Lecture 9:
 Evidence for Evolution
 and Plant Adaptations
•   Evidence for evolution in living organisms:
•   1. Comparative anatomy
•   2. Protective coloration
•   3. Developmental biology
•   4. Biogeography
•   5. DNA
•   Evidence from extinct organisms: Fossils
•   Adaptations
•   Coevolution
Evidence in support of evolution
• Evidence of evolution can be found in
  extant organisms (living organisms):
• 1. Comparative anatomy
• 2. Mimicry and protective coloration
• 3. Developmental biology
• 4. Biogeography
• 5. Biochemistry and Molecular Biology
         1. Comparative Anatomy
• Homologous organs: organs similar in form in different
  organisms due to a common evolutionary origin.
• Share same common origin, but may have different
• For example: same bone structure found in a human arm,
  bat wing, dolphin flipper, bird wing…

• Lettuce leaves, vine tendrils, cactus spines – have
  different functions, but same origin (leaf)
Homologous structures in plant
• Analogous structures/organs: organs that
  have similar look and/or functions in different
  organisms, but do not share a common
  evolutionary origin.
• For example:
• Wings of insects vs. wings of birds
• In some plants, stems may look and function
  like leaves… but they have different origins!
               Vestigial organs
• Vestigial organs: organs or parts of organs that
  are non-functional and degenerate
• An organ loses its function, no selective
  advantage to have it, but no selective pressure to
  get rid of it… For example:
• Wisdom teeth, Appendix
• Vestigial leg bones in snakes,
Vestigial Pelvic Bones of Whale
Vestigial Hind Limb Bud of Python
  2. Mimicry and protective coloration
• Mimicry: a harmless species may resemble a
  dangerous species.
• Ex. Some moths resemble wasps
• Coral snake: venomous vs. impostor
• “Red on black, you’re ok Jack.. Red on yellow,
   you’re a dead fellow”
 • Monarch butterfly is toxic, Viceroy is not,
 But Viceroy mimics the Monarch
          Protective coloration
• Coloration that allows an organism to blend
  with environment
• Moths in bark in polluted England
      3. Developmental Biology
• Early embryos of different mammal species look
  very much alike – they share common features
  (gills, tail, etc.).

• Why??? Developmental plan coded for in
  DNA… if organisms have common ancestor…
  have similar genes for early development!
              4. Biogeography
• Unequal distribution of organisms on earth
• Kangaroos in Australia;

• Saguaro Cacti in southwestern
U.S. deserts

• Each species originated only once, in one
place – point of origin…
• Species spread out until they encounter a barrier
(physical, environmental, ecological)
      5. Biochemistry & Molecular
•   Our genes provide an ‘evolutionary record’
•   If we evolved from a common ancestor:
•   We should have same genetic molecule (DNA)
•   We should use the DNA in the same way (dogma)
•   Portions of our DNA should be the same (they’re)
•   Closely related organisms share large portions of
    DNA sequence…
•   Fossils – any trace left by a previous organism
•   Rocks, ice, amber, bogs, tar, etc.
•   Most are preserved in sedimentary rocks
•   Oldest rocks (fossils) have simplest life forms
•   Most recent rocks – have more complex life forms
• Adaptation: A process by which genetic changes
• ADAPTATIONS are traits that promote the
  survival and reproductive success of an organism
  in a particular environment.
• Specific anatomical, physiological or biochemical
  structures/mechanisms that arise during
  evolution, as a response to specific environmental
• Adaptations may originate as mutations in one
  individual organism.
• Adaptations are universal: life occurs
  everywhere on earth…
• Organisms adapt to a specific niche (place in the
• Without adaptations,
  species can become
     Examples of plant adaptations
• Protection: Plants try to avoid predation from
• For example: desert plants with thorns;
• fruits distasteful when not ripe.
• Coloration : Different flower colors attract
  different pollinators.
      Morphological adaptations
• For example: Strawberries grow underground
  stems (stolons) that break so that a new plant
  grows asexually.
• Also, some leaves of desert plants are hairy, to
  reduce water loss, leaves in tropics are smooth
            Plant adaptations
• Leaves: Adapted to many functions in
  different plants
• Coevolution: the long term evolutionary
  adjustment of one group of organisms to
• Coevolution is a reciprocal process in which
  characteristics of one organism evolve in
  response to specific characteristics of
   Ways in which two organisms
           can interact
• Three ways of interaction:
• Parasitism: interaction benefits one organism,
  but is detrimental to the other (pathogens,
  parasites, etc.)                       + -
• Commensualism: benefits one, but neutral to
  the other                              + 0
• Mutualism or symbiosis: both organisms
  benefit                                + +
• Interaction that benefits one organisms, but
  negatively affects another
• Example: Mistletoes, dodder, broomrape
• Interaction benefits one organism, and neutral to
  the other. Examples:
• Epiphytes – plants that grow on top of another
  plant for support and position.
• Orchids, bromeliads, “Spanish moss”
          Mutualism or symbiosis
•   Both organisms benefit (“win-win” situation)
•   Examples:
•   Lichens: Fungus and algae
•   Coral and algae
•   Bacteria and fungi living in roots
•   Flowers and their pollinators
•   Plants and insects
• Mutual evolutionary influence between two
  species (the evolution of two species totally
  dependent on each other). Each of the species
  involved exerts selective pressure on the other, so
  they evolve together.
• For example: Moth and Yucca plant
• Yucca flowers are a certain shape so only that tiny moth
  can pollinate them. The moths lay their eggs in the yucca
  flowers and the larvae (caterpillars) live in the developing
  ovary and eat yucca seeds.
   Plant-Microorganism symbiosis
• Nitrogen-fixing bacteria and legume plants
  – Bacteria receives sugars (food)
  – Plant receives Nitrogen for nutrient

• Mycorrhizae:
  fungal growth in plant roots
  –Fungus receives sugars (food)
  –Plant receives phosphate and water
 Examples of co-evolution: symbiosis
• There’s ANTS in PLANTS!
• Acacia trees and ants –
Pollination: coevolution of plants
           and insects
• Flowers & insects/birds
  coevolution for pollination.

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