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Lec 22 - Arms Races and Virulence - Lecture Outcomes

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Western University
Biology 1001A
Tom Haffie

Tanya Malhotra Lecture 22 – Arms Race and Virulence – Lecture Outcomes 1. Mutualistic, competitive and antagonistic relationships between species, given 'real world' examples  Mutualism: when both species benefit o E.g. plant and pollinators, ants and plants that they live on, domestication  Competition: when both species suffer from interaction o Species that coexist in the same area and compete for resources o Each species is worse off because of the other’s presence  E.g. lions and cheetahs competing for same prey, plants competing for space/sunlight/ soil nutrients  Antagonism: one may benefit at expense of other o Predation – predator benefits and prey suffers o Natural enemies o E.g. disease-causing organisms benefit at expense of host o E.g. herbivore/plant relationships 2. Examples of red queen equilibrium  RQE: may keep escalating until costs outweigh benefits o Have to keep evolving just to keep up with natural enemies and stay in the same place o Lion and wild beast: both keep increasing average speed so therefore the lion cannot catch more prey than his ancestors because although he is evolving to be faster, so are the wild beasts. Neither side is gaining competitive advantage 3. Factors that advantage one side or the other in an evolutionary arms race  Generation time: species with short generation time evolve faster  Population size: Selection = more effective in large populations o There is more variation and more beneficial mutations  Strength of selection: strength varies and can favour one species over the other 4. Meaning of 'life-dinner principle'  Selection on 1 party in race isn’t going to be the same as selection on the other party  Selection is typically stronger on prey species to avoid being captured, because prey is running for life and predator is running for dinner 5. Difference between prudent-parasite hypothesis and trade-off hypothesis, in terms of the evolution of virulence  Prudent-parasite hypothesis: o Parasite that kills host too soon, before colonizing a new host, is doomed o Parasite kills host as slowly as possible because it needs the host to stay alive so it can spread o Therefore optimal virulence is LOW  Trade-off hypothesis: o Balances costs and benef
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