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

http://travel.mongabay.com/grand_canyon/

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