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Microevolution - Evolutionary Forces

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.

Eric Friberg

on 1 March 2016

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Transcript of Microevolution - 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?).
: Refers to the modern theory of evolution (aka the "
Modern Synthesis
"). Explains evolution in genetic terms.
: Change in genetic characteristics 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.
Two or more species reciprocally affect each other’s evolution.

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

Predation Selection
Acts on both predator & prey

examples: camouflage, mimicry, speed, defenses
What it is:
Founder effect
A new population is started by a small group of individuals.
Somes rare traits may be at high frequency (or "
" at 100%); others may be missing (or "
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 traits in a population due to immigration/emmigration


Hard to predict the effects
What it is:
What it is:
Change in the frequency of traits in a population due to gender preferences

change. May seem

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.
How does evolution work?
Traits must be inherited!

...at least to some degree
Modes of selection:
Evolution is a population level phenomenon.

It emerges from the selection of individuals by the environment.
How selection affects a population.
Big Questions
Make Sure You Can
Change in the frequency of traits in a population due to chance events.
Common in island populations (both physical and reproductive--Why?)
Against the mean, towards both extremes
Towards the mean, against extremes
Towards one extreme
Traits can be physiological OR behavioral
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?)

NOT Selective.

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

Recent ice age (~10 kya)

Living cheetahs are as genetically similar to eachother 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 Carribou 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 British Isles during the Neolithic and Bronze ages
The different morphologies of Nemoria arizonaria catterpillars is due entirely to chemicals in their diet, NOT genetic differences
Oak leaf diet
Oak Flower diet
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?

How does evolution affect a population?
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...
Full transcript