6/17/25 Flashcards

Ecology

Messy Phylogeny

• The phylogeny appears messy, but color schemes and lineage traces reveal phylogenetic signals.
• There are three major groups with horizontal transfers between them.

Horizontal Transfer and Endosymbiosis

• Horizontal transfer is associated with endosymbiosis.
• Mitochondria were acquired first, followed by chloroplasts.
• Photosynthetic bacteria were taken up to form chloroplasts.

Key Points of Endosymbiosis

• Mitochondria and chloroplasts are key endosymbiotic features.
• Chloroplasts are more complex than mitochondria.
• Eukaryotes with mitochondria typically have two membranes (inner and outer).
• Chloroplasts have varying numbers of membranes across species.
• Multiple rounds of endosymbiosis occurred.

Chloroplasts and Photosynthetic Pigments

• Distantly related clades have chloroplasts.
• Clades differ in photosynthetic pigments.
• Different pigments mean different bacteria were taken up.
• Some chloroplasts have more than two membranes.
• Red algae, green algae, and land plants typically have two membranes.

Primary and Secondary Endosymbiosis

• Multiple rounds of endosymbiosis start with primary, then secondary, and sometimes tertiary.
• Primary endosymbiosis involves a non-photosynthetic eukaryotic cell engulfing a cyanobacterium.
• The cyanobacterium has two membranes.
• The eukaryotic cell membrane contributes a third membrane.
• One membrane is typically degraded, resulting in two membranes.

Globophytes and Peptidoglycan Remnants

• The earliest branching lineage after the first endosymbiotic event is called globophytes.
• Globophytes have remnants of the cyanobacterium cell wall.
• Peptidoglycan remnants suggest the evolutionary story.

Eukaryotes with Primary Endosymbiosis

• Red algae, green algae, and land plants are a result of primary endosymbiosis.
• Other photosynthetic eukaryotes, including some protists, have undergone secondary endosymbiosis.
• Some lineages have gone through tertiary endosymbiosis.

Secondary Endosymbiosis

• Secondary endosymbiosis involves a eukaryotic cell engulfing another photosynthetic eukaryotic cell.
• Multiple membranes provide evidence of additional endosymbiosis.
• Usually, three membranes are seen, but sometimes four.
• The engulfed cell's nucleus is degraded, but remnants can be seen in early branching lineages.

Contact Question: Eukaryotic Features and Endosymbiosis

• Question: Which feature of eukaryotes has evolved that makes endosymbiosis possible?
• The correct answer is the flexible cell membrane.
• A flexible cell membrane allows the cell to move and engulf other cells.
• Bacteria or archaea with thicker cell walls cannot perform endosymbiosis.

Super Kingdoms of Eukaryotes

• There are eight major lineages recognized:
  • Alveolates
  • Straminopiles
  • Rizarians
  • Excavates
  • Plants
  • Amoebozoans
  • Fungi
  • Animals.
• These diversified during the Precambrian period (1.5 billion to 600 million years ago).
• The origin of eukaryotes is thought to be around 1.5 billion years ago, compared to bacteria at 3.5 billion years ago.

Multicellularity

• Multicellularity is a key innovation in eukaryotic diversity.
• It allowed animals to become larger and more complex.
• Multicellularity enables cell differentiation and compartmentalization of functions.
• Plants, animals, fungi, and brown algae are examples of multicellular eukaryotes.
• Multicellularity evolved multiple times independently.

Artificial Selection Experiments

• Scientists conducted artificial selection experiments to examine multicellularity.
• They used unicellular organisms and selected for traits that favor multicellularity.
• This led to convergent evolution of multicellular forms.
• Unicellular organisms were transformed into multicellular organisms in months.
• This suggests that multicellularity is relatively easy to achieve evolutionarily.

Choanoflagellates

• The closest relative to all animals is the choanoflagellate.
• Choanocytes, found in sponges, resemble choanoflagellates.
• Sponges are thought to be the earliest branching group of animals.
• Choanoflagellates can group together to increase the efficiency of acquiring food.

Alveolates

• Alveolates have air sacs (alveoli) under their cell membranes.
• They are unicellular and mostly photosynthetic.
• Dinoflagellates are a prominent example.
• Dinoflagellates are abundant and contribute to organic debris on the ocean floor.
• Some dinoflagellates are endosymbionts of coral; these are referred to as zooxanthellae.
• Corals use dinoflagellates for carbohydrate production.

Straminopiles

• Straminopiles have rows of tubular hairs on their flagella.
• They have two flagella, but some species have reduced or lost them.
• Examples include unicellular diatoms and multicellular brown algae.
• They have carotenoids, giving them a yellowish-brown color.

Diatoms

• Diatoms have diverse morphologies.
• They deposit silica within structures resembling cell walls, creating different shapes.
• Flagella are reduced or absent, except in male gametes.
• They are photosynthetic and have carotenoid-type pigments.
• Diatomaceous earth contains diatom shells with sharp, jagged edges, used to prevent pest invasions.

