BI111 Lecture Notes - Lecture 5: Recapitulation Theory, Dactyly, Parallel Evolution

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9 Feb 2017
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Systematics
Twin goals of systematics : Reconstruction of evolutionary history and classification of species
Phylogenetic trees come about through successive events of speciation(branching), in which
one species gives rise to two(or more!)
Reconstructing these trees requires comparison of traits (with shared genetic ancestry) in
multiple species
o Homologies are good analogies are not
Use characters to categorize
Binary nomenclature: Genus and species reflect the nested hierarchy of life)
Taxon designation has 3 components
o Name: what group does it belong to?
o Rank (where does it fit into phylogeny)
o Content (relevant to species concept)
What do similarities reflect? Homologies v. Homoplasties
Sharks, dolphins all have similar morphology(similar profiles), similar selective pressures to fill
nice (homoplasties)
Resemblance due to recent common ancestor (homologies)
Converged on the same phenotype with different starting types
Similarities which have risen due to convergent evolution due to similar resemblance
Descent, with modification
Homologous structures reflect underlying genetic similarities
o E.g: bones that support wings of bats, birds and pterosaur all look like modifications of
pentadactyl limb
o Develop from comparable embryonic structures
When no homologies exist, traits are said to be analogous
o Wings of insects are distinct
Homology of Structures
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Often development of an individual 'recreates' its evolutionary history :"ontogeny
recapitulates phylogeny"
Why do analogous structures evolve?
Adaptation to similar selection pressures
Insect pit-fall trap "pitcher' structures developed in response to low soil Nitrogen(evolved
independently)
Convergent evolution- organisms aren't closely related and independently evolve similar traits as a
result of having to adapt to similar environments/ ecological niches( ex: porcupine and hedgehogs)
Parallel evolution-similar traits evolving in closely related, but distinct, species descending form the
same ancestor but different clades
species
Convergent or Parallel Evolution?
Regulatory sites of transcription factors switch on or off downstream genes
o Small changes in regulation produce large changes in morphology
Natural selection still determines success of regulatory genes
Three-spine sticklebacks are parallel evolution
Ancestral and Derived Structures
Individuals show evidence of mosaic evolution
Combination of ancestral and derived characters in evolutionary lineage
Derived characters determined from fossil and embryos
Derived characters appear later in development
Outgroup comparison for derived characters
Cladistics phylogenies based on..
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