Evolution Biosystematics Tremendous Diversity of Life | BOTANY 400, Study notes of Botany and Agronomy

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Evolution - Biosystematics

1. Tremendous diversity of life!

3. Apparently purposive or

adaptive nature of their features

2. Structural complexity of these

organisms

1. How has organic diversity

originated, how is it maintained?

2. How have complex organisms

come into being?

3. What forces have molded their

adaptive features?

4. When and where did the various

organisms appear?

5. Why have organisms (including

humans) appeared?

Thomas Burnet (1681)

Thomas Burnet (1681)

“no truth concerning the Natural

World can be an enemy of religion;

for Truth cannot be an enemy to

Truth, God is not divided against

himself”

Jean Baptiste Lamarck (1744-1829)

Lamarck’s “Ladder”

• Continuum between physical

and biological world (after

Aristotle)

• Scalae Naturae (“Ladder of

Life” or “Great Chain of Being”)

God Angels Demons Man Animals Plants Minerals Non-being Realm of BECOMING Realm of BEING

Being •^ Life^ progresses^ upward^ due^ to^ an

internal drive towards perfection

• Why are primitive organisms still

around?

• Spontaneous generation of new life

constantly

• Mechanisms of change?
  • Inheritance of acquired characters

Lamarck’s “Ladder”

Lamarck’s (1809) fourteen level ladder hierarchy

Lamarck’s “Ladder”

• There is no one

linear ladder

(Georges Cuvier)

Lamarck’s later “Tree”

• Lamarck (reluctantly) influenced

by Cuvier’s arguments

• Appended table in 1809 (vol. 2 of

Philosophie Zoologique )

showing two lines of

spontaneous generation with

subsequent branching

Lamarck’s 1809 appendum

Lamarck’s later “Tree”

• By 1815 Lamarck announced his

conversion to branching as the

fundamental pattern of evolution

• “ In its production of the different

animals, nature has not

fashioned a single and simple

series ”

Lamarck’s 1815 “tree”

Lamarck’s later “Tree”

• His last book ( Analytical System

of Positive Knowledge of Man ,

1820) has gone largely

unnoticed

“ Reptiles come necessarily after fishes. They build a branching sequence, with one branch leading from turtles to platypuses to the diverse groups of birds, while the other via lizards toward the mammals. The birds then build a richly varied branching series, with one branch ending in birds of prey. ” S.J. Gould, 1999

Robert Chambers (1844) Charles Darwin (1859)

only figure in Origin of Species - illustration of ‘descent with modification’ Darwin’s “Tree-thinking” (^) The three main claims of Darwinian evolution

• Living species are related by common ancestry

[descent]

• Change through time occurs not at the organism

but at the population level

• The main cause of adaptive evolution is natural

selection [modification]

Evolution - a definition

The change of genetic materials (DNA,

genes, chromosomes = genotype)

and thus physical attributes

(morphology, physiology = phenotype)

within and among populations and

species through time and space

Evolution & Religion Some conflict already early on between religion and ideas of evolution 1860 debate between Bishop Samuel Wilberforce of Church of England and Thomas Henry Huxley (‘Darwin’s bulldog’) “Surely God’s power and glory were revealed more clearly in natural laws than in a peppering of miraculous interventions.” William Benjamin Carpenter — Christian physiologist and paleontologist — after reviewing Darwin’s Origin of Species Evolution & Religion No conflict among many scientists of faith Evolution & Religion Although major religious denominations uphold the “two books of knowledge” view, the “evolution vs. creationist” debate continues — primarily in the United States The “ Evolution House ” exhibit at Kew Royal Botanic Gardens was the inspiration of the Christian director Sir Ghillean Prance

Evidence for Evolution Evidence for Evolution Nothing in biology makes sense except in the light of evolution Theodosius Dobzhansky Anatomists, cellular biologists, prokaryote geneticists, membrane and protein transport physiologists, gene sequencers, genomicists, etc.... Evidence for Evolution Nothing in biology makes sense except in the light of evolution Theodosius Dobzhansky

... their data only makes sense assuming that chloroplasts are modifications of an ancient blue green bacteria ancestor — endosymbiotic event Evidence for Evolution “what advances in science, engineering, computers, medicine, astronomy, geology, or any other science will be limited because the scientist does not embrace evolution?”

