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EVOLUTION IN LARGE POPULATIONS: SELECTION

This article explores the influences on genetic diversity and the evolution of populations, highlighting the need for adaptation in the face of environmental change. It discusses physiological, behavioral, and genetic adaptations, as well as the role of natural selection in adaptive evolution. The article also examines the impact of selection on quantitative characters and provides case studies on directional, stabilizing, and disruptive selection. Overall, it emphasizes the ubiquity of adaptive evolution in plants and animals with genetic variation.

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EVOLUTION IN LARGE POPULATIONS: SELECTION

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  1. EVOLUTION IN LARGE POPULATIONS: SELECTION

  2. Migration Genetic Drift Mutation Natural Selection Influences upon genetic diversity and the evolution of populations

  3. The need to evolve • environmental change is ubiquitous • Pests, parasites, novel competitors, anthropogenic change, global warming, new diseases • Species must adapt and evolve to avoid extinction

  4. Adaptation • Increased blood O2 affinities at altitude • Linked to structural changes in haemoglobin molecules Weber (2007) Respiratory Physiology & Neurobiology vol 158 132–142 • 3 forms of adaptation: Physiological, behavioural and genetic Physiological adaptation: change in metabolism or biochemistry to deal with an environmental problem Example: High-altitude adaptations in vertebrate haemoglobins

  5. Adaptation • Subset of population uses sponges to probe substrate for fish • Recent co-ancestry • Vertical social transmission among females • Cultural transmission of tool use? Krützen et al. (2005) PNAS vol 102 8939-8943 Behavioural adaptation: the things organisms do to survive Example: feeding specialisations in bottlenose dolphins in Shark Bay, WA

  6. Adaptive evolution Adaptive evolution: long term evolutionary changes in response to natural selection upon superior genetic variants • Adaptive evolutionary changes in animals have been documented in: - morphology, behaviour, colour, prey size, body size, life history, disease tolerance and resistance, biocide resistance, tolerance to pollutants. • Plants evolve in response to: - soil conditions, light regimes, water stress, flooding, air pollution and herbicides. Plant populations adapted to diverse ecological conditions are so common that they have their own term, called ecotypes.

  7. Adaptive evolution and explosive speciation in cichlid fish • Genetic adaptation and adaptive evolution is ubiquitous in species that have genetic diversity Kocher, T (2004) Nature Reviews Genetics 5: 288-29

  8. Adaptive evolution • Take home message: Adaptive evolution is ubiquitous in plants and animals that have genetic variation • Adaptive evolution is important in the following conservation contexts: - Preserving evolutionary potential - Adaptation to marginal environments - Genetic adaptation to captivity - Adaptation of invasive species - Outbreeding depression

  9. Natural Selection

  10. Evolving populations are complex systems • Evolving populations are complex systems influenced by mutation, migration, selection and chance operating within the context of the breeding system

  11. Is Natural Selection the Same Thing as Evolution evolution is directional in producing all the life-forms on earth today from one or several ancestral life-forms billions of years ago

  12. Natural selection is an observable process that is often purported to be the underlying mechanism of unobservable molecules-to-man evolution.

  13. Through natural selection, genetic information (variety) was lost. The long-fur dogs survive better in a cold environment; they are less able to survive in a warm environment and vice versa. A particular characteristic in the dog population was selected for. Dogs are still dogs since the variation is within the boundaries of “kind.”

  14. Selection on quantitative characters • Variation is determined by several loci and environmental effects • Selection affects phenotypic means and variances • 3 forms of selection on quantitative characters: Directional selection: favours phenotypes toward one end of the distribution and shifts mean towards that extreme Stabilizing selection: favours phenotypic intermediates and reduces variation about the mean Disruptive Selection: favours both phenotypic extremes and increases variation about the mean

  15. Case study: directional selection Undesirable evolutionary consequences of trophy hunting in Bighorn sheep Coltman et al. (2003) Nature426, 655-658 Directional selection: favours phenotypes toward one end of the distribution and shifts mean towards that extreme

  16. Case study: stabilizing selection Stabilizing selection for birth weight in humans after Mather, 1973 Stabilizing selection: favours phenotypic intermediates and reduces variation about the mean

  17. Case study: disruptive selection Disruptive Selection: favours both phenotypic extremes and increases variation about the mean Disruptive selection and then what? Rueffler et al. (2006) TREE21, 238-245; Schulter and McPhail (1992) The American Naturalist 140: 85-108 Benthic feeder Plankton feeder

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