Evolution Exam #1

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vestigial structures

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a useless rudimentary version of a body part that has an important function in other, closely allied, species

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The Fact of Extinction

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The fact that many species have gone extinct suggests that Earth's flora and fauna have changed over time

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The Law of Succession

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The resemblance between living and fossil forms in the same region suggests that living organisms are descended with modification from earlier species

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General Observations about Fossils

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-The vast majority of fossils are unlike any species living today
-Some Species go extinct while others disappear
-The deeper the you did the stranger they get

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Catastrophism

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Strata caused by catastrophe destroyed many species
Local regions were populated by species immigrating from other areas

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Transitional Form

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Document the past existence of species displaying mixtures of traits typical of what are today distinct groups of organisms. Evidence for macroevolution.
EX. Archaeopteryx, not claiming that it was on the direct line of descent from dinosaurs to modern birds, but likely represents an extinct side branch of evolutionary tree that connects dinosaurs to birds

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Evidence for common Ancestry- Darwin

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morphological homologies
molecular homologies

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Descent with Modification-Evolutionary Tree

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Visual representation of descent with modification from a common ancestor

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Ring Species

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Some species appear to be in the process of splitting into two. Freely interbreeding populations connect the entires species, but members of certain populations do not interbreed.

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Homology

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organisms show curious similarities in structure and development unrelated to function. Backs up theory of Evolution

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4 postulates of Natural Selection

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1.Individuals within a population are variable for some trait (variability in traits)
2. Trait variability among individuals are, at least in part passed from parents to offspring (heritability of traits)
3. Some individuals are more successful at surviving and reproducing than others (variability in fitness)
4. Survival and reproduction of individuals are not random; instead are correlated to variability in traits (fitness differences associated with traits)

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Artificial Selection

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To increase the frequency of desirable traits

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Darwinian Fitness

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ability of an individual to survive and reproduce in its environment

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Why is the Darwin-Wallace Theory attractive?

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It is testable.

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Discrete Trait

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qualitative... Eye color, hair color

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Continuous Trait

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quantitative... Height

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Adaptation

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natural selection explains the observation that organisms are exquisitely well-suited to their environments and lifestyles (fit between form and function)

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The medium Ground Finch of Daphne Major

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Group of very closely related species of birds endemic to Galapagos Islands
All descendants of a flock that colonized the islands from Central of South America
Great diversity of beak morphology associated with variation n diet- beak size is correlated with the size of seeds harvested

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Finch Test Postulate 1

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Some Geospiza fortis have beaks that are only half as deep as other individuals

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Testing Postulate 2

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The beak depths of parents and offspring are similar. THis observation suggests that some alleles tend to produce shallow beaks, while other alleles tend to produce deeper beaks

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Postulate 3: Is there Variability in Fitness?

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Large majority of birds died due to drought

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Postulate 4: Are survival and reproduction nonrandom?

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During the drought, finches with larger, deeper beaks had an advantage in feeding, and thus surviving.
Selection occurs within generation; evolution occurs between generations

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Nature of Natural Selection

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-Natural Selection Acts on Individuals, but Its Consequences Occur in Populations
-Natural Selection Acts on Phenotypes, but evolution Consists of Changes in Allele Frequencies
-Natural Selection is Not Forward Looking
-New Traits can Evolve Though Natural Selection Acts on Existing Traits
-Selection acts on individuals, not for the good of the species

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Selection Differential

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compare trait value of winners and losers (discrete categories of fitness)

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Selection Gradient

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examines the correlation between traits and fitness (continuous) both are quantitative variables
-equal to the slop of the best fit line in a scatter plot showing fitness as a function of train

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pattern

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is there + of - relationship between natural selection of traits

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strength

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difference between winners and losers

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presence

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is there any trait and fitness seen?

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correlation among traits

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height and weight

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direct vs indirect selection

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for example natural selection favors big beak, but doesn't really care about width

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Directional Selection

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Results in changes in the trait mean value
Results in small decreases to trait variance
Directed toward a certain/specific type of organism
Will keep moving to the right

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Stabilizing Selection

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stabilize selection average trait value
decrease trait variation
- gamma= stabilizing= decreased trait variation

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Do you expect directional or stabilizing selection to be more common in wild pops?

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We would expect stabilizing selection, but you find directional selection more often

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Disruptive selection

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mean is not favored
individual on both ends of the mean are favored
it will increase trait variation
EX. finches with really small or really big beaks are favored, intermediate beaks aren't favored
+ gamma= disruptive=increase trait variation

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Measuring Heritability (h2) of Quantitative Traits

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Need to make comparisons among individuals
-fitness is dependent variable
-used to distinguish the nature vs. nurture

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Prediction Evolutionary Response to Selection

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Breeder Response

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Breeder Response

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R=(h^2)S
estimate how much of the variation in a trait as due to variation in genes, quantify the strength of selection that results from differences in survival or reproduction and put these two together to predict how much the population will change from one generation to the next

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h2

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heritability
Heritability is a parameter that describes what fraction of variation in traits that is explained by variation in genes. It is the slope of the best fit line (calculated using linear regression) describing the relationship between the trait values of parents (x-axis) and the trait values of offspring (y-axis).

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S

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Selection differential

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Beta

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S/variance(t)
The selection gradient is a parameter that describes the pattern and strength of natural selection. It is the slope of the best fit line (calculated using linear regression) describing the relationship between a particular trait (whose values have been standardized) and relative fitness (which you get by dividing individual values for absolute fitness by the population mean fitness).