UNIT II – PLANT DIVERSITY

1. UNIT II – PLANT DIVERSITY Lecture 8: Plant Systematics and Darwinian Evolution

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

3. 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…

4. 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”

5. 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

6. 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

7. 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)

8. 5 KINGDOMS • Living organisms are classified in five kingdoms: • Animalia: animals • Plantae: plants • Fungi: fungi • Protista: algae • Monera: bacteria

9. 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.

10. Species Some members of same species look very different… Same species, are capable of interbreeding, but Morphologically look very different.

11. All these are same species! Examples in plants: species of oaks and sycamores; Broccoli, kale, cabbage, califlower: members same species! Brassica olearea

12. 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

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

14. 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?”

15. 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…

16. 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

17. 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)

18. 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.

19. 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!

20. 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.

21. 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!)

22. Controversy… • The Origin of Species… caused great arguments between scientists and philosophers – both noting the theories failures and strengths. • Huxley’s 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."

23. Darwin’s 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!

24. 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

25. Natural Selection • 1. Variation: Member within a species exhibit individual differences – these differences must be inheritable • Natural selection won’t work in a population of clones! Remember that a key to variation is sexual reproduction.

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

27. Natural Selection • 3. Competition: Individuals compete for the same, limited natural resources. • Darwin called it: “Struggle for existence”

28. 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.

29. 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..

30. 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

31. 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

32. Artificial Selection • Selective breeding as practiced by humans on domesticated plants and animals…. • For example: Dogs

33. Plant artificial selection Teosinte vs. modern corn Tomato

34. 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.

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

36. 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…