Chapter 28 Eukaryote Diversity Notes PDF

Eukaryote Diversity The tour of Eukarya begins with Excavata (the excavates), a clade named for the...

Eukaryote Diversity The tour of Eukarya begins with Excavata (the excavates), a clade named for the observation that some members of this diverse group also have an "excavated" feeding groove on one side of the cell body. Figure 28.3 Exploring eukaryote diversity. Diplomonads and parabasalids lack The mitochondria of parabasalids are also plastids and have highly reduced reduced, but they generate some energy mitochondria, and most species are found anaerobically, releasing hydrogen gas (H2) in anaerobic environments. as a by-product. Many diplomonads are parasites, including The best-known parabasalid is the infamous Giardia intestinalis (Fig. Trichomonas vaginalis, a sexually 28.3), which inhabits the intestines of transmitted parasite that infects about 140 mammals. million people each year worldwide. Figure 28.3 Giardia intestinalis, a diplomonad parasite. Figure 28.6 The parabasalid parasite Trichomonas vaginalis (colourized SEM). The last excavatan group is Euglenozoa, A euglenid has a pocket at one end of the which contains the kinetoplastids and the cell from which one or two flagella emerge euglenids. They are diagnosed by presence (Fig. 28.2). Some euglenids are of a rod with either a spiral or a crystalline mixotrophs: they perform photosynthesis structure inside their flagella (Figure 28.7). when sunlight is available, but when it is not, they can become heterotrophic, Euglenozoa includes photoautotrophs, absorbing organic nutrients from their predatory heterotrophs, parasites, and environment. Many other euglenids engulf mixotrophs. prey by phagocytosis. Figure 28.7 Euglenozoan body schematic and flagellum cross section (TEM). Figure 28.9 Euglena sp., a euglenid commonly found in pond water. Kinetoplastid euglenozoans include species that feed on prokaryotes in aquatic and moist terrestrial ecosystems, as well as species that parasitize animals, plants, and other "protists". Kinetoplastids in the genus Trypanosoma (Fig. 28.8) infect humans and cause sleeping sickness, a neurological disease that is fatal if not treated, afflicts about 10,000 people each year. Figure 28.8 Trypanosoma, a kinetoplastid that causes sleeping sickness (SEM). The "SAR supergroup" was recognized on the basis on whole-genome DNA sequence analyses. These studies found that three major groups form a monophyletic clade: the stramenopiles, the alveolates, and the rhizarians. This supergroup contains a large, extremely diverse collection of "protists". Figure 28.3 Exploring eukaryote diversity. Morphological and DNA sequence data The stramenopiles include diatoms, brown suggest that two of these groups, the algae, and oomycetes. They are diagnosed stramenopiles and the alveolates, by a characteristic flagellum, which has originated more than a billion years ago, numerous fine, hairlike projections. when a common ancestor of these two clades engulfed a unicellular In multicellular stramenopiles, it is usually photosynthetic red alga, which evolved the reproductive structures (zoospores, into a chloroplast (here, originating via sperm) that express the characteristic secondary endosymbiosis). stramenopile flagella. http://digfir-published.macmillanusa.com/morris2e/asset/img_ch27/morris2e_ch27_fig_27_16.html Diatoms are unicellular algae. They are among the most important photosynthetic organisms on the planet. All diatoms have a unique glass-like “wall" (exoskeleton), consisting of two parts that overlap like a shoe box and its lid, made of hydrated silica (SiO2) embedded in an organic matrix. Figure 28.11 Diatoms galore. With an estimated 100,000 living species, Diatoms are one of many "protist" groups diatoms are a highly diverse group of that are largely microscopic and major stramenopiles. components of marine and freshwater communities known as plankton. They are among the most abundant photosynthetic organisms both in oceans Diatoms and other plankton essentially and lakes: one bucket of water scooped drift in the water column, but they are from the surface of the sea may contain unable to actively propel themselves millions of these microscopic algae. against currents. https://en.wikipedia.org/wiki/Plankton Massive accumulations of fossilized Some diatoms may produce toxins that can diatom exoskeletons are major be harmful to humans. Diatoms of the constituents of