1. Evolution and Speciation Sections 9.1 – 9.2
Chapter 9
Evolution and Speciation
Sections 9.1 – 9.2

2. Learning Goal
For students to evaluate the possible impacts an environment change has on natural selection and vulnerable species
To describe some evolutionary mechanisms and explain how they affect the evolutionary development and extinction of various species

3. Section 9.1
Mechanisms of evolution and their effects on populations

4. Introduction
Genetic variation in people within a population makes evolution possible
In species that reproduce sexually, each person inherits a NEW combination of alleles from their parents – which forms genetically different offspring generation to generation
Mutations occur randomly that also accounts for differences in genes among generations

6. Introduction
Although genetic mutations are rare, following laws of natural selection are constantly at play
Individuals with genes that help them survive reproduce, as they pass along their genes to their offspring and increase these genes % in a population

7. Introduction Individual organisms DO NOT EVOLVE, populations DO
Thus, in order for us to see the changes in a population – we must look at the changes that happen in populations

8. Factors that change allele frequencies
Changing % or frequencies of alleles within populations are the small events that lead to evolution within a population
When frequency of an allele in a population change, “microevolution” takes place
Microevolution - is the change in allele frequencies that occur over time within a population

9. Factors that lead to Microevolution
Description
Effect
Mutation
Gene Flow (migration)
Non-random mating
Genetic Drift
Natural Selection

10. Factors A) Mutations
Mutation = a change that occurs in the DNA of an individual – which could affect the entire gene pool of that given population
The more genetic variation there is in a population, the more diverse and higher the chance of selective advantage there will for some people in a changing environment

11. Factors A) Mutations For example
the Norway Rat became immune to poison used to control the rat population in the 1950s.
Some rats survived, already having mutated DNA passed down to them, who then mated, and continued to pass such genes on
By the 1960s, there were many resistant rat populations in Europe

12. Factors B) Gene Flow
Gene Flow = describes the movement of alleles from one population to another because of migration of individuals

13. Factors B) Gene Flow For Example Grey wolves have large territories
Often, a grey wolf from 1 population will mate with a member of a nearby population
This results in genetic diversity in nearby populations to increase
Having greater genetic diversity helps populations survive

14. Factors C) Non-Random Mating
= mating among individuals on the basis of:
mate selection for a particular phenotype or
due to inbreeding (same family)
In contrast – random mating is just like picking names out of a hat, there is no way to predict who will mate with who

15. Factors C) Non-random Mating
Preferred Phenotypes
In animal populations, individuals may choose mates based on their physical and behavioural traits = phenotypes
For example, in herds of caribou, males compete for mates by using their antlers to spar – where the stronger ones would prevail
This is a form of non-random mating because it prevents individuals with particular phenotypes from breeding

16. Factors C) Non-random Mating
Inbreeding
Occurs when closely related individuals breed together (same family)
Recall, that close relatives will share similar genotypes, so inbreeding increases the frequency of homozygous genotypes
Inbreeding does not directly affect the distribution of alleles present
So, as homozygous genotypes become more common, harmful recessive alleles pop up!

17. Factors C) Non-random Mating
The negative effects of inbreeding can be seen throughout history when looking at families of Royalty – where they could only marry common royals
Or religious communities – orthodox Jewish and Amish communities
Recall, if the gene pool is small, then this is why such recessive disorders surface

18. Factors D) Genetic Drift
In small populations, the frequencies of certain alleles can be changed by chance alone
When this happens = Genetic Drift
Where, the smaller the sample size = greater the uncertainty of your results

19. Factors D) Genetic Drift
In nature, sample sizes can affect the gene pool of a population very much!
The smaller the population = less likely to see the parent gene pool in the next generation
The larger the population = better chance that the parent gene pool will be reflected in future generations

20. Factors D) Genetic Drift

21. Factors D) Genetic Drift
The Founder Effect
New populations can be formed by only a few individuals or “founders”
For example – strong winds may carry a single, pregnant fruit fly to a previously unpopulated island, where the fruit fly and her offspring create a new colony
These founders carry some alleles from the original population’s gene pool

22. Cont’d - Founder Effect
Thus, the founders may not be “normal” form the original population and carry some recessive traits
These can become more dominant since the gene pool is much smaller
Hence, the Founder Effect takes place as a change in a gene pool that occurs when a few individuals start a new isolated population

23. Cont’d - Founder Effect
The founder effect can take place in human populations too
The Amish community in Pennsylvania was originally founded in 1700s by only a few families
In their culture, they must only marry other Amish people, where the lack of a large gene pool is why recessive disorders like polydactylism (extra finger / toes) are seen

25. Factors D) Genetic Drift
The Bottleneck Effect
Starvation, disease, human activities, and natural disasters can quickly reduce the size of a large population
The survivors will only have a fraction of alleles that were present originally in the population
Again, the smaller gene pool decreases genetic diversity of the population, and recessive

26. Cont’d Bottleneck Effect
Bottleneck effect occurs when changes in gene distribution that result from a rapid decrease in population size
For example, when a typhoon hit a small island in the Pacific Ocean in 1775, there were only 30 survivors.
One of the survivors had a genetic mutation of colour blindness, when is not present in 10% of the current population

28. Review: Genetic Drift

29. Factors E) Natural Selection
Populations have a wide range of phenotypes and genotypes, and some people are more predisposed to survive and reproduce than others
There is a greater chance of a person with a slightly favourable allele surviving and reproducing
Thus, natural selection causes changes in the frequency an allele is present, which can lead to evolutionary changes

