Population genetics reveals adaptive signatures of Exidia glandulosa across diverse climates from China

Fungi are the silent engineers of the forest floor, breaking down fallen wood and recycling nutrients back into the soil. While we often think of them as simple organisms, their genetic makeup is surprisingly complex, especially for those that live in the dikaryotic state. In this stage, a single fungal cell holds two distinct sets of genetic instructions, like a library containing two different editions of the same book. This unique biological setup allows them to carry a vast amount of genetic information, which can help them survive in changing environments. For decades, scientists have understood that climate shapes where species live, but figuring out exactly how a single species of fungus adapts to vastly different weather patterns across a massive country has been difficult. Without a complete map of the fungus's genetic code, researchers could not see the specific changes that allow it to thrive in a freezing mountain or a humid southern valley.

A team of researchers has now filled this gap by creating the first high-quality, complete genetic map for Exidia glandulosa, a common wood-decaying fungus found throughout China. This species, which looks like a dark, jelly-like blob on tree bark, was chosen because it lives in an incredibly wide range of climates, from the cold, dry north to the warm, wet south, and even up onto the high, thin-air plateaus of the southwest. By sequencing the DNA of 78 samples collected from these diverse locations, the scientists were able to trace how this single species has split into different groups and evolved unique survival strategies for each environment. The study reveals that while the fungus is one species, its genetic identity is far from uniform, shaped heavily by the specific weather and geography of its home.

The researchers began by assembling a reference genome, which serves as a master blueprint for the species. They found that this blueprint is unusually complex, carrying a very high level of genetic variation within a single individual. This suggests that the ancestors of these fungi either had a rich genetic history or that different genetic lines mixed together long ago. This genetic richness appears to be a key asset, giving the fungus the flexibility to spread across the varied landscapes of China. To understand how this flexibility plays out in the real world, the team compared the DNA of the 78 collected samples. They discovered that the fungus is not a single, blended population but is divided into five distinct groups based on where they live.

One group lives in the temperate north and northeastern regions, while another occupies the subtropical south. A third group exists in the transition zones between these two climates. Two other groups are more isolated: one found in the far northwest and Europe, and another unique group living on the high plateau in the southwest. The genetic analysis showed that the northern, transitional, and southern groups are closely related, likely sharing a common ancestor that spread and then adapted to different temperatures. However, the high-altitude plateau group and the far-northwest group have taken independent evolutionary paths, becoming genetically distinct from the rest. This separation suggests that the extreme conditions of the plateau and the specific climate of the northwest have created barriers that prevent these populations from mixing freely with others.

The study goes deeper to explain how these different groups survive their specific environments by looking at which genes are working hardest. In the temperate north, the fungus has evolved to focus on sensing its surroundings and reacting to stress. It is like a system constantly checking the weather and preparing for sudden changes, using specific genetic tools to manage signals and protect itself from harsh conditions. In contrast, the populations in the warm, humid south have shifted their focus to energy production. Their genetic machinery is tuned to burn fuel efficiently and generate heat, supporting a faster growth rate that takes advantage of the longer growing season in the south.

The most striking findings come from the plateau population, where the environment is harsh, cold, and filled with intense ultraviolet radiation. Here, the fungus has developed a multi-layered defense strategy. It relies on pathways that sense energy levels and recycle cellular waste to survive when resources are scarce. It also activates systems to repair damage to its DNA caused by the sun's rays and uses specific mechanisms to break down and remove damaged proteins. This combination of energy management, waste recycling, and DNA repair allows the fungus to persist in an environment that would be lethal to many other organisms. The researchers found that these adaptations are not just random changes but are the result of long-term natural selection favoring the individuals best equipped to handle the plateau's extreme challenges.

The work also clarifies what does not drive these differences. Despite the fungus growing on many different types of trees, the study found no evidence that the specific host tree determines the genetic makeup of the fungus. Instead, the climate and geography are the primary forces shaping how these populations evolve. Human activity, such as the clearing of forests, may also play a role in separating populations, but the natural climate gradients remain the most powerful factor. By mapping these genetic changes, the researchers have provided a clear picture of how a single species can diversify to conquer a continent.

This research offers more than just a story about a fungus; it provides a valuable resource for future scientific work. The high-quality genetic map created here will allow other scientists to study how wood-decaying fungi interact with their environment, how they break down wood, and how they might respond to a changing climate. It bridges a significant gap in our understanding of fungal evolution, showing that even organisms that seem simple and static are dynamic, constantly adapting to the world around them. The findings confirm that the ability to survive in diverse climates is written into the very code of the organism, a testament to the power of evolution to shape life in the most unexpected places.