PB295E, Topics in Plant Evolution, emphasizes evolution and evolutionary mechanisms in
Angiosperms. Because Paleobotany and Systematics courses are already offered at NCSU,
PB295E emphasizes areas not usually contained in those two approaches to the study of
Evolution in plants.
The course will involve 2 class meetings per week, reading assignments and two exams.
Pertinent videos will be shown during class meetings.
Assignments will include readings from a Course Pac of selected articles and the book, Plant
Variation and Evolution by D. Briggs and S. M. Walters, Cambridge Univ. Press.
Detail of TOPICS included in PB295E, 'Topics in Plant Evolution':
(1) What is Evolution?
Darwin's Theory of Natural Selection
Darwin's dilemma
Modern synthesis
Evidences of evolution (a) Artificial Selective Breeding (b) Comparative Anatomy
(c) Fossil Evidence (d) Molecular (DNA) and (e) Developmental Biology
Tempos of evolution: (a) Gradualism (b) Punctuated Equilibrium
(2) Plant - Green Algae Connection:
Plate Tectonics
Early Earth
Character indicators of algal/plant common ancestry
Proposed mechanism for the Evolution of the Algal Zygotic meiosis life cycle to the
Plant Sporic meiosis life cycle
(3) Sources of the Variation necessary for evolution to occur and how a species'
variation potential is a function of its Breeding System:
Sources of the Variation: (a) Mutations (b) New sexual recombinations
(c) Introgression
Breeding Systems: (a) Out-crossing (b) Selfing and (c) Apomixis (vegetative &
agamospermy)
Adaptations promoting/preventing (a) and (b) above {(1) self-incompatibility genes
(Gametophytic and Sporophytic) (2) Heterostyly (3) Gynodioecy (4) Temporal
dioecy}
(4) Types of Variation and the type that fuels evolution:
Genetic vs. Environmental variation {Turesson, Clausen, Keck and Hiesey} Common Garden Experiments
Ecotype concept and Challenge to Ecotype concept i.e., Clines
Methods of studying presence/absence/degree of genetic variation in plant
populations: (a) Isozymes (b) Chromatography (c) RFLP (d) RAPD (e) DNA
Sequencing (chloroplast, mitochondria and nuclear)
(5) Hardy-Weinberg Equilibrium:
Population Genetics definition of Evolution
Hardy-Weinberg Equilibrium - (a) the criteria necessary for no evolution to occur
in a population (b) Derivation of H-W Equilibrium equation,
Sample case studies illustrating usefulness of H-W
(6) Deviations from Hardy-Weinberg i.e., why evolution DOES occur in natural
populations:
Case Studies of real plant populations illustrating reality of (a) mutations (b) gene
flow (c) non-random mating (d) chance events {Genetic drift e.g., founder
effects, bottlenecks} (e) natural selection {examples of stabilizing selection,
directional selection, disruptive selection}
(7) Species and Speciation:
Species (a) definitions (b) The Species Problem (c) Incipient species
(d) Species delimitation
Speciation modes - Allopatric, Sympatric
Examples of Pre and Post Zygotic isolating mechanisms in plants: (a) Temporal
Isolation (b) Floral Isolation (c) Mechanical Isolation (d) Ecological Isolation
Results of isolating Mechanisms
Case Studies of Allopatric Speciation in Plants including Adaptive Radiation
(8) Hybridization:
Hybridization - definition
Hybridization in nature: (a) Role of habitat disturbance (both nature and man caused)
in hybridization (b) Hybrid Zones (c) Hybrid Swarms (d) Are all hybrids new
species? (e) Views on hybrid origins
Examples of Various Possible Consequences of Hybridization: (a) fully fertile
hybrid (b) semi-fertile hybrid (c) asexually reproducing sterile hybrid (d)
polyploidy (e) hybrid inviability
Introgression - (a) definition (b) methods of detection (c) evolutionary
consequences
Two detailed case studies - Natural Hybridization and Introgression in the Louisiana
Irises
(9) Polyploidy:
Polyploidy - (a) frequency in plants? (b) base numbers (c) ancient
polyploid series
Polyploid Detection Studies (a) Karyotypes (b) Isozymes (c) Chromatography
(d) Nuclear DNA content (e) Colchicine
Polyploidy Types - Allopolyploidy, Autopolyploidy, Segmental Polyploidy
Case studies of polyploidy including Tragopogon, and Triticum turgidum (bread
wheat)
Polyploid Origins - 2 mechanisms (a) Somatic Doubling (b) Unreduced Gametes
Mechanisms of Meiotic Dysfunction
Persistence of Polyploids
(10) Flower and Fruit Evolution:
Appearance of Angiosperms
Plate Tectonics - continent positions at time of Angiosperm Appearance
Angiosperm Ancestry
Unique Angiosperm Characteristics
Old and New views of characteristics of earliest flower
Evolutionary Trends of Flowers - (a) ovary position (b) floral symmetry
Agents of floral evolution - pollinators
Evolution of floral characters in response to selective pressure of attracting
pollinators: (a) pigments (Carotenoids, Flavonoids, and Betacyanins) (b) flower
shape (c) fragrances (d) floral markings, (e) nectar production
Evolution of fruit characters in relation to the selective pressure of promoting fruit
dispersal: (a) wind, (b) water (c) self projected and (d) animal dispersed fruit
characters
(11) Evolution of Secondary Metabolites - Evolution of chemical compounds in response
to the selective pressures of herbivores and pathogens
Alkaloids - examples of plants having evolved (a) Morphine (b) Cocaine (c) Nicotine
(d) Caffeine
Terpenoids - examples of plants having evolved (a) Isoprene (b) Essential oils
(c) Rubber (d) Cardiac Glycosides
Phenolics - examples of plants having evolved (a) Tannins (b) Salicylic Acid
(c) Lignins
(12) Detailed Examination of Several Case Studies of Co-evolution - identifying the
selective pressures exerted by both participants
Dodo bird and Sideroxylon grandiflorum tree on Mauritius- fruit and fruit disperser FACT or FALACY - a controversy
Ants and Acacia trees in Central America
Mistletoe and the Mistletoe birds in Australia
Yucca plants and the Yucca moth in USA
Sycamore Fig and Fig Wasps in Africa
Goldenrod and the Gallfly in USA
(13) ABC Model of Flower Development - Genetics of Floral Evolution
Model research organism - Arabidopsis thaliana
Stages in floral development
Developmental fields of Gene Expression
5 genes specifying floral organ identity in Arabidopsis
Loss of gene function: (a) Loss of A function (b) loss of B function (c) loss of
C function
LEAFY gene and mutation of LEAFY
E function genes
Unanswered questions
(14) Evolution instigated by man's activities
Heavy metal pollution and evolution of resistant plants
Evolution for herbicide resistance in crop plants
Genetically modified organisms
Habitat disturbance favoring evolution by hybridization
Alien Introductions and evolution by hybridization/ introgression
(15) Evolutionary Stasis:
Three case studies: (a) Wollemi pine (b) Ginkgo biloba (c) Metasequoia
Characteristics associated with evolutionary stasis within a plant group