Parsimony methods the evolutionary tree to be preferred involves ‘the minimum amount of evolution’ Edwards & Cavalli-Sforza Reconstruct all evolutionary changes along any possible tree Find tree with least number of changes

A simple example Characters Species Alpha Beta Gamma Delta Epsilon Evolutionary changes: 0  1 and 1  0 Root: 0 or 1

A simple example AlphaBetaDeltaGammaEpsilon character 1

A simple example AlphaBetaDeltaGammaEpsilon character

A simple example AlphaBetaDeltaGammaEpsilon character

A simple example AlphaBetaDeltaGammaEpsilon character 2

A simple example AlphaBetaDeltaGammaEpsilon character 2

A simple example AlphaBetaDeltaGammaEpsilon character 2

A simple example AlphaBetaDeltaGammaEpsilon character 2

A simple example AlphaBetaDeltaGammaEpsilon character 3

A simple example AlphaBetaDeltaGammaEpsilon character 3

A simple example AlphaBetaDeltaGammaEpsilon character 4

A simple example AlphaBetaDeltaGammaEpsilon character 4

A simple example AlphaBetaDeltaGammaEpsilon character character 5

A simple example AlphaBetaDeltaGammaEpsilon character 6

A simple example Characters number of changes required total number of changes required = 9. this first hypothesis requires a total of 9 evolutionary changes

A simple example AlphaBetaDeltaGammaEpsilon colour indicates derived status ( =0, =1) character number

A simple example AlphaBetaDeltaGammaEpsilon this alternative hypothesis requires but 8 evolutionary changes.

A simple example AlphaBetaDeltaGammaEpsilon ² 4 homoplasy: the same status arises more than once on the tree

A simple example AlphaBetaDeltaGammaEpsilon ² 4 homoplasy: the same status arises more than once on the tree

Rooted and unrooted trees GammaBetaDeltaAlphaEpsilon ² 4 yet ‘another’ hypothesis requiring but 8 evolutionary changes

A simple example AlphaBetaDeltaGammaEpsilon ² 4 GammaBetaDeltaAlphaEpsilon ² 4 the two rooted hypotheses requiring 8 changes yield similar unrooted trees

Rooted and unrooted trees Alpha Delta Gamma Beta Epsilon 6 5 4

Rooted and unrooted trees AlphaBetaDeltaGammaEpsilon AlphaBetaDeltaGammaEpsilon unrooting trees reduces the number of alternative solutions character 2

Rooted and unrooted trees Characters number of changes required # alternative trees (rooted) # alternative trees (unrooted) unrooting trees reduces the number of alternative solutions

Methods of rooting a tree 1.Use an outgroup 2.Use a molecular clock

Methods of rooting a tree 1.Use an outgroup Ape3 Ape2 Ape1 Ape4 Monkey root must be along this lineage

Methods of rooting a tree 1.Use an outgroup 2.Use a molecular clock only the root is equidistant to all tips

Branch lengths Gamma Delta Alpha Beta Epsilon Characters # alternative trees (unrooted) branch lengths are computed as the sum of all character changes (each divided by # alternatives)

Branch lengths Gamma Delta Alpha Beta Epsilon the sum of all branch lengths is called the ‘length’ of the tree

Branch lengths Gamma Delta Alpha Beta Epsilon

But how to… 1.count the number of changes in large datasets 2.reconstruct states at interior nodes 3.search among all possible trees for the most parsimonious one 4.handle DNA sequences (4 states) 5.handle complex morphological characters 6.justify the parsimony criterion 7.evaluate statistically different trees