Emma Wilson
Fungi are a highly diverse clade of eukaryotes found in virtually all environments, particularly terrestrial ecosystems. They are neither plants nor animals. Fungi evolved around 1.5 billion years ago from a single common ancestor with animals and as a separate group of living organisms. The first fungi were likely aquatic and probably colonized the land around 460-500 million years ago, around the same time as plants. Fungi have since evolved into complex multicellular organisms, adapting to diverse ecological niches and playing key roles in nutrient cycling and decomposition. They can act as predators, pathogens, parasites, and symbionts with other organisms. The evolution of mushroom-like morphologies from resupinate ancestors is an example of morphological adaptation in fungi, with pileate-stipitate fruiting bodies providing efficient spore production and protection from precipitation. Fungi have also adapted by increasing spore wall thickness and secreting exoenzymes and hydrolytic enzymes to digest organic material and large organic molecules, respectively.
| Characteristics | Values |
|---|---|
| Earliest fossils | 2,400 million years ago (Ma) |
| Earliest terrestrial fossils | 635 million years ago |
| Diversification of ecological strategies for obtaining nutrients | Parasitism, saprobism, and the development of mutualistic relations |
| Evolutionary transition | Acquisition of a parasitic lifestyle, establishment of symbiosis, changes in body-plan or cellular organization |
| Terrestrialization | Co-evolution with the ancestors of land plants (the 'green' scenario), acquisition of saprotrophic habits and colonization of damp land (the 'brown' scenario), adaptation to frozen environments (the 'white' scenario) |
| Adaptation to dry environments | Gradual sequestration of the hymenium, evolution towards an underground, truffle-like lifestyle |
| Adaptations for efficient extraction of nutrients | Secretion of hydrolytic enzymes to digest large organic molecules, absorption of smaller molecules as nutrients |
| Adaptations for protection | Increased thickness of spore walls, stronger and thicker cell walls made of chitin |
| Role in ecosystems | Cycling nutrients, providing shelter and sustenance to animals, promoting disease resilience, conserving soil, symbiotic relationships with plants and algae, decomposing organic matter |
| Mycotoxins | Aflatoxins, ergot alkaloids, ochratoxins, patulin, trichothecenes, fumonisins |
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What You'll Learn
The evolutionary history of fungi
Fungi are neither plants nor animals, and they are believed to have evolved about 1.5 billion years ago from a single common ancestor with animals. The fossil record of fungi is sparse, but they likely first appeared about one billion years ago. The earliest fossils with features typical of fungi date to the Paleoproterozoic era, some 2,400 million years ago. These multicellular benthic organisms had filamentous structures capable of anastomosis, where hyphal branches recombine. Other studies estimate the arrival of fungal organisms at about 760–1,060 million years ago by comparing the rate of evolution in closely related groups.
For much of the Paleozoic Era (542–251 million years ago), fungi appear to have been aquatic and consisted of organisms similar to the extant Chytrids, bearing flagellum-bearing spores. Phylogenetic analyses suggest that most fungal species lost their flagella early in their evolutionary history. The evolutionary transition from an aquatic to a terrestrial lifestyle required the diversification of ecological strategies for obtaining nutrients, including parasitism, saprobism, and the development of mutualistic relationships.
Fungi likely colonized the land during the Cambrian, over 500 million years ago, and possibly 635 million years ago during the Ediacaran. The earliest terrestrial fungus fossils, or at least fungus-like fossils, date to around this time and were discovered in South China. These early fungi may have contributed to oxygenating the Earth's atmosphere after the Cryogenian glaciations. By the Devonian period, 400 million years ago, terrestrial fossils become more common and uncontroversial.
Around 250 million years ago, fungi were abundant and possibly even dominant in many areas. They played a crucial role in the evolution of land plants by breaking down detritus and releasing nutrients, facilitating the spread of photosynthetic organisms. Fungi form vast webs in the soil, transferring chemical signals, food, and water, and they are the primary decomposers of organic matter in ecosystems worldwide. They cycle nutrients, provide shelter and sustenance to other organisms, promote disease resilience, and conserve soil. Fungi have highly symbiotic relationships with many plants and algae, and their unique ability to create symbiosis was key to the evolution of plant life on Earth.
