'Tipping point' discovered in fungi evolution that impacts their shape and growth rate

Fungi and their evolution play a critical role in keeping our ecosystems in balance. These master decomposers thrive within the forest floor, steadily breaking down fallen leaves, dead trees, and other organic matter to release essential nutrients back into the Earth.

When we imagine fungi, mushrooms often come to mind first. However, beneath the surface lies a vast and complex network of fungal structures.

Hyphae in fungi

Deep within the soil, fungi develop a vast network of thin strands called mycelia. These structures consist of numerous interconnected, microscopic tubes referred to as hyphae.

Hyphae extend through the soil, seeking nutrients to sustain their growth. To facilitate this growth and movement, hyphae inflate, enabling them to traverse their surroundings and assimilate nutrients efficiently.

The tips of these hyphae vary in shape: some are round, others are sharply pointed, and a few exhibit unusual, lumpy appearances.

Why the different shapes? Researchers at New York University (NYU) have solved that puzzle.

“A major challenge in biology is to identify the specific evolutionary factors that determine the shape — or form — of a given organism,” says Enrique Rojas, assistant professor of biology at NYU and senior author of the study.

Fungi hyphae: Shaped by more than evolution

To figure out why fungi boast such diverse hyphae shapes, Rojas and his team combined theoretical models with observations of fungi in nature.

First, they used physics-based simulations to map out all the “possible” shapes hyphae could take based on how they grow.

Surprisingly, they found that the array of forms actually seen in the fungal world was only a small fraction of those possibilities.

This raised an intriguing question: were the limited hyphae shapes observed in nature a testament to “survival of the fittest”?

Evolutionary shapes and forms of fungi

For example, certain hyphae shapes might be better at helping the fungus find food, grow strong, and reproduce.

These fitter shapes get passed on, whereas shapes that don’t help the fungus thrive wouldn’t stick around in the long run, fading away as evolutionary rejects.

To test this idea, researchers set their sights on determining which shapes help fungi grow the fastest and strongest.

“Our eureka moment was when we realized that the shapes of hyphae were intimately connected to their ability to grow fast,” explains Maxim Ohairwe, a PhD student in NYU’s Department of Biology and the lead author of the paper.

The tipping point limits fungal shapes

Let’s introduce a concept from evolutionary biology, a fitness landscape. This framework helps us understand how well a species adapts and evolves.

In this context, researchers have found that the fitness landscape for fungi includes a significant feature — a cliff. This cliff, or ‘tipping point’, signifies a boundary beyond which certain hyphal shapes become less stable and disadvantageous.

The presence of this tipping point acts as a barrier, limiting the range of shapes that fungi can evolve into. Importantly, fungi with shapes approaching this tipping point are highly susceptible to even minor environmental changes, which can have profound effects on their survival and function.

Tipping point and fungi evolution

The team put this theory to the ultimate test. They took fungi near the tipping point and exposed them to tiny amounts of carefully selected chemicals that messed with hyphae growth — some messing with internal pressure, others affecting how the cell builds itself.

Surprisingly, those treated hyphae slowed dramatically, and they grew strange, bulbous shapes rarely, if ever, seen in natural fungi.

“Our findings explain hyphal shape diversity in an enormous, diverse, and important group of species,” said Rojas. “More broadly, they also demonstrate an important new evolutionary principle: that fitness landscapes can have instabilities, or tipping points, that impose strict constraints on complex traits, like biological form.”

Potential applications

Understanding the evolutionary “tipping point” in fungi, as highlighted by recent research, could revolutionize sectors like agriculture, medicine, and environmental conservation. In agriculture, knowledge of how fungi evolve offers the potential for smarter crop disease control.

By targeting the weaknesses created by a fungus’s evolutionary trajectory, researchers could design more precise and less ecologically harmful treatments to stop crop-destroying diseases.

Overall, this holds the promise of increased food security and reduced reliance on the broad-spectrum pesticides that can harm beneficial organisms and the environment.

Medical field

The findings aren’t just a boon for farmers — the medical field stands to gain as well. Traditional antibiotics are becoming a less reliable weapon against infection as resistance spreads.

But, by pinpointing the constraints evolution places on disease-causing fungi, we could develop highly targeted antimicrobial treatments.

These new drugs might sidestep existing resistance mechanisms and work more effectively, potentially saving lives and lowering healthcare costs.

Conserving the evolution of fungi

Understanding fungal tipping points can be an ace up the sleeve of conservationists. Fungi are integral to healthy ecosystems, breaking down materials and cycling nutrients.

Predicting how fungi might react to the pressures of climate change will be key in preserving biodiversity.

It might even allow us to encourage the growth of fungi that help fight climate change, such as those that lock carbon away or clean up pollutants.

Sometimes the smallest and strangest organisms teach us the biggest lessons. This discovery of evolutionary tipping points in fungi highlights how unpredictable and complex the natural world can be.

The study is publsihed in Cell Reports.

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