1. Evolutionary Processes

2. Accumulating Evolutionary Changes
Terms to know…
Population - all the members of a single species that can interbreed in the same area
Gene Pool – the genes that are present in a population
Population genetics – the study of variations in gene pools

3. MICROEVOLUTION – small changes in the gene pool/future population
MICROEVOLUTION – small changes in the gene pool/future population. (example: wolf ancestors evolving into dogs)
*Basically, microevolution studies small changes in alleles that occur within a population. Over time, these small changes can accumulate, resulting in major differences within the population. Dogs have been artificially selected for certain traits, resulting in a wide range of breeds with very different characteristics*

4. The Peppered Moth (microevolution example)-
As trees became darker due to industry, darker moths had a better chance of survival. Over time, more darker alleles were present in the population.

5. MACROEVOLUTION – when the accumulation of small changes over extended periods of time lead to BIG changes in the gene pool/population (example: manatees and elephants descending from the same ancestral species)

6. Since we can’t see macroevolution occur in our lifetime, is it even possible?

7. A.  Causes of Evolution
1.  Genetic mutations or variation – differences either already occur in the population (e.g. color variations) or they appear through random mutation. Different environments lead to the increase or decrease of these traits through natural selection.
Note: Some mutations may at first appear harmful, but give an advantage if the environment changes, (an increase in FITNESS)

8. Does gene flow increase or decrease diversity?
2.  Gene Flow- as members of one population leave an area and move to another, they sometimes bring new genes with them. This increases variation and can lead to natural selection. It also may prevent two populations from becoming separate species (speciation).
Does gene flow increase or decrease diversity?

9. Example of GENE FLOW
Each rat snake represents a separate population of snakes
These snakes remain similar and can interbreed
This keeps their gene pools somewhat similar
They are considered subspecies

10. Which populations do you think are the LEAST similar?
Figure 18.3
Which populations do you think are the LEAST similar?
Why?

11. 3.  Nonrandom Mating- being the fittest means reproducing, not necessarily living longer. If certain individuals reproduce more than others (regardless of how long they live), then natural selection is occurring and their traits will become more common in future generations. Also called “sexual selection” a. Random mating is pairing by chance b. Nonrandom mating – individuals choose their mates 
Which method of mating do humans use?
Can you think of any organisms that mate randomly?

12. This results in some extreme characteristics.
Sexual selection occurs when males compete for the right to reproduce and the female selects males of a particular phenotype. (guppies, lions)
This results in some extreme characteristics.
Sexual dimorphism - when males and females of a species look different.

13. 4. GENETIC DRIFT-
changes in the gene pool due to random chance. This really only occurs in very small populations.

14. Bottleneck Effect – a type of genetic drift caused by a sudden and severe reduction in population. It reduces overall diversity, and can lead to extinction. Ex Cheetah

15. Cheetahs have very little diversity in their gene pool due to bottleneck

16. FOUNDER EFFECT
Another example of genetic drift where rare alleles or combinations are found in the original individuals establishing a small and isolated population
Dwarfism is really common in Amish communities due to the higher than average rate of this allele (by random chance) that was found in the original German founders.

17. Five in Five, Five Words or Less
1. Gene Pool
2.  Microevolution
3.  Gene Flow
4. Phenotype
5. Genetic Drift

18. Those can cause Natural Selection…
So what happens next?

19. A. Results of Natural Selection
1.  Directional Selection  One phenotype is favored over another and gradually becomes more common; Causes a shift in one direction of the overall appearance of the species over many generations Ex: horses get larger, peppered moth

20. 2. STABILIZING SELECTION
occurs when all extreme phenotypes are eliminated and the average phenotype is favored; causes the population to become more similar over many generations
Ex: number of eggs per nest

21. Human babies have an average size due to stabilizing selection
Human babies have an average size due to stabilizing selection.  Babies that are too big can't get through birth canal while babies that are too small have low survivability after they are born. Too big and too small have been selected against for millennia, leading to most babies weighing between 5 and 9 pounds at birth.
How do you think the future of baby birth weight will change thanks to modern medicine? Are we still experiencing stabilizing selection?

22. 3. DISRUPTIVE SELECTION -- occurs when extreme phenotypes are favored and the middle trait is selected against; can lead to a population splitting and forming two separate species.

23. Imagine this scenario....
Sleebos come in many sizes, the most common Sleebo is 4 inches long, but some can be 10 inches and others can be as small as 1 inch.    A new predator is introduced to the Sleebo island.  Small sleebos are able to hide under rocks and avoid being eaten.  Large sleebos are too big for the predator to eat.  
What will happen to the Sleebo population?

24. Types of Selection

25. Back to MACROEVOLUTION
All of these evolutionary changes accumulating over time can result in so many differences that scientists elect to reclassify the future generations as a new species.
Speciation – the splitting of one species into two or more species

26. Scientists decide when speciation occurs, so it’s important to know how we define a species. Surprisingly, this is not actually an easy idea to define…
A species is a group of similar individuals who can SUCCESSFULLY and NATURALLY interbreed (However, this is one of MANY definitions)

27. When species collide…
Hybrids occur when members of different (but very closely related) species produce viable offspring. However, hybrids are rare in nature and often are not very healthy.
Lion + Tiger =  Liger

28. Horse +
Donkey =
Mule
Zebra +
Donkey =
Zonkey

29. Flycatcher species Empidonax minimus Empidonax virescens
Example of SPECIATION
Flycatcher species
Empidonax minimus
Empidonax virescens
Empidonax tralli
These birds all live in the same area. In order to be separate species, they cannot interbreed. Any idea what stops them from mating with each other?

30. What would happen if two of these birds did mate?
Figure 18.10c
Each species has a unique song and each species occupies a different habitat during their mating season.  
What would happen if two of these birds did mate?

31. How to make a new species…
In order for speciation to occur, a population must be split reproductively and prevented from interbreeding. Here is how this happens…

32. REPRODUCTIVE ISOLATING MECHANISMS
A. PREZYGOTIC - before zygotes
1. Habitat Isolation – different locations
2. Temporal Isolation – different reproductive timing
3. Behavioral Isolation – not attracted to one another (i.e. different songs)
4. Mechanical Isolation – the anatomy doesn’t fit
5. Gamete isolation – the sperm and egg don’t work together
Damselfly penises

33. REPRODUCTIVE ISOLATING MECHANISMS
B. POSTZYGOTIC – after the zygote
1. Zygote mortality – miscarriage
2. Hybrid sterility – the offspring can’t reproduce
3. F2 fitness – the hybrids are selected against because they are not healthy

34. MODES OF SPECIATION
1. Allopatric Speciation- Populations are physically separated by geographic barriers and genetic variations accumulate over time

35. 2. SYMPATRIC SPECIATION
Members of a population stop interbreeding, but without any physical barrier, usually caused by mutation or sexual selection Ex. A mutation changing chromosome number Ex. Mate preference

36. Sympatric vs Allopatric

37. Speciation can occur through splits or just the simple (linear) accumulation of differences.

38. ADAPTIVE RADIATION
speciation in multiple directions; a single ancestral species becomes several different (but similar) species