High School
SAT
ACT
University
MCAT
LSAT
DAT
Wize University Biology Textbook > Speciation

Origin of Species

Hardy-Weinberg EquationPrevious Section
Sexual SelectionNext Section
Popular Courses
Find My Course
0:00 / 0:00

Origin of Species

This sections deals with how species are created and maintained in the real world

How does variation persist?

  • All of the ways that variation is created
  • Mutation
  • Recombination
  • Independent Assortment of Chromosomes
  • Fertilization
  • Disruptive Selection
  • Gene Flow
  • Negative Frequency-Dependent Selection: a trait is only advantageous when it is rare
  • Heterozygote Advantage: having two different alleles for the same gene produces the greatest fitness Example: Sickle-Cell Anemia


PAGE BREAK

Types of Evolution

  • Microevolution: evolution within populations or species (smaller changes)
  • Can accumulate to become macroevolution
  • Macroevolution: evolution above the species level
  • Novel traits ("game changers")
  • Can result from mass-extinction which open up the environment for rapid evolution


Photo by Javier Abalos | CC BY

PAGE BREAK

Biological Species Concept

  • Biological Species Concept: a "species" is a group of interbreeding organisms that can produce viable offspring in nature
  • Issues:
  • doesn't work with asexual organisms
  • some species can reproduce with other species: hybrids
  • Reproductive Isolation: a "species" should not be able to breed with other "species"
  • Prezygotic Isolation: barriers to reproduction before fertilization
  • Ecological
  • Temporal
  • Behavioral
  • Mechanical
  • Gamete
  • Postzygotic Isolation: species can mate, but the resulting offspring fail
  • zygote death
  • infertile F1 offspring
  • low hybrid fitness Example: "Hinny" is a sterile cross between Horse and Donkey
Photo by Just Chaos | CC BY

Wize Tip
The difference between postzygotic and prezygotic reproductive isolation is often tested on exams!

PAGE BREAK

Speciation

  • Allopatric Speciation: speciation occurs due to a geographic barrier
  • most common
  • after two groups become isolated they differentiate

Photo by Andrew Z. Colvin | CC BY
  • Sympatric Speciation: speciation without a geographic barrier
  • rare
  • assortative mating
  • microhabitat specialization
  • disruptive selection
  • After reproductive isolation
  • no gene flow between populations
  • evolution occurs separately for the two populations
  • eventually the two populations become different enough to prevent mating
Photo by Andrew Z. Colvin | CC BY

Wize Concept
Sympatric speciation is quite rare, some scientists question whether it is really possible

Practice: Species

Which of the following is not a mechanism that creates variation in a population? (select all that apply)

Practice: Species

True or False: Enough microevolutionary events can accumulate to create a macroevolutionary event.

Practice: Isolation

Which of the following is NOT an example of prezygotic Isolation?
Extra Practice
A group of individuals that are of the same species in the same area are termed a?
State whether the following isolating mechanisms are pre- or post-zygotic mechanisms. State whether the following isolating mechanisms are pre- or post-zygotic mechanisms.
a) Land snakes cannot fertilize water snake eggs
b) Ligers (tiger and lion hybrid) are sterile
Which of the following is an example of a prezygotic reproductive barrier?
Which of the following terms describes a group of organisms of a single species that live in the same space, same time and reproduce with one another?
Which of the following represents sympatric speciation?
Which of the following does not tend to promote speciation?
A certain community in rural Alberta was identified as being genetically unique at many loci from all neighbouring populations. Further assessment shows that this group is derived from a small group from “Chocoland” and that they do not outbreed. Which of the following likely explains their uniqueness?
The phenomena that creates diversifying selection of flower traits is called __________ shift.
This phenomena leads to speciation by establishing _____________ isolation.
Practice: Speciation
Consider a species of finch that is distributed along the east coast of Central America. In the following scenarios state what type of speciation is occurring.
Practice: Species Concepts
According to the species concepts, what is the definition of a "species" under each? Which definition is more practical in usage?
Under the biological species concept:
Which species concept can be applied to all organisms/populations?
Why is the term species so complicated to define that multiple concepts exist?
Speciation
What type of selection promotes sympatric speciation?
Speciation
What is the one requirement for speciation to occur under any speciation mode?
Speciation
In which mode of speciation does speciation proceed despite opportunity for gene flow?
Two different groups of aliens from the same planet come visit Earth. They don’t have
evolutionary biologists on their planet so they are not sure if they are the same species
of different species. Biologists encourage them to mate and they find that the mating
Sympatric speciation can result from:
Match the following definitions with their terms corresponding to different types of pre-zygotic isolation
Which of the following are disadvantages to using the biological species concept?
Cannot be used to classify organisms with high sexual dimorphism
Cannot be used to classify organisms whose species ranges never overlap
Which of the following are examples of pre-zygotic isolation?
Two groups of field crickets do not mate because one emerges for mating at the start of the summer, and the other at the end of fall.
A bird’s mating display is only attractive to birds of a certain species.
Which of the following is not a pre-zygotic barrier to fertilization?
Which of the following is a pre-zygotic barrier?
Fill in the blanks: The scenario below is an example of _________ which caused _____________
Original population:
New species arises:
Which of the following represents sympatric speciation?