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Unnatural selection: adaptive evolution driven by chemical pollution

Unnatural selection: adaptive evolution driven by chemical pollution. Bruce C. Coull Dean, School of the Environment University of South Carolina, Columbia. Evolution occurs via Natural Selection.

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Unnatural selection: adaptive evolution driven by chemical pollution

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  1. Unnatural selection: adaptive evolution driven by chemical pollution Bruce C. Coull Dean, School of the Environment University of South Carolina, Columbia

  2. 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 Mendel’s work on garden peas established the nature of inheritance • Neodarwinists investigate biological adaptation to the physical world

  3. Different types of natural selection • Response to environmental stress • Temperature • Light • Space • Food • Sexual selection • Mate choice • Territoriality

  4. Human impact on increase • Increased contaminants • Point source • Non-point source • Global warming • Habitat alteration • Erosional processes • Altered hydrology • Increasing development

  5. 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

  6. What is evolution? In the broadest sense, genetic change… More narrowly, changes in genetic frequency in a population

  7. Any change is evolution— Whether it is directly selected or a product of random chance

  8. Case study of estuarine copepod Use of a “neutral” genetic marker for toxicological study

  9. Model Organisms: Copepods Microarthridion littorale (Poppe 1881)

  10. 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

  11. GROUP II GROUP III GROUP I Cytochrome b variants within SC

  12. North Carolina Shallotte River South Carolina Murrells Inlet North Inlet Buck Hall Charleston Harbor Georgia Rathall Creek Shipyard Creek Beaufort New Market Creek Diesel Creek Savannah

  13. GROUP I North Carolina GROUP II GROUP III Shallotte River South Carolina Murrells Inlet North Inlet Buck Hall Charleston Harbor Georgia Rathall Creek Shipyard Creek Beaufort New Market Creek Diesel Creek Savannah

  14. GROUP I North Carolina GROUP II GROUP III Shallotte River South Carolina Murrells Inlet North Inlet Buck Hall Charleston Harbor Georgia Rathall Creek Shipyard Creek Beaufort New Market Creek Diesel Creek Savannah Stronger correlation for pollution than geographic distance

  15. 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

  16. Low (0.075 g/ml CHPY 0.005 g/ml DDT ) Medium (0.150 g/ml CHPY 0.010 g/ml DDT ) High (0.225 g/ml CHPY 0.015 g/ml DDT ) Control 24 h exposure 450 F 150 M 450 F 150 M Rep 1 450 F 150 M 450 F 150 M Rep 2          450 F 150 M 450 F 150 M Rep 6 

  17. 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

  18. Control Treatment N=141 N=174 0.5 0.5 0.4 0.4 0.3 0.3 I 0.2 0.2 0.1 0.1 0 0 1 2 3 4 5 6 1 2 3 4 5 6 0.5 N=149 N=103 0.5 0.4 0.4 Proportion of Group Surviving 0.3 0.3 II 0.2 0.2 0.1 0.1 0 0 1 2 3 4 5 6 1 2 3 4 5 6 0.5 0.5 N=156 N=111 0.4 0.4 0.3 0.3 III 0.2 0.2 0.1 0.1 0 0 1 2 3 4 5 6 1 2 3 4 5 6 Replicate Group I increases (% basis) and others decrease relative to controls (=0.05)

  19. 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

  20. However… some organisms directly respond to chemical threats—

  21. 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)

  22. Thus: Pollutants are an increasingly important evolutionary force

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