Chap 24
Origin of Species
Changes within a species
Accumulation of changes leading to a new species
Accumulation of changes leading to a new species
Branching evolution which results in more species and more diversity
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 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
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
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
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
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 Radiation-flurries of allopatric speciation
P471 Adaptive Radiation-flurries of allopatric speciation
p451 four conditions which favor 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
Dubautia waialealae
KAUA'I5.1
millionyears
O'AHU3.7
millionyears
LANAI
MOLOKA'I1.3 million years
MAUI
HAWAI'I0.4
millionyears
Argyroxiphium sandwicense
Dubautia scabra Dubautia linearis
N
21.5
The bright yellow and red-crowned 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
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
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
There are different ways for allopolyploidy to occur
P 474
Odd # of chromosomes
Meiotic error
Eldridge and Gould
Eldridge and Gould
DarwinDarwin
476
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
Newborn 2 5 15 Adult
(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.
Age (years)
21.8
Allometric Growth
difference in the relative rates of growth of various parts of the body help to shape the organisms
Allometric Growth
difference in the relative rates of growth of various parts of the body help to shape the organisms
Paedomorphosis-Changes in developmental timing
ex: human brain is larger because growth of brain switched off much later than chimps
Paedomorphosis-Changes in developmental timing
ex: human brain is larger because growth of brain switched off much later than chimpsHeterochrony
temporal changes in development lead to evolutionary novelties
Heterochrony
temporal changes in development lead to evolutionary novelties
Timing of growth effects the shape, development and evolution of organisms
Timing of growth effects the shape, development and evolution of organisms
Small changes in timing can lead to large phenotypic change
Different allometric patterns
– Contribute to the contrasting shapes of human and chimpanzee skulls
Chimpanzee fetus Chimpanzee adult
Human fetus Human adult
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 chimpanzeeinto 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
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
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
Duplication of the Hox homeotic genes led to vertebrates
Duplication of the Hox homeotic genes led to vertebrates
One gene that controls for one segment can be duplicated and modified to control for another segment
Exaptation
genes take on different functions in another context
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
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
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