• Classification 
• Hierarchical distribution of traits 
• Homology 
• Vestigial Structures 
• Fossil record 
• Biogeography 
• Variation among populations 
• Speciation 
• Agreement between gene trees   = examined in this course to various degrees Evidence for Evolution - Common Ancestry “trees” Genealogical tree of Queen Victoria (1819-1901) Pigeon breeding lineages from ancestral rock pigeon

1. Hierarchical Classification Rose pedigree IndoEuropean^ Language^ Tree
2. Hierarchical Classification Darwin’s 1st species notebook (1837) back in time extinction speciation A B C
3. Hierarchical Classification

1. Hierarchical Classification Darwin’s major finding was a scientific explanation (using the tree metaphor) for: (1) why organisms appear similar to other organisms, and (2) why these organisms appear related in a hierarchical (nested) fashion

• Groups of species appear more similar than they do with other groups

1. Hierarchical Classification Vascular tissue Chloroplasts Water-tight egg Four limbs Ladder of Life Phylogenetic Tree

• That observation alone could be consistent with a number of explanations of the origin of life’s diversity
• Humans and various members of the great apes show a lot of “similarity” Human vs. chimpanzee chromosomes (23 vs. 24) 99.4% DNA identity (... and the resulting morphology & behavior!)

1. Hierarchical Classification

• Darwin’s simple explanation was that each species did not independently acquire every character

1. Hierarchical Classification Vascular tissue Chloroplasts Water-tight egg Four limbs

• but rather each inherited it from a common ancestor who first derived it — a “fossil” footprint = shared-derived characters Characters are “fossil” footprints indicating ancestry

1. Hierarchical Classification Vascular tissue Chloroplasts Water-tight egg Four limbs

• Groups are “nested” within successively larger groups, each “clade” defined by its own set of evolutionary novelties The distributions of characters in a hierarchical fashion is only explained by “trees” eukaryote

1. Hierarchical Classification = shared-derived characters Vascular tissue Chloroplasts Water-tight egg Four limbs On the ordinary view of each species having been independently created, we gain no scientific explanation of any one of these facts. We can only say that it has so pleased the Creator... that He has impressed on them the most extraordinary resemblances, and has classed them in groups subordinate to groups. Tree of Life & Special Creation Darwin, The variation of animals and plants under domestication. 2 vols. 2nd edn. New York, D. Appleton & Co. 1883. Evolution thus predicts that species descended from a common ancestor should share homologous characters - derived from the same structure(s) - but that they will show divergence in these characters through time Character modification — homologous parts The forelimb of all these vertebrates are homologous but modified: grasping leaping flying swimming running
2. Evidence through Homology

“On my theory, unity of type is explained by unity of descent ” Darwin, 1859

• Darwin’s work on orchids convinced him that all species possess the basic homologous floral parts
• although these are highly modified for roles in quite different pollination systems
  2. Evidence through Homology “On my theory, unity of type is explained by unity of descent ” Darwin, 1859
• Darwin published an entire book on pollination and the varied flowers and pollinators coming from a “unity of type” Angraecum sesquipedale (Orchidaceae)

2. Evidence through Homology
   2. Evidence through Homology EvoDevo studies now provide genetic bases for the homology (or not) of basic features in plants and animals ABC model of floral identity And how they have been modified
3. Evidence through Homology

• few gene differences involved in quite different looking flowers ( Mimulus - monkey flowers)
• transcription factors not structural genes important in trait differences

Gene family, spatial organization, development Molecular tinkering - major process for forming the diversity of life

2. Evidence through Homology Hox Genes - EvoDevo Molecular tinkering - major process for forming the diversity of life Halteres into wings Antennae into legs
3. Evidence through Homology Hox Genes - EvoDevo
4. Vestigial Structures Evolution predicts that species occupying very distinct environments from that of a common ancestor might show vestigial structures Vestigial structures — homologous parts Rudimentary tooth in lower jaw of a baleen whale
5. Vestigial Structures Evolution predicts that species occupying very distinct environments from that of a common ancestor might show vestigial structures (^) The pelvic girdle seen in reptiles and mammals as an adaptation for support in tetrapods, is vestigial in whales — it is a “fossil” footprint of their ancestry and serving no function today in swimming descendants of tetrapods. Vestigial structures — homologous parts

