UNIT II

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UNIT II PLANT DIVERSITY

• Lecture 8 Plant Systematics and Darwinian
  Evolution

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Today Part I

• Plant systematics
• Taxonomic hierarchy
• Concept of species
• Carolus Linnaeus
• Evolution
• Charles Darwin
• Natural Selection
• Rates of evolution gradualism vs. punctuated
  equilibrium

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PLANT SYSTEMATICS

• Common names
• Have evolved over centuries in a multitude of
  languages
• Sometimes used only in a limited geographical
  area
• Problem with common names
• One plant may be known by several names in
  different regions, and the same name may be used
  for several different plants

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Scientific names

• Similar plant species form a group called a genus
  (plural genera)
• Genera are grouped into families
• Families into orders, classes, divisions and
  kingdoms
• Kingdom Division Class Order
  Family Genus Species
• King David Came Over For Great Spaghetti
• King David Conquered Our Fifty Great States

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Species name

• Each species has a single correct scientific name
  in Latin called a binomial (two names) it is
  always italicized or underlined.
• First name is genus name.
• Second name is species name
• Human Homo sapiens
• Cat Felis catus
• Dog Canis familiaris Wolf Canis lupus

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Examples

• Genus of maple trees is Acer
• It has many species including
• Common name Scientific name
• Red maple Acer rubrum
• Sugar maple Acer saccharum
• Black maple Acer nigrum

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Taxonomic hierarchy

• Species that have many characteristics in common
  are grouped into a genus.
• Related genera that share combinations of traits
  are grouped into families.
• Families are grouped into orders.
• Orders into classes
• Classes into divisions (or phyla for animals)
• Related divisions/phyla are grouped into kingdoms
• (e.g. house, street, city, county, state,
  country, continent, planet)

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5 KINGDOMS

• Living organisms are classified in five kingdoms
• Animalia animals
• Plantae plants
• Fungi fungi
• Protista algae
• Monera bacteria

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What is a species?

• Species a set of individuals that are closely
  related by descent from a common ancestor and
  ordinarily can reproduce with each other, but not
  with members of any other species.
• Biological species a group of interbreeding
  populations. Offspring are fertile.

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Species

• Some members of same species look very different

Same species, are capable of interbreeding,
but Morphologically look very different.
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All these are same species!

• Examples in plants species of oaks and
  sycamores
• Broccoli, kale, cabbage, califlower members same
  species! Brassica olearea

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Definition of species

• However, some plants look the same, but due to
  polyploidy (more than the diploid number of
  chromosomes), they cannot interbreed.
• For example Ferns evening primrose

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Carolus Linnaeus

• Swedish scientist Carl von Linne(doctor and
  botanist) born in 1707.
• Called the Father of Systematic Botany
• Established modern system of nomenclature

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Linnaeus

• Carolus Linnaeus used risque language for his
  time
• Classifying plants by their flowers, he compared
  flower parts to human sexuality stamens were
  husbands (many) and the pistil was the wife the
  flower was the bed!
• Many were shocked. Dr. Johann Siegesbeck such
  loathesome harlotry as several males to one
  female would not be permitted by the creator Who
  would have thought that bluebells, lilies and
  onions would be up to such immorality?

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Linnaeus legacy

• His binomial system of nomenclature, in which the
  genus and species names are used.
• He classified 12,000 plants and animals,
  published Systema Naturae in 1753, and many of
  the names he first proposed are still in use
  today

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EVOLUTION

• A genetic change in a population of organisms
  that occurs over time, often adapting to an
  environment or way of life.
• Evolutionary changes must be genetically
  inherited, not acquired.
• Creationism was the main belief all organisms
  were specially created, unchanging

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Evolution of Evolutionary thinking(Pre-Darwinian)

• Jean-Baptiste Lamarck (1744-1829) French
  naturalist, proposed a theory that organisms were
  driven by some inner force toward greater
  complexity. But thought that org. could pass on
  traits to their offspring that they acquired
  during their lives. (Lamarckism, proposed in
  1809)

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Lamarckism

• Lamarckism holds that traits acquired (or
  diminished) during the lifetime of an organism
  can be passed to its offspring.
• Lamarck based his theory on two observations
  thought to be true in his day
• Use it or lose it - Individuals lose
  characteristics they do not require and develop
  those which are useful.
• Inheritance of acquired traits - Individuals
  inherit the acquired traits of their ancestors.

