Lecture 2: Human - Agricultural Coevolution

Question 1

Coevolution

Answer 1

• Reciprocal evolutionary responses in a pair of species caused by selection imposed by each other

Question 2

Sexual coevolution

Answer 2

• Reciprocal evolutionary responses in the two sexes caused by selection imposed by each other

Question 3

Human agricultural coevolution

Answer 3

• Reciprocal evolutionary responses in humans and their agricultural species
• Evolution by natural selection is genetic and ecological process. Ecology produces selection, genetics provide material transmitted across generations
• Ecology includes culture and organisms we interact with

Question 4

Lactase

Answer 4

• Humans digest milk using lactase enzyme
• Humans get many milk-based products
• Lactase production declines in adulthood
• Lactase production persist through adulthood in people of European origin

Question 5

Evolution in European Cattle Farming Cultures

Answer 5

• Genetic hypothesis: substitutions are casual variants, genes kept on
• Evolutionary hypothesis: lactase production favored by natural selection

Question 6

Predictions

Answer 6

• For genetic hypothesis, other human populations with lactase persistence should have same substitutions
• For evolutionary hypothesis, other human populations practicing dairy agriculture should have lactase persistence phenotypes

Question 7

Results

Answer 7

• African cultures with dairy farming also have distinctive forms of lactase gene.
  
  • DNA sequence differences correlate significantly with ability to digest lactose
• Strengthen inference that molecular variants actually affect phenotype
• Independent evolution of same phenotype in different populations support driving force of natural selection

Question 8

Convergent evolution

Answer 8

• Independent evolution of same trait in different groups
• Allow more confident determination that selection is at work

Question 9

AMY1 evolution

Answer 9

• AMY1 encode salivary amylase
• Shows copy number variation -> more copies, more digestion
• Copy number expansion in humans linked to agriculture

Question 10

How does selection affect genome

Answer 10

• Expect:
  
  • Differences in fate of those mutations that change amino acids (non-synonymous) vs. those that don’t (synonymous)
  • Lower genetic variability in regions of the genome that experience selection
  • More differentiation between populations at selected sites than rest of the genome

Question 11

Mutational Consequences of Genetic Code

Answer 11

• Neutral(don’t affect fitness): expect similar properties of both replacement and synonymous mutations
• Deleterious(negative effect on fitness): lower population frequencies for replacement mutations
• Beneficial(improve fitness): more replacement mutations than synonymous

Question 12

Predictions for DNA differences between species

Answer 12

• Neutral: equal rate of substitution for replacement(dN) and synonymous(ds) sites. dN/ds = 1
• Deleterious: Substitution rate for synonymous sites will exceed replacement sites. dN/ds < 1
• Beneficial: Substitution rate for replacement sites will exceed synonymous sites. dN/ds > 1

Question 13

Effects of selective sweep on nearby variation

Answer 13

• As beneficial mutations fix, they drag along them nearby mutations(genetic hitchhiking)
• Consequently, genetic variation in these regions go down
• Region size depends on the rate of recombination