Evolution Biol 4802

Lecture 5, Chapter 3


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

Figure 3.5 (old Fig. 3.4)

What have we learned by mapping traits onto phylogenies?

  1. New features are most often modifications of pre-existing features

·        Homologous features are inherited from a common ancestor

o       Homologous characters may be modified

·        Same basic structure

·        Same position relative to other parts of the body

·        Change in size, shape and/or function

  1. Homoplasy is common
    1. Causes?

b.      Convergent evolution

                                                                          i.      Developmental clues

1.      thorns – modified branches

2.      prickles – modified outgrowth of the epidermis

3.      Spines - modified leaves

c.      Parallel evolution

                                                                          i.      Independent evolution of change using the same genetic mechanism

d.       Reversal

                                                                          i.      Molecular

                                                                        ii.      Morphological

3.      Parallel Evolution 

1.      Same genetic control, different lineages

                                                              i.      Genes off, develop feeding structures (maxilla)

                                                            ii.      Genes on, get legs

                                                          iii.      Genes partially on, get “feeding legs” (maxillipeds)

Figure 3.7 (same in old and new)

4.      Characters can revert back to previous states

Figure 3.9 (not in the older edition of the book)

5.      Characters evolve at different rates – mosaic evolution

                                      i.      Conservative

                                    ii.      Labile

1.      Size and shape

1.      Evolution is often gradual

Figure 3.12 (old Fig. 3.9)

2.      Change in form often associated with a change in function

Figure 3.25 (old Fig. 3.24)

3.      Similarity among species changes through development

Figure 3.14 (old Fig. 3.9)

                                      i.      Von Baer’s Law: species are often more similar as embryos than as adults

1.      Tetrapod vertebrate embryo

a.      Gill slits

b.      Notochord

c.      Segmentation

d.      Paddle-like limb buds

Examples of changes in development

1.      Individualization – change to a distinct entity

Figure 3.15(old Fig. 3.11)

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

Figure 3.16 (old Fig. 3.13)

a.      Paedomophosis: accelerated maturity

b.      Peramorphosis: delayed maturity

Cubo and Arthur 2001 - Link on web

3.      Allometry – differential rate of growth

Figure 3.18 (old Fig. 3.15)

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

5.      Changes in complexity

Figure 3.21(old Fig. 3.20)

a.      Increases evident in path to multicellularity

b.      Decreases associated with functional efficiency