Plant Speciation

1
Plant Speciation Evolution (PBIO 475/575)

• Brief History
• of Evolutionary Theory

2
What is evolution?--Definitions

• A gradual process in which something changes into
  a significantly different, especially more
  complex or more sophisticated, form
• Biology. The theory that groups of organisms, as
  species, may change with passage of time so that
  descendants differ morphologically and
  physiologically from their ancestors

3
What is evolution?Definitions (cont.)

• The historical development of a related group of
  organisms phylogeny
• The developmental or historical process of
  something, as of a social institution,
  geographical division, or system of thought
• (all from American Heritage Dictionary)

4
Evolutionary Processes

• Underlie the origin, diversification and
  maintenance of life on earth
• Example 1--Metabolic and replicative life
  processes

Raven et al. (1992)
5
Evolutionary Processes

• Example 2--Diversity and convergences of plants
  in natural systems/communities

Raven et al. (1992)
6
Evolutionary Processes

• Example 3Evolutionary radiations

Galapagos finches
Givnish and Sytsma (1997)
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Evolutionary Processes

• Example 4Specializations and species
  interactions

Platanthera orchids
Givnish and Sytsma (1997)
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Evolutionary Processes

• Example 5Variation within species

Grant (1991)
9
Evolutionary Processes

• Nothing makes sense in biology except in the
  light of evolution
• Theodosius Dobzhansky, 1973

10
History of Evolutionary Theory

• Immutability of species and the Creation (1700s)
• Espoused by John Ray, Karl Linnaeus, et al.
• Life organized into fixed number of species
• Species arose during the Creation and were
  invariant
• Number of species was fixed, all species were of
  same age

Raven et al.(1992) Briggs Walters (1997)
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History of Evolutionary Theory

• Immutability of species and the Creation (cont.)
• "Chain of Being
• All species with fixed position in chain
• Humans below angels but above all others
• Perspectives influenced strongly by church
  doctrine
• Origins of natural diversity strictly
  supernatural/divine
• Linnaeus modified his views near end of his life
• Hybridization "creates" new variation, adds new
  species
• Genera formed at the Creation, fixed
• Species formation a more recent process, flexible
  

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History of Evolutionary Theory

• Emergence of scientific explanations (mid-1700s
  to early 1800s)
• Buffon (1761) suggested modifications to species
  by climatic change
• Lamarck's (1809) "Inheritance of Acquired
  Characteristics"
• All species are not the same age
• Species changed by growth in different
  environments
• Modifications acquired in one generation
  inherited by next one

13
History of Evolutionary Theory

• Advent of Darwin
• Presented principles of evolution by natural
  selection
• Plant and animal species vary
• Without external checks, organisms reproduce in
  geometrical increase
• With these checks, individuals with inherent
  advantages survive over others in a population
  (natural selection)

Raven et al.(1992)
14
History of Evolutionary Theory

• Advent of Darwin (cont.)
• Principles of evolution by natural selection
  (cont.)
• Better-fitted individuals pass on "advantages" to
  offspring
• Selection proceeds through thousands of
  generations
• In rapidly changing environment, new forms
  replace earlier ones

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History of Evolutionary Theory

• Advent of Darwin (cont.)
• Darwin was first to
• clearly explain natural selection as a plausible
  mechanism for evolution
• put evolution in geological context
• give abundant examples for key points
• Darwin-Wallace principles developed in ignorance
  of genetics
• Neither author "invented" evolution or natural
  selection, both gave first well-developed,
  scientifically based explanations

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History of Evolutionary Theory

• Post-Darwinian developments (late 1800s, early
  1900s)
• Transplant experiments
• ecotypic variation in alpine plants (Bonnier
  1882-1920)
• variants maintained in common gardens--genetic
  basis of variation but Lamarckian in
  interpretation!
• ecological adaptations influenced by climate

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History of Evolutionary Theory

• Post-Darwinian developments (cont.)
• Mendelian genetics
• Characterized inheritance of characteristics by
  "factors"
• Developed principles of "Segregation" and
  "Independent Assortment"
• Demonstrated interpretable ratios in offspring of
  inherited, observable differences from parents

Raven et al. (1992)
18
History of Evolutionary Theory

• Post-Darwinian developments (cont.)
• First experiments on natural selection
• Crab, Carcinus maenas (Weldon 1898)--population
  numbers and morphology changed with substrate and
  water quality
• Praying mantis, Mantis religiosa (Di Cesnola
  1904)--green morph predominated in grass, brown
  in dead grass
• Early- and late-flowering eyebright, Euphrasia,
  and other species (von Wettstein 1895)--abundance
  correlated with haying

