Download File

Name:
Evolutionary Processes
Workbook 4
Year 13 Science
2016
Allopatric and Sympatric Speciation
Speciation is the formation of new species.
Allopatric speciation occurs through geographical isolation resulting from the formation of some
sort of geographical barrier – e.g. mountain range, river
Vicariance occurs when the formation of barriers to dispersal and gene flow isolate a population and
lead to speciation.
Sympatric speciation occurs without geographical isolation.
1.
What barrier has led to allopatric speciation in the diagram above?
river
2.
Write a definition for each of the key words in the table - in your own words
Keyword
Speciation
definition
the formation of new species
b.
allopatric
speciation
occurs through geographical isolation resulting from the formation of
some sort of geographical barrier
c.
sympatric
speciation
occurs without geographical isolation
d.
vicariance
occurs when the formation of barriers to dispersal and gene flow isolate
a population and lead to speciation
a.
Allopatric Speciation
Allopatric speciation is speciation involving a period
of geographic separation.
A barrier physically isolates parts of the population
of a species, blocking gene flow. Isolated areas have
differing selection pressures – some areas are
colder, wetter, windier etc. than others.
Once isolated allopatric populations accumulate
genetic differences over time because of natural
selection, new mutations, genetic drift and founder
effect. Phenotypically distinct subspecies may form.
If the geographic barrier is removed and two
populations remain reproductively isolated. Distinct
species have formed with different gene pools from
the ancestral form and from each other.
3.
What could cause geographic separation?
mountains, rivers, seas
4.
What happens to gene flow when a barrier isolates parts of a population of a species?
gene flow is blocked / stopped
5.
What pressures can act on an allopatric population once it is isolated?
natural selection, new mutations, genetic drift, founder effect
6.
What does phenotypically distinct mean?
looks/acts differently
7.
What does reproductively isolated mean?
cannot reproduce
8.
Are species A, B and C distinct from each other?
all different from each other
Initial step of speciation e.g. behavioural
differences
Gene flow is prevented, even though populations
are in the same geographical area.
The two populations remain reproductively
isolated, distinct species have formed with
different gene pools from the ancestral form and
from each other.
9.
What is the difference between allopatric speciation and sympatric speciation?
allopatric – geographic isolation / sympatric – no geographic isolation
10.
Name the type of speciation for each of the following situations.
a.
In the northeast Pacific Ocean, ‘resident’ and ‘transient’ orcas live in the same waters, but
avoid one another and do not interbreed. The two forms have different feeding patterns,
different social behaviours and make different sounds.
sympatric
b.
A population of an ancestral robin from Australia became divided between the Chatham
Islands and the New Zealand mainland, 800 km distant. Gene flow between the two
populations ended and gen frequencies changed. Over a long time, two separate species
formed, each with its own gene pool.
allopatric
The most common form of sympatric speciation involved genetic polymorphism – the formation of a
polyploid, able to breed only with individuals with the same chromosome set, but not with the
original parents. Separated from the parent species by a reproductive isolating mechanism, the
formation of the polyploid species represents instant speciation.
Polyploidy is much more common in plants than in animals. Plant breeders induce polyploidy by
treating desirable hybrids with chemicals, such as colchicine. The resulting plants are fertile and
show hybrid vigour – bigger, stronger.
Triploidy may be used to ensure hybrid sterility so others cannot breed from the hybrid plants.
11.
What plants are triploids?
banana
12.
Why are the triploids sterile?
3n = 27 , can’t divide evenly during meiosis
Adaptive radiation occurs when many different species evolve from a common ancestor to fill a
variety of different ecological niches, often in different geographical locations.
13.
a.
b.
c.
14.
Write a definition for each of the key words in the table - in your own words
Keyword
Polyploidy
Definition
Cells contain more than 2 paired sets of chromosomes
Instant
speciation
Adaptive
radiation
Offspring have different chromosomes numbers than parents from first
cross
many different species evolve from a common ancestor to fill a variety
of different ecological niches, often in different geographical locations
Distinguish between allopatric and sympatric speciation.
allopatric – geographic isolation / sympatric – no geographic isolation
15.
Explain whether allopatric or sympatric speciation is more likely to occur in adaptive
radiation.
rapid formation of new species from ancestral species with the new species filling
different ecological niches – speciation likely to be allopatric
16.