sediments known as genus Pseudo-nitzschia, for example, can diatomaceous earth. produce domoic acid, which accumulates in shellfish, anchovies, and sardines that These sediments are mined for their feed on them during algal blooms. quality as a filtering medium and for many other uses, such as insect pest If people then eat this shellfish, it can control. cause amnesic shellfish poisoning (ASP). https://hab.whoi.edu/species/species-by-name/pseudo-nitzschia/ ASP results in short-term memory loss, Prior to the PEI incident, domoic acid was seizures, tremors, and sometimes death. known in red algae but had previously not In 1987, three elderly Prince Edward been observed in shellfish. Islanders died and several other people suffered permanant short-term memory In 1998, more than 400 California sea lions loss after eating contaminated mussels. died following an algal bloom. They had This was the first documented outbreak eaten anchovies that had fed on Pseudo- of domoic acid poisoning. nitzschia. Necropsies showed brain damage https://peishellfish.com/pei-international-shellfish-festival-will-go-ahead-with- due to domoic acid poisoning. plenty-of-oysters-on-sept-19-22-2024-at-the-charlottetown-event-grounds/ On August 18, 1961, seabirds "attacked" Brown Algae people in the towns of Capitola and Santa Cruz on Monterey Bay in California. It was The largest and most complex algae are later (in 2012) hypothesized that they brown algae. All are multicellular, and were poisoned by domoic acid. the body is known as a thallus. The Monterey Bay events were Most are marine and many of the species immortalized in Alfred Hitchcock’s 1964 commonly called "seaweeds" are brown movie The Birds. algae. https://www.imdb.com/title/tt0056869 Brown algae are especially common along temperate coasts that have cold water currents. Brown algae owe their characteristic brown or olive colour to the carotenoids in their plastids. Some brown algal seaweeds have specialized structures that resemble organs in plants. Figure 28.12 The sea palm Postelsia live on rocks along the coast of the northwestern United States and western Canada..  The body form of brown algal seaweeds Whereas plants have adaptations (such as consists of a root-like holdfast, which stems) that provide support against anchors the alga, a stem-like stipe, and a gravity, brown algae have adaptations that leaf-like blade. enable their main photosynthetic surfaces (the leaf-like blades) to be near the water Unlike plants, however, brown algae lack surface. true tissues and organs; the structural similarities to plants evolved Some brown algae accomplish this task independently in brown algae. with gas-filled, bubble-shaped floats. https://www.britannica.com/science/Laminaria Giant brown algae known as kelps Laminaria is a source of the relatively rare that live in deep waters have such floats in element, iodine, which is used to promote their blades, which are attached to stipes thyroid health. Laminaria is used in soups that can rise as much as 60 metres from in Japan, where it is known as kombu. the seafloor. The gel-forming substance in the cell walls of brown algae, called algin, is used to Due to the height of the kelps, they thicken many processed foods, including provide protection for creatures that the pudding and salad dressing. open ocean does not often give. https://www.yourlegasea.com/posts/the-sargasso-sea/ https://eos.org/articles/kelps-carbon-sink-potential-could-be-blocked-by-coastal-darkening https://coral.org/en/blog/the-stench-of-sargassum-season-how-seaweed-is-threatening-mesoamerica/ Figure 28.13 Alternation of generations A variety of life cycles have evolved among multicellular algae. The most complex life cycles include an alternation of generations, the alternation of multicellular haploid (n) and diploid (2n) forms as shown in Figure 28.13 for the brown alga genus Laminaria. Although haploid and diploid conditions As detailed in Figure 28.13, the diploid alternate in all sexual life cycles (human individual in this complex algal life cycle is gametes, for example, are haploid) the called the sporophyte because it produces term "alternation of generations" applies spores. The spores are haploid and move only to life cycles in which both haploid by means of flagella; they are called and diploid stages are multicellular. zoospores. The zoospores divide by mitosis and develop into haploid, multicellular Alternation of generations also evolved in male