Evolution Biol 4802

Lecture 5

 

Topics for today

What can you learn about the pattern of evolution by mapping traits onto a phylogeny?

1.      Origin of new features

2.      Kinds of changes

3.      Rates of change

4.      Changes via development

What does it mean to map traits onto a phylogenetic tree?

  1. Start with a tree with strong support that reflects cladogenesis, branching patterns of lineages
  2. Determine evolutionary change in traits, anagenesis, by mapping traits onto the phylogeny using parsimony

What have we learned by mapping traits onto phylogenies?

  1. New features are most often modifications of pre-existing features
  2. Homologous features are inherited from a common ancestor

Homologous characters may be modified

  1. Same basic structure
  2. Same position relative to other parts of the body
  3. Change in size, shape and/or function

What have we learned by mapping traits onto phylogenies ?

  1. Homoplasy is common
  2. Causes?
    1. Convergent evolution

                                                               i.      Developmental clues

1.      thorns – modified branches

2.      prickles – modified outgrowth of the epidermis

3.      Spines - modified leaves

What causes homoplasy ?

1.      Homoplasy is common

2.      Causes?

a.       Convergent evolution

                                                               i.      Developmental clues

3.      Parallel evolution

a.       Independent evolution of change using the same genetic mechanism

4.      Reversal

a.       Molecular

b.      Morphological

Same genetic control, different lineages

  1. Genes off, develop feeding structures (maxilla)
  2. Genes on, get legs
  3. Genes partially on, get “feeding legs” (maxillipeds)

What have we learned by mapping traits onto phylogenies ?

  1. Characters evolve at different rates – mosaic evolution
    1. Conservative
    2. Labile

                                                               i.      Size and shape

    1. Evolution is most often gradual
    2. Change in form often associated with a change in function
    3. Evolutionary divergence of related lineages can occur relatively rapidly
    4. Directional change is less often but occasionally observed
    5. Evolutionary changes often involve modification of development
    6. Von Baer’s Law: species are often more similar as embryos than as adults

                                                               i.      Tetrapod vertebrate embryo

1.      Gill slits

2.      Notochord

3.      Segmentation

4.      Paddle-like limb buds

Changes in development

1.      Individualization – change to a distinct entity

2.      Heterochrony – change in the timing or rate of development

a.       Paedomophosis: accelerated maturity

b.      Peramorphosis: delayed maturity

3.      Allometry – differential rate of growth

4.      Heterotopy – change in the position where a phenotypic character is expressed

5.      Changes in complexity

a.       Increases evident in path to multicellularity

b.      Decreases associated with functional efficiency