Lecture 1: Systematics and Taxonomy

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Lecture 1 Systematics and Taxonomy

• What is systematics? evolution of biological
  diversity
• Goals determine genealogy (phylogeny) and
  properly constituted names (taxonomy)
• Why do systematics? Predictive
• Taxol, cancer and yew

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OUTLINE

•  How Are Phylogenetic Trees Reconstructed?
•  Characters Used in Reconstructing Phylogenies
•  Phylogenetic Trees Have Many Uses
•  Why Classify Organisms?
•  The Hierarchical Classification of Species
•  Biological Classification and Evolutionary
  Relationships
•  The Future of Systematics

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How Are Phylogenetic Trees Reconstructed?

• Phylogenetic trees display history of descent of
  a group of organisms from their common ancestor.

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Figure 23.1

• Figure 23.1

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How Are Phylogenetic Trees Reconstructed?

• Reconstruction based on analysis of evolutionary
  changes in characters of organisms (eg. DNA
  sequences, behavior anatomical feature).
• Traits that are inherited from a common ancestor
  are said to be homologous.

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Figure 23.2

• Figure 23.2

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How Are Phylogenetic Trees Reconstructed?

• Characters that are similar as a result of
  convergent evolution or evolutionary reversals
  are said to be homoplastic.

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How Are Phylogenetic Trees Reconstructed?

• To determine true evolutionary relationships,
  systematists must distinguish between homologous
  and non-homologous (homoplastic) characters as
  well as between ancestral and derived characters
  within a lineage.
• Derived character- one that differs from its
  ancestral form.
• e.g. fins (ancestral)-- limbs (derived)

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Ancestral -----------Derived
6 legs-------------------------- 3 legs
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Figure 23.5

• Figure 23.5

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Traits Used in Reconstructing Phylogenies

• Systematists use fossils and the rich array of
  morphological and molecular data available from
  living organisms to determine evolutionary
  relationships.

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Traits Used in Reconstructing Phylogenies

• The structures of proteins and the base sequences
  of nucleic acids are important data.

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Figure 23.7
figure 23-07.jpg

• Figure 23.7

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Phylogenetic Trees Have Many Uses

• Phylogenetic trees help biologists determine how
  many times evolutionary traits have arisen and
  when lineages diverged.

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Figure 23.8
figure 23-08.jpg

• Figure 23.8

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Figure 23.9
figure 23-09.jpg

• Figure 23.9

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 Taxonomy (science of classification) and
nomenclature (rules for naming organisms)
classification system developed by Carlos Linnaeus
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Why Classify Organisms?

• Classification systems improve our ability to
  explain relationships among organisms and provide
  unique, universally used names for organisms.

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The Hierarchical Classification of Species

• Biological nomenclature assigns each organism a
  unique combination of a generic and specific
  name. (binomial nomenclature)
• Scientific name (unique) vs. common name
• Genus name species name always underlined or
  written in italics.
• e.g. Felis concolor

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Why not use common names? same common name
applied to different species e.g. gopher
refers to tortoises in Florida and pocket gopher
in western US bluebells
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The Hierarchical Classification of Species

• In the Linnaean classification system, species
  are grouped into higher-level units called
  genera, families, orders, classes, phyla, and
  kingdoms.

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Figure 23.11
figure 23-11.jpg

• Figure 23.11

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Biological Classification and Evolutionary
Relationships

• Problem- early classifications were
  non-evolutionary
• Systematists today agree that taxa should share a
  common ancestor (monophyletic). Review Figure
  23.12
• Monophyletic group (clades) contain common
  ancestor and all descendants.

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Figure 23.12
figure 23-12.jpg

• Figure 23.12

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Biological Classification and Evolutionary
Relationships

• Non-monophyletic taxa should be avoided because
  they misrepresent evolution.
• e.g. reptiles as traditionally defined do not
  include birds

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Figure 23.13
figure 23-13.jpg

• Figure 23.13

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The Future of Systematics

• Molecular methods and powerful computers have
  revolutionized systematics.
• Phylogenies are increasingly being used to answer
  questions other than evolutionary relationships.

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RELATIVE TIMING CHARACTER CORRELATION
When and how did tail propulsion evolve in
cetaceans?
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RELATIVE TIMING CHARACTER CORRELATION
hind limbs vestigial
hind limbs reduced sacral
reduction/disassociation fluke
development lumbar elongation
cervical shortening sacral/caudal elongation
(after Buchholtz 1998, Hulbert 1998, Thewissen
1998)