and female gametophytes, which plants. produce gametes. The union of two gametes (fertilization, or Other algal life cycles have an alternation syngamy) results in a diploid zygote, which of isomorphic generations, in which the matures and gives rise to a new sporophytes and the gametophytes look multicellular sporophyte. similar to each other, although they differ in chromosome number. In the genus Laminaria, the two generations are heteromorphic, meaning An example of an isomorphic alga is the that sporophytes and gametophytes are green alga genus Ulva, also known as sea structurally different. lettuce. https://link.springer.com/article/10.1007/s10811-020-02148-7#Fig3 Oomycetes Oomycetes include the water moulds, the white rusts, and the downy mildews. Based on their morphology, these organisms were previously classified as fungi (in fact, oomycete means "egg fungus"). Figure 28.14 (left) closeup of oomycete hyphae; (right) oomycete hyphae extending from a decomposing goldfish. Many oomycetes have multinucleate The sporangia of the oomycete releases filaments (hyphae) that resemble fungal flagellated zoospores, each of which has hyphae. However, there are key hairy flagellum typical of stramenopiles differences between oomycetes and fungi. (Fig. 28.10). Morphologically, oomycetes typically have Data from molecular systematics have cell walls made of cellulose, whereas fungi confirmed that oomycetes form a clade have cell walls made of chitin (both with other stramenopiles and are not cellulose and chitin are polysaccharides). closely related to fungi. https://www.britannica.com/science/Oomycota In oomycetes, the high surface-to-volume Instead, they typically acquire nutrients as ratio of filamentous structures enhances decomposers or parasites. Most water the uptake of nutrients from the moulds are decomposers that grow as environment. cottony masses on dead algae and animals, mainly in freshwater habitats. Although oomycetes descended from plastid-bearing ancestors, they no longer Other oomycetes, such as white rusts and have plastids and do not perform downy mildews, generally live on land as photosynthesis. plant parasites. One of the most significant plant Figure 28.15 The sporangia (reproductive structures) of pathogens is the downy mildew Phtyopthtora infestans can be seen emerging from the Phytophthora infestans (Figure 28.15). leaf's stomates. The tips of the sporangia eventually detach and are carried by This oomycete causes potato blight, wind to nearby plants to start another infection cycle. which turns the leaves, stalks and stems Note also the hyphae extending into the of potato (and tomato; both plants are in leaf (colourized SEM). the genus Solanum) plants into "black slime". https://cropscience.bayer.co.uk/late-blight/  Potato blight contributed to the Alveolates devastating Irish famines of the 19th century, in which a million people died and Alveolates are abundant in many habitats at least that many were forced to leave and include a wide range of photosynthetic Ireland. and heterotrophic "protists". Your text estimates that $1 billion is spent Alveolates are characterized in having globally on fungicides to control potato membrane-enclosed sacs (alveoli) just blight. under the plasma membrane (Fig. 28.16). The function of the alveoli is unknown; researchers hypothesize that they may help stabilize the cell surface or regulate the cell's water and ion content. Alveolata contains three groups: the dinoflagellates; the apicomplexans, a group of parasites; and the ciliates, a group of protists that move using cilia. Figure 28.16 Alveolates are distinguished from other eukaryotes by alveoli (sacs) under their plasma membrane. The cells of many dinoflagellates are reinforced by cellulose plates. Grooves in this cellulose "armour" house two flagella, one of which causes dinoflagellates (from the Greek dinos, Figure 28.17 Dinoflagellates. whirling) to spin as they move through the waters of their marine and freshwater communities (Fig. 28.17a)  Many dinoflagellates are photosynthetic, Many retain chloroplasts and these some being important species of photosynthetic dinoflagellates have a phytoplankton (photosynthetic plankton) flexible metabolism and are mixotrophic. in the oceans. Those dinoflagellates that are Although their ancestors may have photosynthetic are important species of originated by secondary endosymbiosis, phytoplankton (photosynthetic plankton) roughly half of all dinoflagellate species in the oceans. are now purely heterotrophic. A period of explosive population growth, When blooms occur, toxins produced by or bloom, in dinoflagellates sometimes certain dinoflagellates have caused causes an event known as a “red tide" (Fig. massive "kills" of invertebrates and fishes. 