BI111 Lecture Notes - Lecture 7: Mosaic Evolution, Recapitulation Theory, Parallel Evolution
BI111 – L7
Phylogeny, Plants, and Plant Body’s
Systematics:
Twin goals of systematics:
oReconstruction of evolutionary history
oClassification 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
oHomologies are good analogies are not
Use Characters to Organize:
Binary nomenclature: genus and species (reflect the nested hierarchy of life)
Taxon designation has 3 components:
oName: what group does it belong to
oRank: where does it fit into phylogeny
oContent: relevant to species concept
Homologies vs. Homoplasties:
Homologies = resemblance due to recent common ancestor
oDolphins and sharks share similar characteristics (homologies) because they share a
common ancestor
Homoplasties = resemblance due to similar selective pressure to fill niches, analogies
oSharks and whales share characteristics because the traits are selected for
Descent, with Modification:
Homologous structures reflect underlying genetic similarities
oEx. bones that support wings of bats, birds and pterosaur all look like modifications of
pentadactyl wings
oDevelop from similar comparable embryonic structures
When no homologies exist, traits are said to be analogous
oWings of insects are distinct
oAnalogy - no similar genes involved, traits are all independently evolved to be similar
Homology of Structures:
Often development of an individual ‘recreates’ its evolutionary history: “ontogeny recapitulates
phylogeny”
Beaks are an evolutionary innovation
o2 bones fused together
Why do Analogous Structures Evolve?:
Adaptation to similar selection pressures
Ex. Insect pitfall trap ‘pitcher’ structures developed in response to low soil nitrogen
oAt structural level, genetic level the traits are fundamentally different, but they are
superficially alike
Convergent evolution → selective pressures are the same and 2 species evolve the same way to
solve the problem without a common ancestor
Similar niches = similar forms
Convergent or Parallel Evolution:
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Twin goals of systematics: reconstruction of evolutionary history, 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: homologies are good analogies are not. Binary nomenclature: genus and species (reflect the nested hierarchy of life) Taxon designation has 3 components: name: what group does it belong to, rank: where does it fit into phylogeny, content: relevant to species concept. Homologies = resemblance due to recent common ancestor: dolphins and sharks share similar characteristics (homologies) because they share a common ancestor. Homoplasties = resemblance due to similar selective pressure to fill niches, analogies: sharks and whales share characteristics because the traits are selected for. Homologous structures reflect underlying genetic similarities: ex. bones that support wings of bats, birds and pterosaur all look like modifications of pentadactyl wings, develop from similar comparable embryonic structures.
