excluding the other, the team found that the fungi neatly divided their territory amongst themselves—quite literally.
When colonizing pests, the two fungal strains showed an uncanny ability to split up their victim. One strain tacitly invaded the front segments of an insect host, while the other colonized the back segments, with the two invaded territories distinctly separated by a remarkably sharp dividing line between them. This pattern held true whether the chosen victim was a large caterpillar weighing ten grams or a tiny fly weighing less than a single milligram.
“The sharpness of the delineation between where one fungus starts and the other ends looks quite bizarre,” St. Leger noted. “The borders separating the segments from each other are inexplicably clear.”
So, why does this cooperation exist? The researchers believe each strain of fungus adapted their own unique specialties and niches over time, allowing them to partition limited resources.
“It’s becoming clear that sometimes the key to evolutionary success isn’t outcompeting your rivals—it’s learning to share,” St. Leger said.
But just how these fungi orient themselves within their hosts and how they communicate their territorial division remain mysteries. The researchers hope to investigate the mechanisms responsible for these host-sharing strategies and open up new avenues of research on how they could be used to bolster both food security and Earth’s biodiversity.
Understanding how different fungal species interact could help scientists and agriculturalists develop better biological pest control methods and strategies to promote plant growth. St. Leger notes that the fungi already show incredible promise in protecting plants from mercury poisoning, enhancing crop growth and killing disease-spreading insects.
“These fungi have shown that they are very adaptable,” he said. “They’ve been doing this for a very long period of time and have thus evolved an arsenal of novel, sophisticated and subtle tricks. They are also very easy to genetically engineer so their applications are limited only by your imagination.”
Partitioning of resources
Two fungal strains (colored green and red) divvy up resources available in an insect victim's body.
Colonizing an insect
With small insects like flies, one fungal strain (tagged with red) takes the front half and the other (tagged with green) takes the back half. In large insects like caterpillars, they subdivide individual segments (the red individual takes the front half of each segment and the green individual takes the back half).
Credit
University of Maryland, Raymond St. Leger
The paper, “Metarhizium fight club: within-host competitive exclusion and resource partitioning,” was published in the scientific journal Public Library of Science (PLOS) Pathogens on November 7, 2024.
Journal
PLOS Pathogens
Method of Research
Observational study
Subject of Research
Animal tissue samples
Article Title
Metarhizium fight club: Within-host competitive exclusion and resource partitioning
Article Publication Date
7-Nov-2024
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