1. Speciation

2. Agenda Definition of a Species and Speciation
Reproductive barriers between species
Different forms of Speciation
Adaptive radiation
Convergent Evolution
Co-evolution
Rates of speciation

3. What is a Species
A species is a population or group of populations whose members have the ability to breed with one another in nature and produce fertile offspring.
Hybrids can also exist, however they produce offspring with reduced or no capabilities of producing fertile offspring.
Only occur in species close in evolutionary history

4. Hybrids – Tigon (Tiger – Lion)

5. Grolar/Pizzly Bear (Grizzly – Polar)

6. Mule (Horse – Donkey)

7. Exceptions To the Species Definition
Fossils: Cannot be assessed on whether extinct species were able to breed with other species
Organisms that reproduce asexually
Binary Fission

8. Speciation
The production of a new species is referred to as speciation.
A new species only occurs when two species can no longer breed with one another.
This means that each species must be reproductively isolated from one another
This means that two species may look exactly alike but if their reproductive system is different, then they are two distinct species.

9. Example: Western/Eastern Spotted Skunk

10. Reproductive Barriers Between Species

11. Reproductive Barriers
Reproductive barriers are barriers that exist preventing species from breeding with one another.
Often facilitates evolution
There are several types of reproductive barriers:
Geographic Isolation
Habitat Isolation
Other barriers

12. Geographic Isolation
Geographical isolation occurs when a population of species becomes geographically isolated.
The same species will have two populations separated by a geographical barrier (e.g. river, mountain, canyon)
While separated, one of the individual populations may change allele frequencies.
I.e. undergo speciation
Both species will be unable to breed

13. Habitat Isolation
Habitat isolation occurs when similar species adapt to different habitats in the same general location.
E.g. Two similar species of garter snake (land and water habitat)

14. Other Reproductive Barriers
Temporal Isolation: Species have different breeding seasons (e.g. Eastern/Western spotted skunks)
Behavioural Isolation: Species have different mating behaviours (courtships) (e.g. Blue footed booby)
Mechanical isolation: Incompatible reproductive structures

15. Other Reproductive Barriers
Gametic Isolation: Sperm and eggs from different species do not recognize one another
Hybrid inviability: Hybrid offspring does not live a full expected life
Hybrid infertility: Hybrid offspring matures into adulthood but cannot reproduce (e.g. horse + donkey = mule)

16. Different forms of speciation

17. Adaptive Radiation
Occurs when a small population(s) migrates to a new island
This population may undergo evolutionary change (new gene pool)
Some of these individuals may then migrate to another island in the chain where they may undergo an evolutionary change
This process, known as adaptive radiation, may repeat itself

18. Adaptive Radiation And the Galapagos Islands
The Galapagos islands have a diverse and unique amount of species due to adaptive radiation
Adaptive radiation explains why there are various Galapagos finches on the different islands.

19. Convergent Evolution
In convergent evolution, distantly related species that live in similar environments develop similar adaptations.
Recall the Rhea, Emu, and Ostrich

20. Co-evolution
Co-evolution is the process in which one species evolves in response to the evolutionary changes of another species
Occurs most often in predator-prey relations
E.g. The preys will evolve ways of avoiding the predator and the predator will evolve ways of capturing the prey

21. Co-evolution – Zebra and Lion
The zebra is constantly evolving to become quicker, more camouflaged, more agile, a good sense of smell and sight.
The lion will likewise evolve to become quicker, more agile, more stealthy, and also possess a strong sense of smell and sight.

22. Co-Evolution – Garder Snakes And Poisonous newt
Newts are heavily preyed upon by garder snakes
Newts evolved to be poisonous in order to reduce attacks by garder snakes.
Meanwhile, garder snakes co-evolved to be resistant to newt toxins

23. Co-evolution - Mimicry
In mimicry, one species (“the mimic”), resembles another species (“the model”), in order to gain a survival advantage.
E.g. The hoverfly (“the mimic”) and the wasp (“the model)
Wasp has a poisonous sting while hoverfly does not

24. Mimicry E.g. 2 - Monarch and Viceroy

25. Mimicry (Video)

26. Rates of Speciation Darwin proposed the gradualism model
Species diverge and accumulate small changes over time creating two distinct species
Niles Eldredge and Stephen Gould developed the punctuated equilibrium model to explain species development.
Species diverge in spurts of relatively rapid evolutionary change