BIOL 211 Lecture 23: Fungi

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BIOL 211
Bruno Pernet

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Lecture 23 Notes: Fungi Transfer of Pollen Among Plants • Transfer is an essential part of pollination; movement of male microgametophytes (pollen) to the female gametophyte encased in the carpel • “vector” for pollination has a strong effect on the evolution of flower traits • Wind pollination: characteristic of ~20% of angiosperm species, including all grasses o Species tend to have small, inconspicuous green flowers without any particular scent o Very inefficient (most pollen lands in the wrong place and ends up being lost), so wind-pollinated plants produce lots of pollen • Water pollination: very rare, happens only in the few angiosperms that now live in water (rivers, ponds, lakes, oceans) like seagrasses o Flowers are small and inconspicuous, without any scent o Pollen grains tend to be long and stringy; drift in the water until they collide with a flower • Animal pollination: in most (~80%) angiosperms o Flowers have evolved to lure in potential pollinators, typically by offering them a reward of nectar (sugary solution), pollen, or something else o Plants that distribute their pollen more efficiently and get pollinated efficiently leave more offspring, so flower traits (such as color, odor, and shape) have evolved under natural selection to attract and get pollen on to or off of appropriate pollinators o Pollinators that acquire the most rewards from flowers have higher fitness, so pollinator traits have evolved in response to flowers o Evolution of plants and pollinators in response to each other is an example of “coevolution” • Most angiosperms are insect-pollinated; flower traits depend on pollinator traits o Bee pollination: bees are attracted to yellows and blues, so bee-pollinated flowers are these colors ▪ Bees can see in UV, so bee-pollinated flowers often have UV-visible patterns called “nectar guides” ▪ Bees feed on both pollen and nectar, so flowers often provide both ▪ Bee-pollination enhances US crops by ~$15 bil each year ▪ Some species of plants add caffeine in their nectar; at low doses, caffeine improves learning in honeybees o Fly pollination: some flies like to lay their eggs in rotting meat, and some flowers have taken advantage of this by being red and producing a rotting tissue smell ▪ Flies lay their eggs on the flowers, getting pollen on themselves, then transferring the pollen to other flowers when they leave to lay eggs ▪ Fly eggs hatch into larvae that die after being born o Moth pollination: Moths come out at night and have an excellent sense of smell, so flowers are light in color (white or yellow), are very fragrant, and open at night ▪ Ex: yuccas o Bat pollination: Bats are nocturnal; flowers are light-colored, very fragrant (sulfur compounds), and open at night ▪ Bats visit flowers to feed on nectar and sometimes pollen o Bird pollination: Most birds have a poor sense of smell, so bird-pollinated flowers are odorless and often red or yellow ▪ Bird pollinators seek nectar; any movement of pollen among flowers is incidental (hummingbirds) Fungi: Phylogeny and Origin • Fungi are unikonts: cells never have more than one flagellum • Opisthokonts: single flagellum is always located at the posterior end of the cell o Common ancestor of the opisthokonts was likely unicellular and flagellated • Nucleariids (unicellular amoebae) are sister taxon to the fungi o Suggests that multicellularity evolved in the fungi (as well as in the animals, independently) • Oldest clear fossils of fungi are from 460 mya (but molecular data suggests maybe 1–1.5 bya) Nutrition • All fungi are absorptive heterotrophs (specifically absorptive chemoheterotrophs) • Organism absorbs small organic compounds from the external environment and uses them for both energy and a source of carbon • Many fungi secrete enzymes into the environment to break down large organic molecules into small molecules they can absorb o Very diverse hydrolytic enzymes allow for breakdown of proteins, lipids, and complex carbs like cellulose and lignin (hydrolysis) o Used by humans for a wide variety of purposes • Fungi are usually: o Decomposers: break down dead organic matter (animal flesh, fruit, plant cellulose or lignin) and absorb the products o Parasites or pathogens: absorb small organic molecules from the cells of living hosts (ringworm) o Mutualists: absorb small organic molecules from a living host, but also do something positive for the host (lichens) Structure • Chitin – fibrous polysaccharide within the cell walls of fungal cells o Polymer of a version of glucose modified to contain a bit of nitrogen • Two major body forms: o Unicellular fungi (yeasts): relatively rare ▪ Unicellularity seems to have evolved several times in the fungi (common ancestor of fungi was multicellular) o Multicellular fungi: made up of tubular filaments called hyphae ▪ Mycelium – mass of hyphae that makes up the fungal body • Hyphae are multicellular, but in one of two ways: o Septate – cells are separated by incomplete cross-walls called septae ▪ Pores in the septae are often large enough to allow organelles to move from cell to cell o Coenocytic fungi: hyphae have no septae and basically consist of one large cell with many nuclei • In some multicellular fungi, during part of the life cycle (when sexual spores are produced), some of the hyphae get organized into structures called “fruiting bodies” o Ex: mushrooms • When you see a mushroom, recognize that the (probably invisible) mass of mycelia is usually much greater than that of the fruiting body o Fruiting bodies make up only a tiny fraction of an individual’s biomass Life Cycles • Fungi may reproduce asexually, or may have sexual processes in their life cycles, or both
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