Question

It has been hypothesized that fungi colonized land before plants. If true, then what does this mean regarding animals? Explore the relationships between plant, fungi, and animals and discuss why this hypothesis may be supported or rejected. What evidence would need to be found to support it? Why is it unlikely that we will be able to categorically dismiss it?

Be sure to back up your claims with peer-reviewed, primary scholarly sources.

Answer 1

Answer Fungi have ancient origins, with evidence indicating they likely first appeared about one billion years ago, though the fossil record of fungi is scanty. Fungal hyphae evident within the tissues of the oldest plant fossils confirm that fungi are an extremely ancient group. Indeed, some of the oldest terrestrial plantlike fossils known, called Prototaxites, which were common in all parts of the world throughout the Devonian Period (419.2 million to 358.9 million years ago), are interpreted as large saprotrophic fungi (possibly even Basidiomycota). Fossils of Tortotubus protuberans, a filamentous fungus, date to the early Silurian Period (440 million years ago) and are thought to be the oldest known fossils of a terrestrial organism. However, in the absence of an extensive fossil record, biochemical characters have served as useful markers in mapping the probable evolutionary relationships of fungi. Fungal groups can be related by cell wall composition (i.e., presence of both chitin and alpha-1,3 and alpha-1,6-glucan), organization of tryptophan enzymes, and synthesis of lysine (i.e., by the aminoadipic acid pathway). Molecular phylogenetic analyses that became possible during the 1990s have greatly contributed to the understanding of fungal origins and evolution. At first, these analyses generated evolutionary trees by comparing a single gene sequence, usually the small subunit ribosomal RNA gene (SSU rRNA). Since then, information from several protein-coding genes has helped correct discrepancies, and phylogenetic trees of fungi are currently built using a wide variety of data largely, but not entirely, molecular in nature.

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Relationship between plant ,fungi and animals;

A Kingdom Separate from Plants

The fungi (singular, fungus) once were considered to be plants because they grow out of the soil and have rigid cell walls. Now they are placed independently in their own kingdom of equal rank with the animals and plants and, in fact, are more closely related to animals than to plants. Like the animals, they have chitin in their cell walls and store reserve food as glycogen. (Chitin is the polysaccharide that gives hardness to the external skeletons of lobsters and insects.) They lack chlorophyll and are heterotrophic. Familiar representatives include the edible mushrooms, molds, mildews, yeasts, and the plant pathogens, smuts and rusts.

Most fungi are terrestrial, multicellular eukaryotes, the body ( soma) of which is a mass of thread-like filaments called hyphae (singular, hypha), which collectively form amycelium (plural, mycelia). When the fungus reproduces, specialized hyphae pack together tightly and form distinctive fruiting bodies, or sporocarps, from which sexual spores are released. The ordinary edible mushrooms are the fruiting bodies of fungi. Fruiting bodies are temporary structures in the life cycle; the primary body of all fungi is in reality the diffuse, widespreading mycelium.

The fungi reproduce by spores, both asexual and sexual, and the details and structures of the sexual process separate the kingdom into four phyla (see Table 1 ). The zygoteis the only diploid phase in the life cycle; meiosis occurs shortly after the zygote is formed—hence the life cycle is an instance of zygotic meiosis. Chemical signals,pheromones, are exchanged among fungi, especially between pairs preparatory to sexual reproduction.

Fungi are heterotrophs, which release digestive enzymes into their surroundings andabsorb nutrients back. Some fungi are saprobes (saprophytes), as important in decomposition as the bacteria; others are symbiotrophs, living in symbiotic association with plants, animals, protists, and cyanobacteria. Well-known symbioses are: lichens that are associations of fungi and green algae or cyanobacteria;mycorrhizae, associations of fungi and plant roots; and endophytes, fungi and plant leaves and stems. Some fungi are parasites ( fungal pathogens) and responsible for diseases of both plants and animals. Complex life cycles involving one or more hosts have developed between fungal pathogens and their hosts.

The Earth's largest living organism may be a fungus: either the mycelium reported from Washington state that covers 1,500 acres (but probably is disjointed and broken) or the one in Michigan that covers 37 acres (and is estimated to weigh 110 tons—the weight of a blue whale)