Speciation, Speciation, Reproductive Isolation, Reproductive Isolation,

and and Patterns of EvolutionPatterns of Evolution

AP BiologyAP Biology

Evolution IVEvolution IV

SpeciationSpeciation

• Species: a group of individuals capable of interbreeding

• Speciation: the formation of new species (3 main types)– Allopatric Speciation– Sympatric Speciation– Adaptive Radiation

Allopatric SpeciationAllopatric Speciation

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Allopatric SpeciationAllopatric Speciation

• Occurs when a population is divided by a geographic barrier– Barriers: mountains, rivers, regions excluding

vital resources (water, food) areas covered with volcanic lava

• Interbreeding between populations not possible (reproductive isolation)

• Gene frequencies can diverge due to natural selection, mutation, and genetic drift

Sympatric SpeciationSympatric Speciation

                                  

                                  

                                  

apple maggot flies  

apples  

hawthorns

Sympatric SpeciationSympatric Speciation

• The formation of new species without the presence of a geographic barrier

• Occurs by one of 3 ways:– Balanced Polymorphism– Polyploidy– Hybridization

Balanced PolymorphismBalanced Polymorphism

• Suppose a population of insects possesses a polymorphism for color. Each color provides a camouflage to a different substrate (rock, tree stump, etc..).

• When not camouflaged, they are eaten• Thus, only insects with the same color can

associate and mate• Similarly colored insects are reproductively

isolated…so gene pools can diverge.

PolyploidyPolyploidy

• More than 2 sets of chromosomes found in diploid (2n) cells.

• Often occurs in plants (occasionally animals) where triploid (3n), tetraploid (4n) and higher chromosome numbers exist.

• Caused by nondisjunction in meiosis• Tetraploid individuals will continue to

produce diploid gametes – making them reproductively isolated very quickly.

HybridizationHybridization

• Occurs when 2 different forms of a species mate and produce offspring along a geographic boundary called a hybrid zone.

• The genetic variation of the hybrids is greater than that of either parent

• This permits hybrids to adapt to environmental conditions beyond the range of either parent.

• Hybrids can eventually diverge from parent forms when faced with selective pressures

Adaptive RadiationAdaptive Radiation

Adaptive RadiationAdaptive Radiation

• Relatively rapid evolution of many species from a single ancestor.

• Ancestral species colonizes an area where diverse geographic or ecological conditions are available for colonization.– i.e. many available ecological niches for a

population to spread into.– Examples: Darwin’s Finches, Australian

Marsupials

Patterns of EvolutionPatterns of Evolution

• Evolution can take place along the lines of the following patterns:– Divergent Evolution– Convergent Evolution– Parallel Evolution– Coevolution

Divergent EvolutionDivergent Evolution

• Describes two or more species that originate from a common ancestor.

• This may happen as a result of allopatric or sympatric speciation or by adaptive radiation

Convergent EvolutionConvergent Evolution

• Describes two unrelated species that share similar traits.

• Similar traits arise because each species has independently adapted to a similar niche

• These traits are called: Analogous Traits

Convergent ExamplesConvergent Examples

• Sharks, porpoises, and penguins have torpedo-shaped bodies with peripheral fins. These traits arise as a result of adaptations each species has made to aquatic life…not due to a common ancestor.

• The eyes of squids and vertebrates are physically and functionally similar. However they are not from a recent common ancestor, both evolved independently to perform similar functions.

Parallel EvolutionParallel Evolution

• Describes two related species or two related lineages that have made similar evolutionary changes after their divergence from a common ancestor

• Example:– Species from two groups of mammals, the

marsupial mammals and the placental mammals, have independently evolved similar adaptations when ancestors encountered comparable environments

CoevolutionCoevolution

• Describes the evolution of one species in response to new adaptations that appear in another species

• An example: evolutionary arms race between predators and prey…or– Plants and plant eating insects– Pollinators and flowering plants– Pathogens and animal immune systems