Topic
¡å Biology 1020 - Spring 2006 Lecture outlines
¡å Lecture 2 - Biodiversity, evolution and natural selection
¡å slides
• Biodiversity
• Figure 1.13 Drawers of diversity
• Figure 1.14 Classifying life
• PROPINQUITY OF DESCENT
• DESCENT with MODIFICATION
• NATURAL SELECTION
• Figure 22.10 Artificial selection
• Figure 1.20 Summary of natural selection
• Figure 22.8 Overproduction of offspring
• Figure 22.9 Variation in a population
• Figure 1.21 Natural selection
• Figure 22.13 Evolution of drug resistance in HIV
• Figure 22.6 Beak variation in Galápagos finches
• Figure 22.11 Camouflage as an example of evolutionary adaptation
• Figure 1.22 Form fits function
• Figure 1.23 Descent with modification: adaptive radiation of finches on the
Galápagos Islands
• DESCENT with MODIFICATION
• Figure 22.14 Mammalian forelimbs: Homologous structures
• Figure 22.15 Anatomical similarities in vertebrate embryos
• Figure 22.16 Comparison of a protein found in diverse vertebrates
• Figure 22.7 Descent with modification
¡å Introduction, Biodiversity, Taxonomy
• We will be covering a broad range of organisms
• we need some understanding of structure, which requires learning some
morphology and terminology.
• structures that distinguish groups of organisms perform particular functions
for the organisms,
• coping with the complexity of organismal diversity has always been an
overwhelming task.
¡å Biodiversity
¢º Biodiversity - what does it mean?
¢º Just how many organisms are there out there?
¡å history of the view of diversity
• even the first “scientific” classification systems are hierarchical, with
mutually exclusive categories
¢º Aristotle (384-322 BC)
¢º Linnaeus (1707-1778)
• where do species come from?
¢º Darwin’s analogy • Darwinian thinking results in us looking at diversity using an evolutionary
tree as an organizational framework
¢º examples of tree thinking
• Descent with modification
¡å Darwin (1809-1882)
• naturalist on the Beagle (1831-1836)
¡å numerous observations - Galapagos
• recent volcanic origin
• most species were unique
• most were similar to species in South America
• finches showed diversity based on different islands and different
habitats
¡å His theory of evolution
• Descent with modification
• Propinquity - nearness of relationship; kinship;
• Why are species similar to each other ? - propinquity of descent
• Why are they different from one another? - Natural Selection
¡å Natural selection
¢º differential reproductive success
¢º selection occurs through interaction between the environment and genetic
variability among individuals within the population
¢º The product of natural selection is adaptation
• although heritability was important in Darwin’s theory of natural selection he
had no clear idea of how genetics worked - he did know about propinquity of
descent; but he didn’t know how it happened
• he considered inheritance to occur via ‘blending’
• he also knew that variation had to be continually being manufactured - but did
not know about mutation
• Neo-Darwinism - the incorporation of genetics into the theory (1930s)
• definition of evolution: ‘any change in genetic makeup in a population over
time’
• so our main purpose is to use an understanding of evolution to help in the
construction and interpretation of evolutionary trees (show some examples
from the text)
• evolutionary trees are based on divergence (speciation) resulting in branches
¡å Lecture 3 - Natural Selection and Speciation
¡å slides
• Figure 22.7 Descent with modification
• Figure 24.2 Two patterns of evolutionary change
• What causes the tree to branch (divergence)?
• Figure 24.3 The biological species concept is based on the potential to
interbreed rather than on physical similarity
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Figure 24.4 Reproductive Barriers
Figure 24.4 Reproductive Barriers
Figure 24.5 Two main modes of speciation
Figure 24.6 Allopatric speciation of antelope squirrels on opposite rims of
the Grand Canyon
• Figure 24.7 Can divergence of allopatric fruit fly populations lead to
reproductive isolation?
• Figure 24.7 Can divergence of allopatric fruit fly populations lead to
reproductive isolation?
• Figure 24.8 Sympatric speciation by autopolyploidy in plants
• Figure 24.9 One mechanism for allopolyploid speciation in plants
• Figure 24.12 Adaptive radiation
• Figure 24.13 Two models for the tempo of speciation
• Video
• There is one true evolutionary tree (history). How do we find it?
