1. Speciation

2. Introduction Species continue to evolve
Changes that occur within species (microevolution) are easy to understand
Faster-running cheetahs
Colourful male songbirds
Larger brains in humans
But what factors lead to speciation- the evolution of an entirely new species?

3. What is a Species?
A species includes all members of a population that can interbreed under natural conditions
Some species are quite distinct based on their morphology but some species are only distinguished by genetic comparisons

4. Modes of Speciation New species can evolve many ways
Always includes the evolution of distinct features that isolate the new species reproductively, therefore genetically, from other species

5. Mechanisms of Reproductive Isolation
any biological factor that prevents the two populations from interbreeding when living in the same region.
Prezygotic mechanisms: prevents interspecies mating and fertilization
Different breeding seasons, physical or behavioural traits, habitat preferences or the incompatibility of gametes

6. Mechanisms of Reproductive Isolation
any biological factor that prevents the two populations from interbreeding when living in the same region.
Postzygotic mechanisms: prevents maturation and reproduction in offspring from interspecies reproduction

7. Mechanisms of Reproductive Isolation
Prezygotic
Temporal Isolation: Species have different breeding seasons.
Example: Western spotted skunks breed in the fall but the Eastern species breeds in late winter
Western Eastern

8. Mechanisms of Reproductive Isolation
Prezygotic
Behavioural Isolation: Species may have different courtship or mating behaviours.
Example: Eastern meadowlark and western meadowlark are almost identical in everything, except their courtship rituals and songs
Eastern Western

9. Mechanisms of Reproductive Isolation
Prezygotic
Mechanical Isolation: Species may have reproductive structures that are physically incompatible.
Example: Snails of the same species have reproductive structures that align, but snails from two different species part the other species

10. Mechanisms of Reproductive Isolation
Prezygotic
Ecological Isolation: very similar species may occupy different habitats within a region
Example: The mountain bluebird lives at high elevations, while the eastern bluebird prefers lower elevations. The mountain bluebird and eastern blue bird do not encounter each other

11. Mechanisms of Reproductive Isolation
Prezygotic
Gametic isolation: male gametes may not be able to recognize and fertilize an egg of a different species
Example: corals, clams and sea cucumbers release their sperm and eggs into open water. The sperm recognize the egg of their own species through chemical markers on the egg surface.

12. Mechanisms of Reproductive Isolation
Postzygotic
Zygotic Mortality: mating and fertilization are possible, but genetic differences result in a zygote that is unable to develop properly
Example: If you have sheep and goats on a farm, some species of sheep and goat are able to mate, but the zygote is not viable.

13. Mechanisms of Reproductive Isolation
Postzygotic
Hybrid Inviability: a hybrid dies early in development, or lives to maturity but is not healthy and suffers an early death.
Example: Some salamanders species may mate with each other, but most of the offspring do not live to adulthood, or if they do they are weak.

14. Mechanisms of Reproductive Isolation
Postzygotic
Hybrid Infertility: The hybrid offspring mature into adults but are infertile.
Example: A mule is bred from a female horse (left) and a male donkey (centre). Mules are physically healthy but they are infertile.

15. Allopatric Speciation
Most new species form when a single species is separated into two geographically isolated populations
Once physically separated, populations cannot share genetic information
Over many generations the populations will gradually become less alike
Mutations and genetic drift may have caused populations to change
Reproductive isolating mechanisms may have developed

16. Allopatric Speciation
White-tailed antelope squirrel
Harris’s antelope squirrel

17. Sympatric Speciation
The evolution of populations within the same geographic area into separate species
Individuals within a population become genetically isolated from the larger population