Phylogeny
Evolutionary Relationships and Phylogenetic Trees
Phylogenetic Trees: Represent the evolutionary relationships between species, illustrating common ancestors.
Example: A gizzard, a pouch that aids in digestion, can show evolutionary time but is not measured in absolute terms.
Extinction and Extant Species:
Extinct: Organisms that no longer exist.
Extant: Species that are currently living.
Species on the outside edge of the tree signify those that still exist today.
Common Ancestors and Divergence
Common Ancestors: The root of the tree represents an ancestor shared by multiple species (e.g., species a, b, c, d, e).
Divergence: As species evolve, they diverge from their common ancestor (e.g., species a diverges from the shared ancestor, while b, c, d, e, and f also branch off).
Relational Proximity: Species d and e are more closely related to each other than they are to species a due to fewer accumulated differences.
Outgroups and Trait Selection
Outgroup: An external reference point (like a mouse or another mammal) used to determine evolutionary relationships on the phylogenetic tree.
Traits: Selection of traits to be represented on the tree can illustrate various evolutionary adaptations and changes over time.
Phylogenies can be tailored to reflect specific traits or relationships that researchers want to highlight.
Trait Evolution: Convergence and Synapomorphy
Convergent Evolution: Independent evolution of similar traits in non-closely related species due to similar environmental challenges.
Example: Similar bone structures in different animals may arise from convergent evolution.
Synapomorphic Traits: Traits that appear in all descendants of a monophyletic group.
Example: Lungs in tetrapods; once evolved, they are present in all descendants of tetrapods.
Case Studies of Independent Evolution
Example of Independent Evolution:
Hedgehog vs. Tenrec: Both species have spines but evolved them independently as a response to their environments.
Phylogenetic analysis can reveal these independent evolutionary pathways.
Parsimony in Phylogenetic Analysis
Parsimony: A method used to create phylogenetic trees that minimize the number of evolutionary changes necessary.
Finding optimal pathways through trees based on gathered traits can illustrate relationships.
Example: A tree illustrating the evolution of insects (e.g., beetles and dragonflies) prioritizes the simplest explanation for trait development and loss.
Computational Methods in Phylogenetics
Modern Approaches: Utilization of computer programs to assist in constructing phylogenetic trees.
Input data includes species, traits, and sometimes DNA sequences accessed online.
The program analyzes and computes relationships based on evolutionary traits and sequences.