The Madeiran storm petrel is a small seabird that nests on islands in the Atlantic and Pacific
Oceans. In some cases, groups of individuals breed on the same islands, but they visit the island to
breed during different seasons of the year from each other. Scientists have found that seasonal
populations differ genetically within the island groups and gene flow no longer occurs between the
populations in the two groups of islands.
a.
What could be separating the populations, causing them to differ genetically?
populations separated by breeding times – visit islands at different seasons
b.
Name the type of speciation that might be occurring. Explain your answer.
sympatric speciation – there is no geographical barrier separating populations
c.
Explain the biological significance of ‘ceased to exchange genes’.
populations are reproductively isolated – interbreeding is not occurring
selection will bring about genetic differences and create the opportunity for new species
17.
Recent DNA analyses have suggested that cicadas arrived in New Zealand around 11.6 mya
and subsequently evolved into a number of different species. This was a time of considerable
environmental change. The Southern Alps were beginning to form, and the world was entering a
new ice age. This meant that a new alpine environment was available for colonisation. During
glaciations, New Zealand forests were found only in patches in the upper part of the North Island,
while grasslands became widespread.
a.
Define adaptive radiation.
when many species evolve from a common ancestor to fill different ecological niches
b.
Explain how the uplifting of the Southern Alps may have been a factor in the evolution of a
number of different cicada species in New Zealand.
uplifiting of the Southern Alps created different geographical areas – different climate –
cooler with altitude, wetter on the west, dryer on the east
uplifting created a physical barrier that prevented / severely reduced gene glow
leads to allopatric speciation – through different selectiond pressures
populations exposed to different selection pressures – different adaptations would be
selected for – leading to reproductive isolation – new species
18.
New Zealand has at least 37 species of gecko in two genera, Hoplodactylus and Nautinus.
Hoplodactylus has the highest species diversity of all New Zealand’s terrestrial vertebrates.
Geckos are ecologically diverse and found in almost available terrestrial habitats. DNA data suggest
that adaptive radiation in geckos began about 24 mya, a time when New Zealand consisted of a
series of low-lying islands. Since then New Zealand has experienced:
substantial rises and falls in sea level
a period of mountain building and volcanic activity
the glaciations of the Pleistocene Ice Age
a.
Identify the form of speciation that has given rise to New Zealand’s geckos
allopatric
b.
Explain the role of the changes in land mass on the evolution of the 37 gecko species and
any mechanisms that may isolate the various species.
rises in sea levels occurs in warm interglacial periods – creating islands and isolating
populations of geckos in different geographical locations which are then subject to different
selection pressures - over time, populations change such that they come into contact with other
populations and are sufficiently different that they cannot interbreed – speciation has occurred
mountain building and volcanic activity may also similarly act to isolate populations
19.
Plants in the genus Libertia are found throughout New Zealand, Australia and South
America. The table shows the chromosome numbers for several of these Libertia species.
Location
New Zealand
Libertia species
L. puchella
L. grandiflora
L. pereginans (not inland Nelson)
L. pereginans (inland Nelson)
Artificial hybdrids between ixiodes and grandiflora
L. ixiodes
Australia
L. puchella (Tasmania)
L. paniculata
South America L. caerulescens
L. Formosa (Chile)
Diploid chromosome
number
38
114
114
171
171
228
38
76
38
76
a.
Use the information from the table to describe how these different Libertia species have
evolved.
speciation likely to be allopatric – geographic isolation / and sympatric through polyploidy
b.
The diploid number of chromosomes in ancestral Libertia is 38.
Explain how L. paniculata (2n = 76) could have evolved from L. puchella.
L punchella is parent – 2N = 38, L paniculata has 2n = 76
most likely autopolyploidy – with simple doubling of chromosomes after fertilisation
could be complete non-disjunction in two L punchella gametes – 2n to 4n
c.
L. peregrinas from inland Nelson has a different chromosome number, and is different in
appearance, from other populations in this species.
Explain how this inland Nelson population could have evolved, giving evidence from the
table to support your answer.
likely to have developed from hybridisation between L pereginas (2n = 114, n = 57) and L
ixiodes (2n = 228, n = 114) – n + n = 57 + 114 = 171
20.
Cultivated banana crops are triploid (3n). Discuss the evolutionary consequences of being
triploid.
3n means that chromosomes cannot pair up in meiosis – cannot form gametes
bananas are infertile so cannot reproduce sexually – so reproduce asexually
only source of variation is mutation – lack of genetic variation means that bananas are
very susceptible to pathogens
pathogens could infect and kill banana plants – could eliminate all bananas in population –
could lead to extinction