Bio.+1331+L12+Phylogeny+new
Lecture 12: Phylogeny
Overview of Phylogenetics
Phylogenetics is the study of evolutionary relationships among species.
It revolves around understanding how life has changed over the 3.5 billion years of existence.
Isolated Populations
Consequences of Contact
When isolated populations come into contact:
Divergence can be reinforced.
Hybrid zones can occur.
A new species can be formed.
All of the above can happen.
Chapter 25 Openers and Goals
What You'll Learn
The chapter explores:
Methodologies for studying the history of life.
The dynamics of diversity and how significant changes occur.
Key Concepts
Utilize phylogenetic trees and fossil records.
Explore concepts of adaptive radiation and mass extinction.
Anatomy of a Phylogenetic Tree (Table 25.1)
Components
Root: The most ancestral branch in the tree.
Internal Branch: Represents a lineage over time.
Terminal Branch (Tip): Endpoint of a branch indicating a living or extinct species.
Node: A branching point representing a common ancestor.
Outgroup: A species that diverged before those under study; aids in rooting the tree.
Polytomy: A node that shows multiple descendant branches indicating insufficient data to resolve relationships.
Understanding Phylogeny
Definitions
Phylogeny: The pattern and timing of evolutionary branching events; often depicted as an evolutionary tree.
Common Ancestors: These cannot be observed directly; inferred from data.
Generating Phylogenies
Methodology
Biologists generate phylogenies as hypotheses:
Using genetic, morphological, and behavioral data.
Evolutionary Principles
Key Concepts
Evolution: Defined as "descent with modification."
Common Ancestry: Implies that closely related species will have homologous traits.
Synapomorphy: Shared derived traits which help trace evolutionary history.
Distinguishing Traits
Examples of Traits
Hair in Mammals: A synapomorphy used to distinguish mammals from other tetrapods.
Cladogram: A diagram representing the evolutionary relationships based on shared traits.
Inferring Phylogenies
Closely Related Species
Should share informatively derived traits indicating homology rather than analogous traits (convergent evolution).
Requires identifying:
Homologies
Ancestral vs. Derived states
Branch Lengths in Phylogenetic Trees (Table 25.3)
Meaning of Branch Lengths
Branch lengths are not definitive but aid in estimating evolutionary relationships.
The emphasis is on the branching pattern, which shows:
Genetic differences among populations.
Evolutionary time between nodes.
Complications in Phylogenetic Analysis
Challenges
Traits shared for other reasons (e.g., convergent evolution).
Potential reversals to ancestral states complicate interpretations of relationships.
Classification Implications
Definition of Groups
Monophyletic: Includes an ancestor and all its descendants.
Paraphyletic: Includes an ancestor and some, but not all, descendants.
Polyphyletic: Includes multiple lineages without a common ancestor.
Benefits of Phylogenies
Applications
Tracing evolutionary relationships.
Understanding the tree of life.
Classifying organisms and studying trait evolution.
Analyzing adaptive radiations.
Examples of Adaptive Radiation
Specific Cases
Darwin's Finches: Example of adaptive radiation in response to diverse ecological niches.
Cichlid Fishes: Rapid evolution into numerous species from small populations entering new lakes.
Evolutionary Patterns
Patterns Over Time
Evolution can take various patterns including:
Stabilizing selection and directional selection.
Punctuated equilibria with bursts of diversification.
Phylogenetic Applications: Case Studies
Case Study: Newt Toxicity and Snake Resistance
An evolutionary arms race where snakes evolve increased toxicity in response to newt toxicity.
Trait Evolution Examples
Analyzing traits in Sceloporus lizards regarding egg-laying vs. live births.
Evolutionary evidence from genetics linking whales and hippos through shared derived traits.