28.17b). The blooms make coastal waters appear brownish red or pink because of People who eat molluscs that have the presence of pigments called accumulated dinotoxins can exhibit carotenoids, located in the dinoflagellate paralytic shellfish poisoning (a neurological plastid. disorder) or diarrhetic shellfish poisoning https://www.sdcoastkeeper.org/blog/harmful-algal-blooms-san-diego-county/ (a gastrointestinal disorder). https://crie.cr/costa-rica-red-tide-explained/ These dinotoxin poisonings sometimes Apicomplexans are so named because one result in fatalities. end (the apex, “api-”) of the cell contains a complex of organelles specialized for A 2017 study found that ocean warming penetrating host cells and tissues. (caused by ongoing climate change) has facilitated more frequent blooms of toxic Nearly all apicomplexans are parasites of dinoflagellates, making them a growing animals, and virtually all animal species threat to human health. examined so far are attacked by these parasites.  Apicomplexan parasites spread through their host as tiny infectious cells called sporozoites. Although apicomplexans are not photosynthetic, recent data show that they retain a modified plastid (apicoplast), most likely of red algal origin. Figure 28.18 (a) schematic diagram of an apicomplexan and (b) TEM of red blood cell infected with the malaria-causing apicomplexan Plasmodium sp. Plasmodium, the parasite genus that causes malaria, and most other apicomplexans have life cycles with both sexual and asexual stages. Those life cycles often require two or more host species for completion. For example, Plasmodium lives in both mosquitoes and humans (Fig. 28.18). Figure 28.18 The two-host life cycle of Plasmodium, the apicomplexan that causes malaria. Historically, malaria has rivalled But the emergence of resistant varieties tuberculosis as the leading cause of human of both Anopheles and Plasmodium has death by infectious disease. led to a resurgence of malaria. Malaria incidence was greatly diminished About 220 million people in the tropics in the 1960s by insecticides that reduced are currently infected, and 450,000 die carrier populations of mosquitoes of the each year. Where malaria is common genus Anopheles and by drugs that killed there are high frequencies of the sickle Plasmodium in humans. cell allele in human populations. https://ourworldindata.org/malaria The sickle-cell allele (S) is a mutation of the People with two copies of the S allele DNA sequence that codes for one of the produce cystalline hemoglobin, which polypeptides that forms a subunit of the results in sickle-shaped red blood cells. oxygen-carrying protein hemoglobin. Hemoglobin made partly with S-subunits results in red blood cells with irregular shapes, which deter feeding by Anopheles mosquitoes. https://www.shutterstock.com/search/sickle-cell-anemia These sickle-cell shaped red blood cells The prevalence of the S-allele in human result in numerous symptoms that populations in malaria areas is an example together are known as sickle-cell disease. of humans evolving with a lethal pathogen. People with sickle-cell disease suffer anemia, episodes of pain, pulmonary People in a malaria region who have one hypertensionorgan damage, avascular copy of the S-allele and one copy of the necrosis, etc. They face a reduced life unmutatated (ancestral) allele are resistant expectancy of 52.6 years. to malaria. The drawback of the S-allele is that Ciliates are a large and varied group people who have two copies develop the named for their use of cilia to move and genetic disease. feed. Most ciliates are predators and prey upon bacteria or small "protists". This is a classic example of a species adapting to its (in this case local) Their cilia may completely cover the cell environment, but the adaptation comes surface or may be clustered in a few rows with a cost. or tufts. A model ciliate genus is freshwater form Paramecium.  