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Western University
Biology 1001A
Tom Haffie

Biology 1001 Arms Races November 26, 2012 Evolutionary innovations can induce adaptive radiation  Angiosperms use animals as pollinators  Different pollinators -> reproductive isolation  Pollen donor = male  Pollen recipient = female What’s in it for the pollinator?  The bird gets food (nectar) out of it When two species interact…  Both may benefit: mutualism  The plant gets to exchange gametes with another plant, the animal pollinating gets a food reward  Ants receive sheltered/housed by the plant and also fed by the plant, while the ants will defend the plant from other herbivores  Domestication is an example of mutualism  Both species may suffer: competition  Animals compete for sources of food or water  Plants compete for space, light, water, soil nutrients, etc.  Whenever there’s two or more species who need the same resource, there is competition between them  One may benefit at the expense of the other: antagonism  Predator/prey relationships  Insects/plants  Disease-causing organisms: parasites & pathogens benefit at the expense of their host individual Evolutionary arms race  Any of the above can give rise to the evolutionary arms race  Adaptation by species A improves its ability to interact with species B  Selection pressure on species B to evolve counter-adaptation  E.g. garter snakes eat newts in western North America. The newts have high levels of neurotoxins in their skin; anything except a garter snake that touches the newt will probably die, but there’s a particular species of garter snake that has adapted and has a high degree of resistance to the toxin  Selection pressure on A to evolve counter-counter-adaptations  There are trade-offs: loses energy, etc. Improved equipment does not necessarily lead to improved success  Modern day lions are much faster runners than their ancestors, but they’re still not that much better off because their prey has also become faster runners  The other side is evolving too Biology 1001 Arms Races November 26, 2012 Who wins the arms race?  May keep escalating until costs outweigh benefits  Red Queen equilibrium  You have to keep evolving adaptations and counter adaptations just to keep up with your natural enemies  The equilibrium is not always stable; sometimes, one side has the advantage:  Species with short generation time can evolve faster than a species with a long generation time  Selection is more effective in large population sizes; more likely to stumble upon more beneficial mutations  Strength of selection; is there equally strong selection on predators as there are on the prey? Life-dinner principle  Strength of selection of one species may not be equal to the other  Selection strength tends to be stronger for the prey because they lose their life Arms race between mutualis
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