Patterns of Evolution Convergent Evolution Divergent Evolution Adaptive Radiation Artificial Selection Coevolution

Convergent Evolution Organisms appear similar, but aren’t closely related Why? Similar environments select for similar traits

Divergent Evolution Related populations or species become less and less alike Adaptive Radiation

Adaptive Radiation Generally means an event in which a lineage rapidly diversifies, with the newly formed lineages evolving different adaptations.

A Second Type Of Divergent Evolution Artificial Selection Humans, rather than nature, select traits

One More Example of Artificial Selection

Coevolution Two or more species in close association w/one another change together Predator/Prey Parasite/Host Plant/Pollinator

On the Origin of Species by Means of Natural Selection (1859) Summary of Theory of Natural Selection: 1. Overproduction of offspring 2. Struggle to survive  competition 3. Variation within population 4. Successful reproduction – “survival of the fittest” (best adapted organisms are “naturally selected”) Overproduced variations struggle to successfully reproduce… 9

Fitness The success of an individual in surviving and reproducing.

Natural Selection Natural Selection acts on a POPULATION, not an INDIVIDUAL! An individual influences this based on his / her fitness.

3 General Types of Natural Selection Stabilizing Selection Directional Selection Disruptive Selection Nature selects the average form of a trait (human baby size) Nature selects one extreme form of a trait (e.g. only the very long tongue in anteaters, not the short tongue) Nature selects both the extreme forms of a trait (e.g. very bright shell and very dull shell)

The 3 Types of Natural Selection Disruptive Selection Stabilizing Selection Directional Selection

Sexual Selection: A Special Type of Directional Selection Individuals of one sex (usually males) of a species are more likely to get picked as partners by the other sex if their characteristics are bolder, brighter, louder or stronger than other members of the same sex.

Sexual Selection in Peacocks

Of Course, Being More Noticeable Does Have Its Disadvantages . . .

Other Factors Can Affect Genetic Variation In A Population Other factors besides meiosis/sexual reproduction and mutations create the variation in the genetic material (gene pool) of a population on which natural selection acts Migration Assortative (nonrandom) mating = sexual selection Genetic Drift

DNA frequency in a population changes simply by CHANCE not fitness GENETIC DRIFT DNA frequency in a population changes simply by CHANCE not fitness Survivors are lucky, not more fit Deceased are unlucky, not less fit 19

Genetic Drift Change In Allele Frequency Caused By Random Chance Random chance = natural disasters, disease, hunting, etc. Has a greater affect on small populations Often causes reduction in alleles (not always the weakest alleles) present in the gene pool.

some individuals of a population colonize a new habitat Types of Genetic Drift 1. Founder’s Effect some individuals of a population colonize a new habitat 2. Bottleneck Effect few survivors are left to reproduce 21

The Bottleneck Effect A direct result of genetic drift As a result of some random event, several alleles are lost from a population when only a small number of individuals in the population survive to reproduce. Northern Elephant Seals – pop. reduced to 20 individuals due to hunting in 1890’s. Pop. rebounded to 30,000 now Very little genetic variation

FOUNDER'S EFFECT: some individuals of a population colonize a new habitat ex: Columbus bringing organisms to USA S. America: DNA Frequency 25% pink 75% red Spain: DNA Frequency 66% pink 33% red 23

HOW DOES GENETIC DRIFT AFFECT THE DIVERSITY OF A POPULATION OVER TIME? 24

Genetic drift = decrease in DNA diversity Genetic drift decreases diversity. In this case yellow and pink DNA are gone, and red DNA is now the majority. Genetic drift = decrease in DNA diversity 25

Geographic Isolation = New Species: An Example 2 Species of Squirrels Formed When They Were Separated By The Grand Canyon

Prezygotic Isolating Mechanism #1: Temporal Isolation Species isolated because they reproduce in different seasons or times of day Prevents species from ever breeding together – keeps two species separate but usually arises after species have formed.

Prezygotic Isolating Mechanism #2: Behavioral Isolation Species Differ In Their Mating Rituals (e.g. different bird songs, mating colors, dances, pheromones, etc.)

Prezygotic Isolating Mechanism #3 Ecological Isolation Species inhabit the same area, but different habitats, so they don’t encounter each other

Prezygotic Isolating Mechanism #4: Mechanical Isolation Body structure prevents mating In layman’s terms - the parts don’t fit Bush Baby

Prezygotic Isolating Mechanism #5 Gametic Isolation The sperm is unable to fuse with the egg.

Postzygotic Isolation Some barriers to successful breeding arise after fertilization and are called postzygotic isolating mechanisms Hybrid sterility Sterile offspring (e.g. Horse + Donkey = Mule)

How quickly do new species form? 2 hypotheses Gradualism Many transitional forms between common ancestor and modern organisms Punctuated Equilibrium Sudden shifts in form from an ancestor to newer organism, so not many transitional forms between common ancestor and modern organisms