Phylogeny Reconstruction II

The edges of tree can be freely rotated without changing the relationships among the terminal nodes. Trees are like mobiles = =

Bifurcating and Multifurcating Trees When all the internal nodes in a cladogram are connected to three different nodes, the cladogram is said a bifurcating tree. When one or more internal nodes in a cladogram are connected to more than three different nodes, the cladogram is a multifurcating tree. The internal node is referred as polytomy. polytomies Multifurcating trees Bifurcating trees

Polytomy - Polytomy explains unresolved relationship of taxa. - Polytomies can represent two different situations: polytomies ?

Polytomy - Polytomy explains unresolved relationship of taxa. - Polytomies can represent two different situations: i) simultaneous divergence – all the descendants evolved at the same time (a “ hard” polytomy) ii) uncertainty of phylogenetic relationships or lack of resolution due to insufficient data (a “soft” polytomy) polytomies

Polytomy “hard” polytomy (simultaneous divergence) “soft” polytomy (uncertainty) or or……

Rooted and Unrooted Trees - Unrooted tree explains phylogenetic relationshiops of taxa. Rooted tree explains phylogenetic relationships of taxa and also the direction of evolution of the taxa. - Root is located at the base of a phylogenetic tree. It represents the immediate ancestor to all the terminal taxa of the tree. Unrooted tree Rooted tree root root

Tree Rooting unrooted tree rooted tree 1 rooted tree 2 rooted tree 3 rooted tree 4 rooted tree 5 rooted tree 6 rooted tree 7

Number of taxa Number of unrooted tree Number of rooted tree , ,135 2,027, , ,135 2,027,025 34,459,425

Shorthand for Trees Trees can be represented by a shorthand notation that uses nested parentheses. Each internal node is represented by a pair of parentheses that enclose all descendants of that node. This format makes it easy to describe a tree in the body of some text without having to draw it. The format is also used by many computer programmes to store trees in data files. A B C D E (((A,B),C),(D,E))

A CLADOGRAM Give a shorthand tree for the cladogram below. A B C D E F G H I J

A CLADOGRAM Give a shorthand tree for the cladogram below. A B C D E F G H I J (((A,B),C),((D,E),((F,G),(H,I,J))))

Sister taxa/group Sister group(s) i) In cladistics two taxa or clades which meet at a node; or in other words two lineages which diverged from that particular common ancestor. Because sister groups share a common ancestor, they are each other's closest relatives. ii) Evolutionary theory: The two clades resulting from the splitting of a single lineage. iii) a species or higher monophyletic taxon that is hypothesized to be the closest genealogical relative of a given taxon exclusive of the ancestral species of both taxa.

A B C D E F G H I J Sister taxa/group Sister taxa/group of (F,G)? Sister taxa/group of B? Sister taxa/group of C? Sister taxa/group of (D,E,F,G)?