¢º Darwin’s finches again
¡å reproductive isolation leads to divergence
• as mentioned last time, the lack of migration among islands means that
changes that occur in one population via selection, drift or whatever
means, cannot be passed on to another population
• when this occurs the populations diverge
• as time passes and more differences accumulate, speciation may occur;
i.e. even if the two populations were in contact again, they would not
interbreed
• divergence in the tree is then thought to represent a speciation event.
¡å Biological species concept
• members have the potential to interbreed in nature and produce viable
fertile offspring but are unable to produce viable, fertile offspring with
members of other populations
¡å Kinds of reproductive barriers
¢º Prezygotic
¢º Postzygotic
¡å modes of speciation
¢º Allopatric speciation
¢º Sympatric speciation
¡å tempo of speciation
• when does divergence occur
• does the rate change or is it constant?
• punctuated equilibrium
¡å Lecture 4 - Phylogeny
¡å slides
¡å Construction of phylogenetic trees
• 1. Choose a group to study (e.g. lilies, fungi, beetles, bears)
• 2. Decide what the closest relative is to the group you want to study.
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That will be the outgroup
• 3. Choose characters to score or analyze. (e.g. flower colour, #legs,
shape of the skull)
• 4. Determine which of the character states is ancestral and which is
derived, usually by ‘ outgroup comparison’.
• 5. Score the characters for each of the “taxa” within the group.
• 6. Construct the most parsimonious tree (often done with a computer)
The principle of Parsimony
• based on the idea that evolution proceeded by a smaller rather than a
larger number of events
Figure 25.15 Applying Parsimony to a Problem in Molecular Systematics
Figure 25.11 Constructing a cladogram
Figure 22.14 Mammalian forelimbs: Homologous structures
Similarity Differences define group types
Frog photo - 3 digits
Figure 25.10 Monophyletic, paraphyletic, and polyphyletic groupings
The three groups can also be defined by what they include
¡å monophyletic groups
• common ancestor and all of its descendants
¡å paraphyletic groups
• common ancestor and some of its descendants
¡å polyphyletic groups
• common ancestor is excluded from the group
Figure 25.16 Parsimony and the analogy-versus-homology pitfall
Modern systematics is shaking some phylogenetic trees
Figure 25.9 The connection between classification and phylogeny
Figure 26.21 Whittaker’s five-kingdom system
The three domains of life
Figure 26.22 One current view of biological diversity
Figure 26.22 One current view of biological diversity
Figure 27.12 A simplified phylogeny of prokaryotes
Figure 28.4 A tentative phylogeny of eukaryotes
Figure 29.7 Highlights of plant evolution
Figure 31.9 Phylogeny of fungi
Figure 29.4 Three clades that are candidates for designation as the plant
kingdom
Figure 32.10 One hypothesis of animal phylogeny based mainly on
morphological and developmental comparisons
Figure 26.20 The history of continental drift during the Phanerozoic
Not all evolutionary trees are constructed the same way.
Phylogeny based on DNA similarity, not synapomorphies
Figure 25.18 The universal tree of life
Evolutionary tree video
• if there is one true evolutionary history experienced by organisms on earth,
there there is one true evolutionary tree that reflects that history. How can we
determine what that tree is?
¡å Phylogenetic (Cladistic) methods.
¡å the branches of the tree show two aspects of evolution
¢º anagenesis
¢º cladogenesis
¢º determining the branching points
• Principle of parsimony
¡å symplesiomorphies (ancestral homologies) versus synapomorphies
(derived homologies)
• only synapomorphies show relationship
¢º symplesiomorphies show no evidence of relationship
¡å homology and analogy
• shared derived characters are homologies; they are present in the
common ancestor; ancestral characters are homologies
¢º parallelisms or convergences are analogies; they are not similar due to
common descent
¡å organisms can then be similar for three reasons
• synapomorphies (derived homologies)
• symplesiomorphies (ancestral homologies)
• homoplasy or analogies (Convergences/parallelisms)
¡å we then can therefore think of three different kinds of groups
¢º monophyletic groups
¢º paraphyletic groups
¢º polyphyletic groups
• only monophyletic groups reflect the branching pattern of the tree. They
are therefore considered the most useful.
• some of our system is still based on overall similarity (or difference) rather
than strict cladistic methodology