KK8 - phylogenetic trees

Phylogenetic tree

• A diagram that shows the evolutionary relationships between different species

  • Describes the organism’s relationships to other organisms both past and present

  • Illustrates evolutionary relationships between species

• Can be useful in displaying

  • The timeline of lineages

  • Relatedness between taxa

  • Shared characteristics of different taxa

Structure of phylogenetic tree

• Root - A line at the origin, representing the earliest common ancestor

• Branch - Each line on the phylogenetic tree

• Node - A point where the branches split from each other, representing a divergence between those two taxa 

• Leaf - The end of a branch, representing where the present-day or extinct species are found. They are labelled with the species or taxa name

Interpreting phylogenetic trees

• Can be read backwards to determine the most closely related species to a taxon

• May include a time scale to show the time points of divergence events

  • Branch length represents time

Constructing phylogenetic trees

Uncertainties in phylogenetic trees

• Dating techniques are not always accurate and fossils are not typically perfectly preserved

  • Can be expressed using phylogenetic trees

• Lack of node between Y and Z means that the divergence point is unknown

• Break between W and X means that W is possibly an ancestor of X but there is no evidence of transitional fossil between the two species

• Branch with species S does not reach the end of the tree, indicating it is extinct

• Nodes usually split into two lineages but can be split into three or more

  • Means that it is unclear which species diverged from the others first

• Occurs if there is insufficient data or if two speciation events occurred closely together (like adaptive radiation)

Exchanging genetic material between groups

• Genetic material is passed between groups after they have diverged

• Depicted using a line between branches