Brown Algae

• Brown algae are multicellular straminopiles.
• They have carotenoids, giving them a brownish color.

Rizarians

• Rizarians use pseudopods to move and feed.
• Pseudopods are extensions of the cytoplasm with cytoskeletal elements.
• Examples include Foraminifera (forminifrons) and Radiolarians.

Foraminifera

• Foraminifera have shells made of calcium carbonate.
• They create sedimentary deposits that compress into limestone.
• Limestone often contains fossils.

Radiolarians

• Radiolarians exhibit radial symmetry.
• They secrete a glassy endoskeleton.

Amoebozoans

• Amoebozoans are characterized by an amoeboid body form.
• They have lobe-shaped pseudopods.
• Slime molds are a good example.

Cellular Slime Molds

• Cellular slime molds are single-celled but can form aggregations.
• In a vegetative state, they are single-celled with a haploid nucleus, reproducing through mitosis and fission.
• Under unfavorable conditions, they aggregate to form a slug called a pseudoplasmoidium.
• The slug develops into a fruiting structure, releasing spores produced by mitosis.
• Spores germinate and develop into single cells, continuing the cycle.

Opisthokonts

• Opisthokonts include animals, fungi, and their closest relatives, the choanoflagellates.
• They share a common ancestor.
• If flagella are present, they are on the back (posterior) of the cell.
• Animals and their closest relatives are more closely related to fungi than either are to plants.

Application Question: Coralville Reservoir Fossils

• Question: What major super kingdom of eukaryotes is responsible for the production of limestone in which coral fossils are embedded?
• Rizarians (specifically, Foraminifera) are responsible for much of the limestone production due to their calcium carbonate shells.

Fungi

• Fungi digest food outside their bodies (heterotrophy).
• They are absorptive heterotrophs: cells secrete digestive enzymes, and hyphae absorb nutrients.
• Saprobes absorb nutrients from dead organic matter.
• Most are multicellular, but some (like yeast) are unicellular.

Fungi Structure

• The mushroom is just the reproductive structure; the main body is the mycelium.
• Hyphae are tubular branches that extend immense distances underground.
• The body of the fungus is made up of mycelium.
• Surface area to volume ratio is important for nutrient exchange.
• Hyphae can be modified to serve as anchors.
• Mushrooms contain spore-producing structures.
• Spores are dispersed by wind or water.
• Hyphae can lack septa (coenocytic) or have septa with pores.

Dry Rot

• Fungal infections can encroach within the xylem of plants, causing dry rot.

Land Plants: Origin and Evolution

• The ancestor of plants was unicellular and had chloroplasts (primary endosymbiosis).
• Chloroplasts are a synapomorphy (shared derived trait).
• The first groups to branch off after the primary endosymbiotic event were glaukophytes, red algae, and green algae.
• Green algae are paraphyletic.

Challenges for Land Plants

• Terrestrial environments pose challenges:
  • Desiccation (drying up)
  • Gravity (lack of structural support)
  • Gamete dispersion

Synapomorphies and Adaptations of Land Plants

• A key synapomorphy is the protected embryo.
• Thick walls. Some of the adaptations include:
  • Waxy cuticle to prevent water loss
  • Closable stomata to regulate gas exchange and water loss
  • Gametangia (organs forming gametes) are protected
  • Spores with thick walls for protection
  • Beneficial associations with fungi (mycorrhizae) to promote nutrient uptake

Plant Evolution

• The early lineages are typically algae.
• First land plans paved the way for eventual colonization of animals.
• The earlier lineages of plants were nonvascular and needed to live close to water sources.
• The evolution of tracheids, vascular cells, which are vascular cells which allow for a vascular system to transport water, that gave rigid support to plants to aid in water transport.
• Megaphylls. The evolution of seeds allowed gymnosperms and angiosperms to the development of vascular transport systems.

Alternation of Generations

• Land plants alternate between a diploid (2n) sporophyte stage and a haploid (n) gametophyte stage.
• Gametes are produced by mitosis, and spores are produced by meiosis.
• The sporophyte produces spores, and the gametophyte produces gametes.
• Early land plants (bryophytes) had a large gametophyte body.
• Most plants we see today have a reduced gametophyte stage and a prominent sporophyte stage.

Ferns: Alternation of Generations Exmaple

• Sporangium is located on the underside of the leaf fronds and release haploid spores into the envirnoment upon bursting.
• The tip of the sporangium ruptures, releasing haploid spores into the environment.
• Haploid spores transform into a gametophyte as they find and grow to be a structure near argonium structures.
• The female archegonium produces egg. If fertilization occurs, a diploid zygote is produced.
• The diploid zygote then starts growing out until it forms this new sporophyte. Which means what follows fertilization is a sporophyte which grows out of the gametophyte.