Lecture Notes: Macroevolution

Question 1

Mechanisms of Reproductive Isolation

Answer 1

Pre zygotic & post-zygotic

Question 2

Prezygotic

Answer 2

1. habitat isolation
2. behavioral
3. temporal
4. mechanical
5. gametic

Question 3

Postzygotic

Answer 3

1. reduced hybrid viability
2. reduced hybrid fertility
3. hybrid breakdown

Question 4

populations are constantly evolving so:

Answer 4

1. population today is a “snap shot” of that group

2. difficulty in identifying the characteristics that indicate common ancestry

Question 5

Modes of Speciation

Answer 5

allopatric & sympatric speciation

Question 6

Allopatric speciation

Answer 6

a. populations speciate as a result of segregation by geographical barriers

Question 7

Allopatric speciation favored by:

Answer 7

1. small population size
2. differences in the environments of the isolated habitats
3. Peripheral isolation

Question 8

Sympatric Speciation

Answer 8

new species arise within the same geographical range of the parental species

Question 9

Mechanism to sympatric speciation

Answer 9

polyploidy, resource partitioning, and assortative mating

Question 10

Polyploidy

Answer 10

common in plants

autopolyploidy and allopolyploidy

Question 11

autopolyploidy

Answer 11

chromosomes derived from the same parental species
cannot produce viable gametes
may be able to mate with itself or another tetraploid (reproductive isolation)

Question 12

Allopolyploidy

Answer 12

chromosomes derived from two hybridizing parental species

often fertile because chromosomes can pair during meiosis

Question 13

Resource partioning

Answer 13

limited resources partionined at different levels among individuals

Question 14

assortative-selective mating

Answer 14

segregation of individuals into isolated “morphs” based on selection of mates

ex: cichlids of Lake Victoria

Question 15

shifts in adaptive peaks

Answer 15

• populations occur in both valley and peaks
• several peaks are available within a population, but natural selection maintains population at a single peak
• to shift peaks must go through valleys of low fitness: achieved by genetic drift, non-adaptive radiation
• once peak is reached, NS will leads towards reaching equilibrium
• adaptive landscape can change as the environment changes.

Question 16

What does an adaptive peak represent?

Answer 16

optimal gene pool for success in a particular enviornment

Question 17

Hybrid Zones

Answer 17

a region where two populations interbreed
can change in width over time
typically shown in cline

Question 18

Gradualism

Answer 18

a. microevolutionary changes lead to macrogradualism

b. gradual changes in allele frequency through time lead to divergence and eventually speciation.

Question 19

punctuated equilibrium

Answer 19

fossil record shows long periods of statis punctuated by short periods of rapid change

Question 20

fossil

Answer 20

• preserved remnants or impressions of an organism
• typically found in sedimentary rock
• mineralization of tissues leads to petrification
• some retain organic material
• casts, molds, impressions
• trace fossils
• more complete specimens found in acid bogs, amber, ice, caves, etc

Question 21

Fossilization:

Answer 21

a. a chance event
b. requires rapid burial under the right conditions that slow down decay
c. requires escaping geological forces
d. in order for fossil to be exposed you need weathering
e. hard body parts have a higher chance of fossilization

Question 22

Fossil records

Answer 22

• a catalogue of evolution of life on earth
• incomplete
• biased towards species that: existed longer, more abundant, widespread, had hard parts

Question 23

Relative dating of fossils

Answer 23

strata: sedimentary layers
younger strata above older ones ( rule of superposition)
-igneous rock are younger than the rocks through they cross
-correlate strata in one location with strata in other location.
-Index Fossils: widespread with good record that can be used or correlating strata

Question 24

Absolute dating of fossils

Answer 24

• determines a specific age with error bars

- radiometric dating and racemization

Question 25

Radiometric Dating

Answer 25

measures content of isotopic elements

each element has a specific rate of decay, which is temperature and pressure insensitive

Question 26

Molecular Clocks

Answer 26

• use of amino acid or nucleotide substitutions to determine time of divergence among two groups
• calibrate the clock with the fossil record: know date of divergence for closely related groups
• Assume constant rate of substitution
• ok for closely related groups
• differences in generation time, metabolism are sources of error for non-closely related groups

Question 27

Geological time scale

Answer 27

• geological history of the earth divided into eras, periods, epochs
• boundaries determined by radiations and mass extinctions
• durations of stages not comparable