Speciation

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Speciation

• Process by which a daughter species evolves from
  a parent species
• Genetic Divergence-
  when populations become
  reproductively isolated
• Species-population of individuals who can
  interbreed under natural conditions producing
  fertile offspring
• Does evolution always result in a new species?

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2 Concepts on Speciation

• Evolutionary species concept ? every species has
  its own evolutionary history, part of which is in
  the fossil record, and diagnostic traits
• Biological species concept ? reproductive
  isolation rather than trait differences define a
  species

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Reproductive Isolating Mechanisms

• Any heritable feature of body form, functioning
  or behavior that prevents interbreeding between
  species
• Pre-zygotic and Post-zygotic

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Pre-ZygoticMechanisms

• Behavioral
• Temporal
• Mechanical
• Habitat isolation
• Gametic mortality

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Post-Zygotic Mechanisms

• Hybrid mortality ?lower in fitness, early death
• Hybrid sterility
• Would natural selection favor pre- or
  post-zygotic mechanisms?

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Types of Speciation Processes

• Allopatric Speciation-species form due to
  physical barriers that prevents gene flow
  mountain range, river, island
• BARRIER
• Species A becomes distinct from species B cannot
  mate with each other

A
B
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Allopatric Speciation

• Salamanders in Central California
• Washington Sockeye salmon in lakes vs rivers

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Allopatric Speciation Adaptive Radiation

• A single ancestral species gives rise to a
  variety of species, each adapted to a specific
  environment
• Hawaiian honeycreepers
• Occurred after dinosaur extinction ? mammals
  diversified in only 10 million yrs!

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Types of Speciation Processes

• Sympatric speciation-species forms within the
  home range of an existing species in absence of
  physical barrier
• Species
  A-blue
• Species
  B-purple
• Species A and B cannot mate

A
B
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Sympatric Speciation

• Polypoidy in plants
• Autopoidy ? diploid plant produces diploid
  gametes
• Alloploidy? hybrid plant doubles it chromosome

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Models of Macroevolution

• Gradual Model-new species formed through gradual
  changes in traits over time most consistent with
  fossil record

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Models of Macroevolution

• Punctual Model-new species formed in a short
  amount of time occurs through bottlenecks/founder
  effects, mutations, directional selection
  (natural selection)

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Developmental Genes and Macroevolution
all animals share the same control switches for
development

• Development of eyes is controlled by Pax6 gene
• It did not matter if it was a lens or compound
  eye
• Loss of gene results in failure of eye to develop
  in mice, humans

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Developmental Genes and Macroevolution

• Development of overall shape is controlled by Hox
  genes
• Control number and appearance of repeated
  structures
• Differential expression in chickens vs snakes

animal diversity is due to variation in the
expression of ancient genes
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Evolution of the Modern Day Horse
Macroevolution is not goal-oriented

• Does not fit a gradual model perfectly
• Trends observed
• Increase in size
• Toe reduction
• Change in tooth size/shape
• Modern horse evolved 4 mya adapted for living in
  open plains

speciation, diversification, and extinction are
common occurances
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Darwins drawing in The Origin of Species