Lecture 11: Isolation and Divergence in Allopatry

Question 1

S____ begins when gene flow between
populations is reduced or eliminated, causing
genetic isolation

Answer 1

Speciation

Question 2

G_____ isolation happens when populations
become geographically separated

Answer 2

Genetic isolation

Question 3

DEF: Populations that live in different areas

Answer 3

Allopatry

Question 4

Speciation that begins with geographic isolation is
called a_____ speciation

Answer 4

Allopatric speciation

Question 5

Geographic isolation occurs in one of 2 ways:

Answer 5

1. Dispersal
2. Vicariance

Question 6

DEF: A population moves to a new habitat, colonizes it, and founds a new population

Answer 6

Dispersal

Question 7

DEF: the physical splitting of a habitat
- A physical barrier splits a population into subgroups that are physically isolated from each other

Answer 7

Vicariance

Question 8

DEF:
the study
– of how species and populations are distributed
geographically
– Can tell us how dispersal and vicariance events occur

Answer 8

Biogeography

Question 9

Colonization events can lead to speciation
– Peter and Rosemary Grant compared parents and
offspring from large ground finches that remained on the island of Daphne Major (c_____) with those from the home island (m____)

Answer 9

Colonists, migrants

Question 10

• New population is not a separate species yet, because
  there is still some gene flow
  – Over time, the populations could continue to diverge

T or F

Answer 10

True

Question 11

When there is a physical barrier such as a mountain
range uplifting or a river splitting the geographic range of a species, v_____ has occurred

Answer 11

Vicariance

Question 12

Example: Researchers compared the DNA sequences
of trumpeters from different areas of the Amazon
basin to the geological events that occurred
– They found evidence of isolation of populations by
vicariance
▪ Initially, the formation of the Amazon split the ancestral
population
▪ The formation of the river systems then subdivided the
populations

T or F

Answer 12

True

Question 13

DEF: Populations or species that live in the same
geographic area—close enough to interbreed—
live in s_____

• Serves as a source of new branches on the tree of
  life
• Speciation that occurs among populations within the same geographical area

Answer 13

Sympatry

Question 14

Sympatric speciation can be initiated by two types
of events:

Answer 14

1. External events
   ▪ Example: Disruptive selection based on different
   ecological niches or mate preferences
2. Internal events
   ▪ Example: Chromosomal mutations

Question 15

DEF: The range of ecological resources that a species can use and the range of conditions it can tolerate

Answer 15

Niche

Question 16

Even though sympatric populations are not
geographically isolated,
– They may be reproductively isolated by adapting to
different ecological niches via disruptive selection

T or F

Answer 16

True

Question 17

Apple maggot flies mate on apple fruits, and their
larvae use the apple for food source
* Hawthorn maggot flies feed and mate on
hawthorn fruits
* Apple maggot flies originated from hawthorn flies
after apples introduced in North America

T or F

Answer 17

True

Question 18

Experiments show that
– Each species responds most strongly to its own fruit’s
scent
– Each species avoids the scent of the other fruit
– A fly’s ability to distinguish between scents has a
genetic basis
▪ Different alleles are associated with the attraction to different fruits

T or F

Answer 18

True

Question 19

Hybrid individuals do not orient to fruit scent as well as
their parents do,
– resulting in lower reproductive success (since they do
not find fruit and mates as well as do parents)
* Has the potential to cause rapid divergence
among sympatric species
– SWITCHING HOST PLANTS has been a major trigger for speciation throughout the course of insect evolution.

T or F

Answer 19

True

Question 20

If populations become isolated, it is unlikely that
mutation alone could cause them to diverge
appreciably since it occurs at a low rate

One type of mutation, p_____, is important in
speciation

Answer 20

Polyploidy

Question 21

DEF: Occurs when an error in meiosis or mitosis results in more than two sets of chromosomes

Answer 21

Polyploidy

Question 22

Polyploids may be (2 points):

Answer 22

1. Autopolyploid
2. Allopolyploid

Question 23

DEF:
- Individuals produced when a mutation results in a
doubling of the chromosome number
- Chromosomes are all from the same species

• less common than allopolyploidy
• Example: Researchers found a population of
  tetraploid (4n) maidenhair ferns within a normal
  population
  – These were offspring of a parent that produced diploid
  gametes and then self-fertilized

Answer 23

Autopolyploid

Question 24

DEF:

• Individuals are created when parents of different species
  mate and an error in mitosis occurs, resulting in viable,
  nonsterile offspring (also known as ….?)
• Produces offspring with two different sets of
  chromosomes
• POLYPLOID individuals like these are reproductively
  isolated from the original population
  – TETRAPLOID individuals can successfully breed with other tetraploids but not with diploids, because breeding between tetraploid and diploid individuals produces STERILE OFFSPRING
• According to the biological species concept,
  speciation occurred in a SINGLE GENERATION

Answer 24

Allopolyploid

Question 25

Allopolyploidy:
* New tetraploid species may be created when two
diploid species hybridize
* Usually the offspring will be sterile
– If an error occurs during mitosis creating diploid
gametes in the adult offspring, meiosis proceeds, and
gametes fuse during self-fertilization, a tetraploid
individual results
– Allopolyploid offspring has two copies each of two sets
of chromosomes

T or F

Answer 25

True

Question 26

Many diploid plant species have closely related
polyploid species
– This supports the claim that speciation by polyploidy is
important in plants
* Polyploids have higher levels of heterozygosity
than do diploids

T or F

Answer 26

True

Question 27

Polyploids can tolerate higher levels of self-
fertilization
– they are NOT AS AFFECTED by inbreeding depression as are diploids
* Genes on duplicated chromosomes can diverge
independently
– This INCREASES GENETIC VARIATION in the population

T or F

Answer 27

True