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The evolution of mushrooms
Fungi, including mushrooms, are a highly diverse clade of eukaryotes found in virtually all environments, particularly terrestrial ecosystems. They are neither plants nor animals. Fungi are estimated to have evolved around 1.5 billion years ago from a single common ancestor with animals, though some fossils suggest an even earlier origin. The earliest fossils with fungal features date to the Paleoproterozoic era, around 2.4 billion years ago.
Fungi were likely first aquatic and then colonized land during the Cambrian, around 500 million years ago, though some estimates suggest it could have been earlier, around 635 million years ago during the Ediacaran. The earliest terrestrial fungus fossils have been found in South China and are estimated to be around 635 million years old. The first fungi may have contributed to oxygenating the Earth's atmosphere after the Cryogenian glaciations.
Fungi have evolved complex multicellularity through filamentous intermediate stages, developing integrated multicellular structures that enable them to adapt to diverse ecological niches. This evolutionary adaptation from an aquatic to a terrestrial lifestyle necessitated a diversification of ecological strategies for obtaining nutrients, including parasitism, saprobism, and the development of mutualistic relationships. Some fungi produce toxins, such as mycotoxins, which may provide fitness benefits in terms of physiological adaptation and competition with other microbes and fungi.
Fungi play key ecological roles, such as cycling nutrients, acting as predators or parasites, and forming symbiotic associations with plants, algae, animals, and other organisms. They are the principal decomposers in ecological systems and are vital for the carbon cycle as the primary decomposers of organic matter. Their ability to secrete exoenzymes allows them to digest organic material and absorb nutrients. Over time, fungi have also adapted by increasing the thickness of their spore walls, providing better protection and survival in new environments.
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How fungi adapt to different ecosystems
Fungi are a highly diverse group of organisms found in almost all environments, particularly terrestrial ecosystems. They are both micro and macroorganisms with high and varying functional diversity, as well as great variation in dispersal modes. They play key roles in maintaining the intricate balance of life on Earth, from decomposing organic matter to forming symbiotic relationships with plants and animals, and even other fungi.
Fungi have evolved to adapt to different ecosystems through their ability to transition between different lifestyles and associate with a wide variety of hosts in various environmental conditions. They can rapidly adapt to novel environments and hosts due to genomic instability, which is often facilitated by hybridization. This allows them to inhabit extreme but vast areas, such as drylands, and play a role in rock weathering and soil formation, creating microhabitats for other organisms.
The diverse secretome of fungi, or the total set of molecules secreted by cells, contributes to their metabolic versatility. These secretomes enable fungi to extract nutrients from complex substrates and protect them from hostile environmental conditions. Fungi can also act as decomposers, breaking down complex organic matter and returning vital nutrients to the soil, which is essential for the nutrient cycling process in ecosystems.
Additionally, fungi form intricate networks with plant roots, known as mycorrhizal associations, which are crucial for the survival, growth, and resilience of over 90% of plant species in various ecosystems. These networks facilitate the sharing and reconfiguration of water and nutrients, enhancing the diversity of the soil microbiome. Endophytic fungi, which reside within plant tissues without causing harm, also contribute to the overall health and resilience of plant populations by increasing their resistance to diseases and pests.
Fungal reproductive and dispersal traits are central to their adaptation and dispersal to new environments. However, our understanding of fungal lifestyles and interactions is still developing, and we need better tools and analytical approaches to fully comprehend their complexity and influence on ecosystems.
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The role of fungi in the carbon cycle
Fungi are neither plants nor animals. They are a highly diverse clade of eukaryotes found in virtually all environments, particularly in terrestrial ecosystems. They are believed to have evolved about 1.5 billion years ago from a single common ancestor with animals. The first fungi were likely aquatic and colonized the land about 460-635 million years ago, around the same time as plants.
