1. SPECIATION
UNIT 5 EVOLUTION

2. Speciation
Speciation – the process of one species splitting into two or more species
Creates a diversity in life
Shows how organisms share a common ancestor
Forms a bridge between microevolution and macroevolution
Microevolution – changes over time within a population
Macroevolution – changes over time above the species level

3. Species Commonly known as a biological species concept
Species – a population whose members have the potential to produce offspring with each other but not with members of other groups.
Humans belong to the SAME species
Species genetically resemble each other due to gene flow
Gene Flow – the transfer of alleles between populations
Absence of gene flow results in the formation of new species

4. The Fish Species

5. Reproductive Isolation
Species are often identified by their reproductive capability
Reproductive Isolation – the existence of barriers to prevent members of two species from producing offspring together
Limits the formation of hybrids
Hybrids – offspring produced through mating

6. Barriers
Prezygotic Barrier – a barrier that prevents fertilization from occurring
“Before the zygote”
Can act in three different ways
By preventing members of different species from attempting to mate
By preventing an attempted mating from successfully completing
By preventing fertilization, if mating has already occurred
Postzygotic Barrier – a barrier that occurs after the zygote is formed
Contributes towards reproductive isolation
Can create developmental errors and can affect a hybrid’s chance of survival

7. Prezygotic Barriers
These barriers can disrupt mating or prevent fertilizations from completing

8. Habitat Isolation
Occurs when two species living in different habitats within the same area stop interacting with each other
These species are not isolated by physical barriers – mountain ranges, hills, valleys, etc.

9. Temporal Isolation
Species often breed during different times of the day, different seasons, or even different years
Occurs when these species are not able to mix their gametes with each other

10. Behavioral Isolation
When species perform rituals as a method of mate recognition
Mate Recognition – a way to identify potential mates of the same species
These are very effective reproductive barriers

11. Mechanical Isolation
When mating is attempted, but cannot be completed due to morphological differences

12. Gametic Isolation
Occurs when the sperm of one species cannot fertilize with the eggs of another species
A male species may not be able to survive within a females reproductive tract due to this

13. Postzygotic Barriers
These barriers can prevent a hybrid zygote from developing into a completely viable and fertile adult

14. Reduced Hybrid Viability
Genes of different parent species can interact with each other in different ways
The interactions can affect the hybrid’s development or survival in an environment

15. Reduced Hybrid Fertility
If the chromosomes of two species have even the slightest difference, meiosis can prevent the production of normal gametes
If hybrids cannot produce offspring when they mate, genes cannot flow smoothly between species

16. Hybrid Breakdown Some hybrids can be completely viable and fertile
However, when they mate, their offspring can be sterile and unable to reproduce.

17. Barrier Limitations
Does not apply to organisms that reproduce asexually
Example – Prokaryotes

18. Other Species Concepts
Morphological Species Concept
Example – body shape and structural features
Ecological Species Concept
Example – a species in relation to their ecological niche
Phylogenetic Species Concept
Example – the smallest group of individuals from a common ancestor

19. Allopatric Speciation
Allopatric Speciation – when a population becomes SEPERATED by a physical barrier
“Geographic Speciation” or “Other Country Speciation”
Creates an interruption in gene flow
Example:
The overflowing of a lake resulting in two or more smaller lakes home to separate populations
A river dividing a population of animals that cannot cross it
Occurs without genetic remodeling

21. Sympatric Speciation
Sympatric Speciation – when populations of the same species AND habitat become reproductively isolated from each other
“Same Country Speciation”
Less common than allopatric speciation
Occurs when gene flow is reduced
Can be caused by many factors
Polyploidy
Sexual Selection
Habitat Differentiation

22. Polyploidy
Polyploidy – when a new species is created due to accidents in cell division, resulting in an extra set of chromosomes
Occurs more commonly in plants
There are two types of polyploidy
Autopolyploid
Allopolyploid
Polyploidy

23. Polyploidy Autopolyploid – when chromosomes come from the SAME species
Allopolyploid – when chromosomes come from DIFFERENT species
Creates a new biological species
Hybrids are usually sterile
Example – a mule produced from a male donkey and female horse

26. Sexual Selection
Sexual Selection – a selection based off a preference by one sex for certain characteristics in individuals of the other sex.
Examples – color, fur, horns, size, wings, tails

27. Habitat Differentiation
When a subpopulation uses a habitat or resource not used by the parent population
Mutations allow individuals to exploit different conditions of the same environment

28. Allopatric and Sympatric Speciation Recap
Allopatric Speciation - when a population becomes SEPERATED by a physical barrier
Can cause an interruption in gene flow
Many barriers restricting reproduction
Sympatric Speciation - when populations of the same species sharing the same habitat become reproductively isolated from each other
Polyploidy
Sexual Selection
Habitat Differentiation