Evolution of Animal Diversity 3

• Nonrandom mating: individuals choose mates based on some phenotypic trait (assortive mating)
• Positive assortive mating: mating between individuals with similar phenotypes
• Point mutations: usually harmless, but could have a large effect on phenotype in right circumstances
• Genetic drift: random fluctuations in allele frequencies (e.g.) bottleneck effect
• Migration

  • can result in the movement of genes among populations
  • reduces level of population differentiation
• Natural selection

  • only natural selection results in the adaptation of populations
• Types of Natural Selection

  Directional

  • favours variants a 1 extreme of distribution
  • shifts frequency curve for a character in one direction
• Types of Natural Selection

  Disruptive

  • favours variants at both ends of distribution
  • shifts frequency curve so intermediate is at disadvantage
• Types of Natural Selection

  Stabilizing

  • favours variants from intermediate side of distribution
  • shifts frequency curve so both extremes at disadvange
• Sexual Selection: traits that increase reproductive success so that genes may be passed on
• Types of Sexual Selection

  Intrasexual

  • selection within same sex (e.g. males compete against other males for females)
• Types of Sexual Selection

  Intersexual

  • individuals of one sex selectively choose mates (usually females choose mates)
• Macroevolution: The evolution of large groups of organisms over time (macroevolution = new species)
• Why are some lineages so much more diverse?

  due to high speciation rates with low extinction rates and species selection
• Speciation - the process by which a population of organisms becomes reproductively isolated from other populations
• Species Selection - The process by which individuals of one species are selected to survive and reproduce
• How do we know what caused the Cretaceous mass extinction?

  thin layer of clay enriched with iridium in sediment which is common in meteorites
• Mass Extinction Consequences

  • long period to regain a level of diversity
  • alters ecological communities
  • large adaptive scale
  • formation of new species
• Taxonomy - formal system for naming and grouping species
• Systematics - study of variation among animals groups to understand their evolutionary relationships
• Linnaean taxonomy - a system of classification based on the idea that all organisms are related to one another (hierarchial system)
• Order in Diversity: 8 Mandatory Ranks

  • Species
  • Genus
  • Family
  • Order
  • Class
  • Phylum
  • Kingdom
  • Domain