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Lamarckism

• Examples include the stretching by giraffes to
  reach leaves leads to offspring with longer
  necks
• Strengthening of muscles in a blacksmith's arm
  leads to sons with like muscular development.

This theory was later disproved!
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Charles Darwin

• Charles Darwin (1809-1882)
• Born in England, studied medicine,theology
• Takes a 5-year trip around the world as a
  naturalist on the HMS Beagle.
• Observes plant and animal species in Galapagos
  Islands, Australia, NZ, etc.
• Observed Island animals are similar to mainland
  animal species (descended), but they show
  differences due to the conditions on their island.

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On the Origin of Species

• Came home, marries cousin,worked for 16 years
  analyzing his data
• Darwin publishes the most influential text of all
  times On the Origin of Species by Means of
  Natural Selection in November 24, 1859.
• (The entire printing (2500 copies) was sold that
  same day!)

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Controversy

• The Origin of Species caused great arguments
  between scientists and philosophers both noting
  the theories failures and strengths.

• Huxleys famous debate in June 1860, at Oxford.
• Archbishop Samuel Wilberforce ridiculed
  evolutionary theory
• Do you descend from an ape on your
  grandmother's side or your grandfather's side?
• Huxley replied "I would rather be the
  offspring of two apes than be a man and afraid to
  face the truth."

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Darwins revolutionary thoughts

• Darwin thought of organisms not as constant,
  unchanging or specially created beings.
• Could not believe that organisms today appeared
  as they have always appeared
• Darwin changed biological thought forever with
  the concept of Natural Selection!

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Natural Selection

• Has four premises
• 1) Variation Members of a population have
  individual differences that are inheritable
• 2) Overproduction Natural populations
  reproduce geometrically
• 3) Competition Individuals compete for
  limited resources
• 4) Survival to reproduce Only those
  individuals that are better suited to the
  environment survive and reproduce

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Natural Selection

• 1. Variation Member within a species exhibit
  individual differences these differences must
  be inheritable
• Natural selection wont work in a population of
  clones! Remember that a key to variation is
  sexual reproduction.

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Natural Selection

• 2. Overproduction Natural populations increase
  geometrically, producing much more offspring than
  will survive

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Natural Selection

• 3. Competition Individuals compete for the
  same, limited natural resources.
• Darwin called it Struggle for existence

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Natural Selection

• 4. Survival to reproduce Only those
  individuals that are better suited to the
  environment will survive and reproduce (Survival
  of the fittest).
• Fit individuals pass on to a portion of their
  offspring the advantageous characteristics.

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Natural Selection

• Works on the individual phenotype ? which in turn
  changes the population gene pool.
• Time long periods of time must be available in
  order to change to a completely different
  species changes are slow..

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Natural Selection

• Offspring that inherit the advantageous traits
  (favorable genes) are selected for
• Their chances of survival are greater
• May live to reproductive age
• May pass on those desirable attributes to future
  generations

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Natural Selection

• Those that do not inherit these traits
  (unfavorable genes), are not likely to
  survive/reproduce.
• Gradually, the species evolves (changes) as more
  individuals carry these traits.
• Over time, enough changes ? New species

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Artificial Selection

• Selective breeding as practiced by humans on
  domesticated plants and animals.
• For example Dogs

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Plant artificial selection

• Teosinte vs. modern corn

Tomato
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Rates of evolution

• Two interpretations about the pace/speed of
  evolution based on the fossil record
• 1. Gradualism (a traditional view) states that
• Evolution occurs as a slow and steady
  accumulation of changes in organism (Darwinian
  evolution) Not much evidence.

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Rates of evolution

• 2. Punctuated Equilibrium evolution proceeds
  with periods of inactivity, followed by periods
  of very rapid evolution (Gould Eldridge model).

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Punctuated Equilibrium

• Fossil record supports this view
• Long periods of stasis (no change in species)
• Followed by rapid change
• However, fossil record is evidence only of
  Morphology (structure), while evolution
  encompasses morphology, ecology, biochemistry,
  and behavioral changes
• That is, there may be stasis in morphology, while
  there is still active evolutionary changes going
  on