Bio 117 Lecture 8 Speciation

Front 1

Speciation

Back 1

emergence of a new species from a previous one, usually getting two species from one.

Front 2

What are the general types of specition

(3)

Back 2

1. Allopatric Speciation

2. Parapatric speciation

3. Sympatric speciation

Front 3

Describe Allopatric speciation

Back 3

The geographical separation of one gene pool into two concurrent gene pools resulting in the reproductive isolation of the gene pools.

Front 4

HWhat does geographic isolation arise from?

(2)

Back 4

1. Viacriance

2. Colonization

Front 5

Describe Vicariance

(one of the things allopatric speciation arises from)

give example

Back 5

Vicariance- the physical habitat splitting across a species range, such as by continental drift

(ex. Ratite flightless birds), oxbow lake formation, flooding, geological faulting.

Front 6

Colonization

(one of the things allopatric speciation arises from)

give example

Back 6

Colonization is the movement of organisms across some barrier, such as by rare unidirectional rafting across the sea during a storm

example- iguanas as probably occurred from SA to the Galapagos Isles.

Front 7

The founder events of Colonization can lead to founder effects (significant changes in gene frequencies) because of what 3 things?

Back 7

1. rapid natural selection due to small population sizes of colonists

2. Inbreeding (causes extinction of alleles that in the homozygous state are deleterious)

3. genetic drift (colonists have change differences in gene frequency from the source population)

Front 8

Give an example of Colonization

Back 8

Founders on islands leading to Endemism= species found and originating at only one location. Speciation and endemism are high on islands (Hawaiian island finches and silverswords). There is extreme diversity of morphological characteristics of different species that emerged after a colonization event of a single ancestral species in each case.

Front 9

Parapatric Speciation

Back 9

Non-geographic barriers to gene flow. An extremely sharp gradient in the environment and strong selection pressure to remain within one zone or an adjacent zone (such as in non-mobile plants)

Front 10

Give an example of parapatric speciation

Back 10

Anthoxanthum odoratum (sweet vernal grass) has evolved tolerance to heavy metal contamination. A pleiotropic effect of this gene for heavy metal tolerance also caused the timing of stigma and anther emergence in one population of grasses to occur a week ealier than the same grass species 65 feet away outside the gradient, allowing complete isolation of flowering and pollination between the locations HENCE reproductive isolation and the emergence of two species from one.

Front 11

Sympatric speciation

Back 11

isolating of two gene pools within the same geographic location as the original population.

Front 12

Sympiatric speciation

There are two ways of subdividing a gene pool at a geographic location without vicariance or sharp gradients. They are??

Back 12

1. mutation

2. Disruptive selection

Front 13

mutation

Back 13

any change in the genome of an individual, either in base sequence or in the number of chromosomes represented

Front 14

Two types of mutations

Back 14

1. Allopolyploidy

2. Crossbreeding

Front 15

Allopolyploidy

Back 15

chromosome multiplication

common in plants

multiplication of chromosomes. doubling of chromosome number in a certain cell ex. 2n ->4n

Front 16

What happens with the tetraploid in an Allopolyploidy mutation?

Back 16

The teetraploid is reproductively isolated from both parent stocks, creating a new sympatric species spontaneously

Front 17

Example of Allopolyploidy

Back 17

Three species of Tragopogon weed were introduced into western NA from Europe. Hybrids of these introduced species have repeatedly created new tetraploid species by allopolyploidy, indicating that allopolyploidy is a common event

Front 18

How often does an allopolyploidy occur?

Back 18

over 70% of plant species, and over 95% of ferns, have created these tetraploid species

Front 19

What are two types of muations?

Back 19

Allopolyploidy

and

Crossbreeding between species

Front 20

How often does crossbreeding occur?

Back 20

Crossbreeding is a rare occurrence. Hybrids usually die or result in competitively inferior offspring relative to those from parent species

Front 21

Disruptive Selection

(type of Sympatric Speciation)


What is disruptive selection cause by?

Back 21

Disruptive selection is caused by introduced food species

Front 22

Disruptive Selection is caused by introduced food species with:

what two things?

Back 22

1. Temporal difference in foor availability

2. Structural difference in food availability

Front 23

Example of Temporal difference in food availability

Back 23

Apple maggot fly usually breed on hawthorn fruits but some switched over to apples

since apples fruit later than hawthorn, the two genetic lines of flies have temporal separation of breeding activity

Front 24

Insipient Species

Back 24

The hawthorn and apple populations of flies.

