BIOL 110 Chapter Notes - Chapter 22: Peppered Moth, Horseshoe Crab, Anostraca
Tutorial 22
Thursday, October 27, 2016
9:17 PM
Genetics, Selection, and Speciation
• Fitness and Selection
o Many characters show variation in the form of alternative traits
o Some vary continuously; quantitative characters
• Height in humans
o Other traits vary discretely
• Eye color
o Differential reproductive success; they are more fit
• Natural selection
• The salmon example
o Organisms' success has to do with reproduction, not longevity
o Salmon live in seawater but migrate to freshwater to breed
• Die in streams where they were born
• Nutrients released from the dead salmon enrich the stream and feed algal blooms and
invertebrates
• Key food source for the offspring that hatch there
• Natural selection
o How a population adapts to its environment
o Natural selection can only act on available phenotypic variation within the population
o Adapt to environment at the time
o 160 documented cases of natural selection in wild populations
• Peppered moth
• Adaptation and the environment
o Fairy shrimp have adapted to vernal pools, complete their life cycle in two weeks - well
adapted to their environment
o Rarely does a single species live in a particular environment
o Life is a competition
• Types of selection
• Stabilizing selection
o Favors intermediate phenotypic variants by acting against extreme phenotypes
o Organisms may show ancestral character traits
o Stable environment favors this
o Occurs when extremes are a disadvantage
• Birth waits in humans
• Horseshoe crab
• Directional selection
o Favors individuals with phenotypes that are at one end of the phenotypic range
o Seen during periods of environmental change
o Favors one extreme by selecting against the other extreme
o Can be caused by changes in weather patterns
o Peppered moth
• Diversifying selection
o Also called disruptive selection
o Favors individuals at both extremes of the phenotypic range
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