Unnatural selection: adaptive evolution driven by chemical pollution

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Unnatural selection adaptive evolution driven by
chemical pollution

• Bruce C. Coull
• Dean, School of the Environment
• University of South Carolina,
• Columbia

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Evolution occurs via Natural Selection

• Darwin (1859) first noted the link between
  heredity of traits and their impact on
  survivorship in perpetuating a population
• Rediscovery of Gregor Mendels work on garden
  peas established the nature of inheritance
• Neodarwinists investigate biological adaptation
  to the physical world

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Different types of natural selection

• Response to environmental stress
• Temperature
• Light
• Space
• Food
• Sexual selection
• Mate choice
• Territoriality

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Human impact on increase

• Increased contaminants
• Point source
• Non-point source
• Global warming
• Habitat alteration
• Erosional processes
• Altered hydrology
• Increasing development

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Organisms respond to new stresses

• Non-adaptive
• Increased tumor frequencies in natural
  populations (e.g., mammals, fish, and copepods)
• Endocrine disruption (e.g., Tributyltin in
  snails, ?-estradiol mimics in plastics)
• Adaptive
• Antibiotic resistance in bacteria
• Pesticide resistance in insects

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What is evolution?

• In the broadest sense, genetic change
• More narrowly, changes in genetic frequency in a
  population

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Any change is evolution

• Whether it is directly selected or a product of
  random chance

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Case study of estuarine copepod

• Use of a neutral genetic marker for
  toxicological study

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Model Organisms Copepods
Microarthridion littorale (Poppe 1881)
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Cytochrome b apoenzyme

• Gene in the mitochondrial genome
• involved in electron transport chain
• maternally inherited clonal
• no introns or recombination
• Evolves relatively rapidly
• many silent mutations at third positions
• good population genetic marker

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Cytochrome b variants within SC
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Stronger correlation for pollution than
geographic distance
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Can we recreate this pattern in the lab?

• Use samples from a site with nearly equal group
  distributions
• Establish mixed pesticide levels (CHPY/DDT) to
  induce selection
• Test for differential survival of groups

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?
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What do we expect?

• Pesticide exposed treatments survived to 15
  levels of controls
• Following results are for survivors only
• From field data Group I individuals should
  increase-- Groups II III should decrease
  compared with controls

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Group I increases ( basis) and others decrease
relative to controls (?0.05)
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Conclusions and Considerations

• Variation at a single locus (Cyt b) is related to
  pollution history in the field and lab
• Some groups marked by Cyt b are better survivors

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However some organisms directly respond to
chemical threats
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Examples of organisms adapting to chemical threats

• Changes in grasses on mine tailings (Antonovics)
• Changes in oligochaetes in response to heavy
  metals (Maritinez and Levington)
• Resistance to antibiotics by Streptococcus and
  Tuberculosis
• Mosquito resistance to dieldrin (cyclodiene)

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Thus Pollutants are an increasingly important
evolutionary force