Biology 1001A Lecture Notes - Lecture 23: Herpes Labialis, Vertically Transmitted Infection, Myxoma

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BIO1001ALecture23EvolutionaryArmsRaces
Whentwospeciesinteract…
Bothmaybenefit:Mutualism
● Example:Acaciaplantsandacaciaants
○ Plantsprovideantswithfoodandshelter,whiletheantsprotecttheplantinturn
● Example:Plantsandpollinators
○ Plantsgettospreadtheirgametes,whilepollinatorsgetnectar
● Example:Domesticanimalsandtheirowners
Bothmayincurcosts:Competition
● Twoormorespeciescompetingforthesamelimitingresource
● Bothspeciesareincurringcoststhatwouldn’toccuriftheotherspeciesweren’tthere
○ Bothspeciesthatareinvolvedsuffer
○ Loselosesituation
● Example:Lionsandcheetahs
○ Thefoodthatthelioneatsisnotavailabletocheetahs,andviceversa
● Example:Talltreescompetingforsunlight
Onebenefits,theotherincurscosts:Antagonism
● Example:Predatorpreyrelationships
○ Predatorspeciesbenefitsbygettingfood,preyspeciesincurscostsbylosingthe
livesofmany
● Example:Herbivoresandplants
○ Similarreasonsaspredatorprey
○ Mayjustreduceplantgrowthrateandlongevity,notkilltheplant
Evolutionaryarmsraces
● Ifeachspeciesposesaselectionpressureontheother,itgivesrisetoanevolutionary
armsrace
○ Recall:TheRedQueenmetaphor
● Whenaparasiteiscoevolvingrapidly,thehostspeciesneedstocoevolvejustasfast
simplytokeepup
● Selectionpressure
givesrisetoadaptationsinonespeciestoimproveabilitytointeract
(combat)withtheotherspecies
○ Thesecondspeciesdevelopsacounteradaptation
○ Acycle
ofadaptationscontinues
● Example:Gartersnakeeatingroughskinnednewt
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○ Newtreleasesatoxinthatcontinuallyadaptstobestrongerandmorepotent,but
○ Snakeadaptsinabilitytobreakdownthenewtoxin
Improvedequipmentdoesnotequalimprovedsuccess
● Sincebothpartiesareevolving,neitherpartyisbetteroffwiththeadaptations
● Despitetheadaptationschangingtheirphenotype,itdoesn’tchangetheirrelative
success/fitnessagainsttheotherspecies
○ Example:Strongdirectionalselectionactsonlion(predators)andwildebeest
(prey)tomakethemrunfaster
■ Bothspeciesrunmuchfasternowthaninpastgenerations
■ However,moderndaylionsstillcan’tcapturewildebeestmuchbetter,nor
canthewildebeestbeanymoreimprovedatescapingtheirpredators
● Adaptationscanbeconsideredawasteofresourceswhennotputintomoreusefultraits
○ Example:Traitssuchastoincreasepopulationsize(morefertility,makemore
gametes)
○ Example:Insteadofmakingtreestaller,investmoreinleaves,andmakingmore
pollen
Whowinsthearmsrace?
● Maykeepescalatinguntilcostsoutweighbenefits
RedQueenEquilibrium:
Armsraceshaltwhenbothspecies
cometoapointatthesame
timewhereitismorecostlytoadaptthaninvestinothertraits
● Sometimes,aspeciesmaywin,ifonespecies...
○ Hasafastergenerationtime
■ Theyhavethepotentialtoevolvefaster,soselectionoperatesquicker
○ Hasalargerpopulationsize
■ Increaseslikelihoodoffavourablemutations,andthusinfluences
selectionspeed
○ Isgivenastrongerselectionpressurefromtheotherspeciesthanviceversa
■ Lifedinnerprinciple
Lifedinnerprinciple
● Predatorvs.preysituations
● Selectionactsstrongeronthepreyspeciesthanthepredatorspecies
○ Thisisbecausethepreyneedsadaptationstostayalive,whilethepredatorjust
needsthemtogetmorefood(prey)
○ Example:Roadrunnervs.WileE.Coyote
■ Ifroadrunnerloses,he’sdead;whereasifcoyoteloses,hejustdoesn’t
eatthatday
Armsracesbetweenmutualists?
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