The Origin of Eukaryotes

DOMAIN Eukaryota (Eukaryotes)

Single-celled eukaryotes are more complex than prokaryotes Most Eukaryotes are Single Celled Organisms. Mostly called protists Eukaryotic fossils date back 2.1 billion years and "chemical signatures" of eukaryotes date back 2.7 billion years For about 2 billion years, eukaryotes consisted of mostly microscopic organisms known by the informal name "protists."

SPECIAL TOPICS: Algal Blooms

Sometimes populations of algae grows in enormous masses called blooms Algal Blooms, characterized by explosive population growth; cause "red tides" in coastal waters. The blooms can be brown, red or pink, orange. Toxins produced by some red-tide organisms have produced massive invertebrate and fish kills. Blooms deplete the water of nutrients, oxygen (when the bloom decays) and can release toxins into the water

Lynn Margulis (1938-2011)

Lynn Margulis was an American evolutionary biologist, and was the primary modern proponent for the significance of symbiosis in evolution. "spokesperson for the microcosm" "On the Origin of Mitosing Cells" (1966) - rejected by 15 journals before its publishing in the Journal of Theoretical Biology "Symbiosis in Cell Evolution," followed in 1981, and though it challenged the presumptions of many prominent scientists, it has since become accepted evolutionary doctrine. "Lynn Margulis's name is as synonymous with symbiosis as Charles Darwin's is with evolution."

Evolution of Protists

"Protista" means "the very first" which is appropriate because they were the first eukaryotic organism on Earth It is hypothesized that the first Protists evolved from a symbiosis of several prokaryotic cells 1. Karyogenic Ho: In this theory, the nucleus and it's enclosing membrane were gradually acquired through some (unspecified) segregating process. Your book seems to subscribe to Model 1 2.Competing Endokaryotic hypothesis: posits that the nucleus like other organelles enclosed in other double membranes (like cholorplasts and mitochondrion), was gained by a symbiotic relationship. This is the most parsimonious explanation for the double membrane formation, although the symbiont in this case took control. Second Ho: based on analysis of the 70 kDa heat shock protein (HSP70). 2 paralogous HSP70 genes are found in the euks - nad other evidence. Briefly, one in the cytoplasm and one in the endoplasmic reticulum that are very similar to one in the gram-negative bacteria (but not the gram-positive eubacteria, halobacteria and menthanogens)

Changing Kingdom of Protists

"Protists" Discovered by Antoni Van Leeuwenhoek in pond water Once considered 1 kingdom, now known to be paraphyletic •Some closer to other eukaryotic kingdoms than other protists) •So... Kingdom Protista dissolved and now used as a general term Each lineage is separate kingdom

Antoni van Leeuwenhoek

(1632-1723) - first to observe bacteria and protozoa "No more pleasant sight has met my eye than this, of so many thousands of living creatures in one small drop of water" Later became known as the "Father of Microbiology

Diversity of plastids produced by 2o endosymbiosis

(1o endosymbiosis). That ancestor diversified into red and green alga, some of which were subsequently engulfed by other euks (2o endosymbiosis)

Prorocentrum micans King Harbor, Redondo Beach (May 2006)

(unknown if a toxin was produced during this bloom)

General Features of Microbial Eukaryotes

*Size Single-celled (mostly); size range ~ <2 μm to 1 mm (most between 10-20 μm) *Diversity and Classification Tens of thousands of described species. Incredibly diverse! *Nutrition (3 modes) 1. Photoautotrophs - contain chloroplasts ("plantlike") 2. Heterotrophs - absorb organic molecules or ingest food particles (bacteria, cyanobacteria, algae, other protozoa digestion in vacuoles or absorption for pathogens) 3. Mixotrophs - combine both photosynthesis and heterotrophic nutrition

Animal-like Protists (Heterotrophs)

Can't make their own food. Must eat prey or absorb needed carbon and nutrients Many are capable of locomotion (moving) Ex: flagellates, cilliates, and sarcodines

Darwin vs Margulis

Darwin did not consider the significance of symbiotic associations in his theory of evolution. Structures like organelles represent such a drastic change from the prokaryote cell that a more complex explanation is required... Enter Lynn Margulis and the radical concept of endosymbiosis for acquisition of the mitochondrion and the plasmids

Diatom Pseudo-nitzschia Harmful Algal bloom

Domoic Acid Amnesic Shellfish Poisoning > 1,500 mammal strandings in 2003 also kills fish eating birds in the thousands

Endosymbiosis

Endosymbiosis unites different cells into one organism. glowing thing symbiosis = metabolic cooperation

Mixotroph posterchild

Euglena, a single celled mixotrophic protist. Use chloroplasts for photosynthesis if light is available or live as a heterotroph by absorbing organic nutrients or feeding on prey from the environment.