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History of Evolutionary Theory

• Post-Darwinian developments (cont.)
• Short-lived tangents
• Mutation Theory of Evolution by de Vries (1905)
  and others--based on bizarre breeding systems,
  e.g., Oenothera
• Blending inheritance

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History of Evolutionary Theory

• Genetic revolution (especially early to
  mid-1900s)
• Physical basis of Mendel's "factors"--genes with
  multiple alleles, borne on chromosomes (e.g.,
  Yule 1902)

Suzuki et al. (1989)
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History of Evolutionary Theory

• Genetic revolution (cont.)
• Molecular basis of heredity
• Genes as complex organic molecules (Schrödinger
  1944)
• Helical structure of DNA (Watson Crick 1953)
• Characterization of DNA replication, protein
  translation

Raven et al. (1992)
22
History of Evolutionary Theory

• Genetic revolution (cont.)
• Molecular basis of heredity (cont.)
• DNA changes linked to changes in proteins and
  biochemical developmental pathways
• Insights into mutation, chromosomal changes,
  non-Mendelian inheritance

Suzuki et al. (1989)
23
History of Evolutionary Theory

• Genetic revolution (cont.)
• Population genetic theory by Fisher, Haldane and
  Wright (mid-1900s)
• Methods of phylogenetic analysis (including
  cladistics) by Hennig and others (mid-1900s)
• Laboratory characterization of molecular
  variation (1970s to 1990s)

Crow Kimura (1970)
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History of Evolutionary Theory

• Neo-Darwinian evolutionary theory
• Evolution is change of allele frequencies in gene
  pool over many generations
• Species gene pools are isolated gene pool in a
  species is cohesive through gene flow
• Individuals of sexual species represent only
  one-half the contribution of alleles to offspring
  (mating required)
• Mutations are the ultimate source of new genes

25
History of Evolutionary Theory

• Neo-Darwinian evolutionary theory (cont.)
• Individuals favored by natural selection
  contribute more adaptive alleles to gene pool of
  next generation
• Populational changes in allelic frequencies over
  time arise through natural selection, although
  random genic and chromosomal changes frequently
  occur
• Subpopulations of species diverge genetically and
  phenotypically only with barriers limiting gene
  flow
• Speciation is complete when gene flow is
  prohibited between divergent and parental
  populations

26
Exciting Frontiers

• Hypothesis testing of speciation models and
  evolutionary processes
• Examining radiations and evolution of adaptive
  syndromes using molecular bio
• Reevaluation of "classic" cases using modern
  methods
• Molecular dissection of evolutionarily
  significant traits to determine genetic basis of
  evolutionary differentiation

27
Bibliography

• Briggs, D. and S. M. Walters. 1997. Plant
  variation and evolution, 3rd ed. Cambridge
  University Press, Cambridge, United Kingdom. 512
  pp.
• Crow, J. F. and M. Kimura. 1970. An introduction
  to population genetics theory. Burgess Publishing
  Company, Minneapolis, Minnesota. 591 pp.
• Givnish, T. J. and K. J. Sytsma (eds.). 1997.
  Molecular evolution and adaptive radiation.
  Cambridge University Press, Cambridge, United
  Kingdom. 621 pp.
• Grant, V. 1991. The evolutionary process A
  critical study of evolutionary theory, 2nd ed.
  Columbia University Press, New York, New York.
  487 pp.

28
Bibliography

• Nitecki, M. H. (ed.). 1990. Evolutionary
  innovations. University of Chicago Press,
  Chicago. 304 pp.
• Raven, P. H., R. F. Evert, and S. E. Eichhorn.
  1992. Biology of plants, 5th ed. Worth
  Publishers, New York, New York. 791 pp.
• Suzuki, D. T., A. J. F. Griffiths, J. H. Miller,
  and R. C. Lewontin. 1989. An introduction to
  genetic analysis, 4th ed. W. H. Freeman and
  Company, New York, New York. 768 pp.
• Wiley, E. O., D. Siegel-Causey, D. R. Brooks, and
  V. A. Funk. 1991. The Compleat Cladist. Museum of
  Natural History, Lawrence, Kansas. 158 pp.