Download True or False

True or False
1.
2.
Speciation can be observed only over
millions of years.
Some features (such as the human eye) are
too complex to evolve by natural
selection.
Imagine this scenario. A few birds are blown from the mainland to a
remote volcanic island. There is limited vegetation on the island. The
few plants have very large seeds. The birds establish a small, viable
population on the island.
Select all correct statements.
a.
The birds will evolve larger bills in order to eat the large
seeds.
b.
Birds with large bills will have greater evolutionary
fitness than birds with small bills.
c.
The bill size of all birds will gradually increase in the
population.
d.
Alleles for large bills will arise by mutation because of
selection for large bills.
e.
Birds with large bills will come to make up a larger
percentage of the population.
Biological Species Concept
1.
A group of populations whose members have the
potential to interbreed in nature and produce viable,
fertile offspring – but do not produce viable, fertile
offspring with members of other such groups
Alternative concept of species
(emphasizes unity within a species)
1.
2.
3.
Morphological – can be applied to sexual and
asexual species/subjective/used most often
Ecological – in terms of niche/emphasizes role
of disruptive natural selection/can be applied to
sexual and asexual species
Phylogenetic – smallest group of individuals that
share a common ancestor/compare morphology
or molecular sequences to other
organisms/degree of differences required????
For the following questions, consider 2 populations of birds: the original
one on the mainland and the small population on the volcanic island.
Consider each species concept in turn: biological, morphological,
ecological, and phylogenetic.
1.
Which information is most relevant to the biological species
concept?
a. The physical appearance of the birds in the two populations.
b. The percentage of viable, fertile hybrid offspring, formed if the
two populations encounter each other.
c. The degree of genetic difference between the two populations.
d. The range of foods eaten by members of the two populations.
Which information is most relevant to the morphological
species concept?
a.
b.
c.
d.
The physical appearance of the birds in the two
populations.
The percentage of viable, fertile hybrid offspring
formed if the two populations encounter each
other.
The degree of genetic difference between the
two populations.
The range of foods eaten by members of the two
populations.
Which information is most relevant to the ecological
species concept?
a.
b.
c.
d.
The physical appearance of the birds in the two
populations.
The percentage of hybrid offspring formed if the two
populations encounter each other.
The degree of genetic differences between the two
populations.
The range of foods eaten by members of the two
populations.
Which information is most relevant to the
phylogenetic species concept?
a.
b.
c.
d.
The physical appearance of the birds in the two
populations.
The percentage of hybrid offspring formed if the two
populations encounter each other.
The degree of genetic difference between the two
populations.
The range of foods eaten by members of the two
populations.
24.2 – Speciation can take place with or without
geographical separation
Allopatric speciation – geographic separation
restricts gene flow(depends on ability of
organism to move about)
Ex) mountain ranges, glaciers, land bridges,
splintering of lakes
2. Sympatric speciation – geographically
overlapping populations/gene flow restricted by
chromosomal changes, nonrandom mating
1.
Allopatric speciation
Mechanisms by which gene pools may begin
to diverge:
a. Different mutation rates
b. Different selective pressures
c. Genetic drift alters allele frequencies
Fruit fly experiment – Diane Dodd
Sympatric speciation
-
-
new species arise within the range of the
parent population
Gene flow may be reduced by such factors
as:
polyploidy, habitat differentiation, and
sexual selection
Autopolyploidy
-
-
an individual with more than 2 sets of
chromosomes all derived from a single
species
Reproductive isolation in a single
generation
Allopolyploidy
-
-
-
more common
When 2 different species mate to produce
offspring
Hybrids usually sterile
Propagate asexually
If fertile, can mate with each other
Sympatric speciation in animals
Ex) North American maggot fly – hawthorne
tree vs apple tree
http://www.nsf.gov/news/news_summ.jsp?cnt
n_id=114129
24.3 Hybrid Zones


An opportunity to study factors that cause
reproductive isolation
Possible outcome if allopatric populations
come back into contact with one another
Patterns within hybrid zones



Fig. 24.13 p. 498 – What’s causing the
pattern here?
What is the obstacle to gene flow?
Other hybrid zones ground crickets of
the Appalachian mountainshybrid fitness
varies from year to year
Hybrid zones over time

1.
2.
3.
Fig. 24.14 p. 499 – 3 possible outcomes
Reinforcement – hybrids gradually cease
to be formed
Fusion – the two species fuse
Stability – continued production of hybrid
individuals
Reinforcement
-
-
-
Barriers to hybridization should be stronger
for sympatric populations than allopatric
populations
Ex) pied flycatcher vs collared flycatcher
Allopatric populations male flycatchers
of the two species resemble one another
How about in sympatric populations?
Fusion




Barriers to reproduction are weak,
speciation process reverses
Ex) cichlids of Lake Victoria – fig. 24.12female mate choice
Question: What is responsible for the
decline in the number of cichlid species?
http://evolution.berkeley.edu/evolibrary/ne
ws/090301_cichlidspeciation
Stability



Bombina hybrid zone – Why isn’t reinforcement
occuring?
May be due to the narrowness of the hybrid zone
and the extensive gene flow from outside the
zone
Allonemobius hybrid zone – some hybrids more
fit than parent species/hybrids mate with each
other and with both parent speciesgene pools of
parent species would fuse


Why aren’t we seeing more hybrid species?
Because locations where hybrids form may
appear and disappear rapidly, hybrids
remain uncommon and fusion of gene
pools do not occur