Evolutionary Biology BIOL 3350 Dr Lisa Rapaport Lecture 4 Notes Merger of Darwin and Mendel I Dilemmas Critiques for Darwin A Stability and Effectiveness of Change 1 Natural selection is only effective to an extent 2 Small differences are not large enough to alter allele frequencies within a population Species differ from one another because they have a lot of allele that are different between them 3 Breaking the selection plateau Castle s selection experiment involved artificial selection on racing stripe width in hooded rats chose different widths Maybe selection modifies the gene Should reach a plateau if keep selecting for racing stripe 4 Castle s selection experiment Multiple factors must be responsible for variation in stripe width multiple genes Refer to corresponding graph shown in Lecture 4 PowerPoint Control did not change much it should not change much He found that he could increase the width of the racing stripe There really was not a plateau at which the changes accumulated The original genes had not changed By having this range of variation show rats were born with original racing stripes Selection can work on continuous variations and the original genes have not actually changed B Maintenance of variation 1 Blending inheritance Fleeming Jenkin 1867 variation among individuals cannot be maintained if blending inheritance occurs Example of blending inheritance skin color in humans This variation is continuous 2 Environmental variation 3 Survival of mutants Most variation was attributed to the environmentally Mutants have greater survival most of the times 4 Continuous variation results from the inheritance of discrete genes Discrete traits determined by a single gene are actually rare Polygenic traits traits determined by multiple genes show continuous variation most traits are determined by polygenic traits 1 About 50 genes and regions if the genome are associated with height in humans Only 50 60 heritability and the rest is caused by the environment like nutrition during growth 5 Polygenic inheritance in corolla length in tobacco Nicotiana longifloria Edward East 1916 Number of genes different numbers of phenotypes were predicted Saw continuous variation in trait expression One gene 3 phenotypes Two genes 5 phenotypes There were individuals at the short end of distribution and at the long end of distribution only took 5 generations until he created the original parental phenotypes C Natural selection could not explain speciation 1 Relationship of divergence to speciation It was thought that no mechanisms promote speciation When populations are isolated from each other they tend to diverge from each other Being geographically separated could cause adaptive divergence Reproductive isolation can evolve as a by product of adaptive divergence in geographic isolation Two populations of the originally same species that are separated geographically will eventually become so adaptively divergent that they will no longer be able to reproduce with each other overtime Each population start to adapt to the specific conditions in which they find themselves Maybe because of the different habitat positions one group starts to produce flowers earlier in the season and the other group starts to produce flowers later in the season This is known as allopatric speciation o Allopatric speciation speciation that is taking place in geographic isolation Benthic and limnetic three spine sticklebacks Benthic consumes invertebrates large body and few short gill rakers Limnetic consumes plankton small body and many long gill rakers Size assortative mating leads to byproduct reproductive isolation Speciation can occur even without geographic barrier limnetic lives in deep part of lake and benthic lives at top in open water 2 They diverged in the presence of one another because they were choosing different sub habitats When it comes to mating benthic were too small for limnetic and limnetic were too big for benthic the preferred mating with their own sizes Preference for spawning with organism of the same size this drove speciation Sympatric speciation speciation in the same place 2 Punctuational not gradual change observed in fossil record Short period of rapid change followed by long periods of stasis Punctuated way of evolution long periods of no change followed by short rapid bursts of evolution Antibiotic resistance and antiviral resistance are examples of rapid evolution and extreme natural selection Bacteria are rapidly evolving to become resistant to antibiotics Antibiotic resistance occurs because bacteria are rapidly evolving to become resistant Viruses also become resistant to treatments Almost all viruses are resistant when it becomes about 20 months of using treatment o This is why a variety of treatments are used in order to 3 Trinidadian Guppies Escape Ability prevent viral resistance Escape ability was found to be a rapidly acquired heritable trait based on the experiments conducted Guppies that were raised in areas of high predation and that were thus used to this stressor had a much higher survival rate when placed in an area containing a predator than those that were raised in areas of low predation and were thus not used to their foreign stressor Long term experiment after 20 years took 6 guppies from low predation and 6 from high predation habitats and put them in enclosure with their natural predators waited until half of the guppies were eaten and saw who were left higher survival rate of high predation guppies higher survival abilities Raised offspring of both types in a lame without any predation at all found that in F2 generation those that had grandparents from high predation areas were more likely to survive Individuals from low predation areas had much brighter colors while higher predation guppies were duller in color and built for faster swimming II The Contributions of Mendel A The heritability problem was solved by Mendel 3 1 The inheritance of discrete traits or traits that are control by a single 2 Variation is produced by the independent assortment and segregation of Mutations produce variation but variation can also be produced gene were studied alleles by other factors B Problems that were not solved by Mendel and his work 1 Inheritance for continuous traits Mendel s laws strictly pertained to discrete variation so they were not based on continuous traits A vast amount of variation in populations is continuous Mendel believed that the environment