Lecture 6

Question 1

How is harvesting determined

Answer 1

• Size thresholds: If larger than X, it gets caught in net. If smaller than X, it swims through holes
• Trophy ornaments: Size of antler racks, size of horns in sheep

Question 2

Continuous traits

Answer 2

• Phenotypes that vary continuously
  
  • Quantitative traits
  • Size, mass, length, time to maturity and behavior
• Versus traits with discrete qualitative categories
  - Mendelian traits
  - Eye color, blood group

Question 3

Architecture of quantitative traits

Answer 3

• Quantitative traits
  - Lots of genes
  - Each gene has very small individual effect on phenotype
  - Influenced by environment
  - Simple rule of thumb(P = G + E + G x E)
• Unlike discrete mendelian traits
  - Cannot infer genotype of a given gene from phenotype
  - Examining frequency of individual SNPs or alleles will not predict phenotypic values
  
  • Must work with statistical descriptions

Question 4

Truncation selection

Answer 4

• Strong form of directional selection
  
  • Individuals with phenotypes above threshold die
  • Those below threshold live
• How to measure intensity of this selection
  - Difference in mean of population after selection compared to before selection
• How will traits involved in this threshold evolve

Question 5

Tracking evolution of quantitative traits

Answer 5

• Measure, predict, follow
• Track genetic changes explicitly

Question 6

Examples of harvest induced evolution

Answer 6

• Atlantic cod: fish selected to be smaller, despite better growth conditions
• Tuskless-ness in elephants

Question 7

Declining density and increasing temperature

Answer 7

• Low density should promote: faster population growth, larger sizes of individuals, population is at low values for (K-N)/K
• Warmer temperatures promote faster growth but are not observed

Question 8

Selection (combined across ages in a year)

Answer 8

• Environmental forces push toward larger fish (temperature and density): low density, high temperature
• Evolutionary forces push toward smaller fish

Question 9

Implications for recovery of a fishery

Answer 9

• Continued fishing can trap a population in the region where smaller and less fecund fish dominate the population
• Slow recovery of population size

Question 10

Tuskless-ness in elephants

Answer 10

• Globally 20,000 elephants poached per year
• Tusks are dimorphic in size, but female elephants have tusks

Question 11

Results

Answer 11

• Pre war: 70% of females have 2 tusks, 18.5% have no tusks
• Immediate survivors: 41% have 2 tusks, 51% have no tusks
• Offspring of survivors: 58% have 2 tusks, 33% have no tusks
• Selection producing evolutionary change, genetic relation to no tusks

Question 12

Is this consequence of bottleneck

Answer 12

• Grey bars are outcomes of natural simulations
• Blue bars are observed data
• Can be seen if tuskless have 5-fold survival advantage
• Selection

Question 13

Genetics of tuskless females

Answer 13

• Dominant X-linked locus that is lethal in males
• Males: XY, Females XX
• wt = x, alternative allele is X
• Males:
  
  • All tusked, so xY
  • XY tuskless males never observed -> die in utero
  • Explains why males are 100% tusked
• Females:
  
  • With tusks are xx
  • Without tusks are xX
• Cross xX female with xY male
  - xY male with tusks
  - XY males, lethal, not born
  - xX females, heterozygotes
  - xx females, with tusks