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.