Download Macroevolutionary Patterns

Zoology 445
Fall 2006
Reading: Text 639-653 & Chapter 17
Macroevolution Handout
I. Phylogeny of life.
Whittaker’s five kingdom classification.
Phylogenies of all life:
Genes involved in the processing and storage
of genetic information
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Genes involved in basic metabolism.
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Three pathways for horizontal gene transfer
1. Transduction – The uptake of naked DNA from the environment. Any part of the bacterial chromosome can be
exchanged.
2. Conjugation – Transfer of DNA mediated by plasmids and transposons. Requires cell to cell contact but occurs
between distantly related bacteria and even between bacteria and eukaryotic cells.
3. Transduction – Transfer of DNA by phage.
Net result: Typically, 10% or more of a bacterial genome can be traced back to a horizontal gene transfer event.
Example: HMGGCoA reductase gene.
Correct depiction of all life.
Conclusion: The phylogeny of a particular gene represents the evolutionary history of that gene, and not that of the
organism. Evolution within and between the Bacteria and Archaea are interconnected due to horizontal gene transfer.
Endosymbiosis and the
eukaryotic mitochndria
and chloroplasts.
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II. Evolution within the Eucarya.
Earlier presentation:
First determined by the suite of fossils. See text section 17.1 pages 664 – 666.
III. The Cambrian Explosion
Adaptive radiation
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The Cambrian explosion.
Fig 17.12 Shows all the major phyla of animals
Implication: All major animal phyla appeared in a time frame of 50 Million Years, which is around 4% of the
total time life has existed on the earth.
During that time the major innovations of animals occur.
a. Radial & bilateral symmetry
b. diploblasts & triploblasts
c. protostomes & deuterostomes
However, molecular clock data based on the neutral theory suggest that the branches for the origination of the
phyla are much deeper than the Cambrian.
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IV. Pattern in evolution
Punctuated equilibrium:
They proposed that ALL morphological
change occurs at speciation events (i.e. nodes
on a phylogenetic tree).
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Traditional gradualism:
Morphological change occurs independently of
speciation.
Set off two debates:
1. Our view of speciation was incorrect. Allopatric speciation is a GRADUAL process and can take a
long time.
a. This was reconciled when population biologists realized that a “rapid” change on a
phylogenetic tree represents a million or more years. A million years is plenty of time for
allopatric speciation.
2. Do species change morphologically only during speciation?
A. Support for Punctuated Equilibrium
Bryozoans
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B. Support for Gradualism
C. Equivocal results
Change without species – chronospecies
introduced earlier in semester.
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V. Is stasis due to a lack of genetic variability?
Hypothesis: Species cannot change in morphology because they do not have the genetic variability to allow
change.
Test: Compare Horseshoe crab lineage (living fossil) with hermit crab lineage (much change morphologically)
for levels of genetic variability.
Growing consensus is that morphology due to “Habitat tracking.”
If environment is stable and unchanging we see stasis.
If habitat is changing constantly we see gradual and constant change.
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