Week 7 Lecture Biology

Week 7 Lecture Biology

1. History

   • Carolus Linnaeus
     • System for classifying enormous diversity of life into hierarchial system
   • Georges Cuvier
     • Documented the succession of fossils in geological strata
     • Deeper the stratum, the more dissimilar fossils were from modern life
   • James Hutton
     • Present day landforms were the result of mechanisms that were currently in operation
   • Charles Lyelle
     • "Uniformitarianism" - notion that the rates of geological processes in the past are the same as today
   • Jean Baptise Lamarck
     • Features change with use
     • Acquired features can be passed onto succeeding generations. "Inheritance of acquired features"
   • Thomas Malthus
     • Human population size can grow at much faster rates than food supplies
   • Charles Darwin
     • Darwin collected many thousands of biological specimens from around the world

2. Darwin's voyage

   • Many plants and animals had geographic aspects in their similarities temperate American species were more similar to tropical American
   • Galapagos islands - different forms of many animal groups on different islands
   • Darwin's Theory
     • Natural variation among individuals exists in all species
     • Much of this variation appears heritable
     • All organisms produce more offspring than can survive to maturity
   • Conclusions
     • Struggle for survival occurs in which many individuals are eliminated. Those fitter than the rest will survive
     • Character of the favoured individuals will be proportionately more common in next generation because survivors will contribute more offspring
     • NATURAL SELECTION weeds out less fit variants from a population
       • maintains fitness of a population in a constant environment
       • Allows a population to adapt a new environment

3. Natural selection conditions

   • Not all individuals are able to survive and reproduce to same extent
     • i.e. competition among individuals within species for survival and reproduction
   • There is variation in some traits and this variation at least partially determines survival and number of offspring produced
     • i.e. fitness is tied to variation in traits
   • Some variation in traits that determine fitness is heritable
     • i.e. fitness has a heritable component
   • THESE THREE CONDITIONS ARE NECESSARY AND SUFFICIENT FOR EVOLUTION TO OCCUR
     • Necessary in sense evolution can't occur without them
     • Sufficient in sense that all three conditions occur, evolution must arise

4. Micro-evolutionary change

   • Changes in allele and genotype frequency from one generation to the next
   • Fitness (W)
     • Measure of relative genetic contribution of an individual carrying a particular genotype to next generation
   • Selection coefficient
     • Proportional amount by which fitness is reduced for a particular genotype relative to population
   • Adaptedness
     • Measure of how well a genotype or individual is able to cope with its environment
   • Teleological
     • Relating to final outcome, purposeful
   • Natural selection
     • IS a difference in survival of different genotypes
   • Selection pressure
     • Proportional amount by which fitness is reduced for a genotype, relative to most fit genotype
     • S = 1 - W

5. Macro-evolutionary change

   • How do we deal with long term patterns of evolution where we may never know genetic bases or even selective bases of changes

6. Evidence for Natural Selection

   • Indirect evidence: artificial selection via domestication
     • E.g. different breeds of dogs
   • Direct evidence: biston betularia

7. Change in allele frequency depends on

   • Selection pressure 's' against genotype (larger S, the greater the change)
   • Initial allele frequency "q" (larger q, the greater the change)

8. Games Theory - the good of the species

   • Prisoner's Dilemma
     • If both players keep mum (i.e. each cooperates) they both get a reward of 3
     • If each defects they get a payoff of 1
       • Cooperation provides the highest rewards
     • If population contains only cooperators and we introduce defector, defector does best
       • Defection can invade cooperation
     • If population contains only defectors and we introduce a cooperator, cooperator does worst
       • Cooperation can't invade defection
     • Conclusions
       • ESS = EVOLUTIONARY STABLE STRATEGY
       • The ESS is defect (it can invade a population of cooperators but it can't be invaded)
       • ESS is NOT optimal for population as a whole
       • Evolution can select for strategies that harm the population
       • Evolution need not work for good of species

9. Allodapine bees

   • All foundresses lay eggs shortly after the nest is started
   • All foundresses help to rear the larvae
   • If all females leave the nest, all the brood die
   • If one female leaves the nest after laying eggs, her nest mates will rear the brood and she can begin a nest with another group
   • "Tit for tat": cooperate on first move, then repeat your partner's strategy for succeeding moves

10. Vampire Bats

    • Unable to survive more than 3-4 days without blood
    • Successful bats will often share their blood meal with unsuccessful individuals who they are able to recognize and interact with repeatedly

11. Fitness differentials and microevolution

    • Selection can operate very quickly even when fitness differentials between alternative genotypes are small
    • Yet most cases it is rare to find obvious real time phenotypic evolutionary changes in natural populations
    • This may be because most beneficial mutations have only small effects on obvious phenotypic traits

12. Tempo and mode of evolution: Macroevolution

    • Gradualism paradigm
    • Evolutionary change of gross features in lab is slow, so probably slow in nature
    • Although the fossil record does not indicate smooth gradual change, it comprises only small and very infrequent 'snapshots' over evolutionary time
    • 'Jumpiness' in the fossil record could be sampling artefact. If this jumpiness is ignored, the fossil record seems to indicate gradual change
    • Gould and Eldredge suggested that jumpiness in fossil record might actually reflect jumpiness in tempo of evolutionary change
      • Punctuated equilibrium
        • long periods of relatively low change punctuated by short periods of very rapid change
        • Some fossil data support the gradualism paradigm, other data support punctuated equilibrium

13. Expecting evolutionary stasis over long time periods

    • Bauplan constraints may make it difficult for evolution to individually change inter-related features without leading to maladaptation
    • Macroevolutionary trends: species were formed by radical genetic 'overhauls' whereby new combinations were formed not as the result of selection 'one gene at a time' but by radical unpresentative samples of genotypes at different loci
      • Radical genetic drift (bottle neck)
      • Species Selection
        • Form of new species is random with respect to parent species but may be consistent selection for species with some features, like greater cranial volume