BILD 3 Lecture Notes - Lecture 5: Daphne Major, Bild, Antimicrobial Resistance
13 Jun 2018
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BILD 3 Lecture 5
4/11/2018
• Daphne Major island drought 1976-1978
o Avg. number of birds with larger beak depth shifted→more birds with bigger
beaks→evidence of natural selection
o The finches that were born the year after the drought had larger beaks: the
population evolved
o This is not a permanent change: after the drought, the rainfall returned to
normal, and as the years went on with normal rainfall, the beak size of the birds
returned to what it was prior to the drought
▪ The eiroet did’t eessaril gie adatage aore to the ig-
beaked finches
▪ This is the process of natural selection via adaptation
o General conclusions:
▪ Variation randomly exists in populations
▪ Environmental changes can suddenly make a certain genotype
advantageous over others
▪ Natural seletio does’t reate a perfet orgais, eause the
environment is always changing
▪ The population has to get by with what they have when the environment
changes→you a’t pik a ariatio that does’t alread eist i the
population
• Natural selection has four requirements
o Organisms must reproduce to form a new generation
o Phenotype must be heritable
o There must be variation in the phenotype among members of the population
o There must be differences in the fitness of organisms associated with their
heritable and variable phenotypes
• Modes of selection
o Directional
▪ The extreme phenotype is the most fit
▪ It changes the population mean
▪ It decreases variation overall
▪ Ex: Dari’s fihes i the Daphe Major islad; atiioti resistae
(MRSA; microevolution)
o Stabilizing
▪ The intermediate phenotype is the most fit
▪ No change in population mean
▪ Decreases variation overall
▪ Ex: human baby birth weight; ball gall fly in gall diameter: the large ones
are eaten by woodpeckers while the small galls are parasitized by the
wasps
o Disruptive
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