A distinctive feature of ciliates is the presence of two types of nuclei: tiny micronuclei and large macronuclei. A cell has one or more nuclei of each type. The micronuclei are reserved for the exchange of genetic information during sexual reproduction that occurs during conjugation (steps 1-4 in Fig. 28.20b). Figure 28.20 (a) structure in the ciliate Plasmodium caudatum. Ciliate conjugation is a process in which two individual ciliates exchange haploid micronuclei but they do not fuse. The macronucleus is the transcriptionally active one and required for producing RNAs and proteins that support everyday functions of the cell. Figure 28.20 (b) life cycle of the ciliate Plasmodium caudatum. The macronucleus is derived from the Ciliates generally reproduce asexually by micronucleus, but is quite different in binary fission, during which the existing content and structure. As the macronucleus disintegrates and a new one macronucleus differentiates, many is formed from the cell's micronuclei. chromosomes are amplified so there are many extra copies (dozens to 1000s) and Check out the videos on ciliate movement the chromosomes can become in Paramecium and in Stentor on page 650 fragmented, with the elimination of of the text. specific genomic regions.  Rhizaria Amoebas move and feed by means of pseudopodia, which are extensions that Rhizarians form another clade of the SAR may bulge from almost anywhere on the supergroup. Many rhizarian species are cell surface. amoebas. Note that amoebas do not constitute a monophyletic group; The amoeba moves by extending a instead, amoebas are dispersed across pseudopodium and anchoring its tip; more many distantly related eukaryotic taxa. cytoplasm then streams into the pseudopodium. https://arcella.nl/wp-content/uploads/Rhizamoeba-1-1.jpg Most amoebas that are rhizarians differ Radiolarians are mostly marine planktonic morphologically from other amoebas by forms. They have delicate, intricately having thread-like pseudopodia. symmetrical internal skeletons that are generally made of silica (SiO2, silicon Rhizarians also include flagellated (non- dioxide). amoeboid) forms that feed using thread- like pseudopodia. There are three major The pseudopodia radiate from the central groups: radiolarians, foraminiferans, and body and are reinforced by bundles of cercozoans. microtubules (Fig. 28.21). The microtubules are covered by a thin layer of cytoplasm and plasma membrane, which engulf smaller microorganisms that become attached to the pseudopodia. The captured prey are then transported into the main part of the cell via a process called cytoplasmic streaming. Figure 28.21 Numerous thread-like pseudopodia radiate from the central body of this radiolarian.  After radiolarians die, their skeletons rain Foraminifera ("forams") are named for down and settle on the seafloor, where their porous shells or tests (Fig. 28.3). they can accumulate as an ooze that is hundreds of metres thick in some Foram tests consist of a single piece of locations. organic material that typically is hardened https://geologyistheway.com/sedimentary/radiolarite/ with calcium carbonate. Unlike the shells Over time, radiolarian skeletal oozes may (exoskeletons) of molluscs and corals, petrify and turn into the rock radiolarite, foram tests are located inside the cell which was extensively used for stone tools. membrane. https://www.alexstrekeisen.it/english/sedi/radiolarite.php https://geologyistheway.com/sedimentary/radiolarite/ Figure 28.3 Globigerina, a rhizarian genus in SAR. This species is a foram, a group whose members have threadlike pseudopodia that extend through pores in the shell, or test (LM). The inset SEM Pseudopodia extend through the pores in shows a foram test, which is hardened by calcium carbonate. the test and function in anchoring the foram, locomotion (swimming), test formation, and in capturing food such as bacteria and diatoms. Many forams also derive nourishment from the photosynthesis of symbiotic algae that live within the tests. Forams are found in both the ocean and Over 50,000 species of forams are freshwater. Most species live in sand or recognized, of which 40,000 are extinct. attach themselves to rocks or algae, but some live as plankton. Along with the calcium-containing remains of other "protists", the fossilized Most forams are less than 1 mm in size. tests of forams are part of marine The largest forams, though single-celled, limestones, including sedimentary rocks have tests measuring up to 20 cm in that are now land formations. diameter. https://geologyistheway.com/urban-geology-nummulites-on-the-stone-walls-of-girona-catalonia/ https://en.wikipedia.org/wiki/Great_Pyramid_of_Giza