Coevolution II

Question 1

Reciprocal selection favours:

Answer 1

• victim traits that decrease the efficacy or frequency of interaction
• exploiter traits that increase the efficacy or frequency of the interaction

Question 2

Symmetry or asymmetry alters

Answer 2

selection strength and type of dynamics between two antagonists

Question 3

Symmetric coevolutionary dynamics

Answer 3

• fitness effects are equally good or bad (hosts and parasites)
• Red Queen, cyclical dynamics

Question 4

Asymmetric coevolutionary dynamics

Answer 4

• ‘life-dinner principle’ (predators and prey)
• Armsrace, escalatory dynamics

Question 5

Describe escalation

Answer 5

• arms race
• reciprocal selection favours increased (or decreased) phenotype values in both victim and exploiter
• alleles expressing those favoured phenotypes fix, until new allele arises

Question 6

Describe cyclical

Answer 6

• Red Queen
• favours exploiters that match the victim phenotype, and victims that mismatch the exploiter phenotype
• Allele frequencies cycle

Question 7

Give an example of an arms race

Answer 7

• Taricha granulosa newts have powerful, anti-predator toxins (TTX)
• Thamnophis sirtalis snakes are major predator – evolved resistance to TTX
• TTX is 100X more powerful than necessary to kill any other predator (including humans), but snakes can be resistant
• Snake resistance is predicted by newt toxicity, as predicted
• Some Garter snake populations have dramatically increased TTX resistance

Question 8

What is the outcome of escalation?

Answer 8

• Endless escalation of phenotypes
• ‘winner’ is the species with greatest response to selection (‘runs away’ or ‘catches up’ the most

Question 9

What is the outcome of cyclical?

Answer 9

• Alleles cycle endlessly
• Exploiter adapts to common victim genotypes
• Should produce an advantage for rare victim genotypes