Vestigial structures — homologous parts Parasitic and non-green dodders retain “fossil” non-functional chloroplasts as a vestigial structure inherited from a common ancestor with morning glories Convolvulus - morning glory Cuscuta - dodder

3. Vestigial Structures 4. Fossil Record ‘Missing links’ — transitional forms - fossil record is rich & consistent with information from hierarchical relationships based on morphology and DNA
4. Fossil Record ‘Missing links’ — transitional forms

• Archaefructus in terms of age and morphology is consistent with an early basal angiosperm
• fossils often now placed in phylogenetic analyses Archaefructus

4. Fossil Record ‘Missing links’ — transitional forms - fossil DNA has also been sequenced (‘Jurassic Park’)

4. Fossil Record ‘Missing links’ — transitional forms

• fossil DNA has also been sequenced (‘Jurassic Park’) “ I see no difficulty in a race of bears being rendered, by natural selection, more and more aquatic in their structure and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale. ” Darwin, in Origin of Species

4. Fossil Record ‘Missing links’ — transitional forms Paleontologist Phil Gingerich with 40 my old Basilosaurus with small hind legs in Egypt

• now a wealth of fossils showing transitional forms from a putative ancestral Mesonychid type to modern whales has been uncovered Early stages were clearly terrestrial

4. Fossil Record 4. Fossil Record ‘Missing links’ — transitional forms - what should ‘missing links’ look like? - intermediate between chimp and human? - No! that is ‘ladder of life’ thinking

X

• each species is a ‘tip’ species with its own derived traits

4. Fossil Record ‘Missing links’ — transitional forms

• what should ‘missing links’ look like?
• in tree thinking, ‘missing links’ are seen in a progression from a common ancestor with a sister species

X

• the common ancestor may or may not look like what features did this common the sister tip species ancestor possess? "... that grand subject, that almost keystone of the laws of creation, Geographical Distribution " Darwin needed two chapters in the Origin of Species to cover his ideas on geographical distributions of organisms “I am prepared to go to the stake, if requisite, in support of the chapters on the geological and geographical distribution of life.” Thomas Huxley after reading the Origin of Species

5. Biogeography of Life Law of Representative Species - repeated biogeographical observation Closely related species replace themselves across a continent
6. Biogeography of Life Succulent stemmed Euphorbia restricted to Africa and Madagascar Succulent stemmed Cactaceae restricted to the American continents Cactaceae Euphorbiaceae Convergent Forms on Different Continents - repeated pattern
7. Biogeography of Life

Convergent structures in bill and body shape in flower visiting birds from four different continents: North America, Australia, South America, and Africa hummingbird honeyeater Ecuadorian honeycreeper sunbird Convergent Forms on Different Continents - repeated pattern

5. Biogeography of Life Distributions of organisms, extant and extinct, provided the first evidence in 1920 for the then heretical idea of continental drift Glossopteris - Permian “fern” Mesosaurus - Permian freshwater reptile Cynognathus - Triassic land reptile Lystrosaurus - Triassic land reptile 5. Biogeography of Life Congruence of distribution patterns and earth history
6. Direct Observation Evolutionary change within and among populations Evolutionary changes in pepper moths ( Biston betularia ) coupled with natural selection Agrostis tenuis growing on a copper mine in Britain — natural selection for copper tolerance in 150 generations
7. Direct Observation Evolutionary change within and among populations

Character displacement of floral color in zones of overlap of the geographic ranges of two similar colored species of phlox Hybrids are sterile, but character displacement of floral color reduces interspecific pollen transfer by pollinators Phlox (Polemoniaceae)

6. Direct Observation Evolutionary change within and among populations
7. Direct Observation Evolutionary change in formation of crop plants Documenting change within 100s or 1000s years

• often with “major” phenotypic modifications but due to small numbers of genes

6. Direct Observation Origin of old species Helianthus anomalus H. paradoxa H. annuus Re-synthesized in the lab

• origin of new polyploid species in last 150 years (multiple times in different places)! Tragopogon - goat’s beard

6. Direct Observation Origin of recent species

7. Molecular Evolution Organisms contain within themselves a “DNA fossil footprint”
8. Molecular Evolution Organisms contain within themselves a “DNA fossil footprint” ... and different stories are told by different genomes