TOPIC 2 – KINGDOM PROTISTABIOL 1030 – SPRING 2008 Instructor: Nandini Rajamani Robin1. General Characteristics of Protista- In the past, taxonomists classified all protists in a single kingdom, Protista. We now know Protista is in fact paraphyletic – it is an artificial grouping.- Some protists are more closely related to plants, fungi, or animals than they are to other protists.- “Kingdom” Protista is being abandoned. - Protist – convenient term to informally refer to all eukaryotes that are not plants, animals, or fungi.1.1. Protists are very diverse- more structural and functional diversity than any other group of organisms- unicellular, colonial and multicellular- very complex at cellular level- nutritionally diverse – photoautotrophs - heterotrophs - mixotrophs - diverse habitats- diverse life cycles – some asexual, others 1.2 Endosymbiosis has a role in evolution of protists (refer Fig. 28.3)- Much of protist diversity is the result of endosymbiosis, a process in which unicellular organisms engulfed other cells that evolved into organelles in the host cell.- The earliest eukaryotes acquired mitochondria by engulfing alpha proteobacteria.- Later in eukaryotic history, one lineage of heterotrophic eukaryotes acquired an additional endosymbiont—a photosynthetic cyanobacterium—that evolved into plastids. This lineage gave rise to red and green algae.- Endosymbiosis gave rise to mitochondria before plastids. How is the hypothesis supported ? (Refer Concept 28.1 inCampbell & Reece 7th ed.)- Secondary endosymbiosis: red and green alga were ingested in the food vacuole of a heterotrophic eukaryote and became endosymbionts themselves. B. Classification and Diversity of Protists- Classification is in a state of flux – we use the phyla in the lab manual with some additions and groupings. - your lab manual leaves out some of the groups that will be covered here- There appear to be eight major lineages of protists within Eukarya - this is very similar to the groupings give in your textbook, but updated based on more recent consilience between molecular and morphological evidence- each lineage contains at least some organisms traditionally placed in kingdom Protista- these lineages are not generally given a formal taxonomic level; instead they are simply unranked taxons- (distinct lineages) often called “supergroups”; however, sometimes some of these are called “superphyla” or even kingdomsThe lineages, in order starting with those that appear to be most distantly related to humans:1. Excavata2. Discicristata3. Alveolata4. Stramenopila5. Rhizaria6. Archaeplastida (includes traditional kingdom Plantae)7. Amoebozoa8. Opisthokonta (includes traditional kingdoms Fungi and Animalia)I. ExcavataA. Features: pronounced “feeding groove”, no functioning mitochondria, although nucleus has some genes derived from mitochondriaB. two major group, Diplomonads and ParabasalidsC. Diplomonads1.“double cell” structure2. have two equal-sized nuclei and multiple flagella3. modified mitochondria called mitosomes4. includes Giardia lamblia, the organism that causes “hiker’s diarrhea” or giardiasis·infects humans and some other animals; found across U.S. in most freshwater·causes nausea, cramps, diarrheaD. Parabasalids1. modified mitochondria called hydrogenosomes that make hydrogen gas2. includes Trichomanas vaginalis, a sexually transmitted parasite in humans· disease called trichomoniasis or “trich” infections· over 7 million new infections each year in the U.S. alone, although many show no symptoms· symptoms are discolored discharges from vagina or penis and painful urination and intercourse· most infected men and about 20% of infected women have no obvious symptomsII. DiscicristataA. Features: mitochondria with distinctive disc-shaped cristaeB. diverse and largest group is the phylum EuglenozoaC. Phylum Euglenozoa (euglenids and kinetoplastids) is the largest group within this clade crystalline or spiral rod in flagellaEuglenids· some photosynthetic (using chlorophylls a and b, like green algae and plants), but some are not· ancestors of photosynthetic forms likely got their chloroplasts from green algae that they ate (“secondary endosymbiosis”) – in other words, this is NOT a synapomorphy that defines a clade· some are facultative heterotrophs, photosynthetic forms that can switch to being heterotrophs if kept in the dark, and switch back to autotrophs if given enough light· characterized by having a helical, flexible protein coat called a pellicle on the outside of cell· only asexual reproduction· important members of many freshwater food chains· example: Euglena. Label the diagram below: Kinetoplastids· single, large mitochondrion that has an organized mass of DNA called a kinetoplast · include trypanosomes – a group that includes some important parasites of humans and domestic animals§ African sleeping sickness: caused by Trypanosomai. carried to new host by biting fly (tsetse fly)ii. Affects cattle and prevents livestock culture in large area of Africa.iii. Why is it difficult for for the human immune system to attack the parasite Trypanosoma ? (Refer Concept 28.3)§ Leishmaniasis (caused by Leishmania)i. carried to new host by biting fly (sand fly) in tropical areasii. causes sores and erosion of skin (4 million people/yr)III. AlveolataA. Features: sac-like “alveoli” that form a continuous layer just under the plasma membraneB. 3 major groups1. Phylum Dinoflagellata (dinoflagellates)2. Phylum Apicomplexa (sporozoans)3. Phylum Ciliophora (ciliates)C. Phylum Dinoflagellata (dinoflagellates)1. unicellular, mostly marine; 2100 species known2. usually have 2 flagella3. most have chlorophylls a and c, so chloroplasts are like those of diatoms, golden algae, and brownalgae, more likely due to secondary endosymbiosis4. have an exoskeleton made up of plates of cellulose5. reproduce mostly by asexual reproduction (sex rare but it does occur)6. important/interesting roles:· zooxanthellae: symbionts (live in mutually beneficial relationship) in other organisms (jellyfish, sea anemones, mollusks, corals)§ zooxanthellae in corals (up to 30,000 cells per cubic mm or coral tissue) do photosynthesis and make carbon products absorbed by coral§ help make coral reefs one of most productive habitats on Earth§ can actually leave the corals and live on their own – probably in response to pollution§ many of the world’s