Protist diversity II Level 1 Biological Diversity Jim

Protist diversity II Level 1 Biological Diversity Jim Provan

Phylogeny of eukaryotes

Diplomonads and Parabasala Amitochondriate: Originally believe to have diverged before acquisition of mitochondria Presence of nuclear gene homologues now suggests that mitochondria have been lost Diplomonads have multiple flagella and two separate nucleii Infectious

Euglenozoa Contain flagella Two main groups: Euglenoids: — — Paramylon (glucose polymer) used as a storage molecule Anterior pocket with one or two flagella Kinetoplastids: — — Contain a single large mitochondrion and a unique organelle (kinetoplast) Symbiotic / pathogenic

Alveolata Encompasses: Photosynthetic flagellates (dinoflagellates) Parasites (apicomplexans) Group that move by cilia (ciliates) Have small, membranebound cavities under cell surfaces (alveoli)

Dinoflagellates Components of phytoplankton – may cause red tides Most are unicellular, some are colonial Some are photosynthetic symbionts, some are nonphotosynthetic parasites Plastids are brownish and contain chlorophylls a and c and a mix of carotenoids (including peridinin) Food stored as starch Chromosomes lack histones and are always condensed Have no mitotic stages

Apicomplexans All parasites of animals: Infectious cells called sporozites Apex of sporozites has organelles for penetrating host cells Life cycles have both sexual and asexual reproduction, often requiring more than one host Several species of Plasmodium cause malaria: Anopheles mosquitoes serve as intermediate host New, resistant forms of Plasmodium are appearing Little success in developing a vaccine: — Plasmodium spends most of its life cycle in blood or liver cells — Has the ability to alter its surface antigens

Life history of Plasmodium

Ciliates Species use cilia to move and feed Most solitary cells in fresh water Cilia are short and beat in synchrony Submembraneous system coordinates beating Some species move on leg-like cirri Others have rows of tightly packed cilia which act as locomoter membranelles Among most complex of cells

Two types of ciliate nuclei Macronucleus: Is large and has over 50 copies of the genome Genes packaged into units, each with hundreds of copies of just a few genes Controls everyday functions by synthesising RNA Necessary for asexual reproduction – macronucleus elongates and splits instead of undergoing mitosis Micronucleus: Small and present in 1 -80 copies Does not function in growth, maintenance or asexual reproduction Functions in the sexual process of conjugation

Conjugation and genetic recombination in Paramecium

Stramenopiles Includes several heterotrophic groups as well as a variety of photosynthetic protists (algae): Oomycota (water moulds etc. ): — — Heterotrophic Ostensibly similar to fungi but have analogous hyphae, cellulose cell walls (as opposed to chitin), prevalent diploid stage and biflagellated cells (true fungi have no flagellated stages) Heterokont algae: — — — Diatoms have hydrated silica shells and generally reproduce asexually Chrysophytes (golden algae) have carotene and xanthophyll accessory pigments and are mostly unicellular Phaeophytes (brown algae) are all multicellular and mostly marine

Seaweeds Have differentiated tissues and organs similar to plants: Analogous: — — — Holdfast root Stipe stem Blade leaf Commercially important: Food (Laminaria and Porphyra) Agar Thickeners Lubricants

Alternation of generations in algae

Rhodophyta (red algae) Have no flagellated stages Accessory pigment: phycoerythrin Not always red: dependent on depth Mostly multicellular Diverse life cycles but alternation of generations is common

Chlorophyta (green algae) Two main groups: Chlorophyceae Charophyceae Share a common ancestor with green plants Unicellular, colonial or multicellular Nearly all reproduce sexually by way of biflagellated gametes

Life cycle of Chlamydomonas

Rhizopods (amoebas) Simplest unicellular protists No flagellated stages Pseudopodia used in feeding and movement All reproduction is asexual Inhabit freshwater, marine and soil habitats Most are free living, although some are parasitic

Actinopods Possess axopodia, slender form of pseudopodia Increase surface area which helps floating and feeding Some prey may stick to axopodia and be phagocytosed Two main groups: Heliozoans (primarily freshwater) Radiolarians (primarily marine)

Plasmodial slime moulds (Myxomycota)

Cellular slime moulds (Acrasiomycota)