Also called semispecies or half species.

Front 25

Example of Structural difference in food availability

Back 25

Soapberry bugs usually feed on large-fruited balloon vine plants, but some bug had shorter proboscis shifted to an invasive plant that had seeds with easier access.

Selection favored both the long and short proboscis length

This is a second case of insipient species evolving in sympatry

Front 26

The process of Speciation include what 3 things?

Back 26

The Subdivision

The differentiation

and reinforcement of gene pools

Front 27

Subdivision of a gene pool causes what?

Back 27

Subdivision of a gene pool causes reproductive isolation of gene pools

Front 28

What are the three categories of the subdivision of a gene pool?

Back 28

Geographic isolation (allopatric speciation)

Strong selection gradient that subdivides a gene pool (parapatric speciation)

Local segregation of reproduction among dispersed individuals within a gene pool (sympatric speciation)

Front 29

What are the four common characteristics that favor reproductive isolatiog of subpopulations?

Back 29

low mobility (star nosed mole)

low dispersal potential (aust. eucalyptus flower pollinated by honey possum)

Fragmented habitat occupation (vernal pool amphibians)

population crashes: isolates individuals in dispersed pockets that may persist over years and remain isolated from the main population (lemmings)

Front 30

Divergence in allele frequencies occurs between what?

(Divergence in allele frequencies is part of the speciation process)

Back 30

There is a Divergence in allele frequencies between the now isolated gene pools.

Front 31

Gene pool divergence (differentiation) requires what?

Back 31

1. Low probability of re-contact (for gene flow), As might be the case after:

a. rare vicariance (continental drift)

b. rare transport (freak storm, tsunami)

c. extreme isolation of colonizers (to remote island)

Front 32

Gene pool divergence (differentiation) can also require what?

Back 32

Rapid frequency change in isolated subpopulation, resulting from:

1. genetic drift

2. inbreeding

3. rapid selection in small populations

Front 33

how does Genetic Drift result in a divergence in allele frequencies?

Back 33

a chance divergence (via sampling) in gene frequencies between two gene pools. It occurs to the degree to which one of the two gene pools is much smaller than the other, such as a few colonists storm-rafting to a distant island

Front 34

How does inbreeding result in a divergence of allele frequencies?

Back 34

Inbreeding leads to the extinction of recessive deleterious alleles that in the heterozygous state may be advantageous and be retained only because of this heterozygote advantage

Front 35

How does rapid selection in small populations contribute to a divergence in allele frequencies?

Back 35

Less dilution of localized effects across a larger population

Front 36

What are the Three Ways speciation occur?

Back 36

1. Subdivision of a gene pool causing reproductive isolation of gene pools

2. Divergence in allele frequencies between the now isolated gene pools.

3. Biological reinforcement of reproductive isolation between individuals from different gene pools.

Front 37

Briefly explain Biological Reinforcement of reproductive isolation

(a way speciation occurs)

Back 37

Biological reinforcement of reproductive isolation occurs between individuals from different gene pools. It is the evolution and refinement of reproductive isolating mechanisms. (There are two major types of mechanisms)

Front 38

What are the two major types of reproductive isolating mechanisms?

Back 38

Post-zygotic mechanisms

and Pre-zygotic mechanisms

Front 39

Post-zygotic mechanisms

Back 39

Allos zygote formation, but offspring are not viable, are sterile, or have lowered fitness

Front 40

What is the post-zygotic mechanism an expression of?

Back 40

The mechanism is the expression of genetic imbalances created by the mixing of two considerably different gene pools.

In addition, it can be the result of selection for traits that terminate the life of zygotes, embryos, or newborns

Front 41

When do post-zygotic mechanisms usually occur?

Back 41

These mechanisms usually occur with the first contact of previously isolated gene pools

Front 42

Pre-zygotic mechanisms

Back 42

Keeps mating from occurring in the first place because of wasteful effects of producing offspring with little/no viability

Front 43

Why does pre-zygotic reinforcement evolve?

Back 43

It evolves because individual traits would be selected for that would not permit any energy loss in misguided courtship or gamete delivery

Front 44

When do pre-zygotic mechanisms evolve?

Back 44

these mechanisms usually evolve after post-zygotic mechanisms

Front 45

What are 5 Common prezygotic traits?

