Lecture 11: Isolation and Divergence in Allopatry Flashcards
S____ begins when gene flow between
populations is reduced or eliminated, causing
genetic isolation
Speciation
G_____ isolation happens when populations
become geographically separated
Genetic isolation
DEF: Populations that live in different areas
Allopatry
Speciation that begins with geographic isolation is
called a_____ speciation
Allopatric speciation
Geographic isolation occurs in one of 2 ways:
- Dispersal
- Vicariance
DEF: A population moves to a new habitat, colonizes it, and founds a new population
Dispersal
DEF: the physical splitting of a habitat
- A physical barrier splits a population into subgroups that are physically isolated from each other
Vicariance
DEF:
the study
– of how species and populations are distributed
geographically
– Can tell us how dispersal and vicariance events occur
Biogeography
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____)
Colonists, migrants
- 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
True
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
Vicariance
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
True
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
Sympatry
Sympatric speciation can be initiated by two types
of events:
- External events
▪ Example: Disruptive selection based on different
ecological niches or mate preferences - Internal events
▪ Example: Chromosomal mutations
DEF: The range of ecological resources that a species can use and the range of conditions it can tolerate
Niche
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
True
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
True
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
True
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
True
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
Polyploidy
DEF: Occurs when an error in meiosis or mitosis results in more than two sets of chromosomes
Polyploidy
Polyploids may be (2 points):
- Autopolyploid
- Allopolyploid
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
Autopolyploid
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
Allopolyploid
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
True
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
True
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
True
