Unit 5 - Ch 18, 20 - Evolution Flashcards
Evolution
How organisms adapt to the environment over time
Microevolution
Small scale changes. Changes in gene frequencies within populations. Not disputed in the scientific community.
Macroevolution
One group giving rise to another. Large shifts occur in the morphology and / or physiology. Disputed in the scientific community.
Darwin’s Premises (4)
- Excess Reproduction
- Variation/Inheritance
- Survival of Fittest - i.e. Natural Selection.
- Gradual Change - i.e. Gradualism.
Excess Reproduction
Darwin’s premise.
Far more offspring are born than can survive to become adults. Malthus
Variation / Inheritance
Darwin’s premise.
Observed in breeding of animals and plants. Also Lamark’s Theory of Acquired Characteristics.
Survival of Fittest - i.e. Natural Selection
Darwin’s premise
The best adapted offspring survive and reproduce. Wallace originally published this idea in 1858.
Gradual Change
Darwin’s premise
Species change gradually over time. Lyell was the founder of uniformitarianism which replaced catastrophism.
Sources of Variation (2)
- Sexual Reproduction - Reshuffles existing genetic information through crossing over (prophase I), independent assortment (Metaphase I), and fertilization.
- Mutation - The only source for “new” genetic information for natural selection to operate on. Occurs randomly so usually harmful.
Evidence of Natural Selection (2)
- Industrial Melanism (Kettlewell) - Biston betularia (peppered moth). During the industrial revolution.
a. 1850 - 99% light/1% dark
1900 - 10% light/90% dark - Resistance - Induced Evolution (by humans)
a. Antibiotic/Pesticide Resistance
3 types of natural selection
- Stabilizing Selection
- Directional Selection
- Disruptive Selection
Stabilizing Selection
The average phenotype is maintained. Extreme variants are eliminated. Beneficial in environments that are stable.
a. Clutch Size (starlings) - number of eggs per nest
b. Albino deer - easier for hunters to spot
Directional Selection
One extreme phenotype is favored over the average - occurs when the environment is changing
a. Disease resistant oysters
Disruptive Selection
Extreme phenotypes become favored over the average in different environments in different parts of the range - may lead to speciation.
Species definition
A group of morphologically similar individuals capable of interbreeding and reproductively isolated from other species.
Isolating Mechanisms (how separation occurs in gene pools) premating and postmating
- Premating
a. Habitat
b. Temporal
c. Behavioral
d. Mechanical - Postmating
a. Gamete Mortality
b. Zygote Mortality
c. Hybrid Sterility
d. Depressed F2 Fitness
Habitat as an isolating mechanism
Occurs premating
Species utilize different micro environments so they rarely encounter one another
Temporal isolation mechanism
Occurs Pre-mating
Timing of reproduction is different between species. Common in plants: pollen release and stigma receptivity to pollen.
Behavioral isolating mechanisms
Species have specific mating rituals or courtship displays. Fire flies.
Occurs premating
Mechanical isolating mechanisms
Reproductive systems are unsuitable for copulation
Occurs premating
Gamete mortality isolating mechanisms
Gametes are not capable of fertilizing gametes of other species. Common in organisms that use external fertilizers like fish and sea urchin.
Occurs postmating
Example of a zygote mortality isolating mechanism
Sheep and goat hybrids form but are usually stillborn.
Occurs post mating
Hybrid sterility isolation mechanisms
The resulting hybrid is sterile. Mules for example: a 2n=64 Horse breeds with a 2n=62 Donkey resulting in a sterile Mule.
Depressed F2 Fitness
This is where we see hybrid vigor in early generations, but eventually die off occurs in future generations.
Post mating isolation mechanism
Speciation
One species giving rise to another.
Restricted gene flow must occur
- Populations becomes reproductively isolated from each other and create separate gene pools.
Allopatric speciation
These have geographic separation between populations. The separation can be relatively small depending in the species’ capabilities to travel.
Sympatric speciation
Polyploids become reproductively isolated from others in the same location. This is common in plants: eventually a 4n plant will isolate from a 2n plant.
Patterns of Evolution (3)
Convergent evolution
Divergent evolution
Coevolution
Convergent evolution
Structure?
Environment?
(coming together)
Unrelated species demonstrate similar adaptations to their environment
- Analagous structures
- Structurally diverse but functionally similar => wings (birds, bats, insects) - Similar environments
- similar selection pressure for similar adaptations
Divergent evolution
Structure?
Environment?
(moving apart)
Related species demonstrate different adaptations to their environment. Suggests common ancestry.
- Homologous structures
- Have structural similarity, but functional diversity. => arm structure in terrestrial mammals and whales. - Different environments
- Different selection pressure
Coevolution
AKA Parallel Evolution
Symbiotic / Mutualistic
Unrelated species with adaptations that are utilized for the survival of both
=> the yucca moth is the only known pollinator of the yucca plant, and the plant is the only known area where the moth completes its life cycle.
