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Chapter 4

BIO220H1 Chapter Notes - Chapter 4: Commercial Fishing, Directional Selection, Zygosity

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John Stinchcombe

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Reading Article: Human-induced evolution caused by unnatural selection
through harvest of wild animals
Humans harvest animals w/ phenotypically desirable traits from wild populations
o= selection that reduces frequencies individual w/ desirable phenotype
oSometimes breed animals w/ goal of increasing frequency of desirable phenotypes
Explore how harvesting affects mating system and modifies sexual selection
Selective removal = genetic change in harvested population if selected phenotype has
genetic basis:
oEX: frequency of elephants w/o tusks increased from 10% to 38%
oEX: Agriculture: Use most productive animals/plants as breeding stock:
Increase frequency of desirable phenotypes
In general in wild animal populations:
oMost desirable individuals harvested, leaves behind less desirable to reproduce +
contribute genes to future generation
o= harvest of wild populations increases frequency of less desirable phenotypes in
wild population
“Unnatural selection”: Undesirable changes observed over time in exploited
populations because of selection against desirable phenotypes:
oUnintended natural selection through exploitation:
Imposed by human activity and not natural selection
Reduces frequency of phenotypes valued by humans
EX: Reduced body size, earlier sexual maturity, reduced antler size
Article Aim:
oSummarize consequences of unnatural selection and sexual selection in wild
oOutline why consequences threaten future yield/population viability
oSuggest measures to address problem
Fish size:
oLarger fish = higher value = caught more frequently in commercial fisheries
o= over-representation of smaller, younger fish, reduce adult size and fishery yield
oReduce future yield:
Maturation becomes earlier under selection
oFishing selection reduces mean adult size
oOpposes natural + sexual selection on these traits
oReduces frequency of desirable phenotypes through directional selection
Selection intensity differs between sexes and ages of fish
oBut in general selection highest in large fish
Game hunting different than fishing
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