THEME 5A AND 5B Flashcards
4 Macroevolutionary Patterns
Adaptive Radiations
Cladogenesis
Anagenesis
Phyletic Gradualism and Punctuated Equilibrium
Cladogenesis
Evolution that results in the splitting of the lineage
Anagenesis
Evolution within a lineage
Adaptive Radiation
Rapid evolution of species occupying NEW NICHES
Phyletic Gradualism vs Punctuated Equilibrium
Phyletic Gradualism: gradual changes over time
Punctuated Equilibrium: changes coming in burst
No clear result, as to which model dominates
Phylogenetic Trees
Shows relationships between species according to the recency of their common ancestor
Homologous characters
characters similar due to its conservation in its lineage.
I.e. Both species have inherited the trait from a common ancestor and kept it in their lineage
Analogous characters
characters that are similar due to adaptations to the same environment.
analogous due to CONVERGENT EVOLUTION
E.g. bat and bird
Analogous vs Homologous for constructing the tree
Homologous, as traits are derived from common ancestry. As such, it can tell us about the common ancestors of species
Character States
Several observed conditions
I.e. the presence or absence of a character. Lungs are present in tetrapods, but not in other vertebrates
Derived Character State
A modified condition of the primitive character state present in a sub-clade of the clade of interest
Synapomorphies
A character which is derived, and because it is shared by the taxa or clared under consideration, is used to infer common ancestry (shared derived state
Parsimony
Choosing the simplest tree, with fewest assumptions –> fewest changes –> simplest
Comparative morphology
like morphospecies concept. Comparing whether organisms have similar features
How to use molecular data to construct phylogenetic tree?
Those with the most recent common ancestor have little differences between their genomes
Descendants of an ancient ancestry have vast difference between their genomes
Molecular clock
Based on studying mutations and the rate at which they are incorporated into the genome. i.e. base changes can occur at a rate of 1 change per 0.56 billion years
Example of how it can be used
a length of DNA from a species differs from the DNA of another species by 4 nucleotide bases.
Assuming the DNA changes at a rate of 1 base per 24 million years, then this implies that the 2 DNA are 100 mya different and their common ancestor lived 50 mya
Why 50 mya?
Because 4 bases imply that 2 base pairs are different from the other 2 base pairs and 2 base pairs ago equates to 2x25 mya = 50 mya
50 mya, they had the same genome, which is their common ancestor
3 types of characters that can be used
morphological
chromosomal
molecular
Homoplasy
Analogous traits
as a result of convergent evolution –> i.e. via adaptations
How to recognize homologous traits? (3 requirements)
Structural similarity
- e.g. bones that support limbs of mice are the same
Same connections to other parts
- e.g. pelvis and femur connected via ball and socket
Same development
- e.g. embryonic development limbs came from same buds
Advantage of using molecular data
The amount of molecular data is sufficient in building a phylogenetic tree
Disadvantage of using molecular data
Most molecular data comes from extant species. Unfortunately, extant species only make up 10% of the taxa
Why is parsimony favoured?
This is due to the principle of fewest assumptions.
Parsimonious –> simplest tree, less evolutionary changes
We like this because most mutations are deleterious, therefore mutations that lead to evolution of new traits are unlikely –> RARE