30. Factors E) Natural Selection
There are 3 different ways natural selection affects the frequency of a heritable trait in a population
Stabilizing Selection
Directional Selection
Disruptive Selection

31. Factors E) Natural Selection
Stabilizing Selection
Directional Selection
Disruptive Selection
Favours an intermediate phenotype and act against extreme variants of the phenotype
The most common phenotype (the intermediate) is made more common by removing extreme forms
Here, reduce variation and improves the adaptation of the population
Favours phenotypes at one extreme over the other
Common during times of environmental change / migrating population
Takes place when the extremes of a range of phenotypes are favoured over intermediate phenotypes
This eliminates intermediate phenotypes from the population

32. Factors F) Sexual Selection
Is a type of Natural Selection, involves characteristics or behaviours that make it more likely for people to choose a mate
Reflects
Competition between males through combat (like caribou)
Visual displays (like peacocks)
Choice from the females
Males and females of various species have many different physical characteristics, as well as courtship are aspects of sexual selection

33. Section 9.2
Speciation: How Species Form

34. Introduction
Speciation – is the formation of a new species from existing species
2 types of populations may become reproductively isolated over time if there is no gene flow between them
Gene flow could be prevented in 2 ways:
Pre-zygotic – prevent mating, prevent fertilization
Post-zygotic – prevent hybrids from developing

35. Pre-zygotic Isolating Mechanisms
Consist of a barrier that either delay or prevents mating between species or fertilization of the eggs if individuals from different species attempt to mate
AKA pre-fertilization barrier

36. Pre-zygotic Isolating Mechanisms Use pgs. 361- 362
Behavioural
Habitat
Temporal
Mechanical
Gametic

37. Post-zygotic Isolating Mechanisms
Are rare cases in nature, where the sperm of 1 species successfully fertilized an egg of another species to produce a zygote
Post-zygotic barriers prevent these hybrid zygotes from developing into viable offspring

38. Post-zygotic Isolating Mechanisms Use pg. 363
Hybrid Inviability
Hybrid Sterility
Hybrid Breakdown

39. Types of Specialization
There are 2 types of specialization: Sympatric and Allopatric
Sympatric – helps populations that live in the same habitat to diverge genetically
Allopatric – occurs when populations are separated by a geographic barrier and then genetically diverge

40. Sympatric Speciation
Seen when populations live in the same geographical area and become reproductively isolated
Factors like chromosomal changes and non-random mating alters gene flow
More common in plants than animals

41. Sympatric Speciation
Under the right conditions, a new species can be generated in a single generation if a genetic change happens due to reproductive barriers between the offspring and the parent population
For example, errors in cell division can lead to mutations and speciation

42. Allopatric Speciation
Happens when a population is split into 2 or more isolated groups because of a geographical barrier
Eventually the gene pool of split population becomes so distinct, that the 2 groups are unable to interbreed, even if brought back together

44. Darwin’s Finches: Ecological Niches
At some point in history, members of an ancestral species reached one of the Galapagos
With no other birds on the island, the ancestral finches moved in and adapted to pre-existing ecological niches
Ecological Niche – the ecological role and physical distribution of a species on its environment

45. Darwin’s Finches: Ecological Niches
During this time on the island, the finches were subjected to different types of selective pressures, and some flew to other nearby islands in order to adapt and survive
Over time, the ancestral finches divided into different populations and evolved into new species as a result of the adaptations required to survive on various islands

46. Darwin’s Finches: Ecological Niches

47. Adaptive Radiation
Is a form of allopatric speciation, which involves the diversification of a common ancestral species into a variety of different adapted species

48. Divergent / Convergent Evolution
Divergent Evolution – a pattern of evolution in which species that were once similar to an ancestral species diverge (differ)
Happens when populations change as they adapt to different environmental conditions
The populations become less alike as they adapt, resulting in the different species

49. Divergent / Convergent Evolution
Convergent Evolution – a pattern of evolution where similar traits are seen because different species have independently adapted to similar environmental conditions – NOT that they have a common ancestor
For example, birds and bats evolved independently at different times, yet in the same environment (the air)
Thus, although they both evolved wings, since they DO NOT have a common ancestor, their wings are different

50. Divergent / Convergent Evolution

51. The Speed of Evolutionary Change
There are 2 models that try to explain the speed at which evolution take place
Gradualism – views evolutionary change as a slow, but steady, before and after a divergence
Punctuated Equilibrium – views evolutionary history as long periods of balance / equilibrium, that are interrupted by periods of divergence

52. The Speed of Evolutionary Change

53. Activity 9.4 – Shaping the Theory
Complete Activity 9.4 on pg. 369
Follow the Procedure (#1-3)
Question – Response in full sentences: Which contributor do you consider the most valuable in helping you understand the modern theory of evolution? Why?

54. Consequences of Human Activities
Human activities can affect the genetic diversity of populations in many ways:
Convert large stretches of wilderness into croplands
Develop wilderness areas for recreation / tourism
Build roads
Build urban subdivisions
Flood large areas of land to build dams for hydroelectric generation
Hunting / killing of organisms

55. Consequences of Human Activities
As with geographic barriers that may lead to natural allopatric speciation (divided by land)
These human made barriers may prevent gene flow between split populations
With time, isolated populations can adapt in order survive within the new environments
Those populations who are unable to adapt successfully can die and eventually become extinct

56. Speciation and Mass Extinctions
The environment is a strong influence on both speciation and extinction
Environmental influences create selective pressure, and these influences can be both positive and negative:
Where a new species can arise as a result of adaptation
Or existing species can become extinct

57. Summary