3-Determining_Evolutionary_Relationships
Lesson 4 – Learning Outcomes
Predict the homologous or convergent nature of structures in different vertebrate taxa based on embryonic origins.
Analyze phylogenetic trees to ascertain relationships between taxa; identify shared characters as homologous or convergent; recognize synapomorphies that differentiate taxa.
Evaluate if a taxon is monophyletic and determine if a character is ancestral or derived.
Determining Evolutionary Relationships
Comparative morphology analyzes organism anatomy to establish evolutionary connections.
Introduction to Phylogeny
Phylogeny: the evolutionary history of organisms, revealing how closely they are related based on shared ancestry. Phylogenies are ultimately testable hypotheses.
Morphological Concepts
Similarities in structures can arise in different ways:
Homoplasy: similar structures in appearance but not due to common ancestry.
Analogous structures: similar functionality but evolutionarily independent.
Homologous structures: share a common ancestry.
Homologous Structures
Example: Front legs of newts and pectoral fins of parrotfish are homologous as they derive from a shared ancestral feature (an ancient placoderm).
Homology, Function, and Appearance
Homologous structures can display similarity in function and appearance.
Similar Appearance Example: Mammal eyes vs. frog eyes exhibit both appearance and function similarity.
Diversity in Function/Appearance: Homologous structures like a narwhal's tusk and a snow leopard's canine tooth—similarity in ancestry, but functional and appearance differences.
Convergent Evolution
Cases where structures serving similar functions arise independently in different taxa, e.g., woodpecker and aye-aye adaptations demonstrate convergence despite functional similarity.
Structures resembling may not indicate homology; could be convergent.
Morphological Concepts Question Examples
Compare electric organs in elephant nose fish and echolocation in little brown bats:
Students consider similarity in function versus homology.
Analyze sounds made by red-winged blackbirds and hardhead catfish:
Investigate embryonic origins and structural similarities.
Evidence for Homology
Comparing scales of garter snakes and African pikes requires investigation into embryological origins to substantiate homology claims.
Importance of Development
Insight into basic vertebrate body plans.
Establish homology based on embryonic origins.
Differences in embryonic origins refute claims of homology.
Characters in Phylogenetic Trees
Protostomes and Deuterostomes differ in embryonic development:
Blastopore forms mouth in protostomes, anus in deuterostomes.
Characters classify as either ancestral (plesiomorphic) or derived (apomorphic). This classification is taxon-relative, dependent on evolutionary history and context.
Ancestral and Derived Characters
Ancestral characters are inherited from distant ancestors; derived characters evolve more recently. Terms are relative, context-dependent.
Example: Deuterostome development is derived for Deuterostomes but ancestral for Chordata.
Synapomorphies
A shared derived character that signifies a synapomorphy, establishing monophyletic groups (ancestor and all descendants).
Phylogeny Problem Examples
Assessing taxa relationships in phylogenetic trees emphasizes elucidation of homology versus analogy, ensuring accurate evolutionary interpretations.
Emphasis on shared derived characters forming the basis of phylogenetic hypotheses.
Divergence and Evolution
Closely related taxa inherit numerous shared characters, but disparity in selection pressures may lead to apparent divergence despite common ancestry.
Divergent Evolution: Character loss and appearance differential even in homologous traits.
Lesson Outline
Introduction to Phylogeny
Chordate Characteristics
Chordate Phylogeny
Vertebrate Phylogeny and Evolution
References: Chapters specified for further reading in the biological context.