Transcript 24originofspecies

Chap 24
Origin of Species
Changes within a species
Accumulation
of changes
leading to a
new species
Branching
evolution
which
results in
more
species
and more
diversity
If closely related species
become SYMPATRIC or if
ALLOPATRIC species start
to hybridize and exchange
genes they will become
ONE species again.
If species are to remain as
separate species, then they
must develop
INTRINSIC REPRODUCTIVE
ISOLATING MECHANISMS
to prevent gene flow and
remain separate
Ecological Species
Definition: if there is
no gene flow between
two populations
because they prefer
different parts of the
ecology or habitat,
they are considered
separate species.
Temporal Isolation
Sexual selection
Artemesiae and nebrascensis are considered
PARAPATRIC SUBSPECIES
although they live in adjacent areas they
don’t mate, however there is still gene flow
between the subspecies through matings
with borealis and sonoriensis
Bonus: write a good
pneumonic device to
memorize this
Speciation starts off with EXTRINSIC ISOLATING MECHANISMS
the populations are ALLOPATRIC
p469 four conditions which favor allopatric speciation
Gene flow is
stopped or
limited
3 Things that will cause the
populations to form
subspecies:
1. Different selection
pressure.
2. Different mutations.
3. Different starting gene
frequencies (founder
effect)
4. Small populations may
be subject to genetic
drift (random change in
gene freq.)
5. If the area is relatively
unexploited, adaptive
radiation may occur.
Some races may become so
specialized that they no
longer interbreed with races
A ring species range is
so large that it circles
back on itself – some
ranges may circle around
the earth
No interbreeding between
the extremes of the cline
Because of sexual selection B and C don’t mate
Because of ecological competition B and C become more
different from each other.
This process can occur many times as long as the
ecology can support the different types of birds
this results in adaptive radiation.
1. How many different species descended from the species that colonized
the first island? Identify them.
three; B, C, and D
2. Why is species A no longer present on these islands? How is that
change different from what happened to species B?
Species A evolved into species B and no longer exists as a separate
species. Species B is the common ancestor of species C and D, and
it continues to coexist with the two newer species.
P471 Adaptive
Radiationflurries of
allopatric
speciation
p451 four
conditions
which favor
allopatric
speciation
Adaptive Radiation
• the evolution of diversely adapted species from a
common ancestor upon introduction to new
environmental opportunities
Dubautia laxa
1.3 million years
MOLOKA'I
KAUA'I
MAUI
5.1
Argyroxiphium sandwicense
million O'AHU LANAI
years
3.7
HAWAI'I
0.4
million
million
years
years
Dubautia waialealae
21.5
Dubautia scabra
Dubautia linearis
The bright yellow and redcrowned Yariguies brush-finch
was found in a remote
Colombian cloud forest
.
P 473
SYMPATRIC SPECIATION
Autopolyploidy- same species forms new sp
Oenothera lamarkia 2N=14
Oenothera gigas 4N=28
Allopolyploidy- two different species mate to form polyploid hybrid
S. martima 2N=60
S. alternaflora 2N=62
S. anglica 2N=122
There are
different ways for
allopolyploidy to
occur
P 474
Odd # of
chromosomes
Meiotic
error
476
Darwin
Eldridge and
Gould
Evolution of the Genes That Control
Development
• Genes that program development
– Control the rate, timing, and spatial pattern of
changes in an organism’s form as it develops
into an adult
21.8
Allometric growth
– Is the genetically controlled proportioning that
helps give a body its specific form
(a) Differential growth rates in a human. The arms and legs
lengthen more during growth than the head and trunk, as
can be seen in this conceptualization of an individual at
different ages all rescaled to the same height.
Newborn
21.8
2
5
Age (years)
15
Adult
Timing of
growth
effects the
shape,
development
and
evolution of
organisms
Heterochrony
temporal changes
in development
lead to
evolutionary
novelties
Allometric Growth
difference in the
relative rates of
growth of various
parts of the body help
to shape the
organisms
PaedomorphosisChanges in
developmental timing
ex: human brain is
larger because growth
of brain switched off
much later than chimps
Small changes in
timing can lead to
large phenotypic
change
Different allometric patterns
– Contribute to the contrasting shapes of human
and chimpanzee skulls
Comparison of chimpanzee and human skull
growth. The fetal skulls of humans and chimpanzees
are similar in shape. Allometric growth transforms the
rounded skull and vertical face of a newborn chimpanzee
into the elongated skull and sloping face characteristic of
adult apes. The same allometric pattern of growth occurs in
humans, but with a less accelerated elongation of the jaw
relative
to the rest of the skull.
21.8
Chimpanzee fetus
Human fetus
Chimpanzee adult
Human adult
Homeosis-Change in
the basic bauplan
(body plan) of the
organism
This can be
accomplished with
genes that act as
Master Switches like
homeotic genes
One gene that controls for one segment
can be duplicated and modified to
control for another segment
Duplication of the
Hox homeotic
genes led to
vertebrates
Exaptation
genes take on
different
functions in
another context
Species Selection
The species that endures
the longest and generates
the greatest number of new
species determine the
direction of an evolutionary
trend
differential species
success