Back 45

1. Differences in copulatory apparatus (loss of lock and key fit)

2. Asynchronous sexual activity

3.Changes in courtship cues (like behavior, sexual pheromones, visual signals- like flash patterns in fire flies)

4. gamete rejection (usually of sperm)- example protein lock and key fit of egg/sperm in sea urchins

5. pollen tubule inhibition in plants (normally forms down the style to the ovary after pollen settles on the female stigma)

Front 46

Pre-zygotic mechanisms are more characteristic of what individuals?

Back 46

Individuals living in the sympatric portions of the two gene pools, where character displacement is common

Front 47

Character displacement

Back 47

a condition where individuals from different demes are more dissimilar in areas of sympatry than they are in allopatry, clearly indicating the evolution of pre-zygotic mechanisms

Reconctact
potential for interbreeding?

Front 48

Sympatric

Back 48

two species close together causes characteristics to diverge (ex calls of tree frogs)

Front 49

What is an example of a pre-zygotic mechanism

(character displacement)

Back 49

Character displacement of the frequency of courtship vocalizations in tree frogs. The call frequency in areas of allopatry are similar, but in sympatry they diverge to be non-ovrlapping because of natural selection against courting with another species that would produce no/few viable offspring

Front 50

When do you really see whether two separate species have evolved?

Back 50

Outcomes of population re-contact after a long period of isolation- this is when you really see under natural circumstances whether two separate species have really evolved

Front 51

What are five things that let us know a species really evolved?

Back 51

1. no interbreeding

2. some hybridization

3. moderate hybridization

4. extensive hybrid swarms

5. complete fusion

Front 52

Explain No interbreeding

Back 52

sufficient genetic divergence evolved in isolation, thus both poulations are separate species, and there is no gene flow between the species

Front 53

Explain some hybridization

Back 53

Some hybridization occurs, but few, if any, breeding offspring are produced. Selection for pre-zygotic reproductive isolation mechanisms is well underway, and character displacement is common. These will likely become insipient species (ex soapberry bug and apple maggot fly)

Front 54

Moderate hybridization

(an outcome of population re-contact)

Back 54

moderate hybridization with the production of viable offspring. Moderate evolution of post-zygotic mechanisms likely occur.the two gene pools are at cross roads.

Front 55

What can the moderate hybridization situation lead to?

Back 55

This situation could lead to the activation of pre-zygotic reinforcement mechanisms or escalate into extensive introgession (spread of alleles from both gene pools into the range of the other gene pool) and hybrid swarms.

Front 56

What sometimes happens to the hybrids when they inbreed with other hybrids?

(moderate hybridization)

Back 56

Hybrids inbreed with the other hybrids and produce offspring that are more viable than the hybrids could have produced by back crossing with members of the two parent populations.

In this case, the hybrid individuals may develop reproductive isolating mechanisms and become a new species

Front 57

Extensive hybrid swarms occur where?

Back 57

Extensive hybrid swarms occur where the two species are in sympatry.

Front 58

Extensive hybrid swarms occur where the two species are in sympatry.


What does this suggest?

Back 58

This suggests that the two species haven't reached full species status (haven't developed reproductive isolating mechanisms yet- prob wont) or are in the process of having these mechanisms breakdown because of the introduction of invasive species or other environmental upsets

Front 59

Complete fusion of any differences occurs between what?

Back 59

Complete fusion of any differences between the two populations with massive 2-way introgression (cross-species movement of genes) occurring across the range of both gene pools- essentially only one gene pool will soon exist.

Front 60

Adaptive Radiation

Back 60

Dramatic speciation events- explosion of species diversity from a single common ancestor- the starburst effect or star phylogeny

Front 61

Pre-requisites for Adaptive Radiation

(2)

Back 61

Key innovation: a trait in a species that is easily modifiable to readily serve a wide range of different functions (adjust to different niches)

Open niches: many different resources (refuges, food) are available

Front 62

Examples of Dramatic speciation events (adaptive radiation)

Back 62

1. Hawaiian silverswords (flower and fruit innovation; now 30 species)

2. Hawaiian honeycreepers (bill of ancestral finch; now 54 species)

3. Darwin's finches (bill of a single finch ancestor; now 15 species)

4. African cichlids- over 300 endemic (originating there and only occurring there) species in lakes in the rift valley of east central Africa.