What do phylogenies show?
They provide a way to quantify how diversity changes over time (shows speciation and evolution of a species).
What is phylogeny?
- History of descent with branching. Ex. a human family tree.
- Way of organizing our knowledge of biodiversity.
What is a branching diagram?
- Shows a relationship between species, often according to the time since a common ancestor.
- Provides a hypotheses of evolutionary relationship between two species.
What is a phylogenetic tree?
Represents the best model of the relatedness of organisms - based on fossil and extant data.
What is the relationship between speciation and the phylogenetic tree?
- When there is a speciation event, there is a node on the phylogenetic tree that splits into two branches.
Explain what the tips of the phylogenetic tree represent.
The tips (terminal node) are like leaves, represents the extant species that is usually being researched.
Explain what the root of the phylogenetic tree represents.
The root represents the starting point, or the common ancestor for all the species recorded in the tree.
What do the branches represent in a phylogenetic tree?
They lead back from the tips, tracing lineage back in time to the common ancestor.
What is a sister group?
Two species that share a common ancestor that isn’t shared by any other species or group.
What is important about the nodes on a phylogenetic tree?
They can be rotated without changing evolutionary relationships, as they all split at the same time in the same spot technically.
What is a phylogram?
A phylogenetic tree where the branch lengths represent the amount of inferred evolutionary time.
What is a cladogram?
A phylogenetic tree where all branches are equal length, don’t represent time.
Can phylogenies only be built for many species?
No, they can also be built among populations or even individuals (ex. human family tree).
What is a monophyletic group?
Includes a common ancestor and all of its descendants.
What is a paraphyletic group?
Includes a common ancestor and some, but not all, of its descendants. Ex. Reptile group shares common ancestor with birds, but they do not have similar phenotypes.
What is a polyphyletic group?
Does not include a common ancestor. Ex. bats and birds both fly, but don’t have same direct ancestor.
How can we infer evolutionary history from a group of organisms?
- Similar traits may suggest shared ancestry, but they can be misleading (ex. birds and bats both flying).
- Can use ‘characters’ that are shared among organisms.
What characters can we use to infer evolutionary history between organisms?
- Morphological
- Chromosomal
- Molecular
- Vary between but not within species, have a genetic basis (tied to evolution)
What is a morphological or DNA character?
- Observable traits of the whole organism.
- There are a number of characters with different character states.
Ex. flower colour (blue or yellow), pea shape (round or wrinkled), DNA sequence (ATCCTA or ATAATA).
Why can character states be similar between species?
They are either homologous characters or analogous characters.
What are homologous characters (homologies)?
- Shared because of common ancestry
- Shared ancestral (early) and derived (near phylogenetic tips) characters
- Want to use these characters to create phylogenetic trees
What are analogous characters (homoplasies)?
- Similarities in appearance or function, but not origin
- Shared because of convergent evolution (evolved similarly because of same environmental conditions).
- Don’t want to use in phylogenetic trees
- Ex. ephors and cacti look similar, but evolution was independent
How are homologies recognized?
- Structural similarity
- Relations between parts (same arrangement of bones, ligaments connect similarly)
- Embryonic development
How do you reconstruct a phylogeny with character states?
- Compare species that share homologies, choose traits that some have but not all (synapomorphies).
- Compare these species to an out group (earlier branch of tree, possible common ancestor).
- The least differences = the most similar to the out group.
