BIO 115 Lecture Notes - Lecture 25: Medium Ground Finch, Heritability, Natural Selection
Charlie Kent
Bio 115
2017 Fall
Human Biology
natural selection
● The Grants and their study of finches on an island in the Galapagos
○ Was tons of diversity in Darwin’s finches
■ Variation in beak size, feeding niches, etc.
○ Medium ground finch:
■ Variation in beak size influences efficiency at eating different types of
seeds
● Invented a pressure machine to determine the functionality of
different beaks ad how they would deal with seeds on the island.
● Birds were eating various seeds.
● These birds don’t leave the island. Closed population for the most
part. Have been able to block off many mechanisms for evolution
since there’s no migration in. had a lot of characteristics to study
NS.
● Capture them all and band them, and could trace families to see
who the parents were for each offspring.
● Beak size evolution
○ Drought resulted in more hard, woody seeds.
■ Favoured larger beaked birds
○ Adaptation: trait that has evolved via natural selection
○ Pink graph
■ Y axis: average depth of offspring beaks
■ X axis: average of the parent’s beak (midparent trait)
■ Did a regression, found the slope of the relationship. H2=0.9
● it’s heritability. Is the additive genetic variation in a trait.
■ Know how close offspring and parent’s’ traits are.
■ Core of NS.
■ Heritability slope: 90% of variability in the offspring is due to parents.
Very high heritability. Good candidate for studying natural selection.
○ What does this trait have to have selected in it ?
■ needs to be associated between beak depth and fitness.
● Measured the two traits in all these finches on the island—
happened to be a drought early on.
● Plant didn’t reproduce.
● Finches died off. Seeds that were mostly dying that everyone could
eat
● Ones that weren’t favoured-harder nut like seeds—were highly
available but populations couldn’t eat them so they died.
○ Population evolved over a generation due to the die off.
○ Beak depth changed significantly.
○ Measured selection differential**
Document Summary
Variation in beak size influences efficiency at eating different types of seeds. Invented a pressure machine to determine the functionality of different beaks ad how they would deal with seeds on the island. Have been able to block off many mechanisms for evolution since there"s no migration in. had a lot of characteristics to study. Capture them all and band them, and could trace families to see who the parents were for each offspring. Drought resulted in more hard, woody seeds. Adaptation: trait that has evolved via natural selection. Y axis: average depth of offspring beaks. X axis: average of the parent"s beak (midparent trait) Did a regression, found the slope of the relationship. Is the additive genetic variation in a trait. Know how close offspring and parent"s" traits are. Heritability slope: 90% of variability in the offspring is due to parents. Needs to be associated between beak depth and fitness.
