Plant Evolution and Classification

Exam Information

  • The final exam is worth 80 points.
  • 20 points will be from new material (evolution and plant ecology).
  • 60 points will be comprehensive.

Evolution and Green Algae

  • The lecture will cover evolution and highlight topics related to it.
  • Green algae are the closest living relatives to land plants.

Introduction to Evolution

  • Microevolution: Focuses on a single species.
  • Macroevolution: Focuses on the relationships between species over larger periods of time.

Species Concept

  • A species is a group of organisms that can reproduce and have fertile offspring.
  • This definition isn't perfect; there are exceptions (e.g., ligers, tigons).
  • Ligers and tigons are fertile offspring of lions and tigers (only in captivity).

Classification of Species

  • Species can be classified into different groups.
  • Focus on features of green algae.

Mitosis

  • Mitosis produces two identical daughter cells.
  • Human cells have 46 chromosomes.
  • Purpose of mitosis: growth, repair, asexual reproduction.

Meiosis

  • Meiosis is a special type of cell division that cuts the chromosome number in half.
  • It is used to create sex cells (gametes): sperm and egg.
  • Gametes have half the chromosome number (23 in humans).
  • Two rounds of cell division in meiosis.
  • Sperm and eggs are not genetically identical; they contain a mix of genes.
  • Timing of meiosis varies; in males, it starts at puberty; in females, it starts before birth.

Haploid vs. Diploid

  • Haploid: A cell with one set of chromosomes (23 in human gametes).
  • Diploid: A cell with two sets of chromosomes (46 in human body cells).
  • Gametes are the only haploid cells in humans.
  • The zygote (fertilized egg) is the first diploid cell of a new individual.
  • Zygote undergoes mitosis to develop into a baby and then an adult.

Haploid Cells and Mitosis

  • In mammals, haploid cells (gametes) do not undergo mitosis.
  • In the plant kingdom, haploid cells can undergo mitosis.

Evolution Definition

  • Evolution is a gradual change in species over generations.
  • Variations suited for a particular environment tend to be passed on.
  • Evolution does not have a directionality or end goal.
  • Environments change, influencing which variations are favored.

Cladogram

  • A cladogram is an evolutionary family tree.
  • It shows the relationships between species and their shared common ancestors.
  • The y-axis represents time.
  • Branches that don't reach the top represent extinction.
  • 99% of all species that ever existed are extinct.
  • Dotted lines on a cladogram indicate uncertainty.

Mutation

  • Mutation is the raw material of evolution.
  • New variations arise, and if favored by the environment, they spread and are passed on.

Selective Breeding

  • Selective (artificial) breeding involves humans deciding who will mate with whom to get desired features.
  • Darwin used artificial selection as an analogy for natural selection.
  • Natural selection is when the environment selects who survives and reproduces.

Examples of Artificial Selection

  • Broccoli, cauliflower, cabbage, brussels sprouts, kohlrabi, and kale are all bred from the same wild species.

Agriculture and Evolution

  • Agriculture can drive evolution, e.g., pesticide use.
  • Rotating pesticides is necessary to prevent pests from developing resistance.

Evidence for Evolution

  1. Sequencing of proteins and DNA (most important tool).
  2. Fossil record.
  3. Geographical distribution of organisms.
  4. Comparative anatomy.
  5. Experiments.

Darwin and Natural Selection

  • Darwin's book, "On the Origin of Species," discusses natural selection.
  • All species have the ability to overproduce offspring.
  • Competition for resources leads to a struggle for existence.
  • Advantageous variations are heritable and become more common over generations.

Peppered Moths Experiment

  • Classic example of experimental evidence for evolution.
  • Before the industrial revolution, light-colored peppered moths were more common due to lichens on tree bark.
  • Lichens are sensitive to pollution and died during the industrial revolution.
  • The bark became darker, and dark-colored peppered moths became more common.

Macroevolution

  • Macroevolution involves the origin of new species.
  • This typically involves some sort of reproductive barrier.
  • Polar bears and grizzly bears can reproduce (growler bears or pizzly bears) due to climate change, blurring species lines.

Isolation and Speciation

  • Species need to be isolated to diverge and become new species.
  • Geographical isolation, mechanical isolation, and other mechanisms can prevent gene flow.

Hybrids and Polyploidy

  • Plants have plasticity and can tolerate changes in chromosome number.
  • Hybrids are offspring produced by two different parents.
  • Polyploidy: having more than two sets of chromosomes (common in plants).
  • Examples: modern wheat (hexaploid), watermelon (octoploid).
  • Polyploidy can result from meiosis failing to cut the chromosome number in half.

Species Concept Revisited

  • The standard definition of species (reproducing and having fertile offspring) is not perfect.

  • Different species concepts:

    1. Morphological species (based on shape and appearance).
    2. Interbreeding species (can reproduce and have fertile offspring).
    3. Ecological species (live in a particular environment).
    4. Biogenetic species (based on genetic similarity).

Taxonomy vs. Systematics

  • Taxonomy is identifying, naming, and classifying organisms.
  • Systematics uses an evolutionary lens to understand relationships between organisms.

Cladistics

  • Cladistics is a method used to create evolutionary family trees (cladograms).

Linnaeus and Binomial System

  • Carolus Linnaeus developed the binomial system of naming species (genus and species).

  • The grouping system:

    • Kingdom
    • Phylum
    • Class
    • Order
    • Family
    • Genus
    • Species

  • Mnemonic: Kings play chess on fat green sofas.

Taxonomy and Evolutionary Relationships

  • Cladograms are built by applying Occam's razor: the simplest solution is usually the right one.
  • The best cladogram has the fewest major evolutionary changes.

Cladogram for Land Plants

  1. Mosses (no vascular tissue).
  2. Ferns (vascular tissue).
  3. Conifers (seeds).
  4. Flowering Plants (flowers).

Comparative Anatomy

  • Homology: similarities that reflect common ancestry.
  • Analogy (convergent evolution): similarities based on adapting to similar environments.
  • Example: cactus (North America) and euphorb (Madagascar).

Protists

  • Protists are a diverse group of simple eukaryotes.
  • They can be unicellular or multicellular.
  • Some protists resemble plants, animals, or fungi in their nutrition.

Green Algae

  • Green algae are the closest living relatives to land plants.
  • They have chlorophyll a and b like land plants.
  • They store food as starch like land plants.
  • Most can reproduce sexually and asexually.

Alternation of Generations

  • Land plants have alternation of generations: a multicellular diploid part and a multicellular haploid part of their life cycle.

  • A haploid cell can undergo mitosis in plants.

  • New terminology:

    • Sporophyte: diploid multicellular organism that produces spores through meiosis.
    • Spore: haploid cell that can undergo mitosis.
    • Gametophyte: haploid multicellular organism that produces gametes through mitosis.

  • Gametophytes produce gametes through mitosis; fertilization leads to a zygote, which grows into a sporophyte.