Transcript BCORchapter24db

The Origin of
Species
Chapter 24
BCOR 012
Jan. 31 and Feb. 2,
2011
Outline for January 31, Feb. 2, 2011:
I. Introduction
II. What is a species?
The biological species concept
Reproductive isolating mechanisms
Alternative species concepts
III. Modes of speciation
Allopatric
Sympatric
the tempo of change
What is a species?
The Biological Species
Concept
The biological species
concept defines a
species as a population
or a series of populations
whose members have the
potential to interbreed
and which are
reproductively isolated
from other such
populations.
Reproductive Isolation and
Isolating Mechanisms
ex. fireflies
Biologists distinguish between prezygotic and
postzygotic isolating mechanisms.
ex:mule
Limitations of the BSC:
• Not applicable to asexually reproducing
organisms
• Useless with respect to the fossil record
Alternative species concepts:
• Ecological species concept - defines a species
in terms of its ecological niche
• Morphological species concept - emphasis is on
unique structural features
• Phylogenetic species concept - emphasis is on
ancestor-descendent relationships
• Pluralistic species concept - acknowledges that,
where species concepts are concerned, one size
may not fit all!
There are an awful lot of
living things; how did there
get to be so many?
Anagenesis is change within a lineage; cladogenesis is the
divergence of one lineage into two.
Modes of
Speciation
There are two general modes of speciation:
• Allopatric (other
homeland)- speciation
takes place in
populations with
geographically separate
ranges
• Sympatric (same
homeland) - speciation
takes place in
geographically
overlapping populations
Ammospermophilus harrisi
S
Ammospermophilus leucurus
N
Allopatric speciation of antelope squirrels in the Grand Canyon
In allopatric speciation, a new species originates
while geographically isolated from its ancestor.
As the new species evolves by genetic drift and
natural selection, reproductive isolation from the
ancestral
species may evolve as a by-product of genetic
change.
Sympatric speciation - a mode in
which a new species arises in the
geographic midst of its progenitor
species.
Copper-tolerant Mimulus guttatus
In plants, sympatric species may arise by polyploidy
a condition that results in extra sets of chromosomes
in the derivative species.
An example from the European holly ferns ….
European holly
ferns
(Polystichum)
P. setiferum
P. lonchitis
P. aculeatum
The origin of
European
Polystichum
aculeatum
P. aculeatum
(4X)
P. setiferum
(2X)
primary diploid
hybrid
P. lonchitis
(2X)
The origin of
European
Polystichum
aculeatum
P.
aculeatum
P. setiferum
P. setiferum
n=41
primary diploid
hybrid
P. lonchitis
Sympatric speciation in animals
East African Cichlids
(sick-lids)
Pundamilia pundamilia
Pundamilia nyererei
a) Normal light
b) Monochromatic orange
light
Non-random mating, in which females select mates having a preferred appearance,
is the main reproductive barrier keeping these two species separate in nature. Thi
is an example of sympatric speciation in response to sexual selection.
Sympatric speciation requires the
emergence of some sort of reproductive
barrier that isolates the gene pool of a
population subset without geographic
separation from the parent population.
Hybrid Zones
The Tempo of Evolution
Darwin’s original idea
was that species diverge
gradually.
More recently, the idea that
there are rapid speciation
events interrupting periods of
no change has become popular.
Punctuated equilibria vs. gradual divergence
http://evolution.berkeley.edu/evosite/evo101/VIIA1bPunctuated.shtml
Punctuated equilibria vs. gradual divergence
http://evolution.berkeley.edu/evosite/evo101/VIIA1bPunctuated.shtml
Possibly include spur story
Pollinator shifts drive increasingly long nectar spurs in columbine flowers.
Hodges, 2007 ---- Nature 447: 706-710.
Whittall and
Outline for January 31, Feb. 2, 2011:
I. Introduction
II. What is a species?
The biological species concept
Reproductive isolating mechanisms
Alternative species concepts
III. Modes of speciation
Allopatric
Sympatric
the tempo of change