1. 5 Agents of Evolution

2. What is an Evolutionary Agent?
Causes a change in heritable traits within a population
 Causes evolution to occur!

3. 1. Natural Selection
The process by which beneficial traits become more common within a population because organisms with those traits have a higher chance of surviving to reproductive age and contributing to the offspring in the next generation.

4. 2. Mutation Any random change in the genetic material of an organism
Primary source of variation in natural selection
Must be passed down to contribute to evolutionary change
Mutation must be present in the gametes of an organism

5. Mutations: Speed of Evolution
Mutations occur randomly and at a low frequency
Alone, mutations do not have a huge effect on evolution.
HOWEVER, paired with another agent of change, such a natural selection or genetic drift, mutation can have a very drastic effect!

6. 3 types of mutations
Positive: the mutation results in the production of a beneficial trait (increases fitness)
Negative: the mutation results in the production of a non-beneficial trait (decreases fitness)
Silent: the mutation does not affect the heritable traits of the individual

7. Sickle Cell Anemia

8. Example: Snake Plant Mutant: Cylindrical Snake Plant
Mutation occurred in the gene that is responsible for producing flat leaves.

9. Evolution before our eyes…
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10. Cat Mutations
Manx (tailless)
American Curl
Polydactyl

11. 3. Genetic Drift
Change in heritable traits in the population based on chance
Some organisms will contribute more offspring to the next generation
Not because they are more fit, because they are lucky

12. Bottleneck Effect
Quick reduction in a population often caused by a natural event (earthquake, flood, volcanic eruption, etc.)
Gene pool of reduced population likely does not mirror original population
Future generations have different proportions of heritable traits than the previous generations

13. Visualizing the Bottleneck Effect
See this video for an explanation!

14. Case Study: Northern Elephant Seal
Humans overhunted the Northern Elephant Seal population
In the 1890s, the Northern Elephant Seal was reduced to only 20 individuals!
Today, the population is
~30,000 individuals, but
the population has reduced
genetic variation
Why could this be a
problem for the species?

15. Founders Effect
The loss in genetic variation that occurs when a new population is established by a very small number of individuals from a larger population

16. Case Study: Anoles

17. Founders Effect: Cultural Isolation
Amish populations in the United States tend to have grown from a few founding families and many have not recruited newcomers
Ellis-van Creveld syndrome is more common in Amish communities than in the entire American population
Symptom: extra fingers or toes

18. 4. Gene Flow A.k.a. migration
Changes in a population’s heritable traits as individuals migrate into or out of a population

19. Gene Flow: Examples
A young male lion leaves his mother’s pride and joins a pride with genetically unrelated females
How does gene flow occur in plant species?

20. 5. Non-Random Mating A.k.a., sexual selection
An individual in a population does not have an equal chance of mating with any individuals of the other gender
(Individuals pick their mates)
Does this occur in humans?

21. Male competition
Male caribou grow large antlers every mating season. These antlers are for intimidating other males or used in combat.
These antlers are shed at the end of every season and regrown the next year!
Males who are able to grow large antlers are seen as more fit, and more females will mate with them.

22. Female Choice Females choose their mate based on their traits
Can lead to some extravagant adaptations!

23. Heritable traits can be instinctive behaviours too!

24. Looking to the future…
Monday: We have a guest presenter coming in from the organization GeneSkool. They will be putting on an interactive workshop about evolution with us!
Wednesday: Group work to study the Agents of Evolution
Friday: Agents of Evolution Quiz! Also fun Halloween lecture 