1. Speciation

2. What is a species? Species == “kind” or “type” in Latin
Typological (morphological) species == a group of organisms that share certain characteristics which are different than other groups—usually differences in anatomy.
Each kind of organism is fixed and immutable and can be represented by an ideal individual, the type specimen (Linnaean Nomenclature)

3. What is a species?
2. Biological species concept== Reproductively isolated group of actually interbreeding natural populations that produce fertile offspring
This definition is hard to apply because most organisms don’t live together and never have a chance to interbreed.

4. A B B A Easy Hard How do we know if 2 species interbreed?
Sympatric species = ranges overlap
Allopatric species = ranges don’t overlap A B B A
Easy
Hard
How can we test if two populations are 2 species?
Biological species definition used 10% of the time
Morphological & chem. differences used 90% of the time.

5. Problems in identifying species:
1. Polymorphic species = species with many different types of individuals

6. Problems in identifying species:
2. Sibling species = virtually identical species

7. Problems in identifying species:
3. Sibling species = virtually identical species
Madagascar’s Supportive Lemur
Lepilemur mustelinus
One species 7 species

8. Problems in identifying species:
4. Ring Species = continuous gradual shift in phenotype over a large range.
The end populations
can’t interbreed.

9. Problems in identifying species:
5. Asexual species = can’t use biological species definition
6. Fossil species = can’t use biological species definition

10. What Keeps Species From Interbreeding ?
Reproductive Isolating Mechanisms

11. Reproductive isolating mechanisms
Pre-zygotic Barriers before zygote formation
Ecological (Habitat) Isolation
Share territory, but occupy different regions
Behavioral Isolation
e.g. frogs only respond to calls of the same species

12. Pre-zygotic Barriers cont’
3. Mechanical Isolation == Distinct reproductive parts
Gametic Isolation
Mating occurs but
egg and sperm are incompatible due to lack of interaction of receptors on the cell membranes

13. Post-zygotic Barriers= after zygote
Hybrid inviability fertilization occurs but zygote, embryo or larva dies
Hybrid Sterility. Healthy hybrid unable to reproduce due abnormal gametes; e.g. mules.
Populations do not strive to become species

14. How are Species Formed?? Microevolution
Mechanisms of Speciation
Allopatric speciation (=geographic speciation)
Two steps:
1. Geographic separation of a once continuous population
2. Reproductive isolation produced during genetic drift or natural selection

15. How Does Geographical Isolation Occur?
Dispersal
2. Barriers
3.Continental Drift

17. Allopatric Speciation

18. Allopatric Speciation

19. Allopatric Speciation
Kaibab Squirrel
Albert’s Squirrel

20. Sympatric Speciation Ecological speciation =
speciation within a population
occurring in a single habitat.
Mechanism?

21. Sympatric Speciation Instantaneous speciation=
new species formed in one generation
Mutation Not probable
Polyploidy. Common in plants
Autopolyploidy—diploid gametes form zygote producing new species e.g. bananas
Allopolyloidy—two different species hybridize and double their chromosomes

23. Hybrid Speciation Spartina alterniflora x Spartina maritina
e.g. Marsh grasses
Spartina alterniflora x Spartina maritina
American British
Spartina townsendii

24. SYMPATRIC SPECIATION 2. Gradual Speciation
E.g.. Tephritid fly specializing on different host trees (hawthorn vs. apple)

25. NEXT TIME: ADAPTATION