Eukaryotes vs Prokaryotes

Eukaryotes: - cell membrane - nucleus - DNA compacted around proteins - more DNA (more chromosomes) - ribosomes - organelles (mitochondria, plastids) Prokaryotes: - cell membrane - loosely organized DNA - ribosomes

"Serial endosymbiosis"

Explains the origin of nucleated eukaryotic cells by a merging of archaebacterial (archaea) and eubacterial (bacterial) cells. The paradigmatic change is that the driving force behind evolution is not ramification but merging.

Plant-like Protists (Autotrophs)

Protists that contain the green pigment chlorophyll and carry out photosynthesis (autotrophic) Plant-like protists "PHYTOPLANKTON" play a major ecological roles on earth They make up a large part of the phytoplankton in ocean surface waters and undertake half of the photosynthesis on the globe However, they are not classified as plants, they are algae (ex: volvox, euglena, and diatoms)

Endosymbiosis explains the evolution of these structures...

The hypothesis was a direct challenge to the prevailing neo-Darwinist belief that the primary evolutionary mechanism was random mutation.

protist

any eukaryotic organism that is not an animal, plant, or fungus Protista was the name fo the former kingdom that comprised unicellular euks. The Kingdom designation has now been abandoned, but the term protist is still used to refer to euks that are neither plants, animals or fungi. Protists exhibit more structural and functional diversity than any other group if aukaryotes

Classification of protists

appearance, physiology, molecular signature

Dinoflagellate, Dinophysis

cause Diarrhetic Shellfish Poisoning

Chlorarachniophytes

engulfed cell becomes a plastid with a vestigial nucleus (nucleomorph), the sequence of which resembles that of green algae Their plastids have 4 membranes inner membranes from the inner and outer membrane of an ancient cyanobacteria 3rd from engulfed algae's plasma membrane 4th outer membrane from heterotrophic eukaryote's food vacuole.

Biological functions are carried out by

organelles in each individual cell

Endosymbiosis and Eukaryotic Evolution

§Unicellular organisms engulfed other cells that became organelles, resulting in diversity of protists §Earliest got mitochondria from alpha proteobacteria §Later a cyanobacterium, yielding red and green algae §Multiple occurrences of secondary endosymbiosis §Became endosymbionts themselves

Ecology

•0.2-2.0 μm, 2-20µm, 20-200μm •High diversity •Abundant and ubiquitous •Microbial loop •Global biogeochemical cycles •*Distribution - nearly every biotic ecosystem on the planet

Lynn Margulis and evidence for the radical concept of endosymbiosis

•Chloroplasts are not the only organelles with prokaryote-like features •Mitochondria also resemble bacteria... •Endosymbiosis explains this resemblance •"communities of microbes so interdependent they were ... single stable organisms" •adaptation to life within other cells •cooperation vs. competition symbiosis leads abruptly to new species

A review of some important prokaryote adaptations

•Evolution of photosynthesis by 2.7 bya •Increase in atmospheric oxygen alters global environment -> Chloroplasts descend from photosynthetic prokaryotes •Evolution of cellular respiration, or the use of O2 in the process of harvesting energy stored in organic molecules -> Mitochondria descend from aerobic heterotrophic prokaryotes (The accumulation of O2 in the atmosphere led to the biological innovation of aerobic respiration, which harnesses a more powerful metabolic energy source. Organisms that could not adapt well enough to oxygen remained in anaerobic environments. The release of oxygen by cyanobacteria was thus responsible for changes in the earth's atmospheric composition, the rise of aerobic metabolism and, ultimately, the evolution of multicellularity)

Animal-like protists with chloroplasts (Mixotrophs)

•Organisms that combine phototrophic and heterotrophic energy and nutrient acquisition strategies. •Simultaneously function at multiple trophic levels •Can significantly affect food web structure and stability •Many form blooms and exhibit toxin production

Key evidence supporting an endosymbiotic origin of mitochondria and plastids:

•Similarities in inner membrane structures and functions •Division is similar in these organelles and many prokaryotes •Mitochondrial and plasid DNA is relatively short and circular •They transcribe and translate their own DNA •Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes

Endosymbiosis in Eukaryotic Evolution

•The plastid-bearing lineage of protists evolved into red algae and green algae •plastid - One of a family of closely related plant organelles that includes chloroplasts, chromoplasts (make tomatoes red), and amyloplasts, leucoplasts (starch storage) etc. Plastids are double membrane bound organelles involved in the synthesis and storage of food (commonly found within the cells of photosynthetic organisms, like plants). •On several occasions during eukaryotic evolution red and green algae underwent secondary endosymbiosis. In this process, they were ingested to generate a more complex protist.

Next, note the resemblance between the photosynthetic organelles of plants and the structure of cyanobacteria

Hans Ris was a pioneer electron microscopist. along with evolutionary biologist Lynn Margulis, he was one of the first to recognize that blue-green algae were a special type of bacteria. He coined the term genophore for prokaryote DNA to highlight its differences from the eukaryal chromosome.