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AP Bio-Forbes- Evolution 3: Evolutionary Forces

3 of 6 of my evolution unit. Image Credits: Biology (Campbell) 9th edition, copyright Pearson 2011, & The Internet. Provided under the terms of a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. By David Knuffke.

Shani Forbes

on 5 September 2012

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Transcript of AP Bio-Forbes- Evolution 3: Evolutionary Forces

Forces of Evolutionary Change Natural Selection Genetic Drift Gene Flow Sexual Selection The Road to NeoDarwinism Darwin was not the last evolutionary biologist.
A lot of things were left unexplained after "Origin".
Particularly the role of genetics (why?).
NeoDarwinism: Refers to the modern theory of evolution (aka the "Modern Synthesis"). Explains evolution in genetic terms. Evolution: Change in allele frequencies of a population over time. If this is the definition, then Natural Selection is NOT the only way that a population can evolve Physiological Selection:
Acts on body functions/structures

examples: disease resistance, physiological efficiency (using oxygen, food, water), biochemical versatility, protection from injury, morphology (anatomy) Sexual dimorphism:
Differences between genders.

Indicative of the effects of sexual selection. Coevolution:
Two or more species reciprocally affect each other’s evolution.

examples: predator-prey, competition, symbiosis What is it? Traits that improve survival or reproduction accumulate in the population.

SELECTIVE & ADAPTIVE change Predation Selection:
Acts on both predator & prey

examples: camouflage, mimicry, speed, defenses What is it? Founder effect:
A new population is started by a small group of individuals.
Some rare traits may be at high frequency (or "fixed" at 100%); others may be missing (or "lost"). Bottleneck effect:
When a large population is drastically reduced by a non-selective disaster: famine, natural disaster, loss of habitat.

Loss of variation by chance event narrows the gene pool Effects of Evolution Change in the frequency of alleles in a population due to immigration/emmigration


Hard to predict the effects What is it? What is it? Change in the frequency of alleles in a population due to gender preferences.


Acts in all sexually reproducing populations.

"The traits that get you mates!" Why does this happen?
Sexually selected traits serve as fitness markers for mating. At what level does
evolution work? Modes of selection: How selection affects a population. Big Questions Make Sure You Can Traits must be inherited! Change in the frequency of traits in a population due to chance events. Common in island populations (both physical and reproductive--Why?) Evolution is a population level phenomenon.

It emerges from the selection of individuals by the environment. Traits can be behavioral or physiological. Reproductive success is ALL that matters. My, what a ridiculous tail you have! Change in beak depth of Medium Ground Finch on Daphne Major following a drought. Differences in frequency of a metabolic gene as a function of latitude in mummichog fish (a "cline") Simulated effects of the environment on the frequency of genes ("alleles") in 2 different populations J.B.S Haldane, Ronald Fisher & Sewall Wright:
3 major contributors to the Modern Synthesis Variation in the lap94 gene as a function of habitat salinity in a mussel species Snakes are one of the few vertebrate species to have movable jaw bones Coevolutionary adaptations in flower & pollinator anatomy Genetic drift has a greater effect on smaller populations (why?) RANDOM change.

NOT Selective.

NOT Adaptive. Polydactly, one sign of Ellis-van Crevald syndrome. Common among the Amish in Pennsylvania Cheetah's have been through 2 bottlenecks in recent history:

Recent ice age (~10 bya)

Living cheetahs are as genetically similar to each other as identical twins.

What problems does this cause? Data showing the effect of habitat destruction on the Illinois population of the Greater prarie chicken. Diagram of a "Bottleneck" Diagram of the Founder Effect Various examples of mimicry among insects: The overlap of these two populations of Caribou allows for gene flow between them. Two island populations of the Great Tit.

Gene flow from the mainland population to the central population may be contributing to the lower survival rate of the central population compared to the eastern population Genetic Marker analysis showing the movement of Scandanavian populations into the Brittish Isles during the Neolithic and Bronze ages Mantis mating behavior results in the death of the male during copulation Any Questions? How has the theory of evolution been expanded since Darwin?

Why does evolution of organisms occur?

At what level does evolution work? Compare all of the evolutionary forces described in this presentation, explain how they can affect a population, and give real-world examples of each.

Explain why evolution is not always adaptive.

Explain how evolution can affect the structure of a population over time. You know what they say about crabs with big claws... You don't REALLY need to survive after mating... How does evolution work? Directional: toward one extreme
Disruptional: toward both extremes; against the mean
Stabilizing : toward the mean It's female choice!! Individuals survive or not
Individuals reproduce or not
Populations evolve!! Mutation What is it? A change in the DNA sequence. changes amino acid sequence
changes protein
changes structure
changes function
changes phenotype and fitness Mutation creates variation new mutations are constantly appearing
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