Transcript Evolution: Macroevolution & origin of species

EVOLUTION:
MACROEVOLUTION & ORIGIN OF SPECIES
Chapter 17
I.
Macroevolution
A. large-scale change at or above species level
B. includes development of new species
C. fundamentally linked to microevolution
•
continued microevolution often leads to development of new sp.
II. What is a Species?
A. many different definitions
B. Ernst Mayr’s “Biological Species Concept”
1. group of interbreeding natural populations
2. produce fertile offspring
3. reproductively isolated from other such groups
4. problems?
C. subspecies
•
geographical variety of the same species
III. Speciation
A.
formation of a new species
1.
key factors are geography and environmental conditions
2.
ultimate goal is reproductive isolation
B.
allopatric speciation
1.
large, continuous pop.  geographical change  pop. split into two
groups  geographic isolation  env. conditions different for each
group  two groups evolve separately due to nat. sel., etc.  reprod. isol.
2.
many processes can lead to
geographic isolation
a.
natural environmental change
b.
human causes
c.
individuals leaving on their own
i.
dispersal
ii.
founder effect
A schematic view of
allopatric speciation
Ensatina eschscholtzi picta
1
Members of a northern ancestral
population migrated southward.
Ensatina eschscholtzi
oregonensis
2
Subspecies are separated by
California’s Central Valley. Some
interbreeding between populations
does occur.
Central
Valley
Barrier
Ensatina eschscholtzi platensis
Ensatina eschscholtzi
xanthoptica
Ensatina eschscholtzi
croceater
Ensatina eschscholtzi
eschscholtzii
3
Evolution has occurred, and in
the south, subspecies do not
interbreed even though they live
in the same environment.
Ensatina eschscholtzi
klauberi
Fig. 17.8
Allopatric speciation
in salamanders
Fig. 17.9 Allopatric speciation among sockeye salmon. In Lake Washington, salmon that matured
(a) at Pleasure Point Beach do not reproduce with those that matured in (b) Cedar River. The females
from Cedar River are noticeably larger and the males are more slender than those from Pleasure Point
Beach, and these shapes help them reproduce in the river.
C. sympatric speciation
1.
occurs in pops. occupying the same area
•
no geographic isolation, but reproductive isolation still occurs
2. most common in plants
•
hybridization, polyploidy, etc.
A schematic view of
sympatric speciation
Fig. 17.12. An example of sympatric speciation – polyploidy in plants. Reproduction between
two species of Clarkia results in a sterile hybrid. Doubling of the chromosome number results in
a fertile third Clarkia species that can reproduce only with itself.
IV. Reproductive Isolating Mechanisms
A.
means by which species maintain their integrity
B.
prevent two species from interbreeding to produce fertile offspring
C.
prezygotic barriers
1.
2.
3.
4.
5.
6.
D.
occur before a zygote
is formed
habitat isolation
behavioral isolation
temporal isolation
mechanical isolation
gamete isolation
postzygotic barriers
1.
2.
3.
4.
take place only if all
barriers are bypassed
zygote mortality
F2 fitness
hybrid sterility
prezygotic
Fig. 17.5 Temporal isolation
Fig. 17.4 Reproductive isolating mechanisms