Chapter 28 The Origins of Eukaryotic Diversity

Introduction to the protists Systematists split protists into many kingdoms In the five kingdom system, anything that wasn’t a prokaryote, plant, animal, or fungus was grouped as a protist. Systematists now divide protists into as many as 20 separate kingdoms.

Protists are the most diverse of all eukaryotes.

General Description of Protists -Very few general characteristics can be cited without many exceptions. -Complex eukaryotes -Most protists are unicellular, but some are colonial or even multicellular. -Various modes of nutrition, mobility, etc.

Nutrition Protists may be autotrophic, heterotrophic, or mixotrophic organisms. Mixotrophic organisms combine photosynthesis and food ingestion. Photosynthetic: algae (plant-like) Ingestive: protozoa (animal-like) Absorptive: fungus-like Motility Most protists are motile, with either flagella or cilia. Some move by gliding or by extensions. Note: Eukaryotic and prokaryotic flagella are not homologous structures.

Life Cycle -A few protists are entirely asexual. -Most reproduce sexually by meiosis and then go on to reproduce asexually. -Whether haploid or diploid dominates varies. -Cysts form at some point during the life cycle of many protists. Cysts are resistant cells that are capable of surviving harsh conditions. -There can be “alternation of generations” in many taxa. Habitat -Most protists are aquatic (but some in soil). -Plankton are organisms that drift or swim near the surface of the water. Phytoplankton are responsible for half of the world’s photosynthesis and O 2 production.

The life cycle of Chlamydomonas

Origin and early diversification of eukaryotes Endomembranes contributed to larger, more complex cells Endomembranes evolved from in-foldings of prokaryotic membranes. Endomembranes allowed for compartmentalization of cellular functions. This contributed to the evolution of increasing complexity and development of new functions.

Mitochondria and chloroplasts (and maybe other organelles) evolved from endosymbiotic bacteria. Heterotrophic prokaryotes were engulfed and function as mitochondria. Photosynthetic prokaryotes were engulfed and function as chloroplasts. Eukaryotic cell is a chimera of prokaryotic ancestors [The term chimera refers to the mixture of three prokaryotes]. a. Original contributes genome b. One becomes mitochondrion c. One becomes chloroplast

Photosynthetic protists have evolved in several clades that also have heterotrophic members. Different episodes of secondary endosymbiosis account for the diversity of protists with plastids. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig

All three domains seem to have genomes that are chimeric mixes of DNA that was transferred across the boundaries of the domains. This has lead some researchers to suggest replacing the classical tree with a web-like phylogeny Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 28.7

A “wave” of diversity followed the origin of eukaryotes.

Protistan diversity: Diplomonadida and Parabasala -Lack mitochondria (probably lost them, rather than never acquired them) Giardia lamblia- example of Diplomonad -Humans ingest cysts by drinking feces-contaminated water. -Parasite absorbs body fluids from host. Trichomonas vaginalis- example of Parabasalid -Parasite of the vagina.

Euglenozoa Characterized by one or two flagella and paramylon which is a glucose polymer. Example: Euglena. Most members of this group are photosynthetic (autotrophs). However,… Kinetoplastids (e.g., Trypanosoma) cause sleeping sickness.

Alveolata Characterized by small cavities under the cell surface (alveola). 3 sub-groups: dinoflagellates,, apicomplexans, ciliates.

Dinoflagellate (phytoplankton) blooms cause “red tide” and produce toxins. Example: - Pfisteria acts as a carnivore: kills fish, feeds on flesh. -Others form the basis of many food chains in the oceans and function as photosynthetic plankton. -Others are bioluminescent and produce light when disturbed to attract fish that eat predators that eat the Dinoflagellates.

Red Tide: A bloom of dinoflagellates

Alveolata- Apicomplexa Apicomplexa are animal parasites with complex life cycles involving more than one host. - e.g., Plasmodium causes malaria.

Alveolata- Ciliophora -Ciliophora use cilia for movement. - e.g., Stentor and paramecium. -These ciliates have one macronucleus and several micronuclei.

Stramenopila Diverse group of heterotrophs and phototrophs (algae) - Usually have “hairy” flagella Four major taxa are within the stramenopila: Oomycota (water molds, but not fungi) Diatoms Golden algae Brown algae Diatoms, Golden algae, & Brown algae also known as Heterokont algae. They are photosynthetic and contain endosymbiotic plastids (chloroplasts).

Water mold: Oogonium

Diatom

An example of diatom diversity.

More diatoms.

A “golden algal species.

Brown algae

Algal life cycles: Alternation of generations Both meiotic/sexual and mitotic/asexual stages have multi- cellular forms. These forms can be very different (heteromorphic) or similar (isomorphic) in appearance. E.g., plants vs. Clamydomonas

Rhodophyta (red algae) -No flagella -Red non-chlorophyll pigments similar to those in cyanobacteria.

Absorption spectra for different algal pigments

Chlorophyta (green algae) Characterized by green chloroplasts, similar to those found in plants. Exist as unicellular (Chlamydomonas), colonial (Volvox), or multi-cellular (Caulerpa) organisms. These are the forerunners of early plants. Multi-cellular chlorophyta (Chara-like species) evolved to become the higher plants.

Chara- very closely related to first land plants

Some protists use pseudopodia for movement and feeding. The examples that follow are of uncertain phylogeny. Pseudopodia are cellular extensions that may bulge from almost anywhere on the cell. Typically heterotrophs. Best known examples are amoebas. 3 main types: Rhizopoda (amoeboids), Actinopoda (“ray foots”, e.g., Heliozoans), Foraminifera.