Fungi play a critical role in the carbon cycle, acting as the primary decomposers of organic matter. They break down dead plants and release nutrients like carbon and nitrogen, which are then absorbed by the hyphae (long strings of cells). This process helps to store carbon in the soil, preventing it from being released into the atmosphere as carbon dioxide. In fact, when plants partner with certain types of fungi, they can store up to 70% more carbon in the soil. This has significant implications for the global carbon cycle and our efforts to address climate change.
Mycorrhizal fungi, in particular, are important players in the carbon cycle. They form symbiotic relationships with plants, enhancing their ability to uptake nutrients and store carbon. However, human activities such as burning fossil fuels can upset the balance by polluting the air with nitrogen, which acts as a fertilizer and disrupts the fungi's ability to store carbon.
Additionally, fungi themselves contribute to the carbon cycle through their enzymatic activities. They produce powerful enzymes that break down organic matter, leading to increased carbon storage in the soil and reduced carbon dioxide emissions. Suillus fungi, for example, can decompose organic matter and potentially reduce CO2 release from forest soils.
Fungi have also played a role in the oxygenation of the Earth's atmosphere. Some evidence suggests that fungus-like organisms contributed to oxygenation after the Cryogenian glaciations. Furthermore, their ability to adapt to diverse ecosystems and form symbiotic relationships with plants and other organisms highlights their significance in the carbon cycle and overall ecological balance.
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The evolution of fungi from a common ancestor
Evidence suggests that the earliest fungi lived in water and possessed flagella, which were lost early in their evolutionary history. The transition from aquatic to terrestrial environments led to the development of diverse ecological strategies for obtaining nutrients, including parasitism, saprobism, and mutualistic relationships. Some of the earliest fossils with fungal characteristics date back to the Paleoproterozoic era, around 2.4 billion years ago, and exhibited filamentous structures capable of anastomosis.
Fungi likely colonized land during the Cambrian period, approximately 500 million years ago, and possibly even earlier during the Ediacaran, around 635 million years ago. Terrestrial fungus-like fossils from this period have been discovered in South China, and they may have contributed to oxygenating the Earth's atmosphere after the Cryogenian glaciations. The scarcity of fungal fossils, due to their soft tissues and simple morphologies, has made the study of their evolutionary history challenging.
The first organisms to branch off from the fungi kingdom were parasites similar to modern-day chytidiomycete fungi, such as Rozella. Over time, fungi evolved diverse mechanisms for dispersing spores, even in species that lost their flagella. For example, mushrooms can "shoot out" spores that can regenerate over long distances. The evolutionary flexibility and ecological adaptations of fungi have allowed them to thrive in almost every ecosystem on Earth, showcasing their ancient origins and long history of diversification.
Fungi play vital ecological roles, such as cycling nutrients, providing shelter and sustenance to other organisms, promoting disease resilience, and conserving soil. They have complex interrelationships with plants, algae, animals, and other organisms, highlighting their significance in the natural world.
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Frequently asked questions
Fungi evolved from a single common ancestor with animals around 1.5 billion years ago. The earliest fossils with fungal characteristics date to the Paleoproterozoic era, around 2,400 million years ago.
Fungi likely colonized the land during the Cambrian, over 500 million years ago, and possibly as early as 635 million years ago during the Ediacaran. The transition from aquatic to terrestrial life required fungi to diversify their ecological strategies for obtaining nutrients, including parasitism, saprobism, and the development of mutualistic relationships.
Fungi have evolved complex multicellularity through filamentous structures called hyphae, which provide a large surface area for efficient nutrient extraction. They also secrete exoenzymes and hydrolytic enzymes to digest organic material and large organic molecules, respectively. Additionally, the ability to form mutualistic associations with plants, algae, and other organisms has contributed to their success.
Pileate-stipitate, or "mushroom-like" morphologies, have evolved multiple times from resupinate ancestors, possibly through coral-like intermediates. The evolution of mushroom stipes and other large organs is associated with growth by volume expansion.
Fungi play crucial roles in nutrient cycling and decomposition, acting as predators, pathogens, and parasites. They also form symbiotic relationships with plants, algae, and other organisms. Mushrooms, as a part of the fungi group, contribute to these ecological functions and provide a source of food and shelter for many organisms, including humans.
