Fish Systematics: How does this stuff work

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Fish SystematicsHow does this stuff work??

• Study of fish diversity and the evolutionary
  relationships among populations, species and
  higher taxa
• Chapter 2
• (Helfman, Collette Facey)

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Systematics

• Develop an understanding of patterns of diversity
  in the context of evolutionary and ecological
  theory.
• trends in where fish groups are found (spatial
  distribution)
• trends in emergence/extinction of evolutionary
  groups

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Systematics

• Sample questions
• What has favored/allowed greater diversity of
  fishes on coral reefs than in lakes?
• What has allowed/favored cypriniforms,
  siluriforms and characiforms to become so
  diverse?
• What factors have allowed/favored the persistence
  of ancient taxa in the Mississippi River basin
  (bowfin, gar, paddlefish, etc.)?
• What is the evolutionary (phylogenetic)
  relationship between salmon and pike?

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Subdisciplines in Systematics

• Taxonomy - the theory and practice of describing,
  identifying and classifying taxa (groups of
  phylogenetically related organisms)
• Nomenclature - the naming of taxonomic groups
• Classification - organizing taxa into like
  groupings

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Focus of Systematics on Species

• Historically, understanding species most common
• group of organisms that can reproduce and
  generate viable offspring
• Today, emphasis is below species level (why?)
• Endangered Species Act
• applies to distinct population segment of a
  species which interbreeds when mature

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Species Concepts

• Morphological (Linnaeus) the smallest group of
  individuals that look different from each other.
• can misclassify based on differences that can be
  maintained within an interbreeding group
• depends only on observable morphological
  differences

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Species Concepts

• Biological (Mayr) group of populations of
  individuals that are similar in form and function
  and that are reproductively isolated from other
  populations
• conventional definition until late 1980s
• includes genetic information
• ignores hybridization
• dependent on geographic isolation to achieve
  species status

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Species Concepts

• Evolutionary (Wiley) a population or group of
  populations that shares a common evolutionary
  fate and historical tendencies
• recognizes more than just genetic and
  morphological differences
• difficult to determine evolutionary fate
• how much diversity is allowed within a common
  evolutionary fate?

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Species Concepts

• Phylogenetic the smallest biological unit
  appropriate for phylogenetic analysis (process
  that rates traits as ancestral or derived and
  then looks for groupings based on similarities)
• does not infer modes of speciation
• nothing is arbitrary
• depends on thorough phylogenetic analysis first

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Species Concepts

• Usefulness of each concept depends on the use -
  for Endangered Species Act, use as much evidence
  as possible
• morphological, physiological, behavioral
• geographic
• life history development
• habitat feeding ecology
• phylogenetics
• evolutionary fate

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Determining Relationships Between Taxa

• Traditional examine and list primitive to
  advanced, link groups based on a few arbitrary
  traits, generate lineage model based on these
  limited data

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Determining Relationships Between Taxa

• Phenetics multivariate statistical approach
• assemble list of traits
• determine degree of similarity among groups based
  on number of similar traits
• ignores evolutionary linkage of groups
  (convergence could put evolutionarily distinct
  lines into a single taxon)

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Determining Relationships Between Taxa

• Phylogenetic (cladistic)
• assemble a list of traits
• classify each taxonomic group on basis of
  presence or absence of each trait
• determine degree of similarity among groups based
  on shared and unique traits

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Determining Relationships Between Taxa

• Phylogenetic (cladistic), continued
• determine degree of similarity among groups based
  on shared and unique traits
• shared traits plesiomorphic traits (ancestral)
• unique traits apomorphic traits (derived)
• shared unique traits synapomorphic traits
• monophyletic group of taxa (common origin) clade

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Cladograms

• Phylogenetic relationships expressed in
  cladograms - branching representation of the
  evolutionary relationships among taxa based on
  shared common traits and shared unique traits

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Constructing a Cladogram

• Listing of traits
• Coding of each taxon by presence or absence of
  each trait
• Assemble groupings based on trait conditions
• Use the simplest branching structure possible
  principle of parsimony

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Which traits do I use?
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Speciation

• How do populations become distinct species? - the
  process whereby gene flow is reduced sufficiently
  between sister populations to allow each to
  become different evolutionary lineages
• Allopatric (with geographic isolation)
• Non-allopatric (without geographic isolation)

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Speciation

• Allopatric (with geographic isolation)
  speciation
• Vicariant - large populations geographically
  isolated (little inbreeding) (United States)
• Founder - small population becomes geographically
  isolated and then reproductively isolated via
  inbreeding, selection, drift (Gilligans Island)
• Reinforcement - early isolation followed by
  sympatry, but selection against hybrids

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Speciation

• Non-allopatric (without geographic isolation)
• Sympatric - sister species evolve within the
  dispersal range of each other, but adapt to
  different habitats - habitat-dependent assortive
  mating
• Parapatric - sister species evolve in segregated
  habitats across a narrow contact zone - little
  mixing in spite of proximity

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Final synthesis on species

• Groupings that are different from each other
• morphology, behavior, physiology, ecology
• Reproduction is isolated in practice
• Mating systems and mate-recognition systems are
  important enforcers of isolation