Transcript Chapter 24 (Sep 9-10)

Chapter 24: The Origin of Species
1. What is a species?
- A population whose members can interbreed in nature and
produce viable, fertile offspring
- aka….reproductive isolation
2. What kinds of barriers keep different species isolated so they cannot mate?
- Figure 24.4
- Pre–zygotic barriers – before mating &/or zygote is formed
- Post–zygotic barriers – after zygote is formed
Figure 24.4 Reproductive Barriers
Prezygotic barriers impede mating or hinder fertilization if mating does occur
Habitat
isolation
Behavioral
isolation
Temporal
isolation
Individuals
of different
species
Mechanical
isolation
Mating
attempt
HABITAT ISOLATION
TEMPORAL ISOLATION
BEHAVIORAL ISOLATION
(b)
MECHANICAL ISOLATION
(g)
(d)
(e)
(f)
(a)
(c)
Gametic
isolation
Reduce
hybrid
fertility
Reduce
hybrid
viability
Hybrid
breakdown
Viable
fertile
offspring
Fertilization
REDUCED HYBRID
VIABILITY
GAMETIC ISOLATION
REDUCED HYBRID FERTILITY HYBRID BREAKDOWN
(k)
(j)
(m)
(l)
(h)
(i)
Chapter 24: The Origin of Species
1. What is a species?
2. What kinds of barriers keep different species isolated so they cannot mate?
3. How are new species created?
- Allopatric speciation
- when a geographic barrier isolates a population blocks gene flow
-
Sympatric speciation
- intrinsic factors such as chromosomal changes (plants) or
non-random mating alter gene flow
Figure 24.5 Two main modes of speciation
(a) Allopatric speciation. A
(b) Sympatric speciation. A small
population becomes a new species
population forms a new
without geographic separation.
species while geographically
isolated from its parent
population.
Chapter 24: The Origin of Species
1. What is a species?
2. What kinds of barriers keep different species isolated so they cannot mate?
3. How are new species created?
- Allopatric speciation –
- when a geographic barrier isolates a population blocks gene flow
- ex. mountain range emerging, new river dividing a field, island
- Adaptive radiation
- evolution of many diversely adapted species from a
common ancestor
- Seen on islands
- Sympatric speciation
- intrinsic factors such as chromosomal changes (plants) or
non-random mating alter gene flow
Figure 24.12 Adaptive radiation
Dubautia laxa
1.3 million years
MOLOKA'I
KAUA'I
MAUI
5.1
million
years O'AHU LANAI
3.7
million
years
Argyroxiphium sandwicense
HAWAI'I
0.4
million
years
Dubautia waialealae
Dubautia scabra
Dubautia linearis
Chapter 24: The Origin of Species
1. What is a species?
2. What kinds of barriers keep different species isolated so they cannot mate?
3. How are new species created?
- Allopatric speciation –
- when a geographic barrier isolates a population blocks gene flow
- Adaptive radiation
- evolution of many diversely adapted species from a
common ancestor
- Seen on islands
- Sympatric speciation
- intrinsic factors such as chromosomal changes (plants) or
non-random mating alter gene flow
- Autopolyploidy
- An individual has more than 2 chromosome sets derived from
a single species from an error in meiosis
Figure 24.8 Sympatric speciation by autopolyploidy in plants
Failure of cell division
in a cell of a growing
diploid plant after
chromosome duplication
gives rise to a tetraploid
branch or other tissue.
Gametes produced
by flowers on this
branch will be diploid.
Offspring with tetraploid
karyotypes may be viable
and fertile—a new
biological species.
2n
2n = 6
4n = 12
4n
Chapter 24: The Origin of Species
1. What is a species?
2. What kinds of barriers keep different species isolated so they cannot mate?
3. How are new species created?
- Allopatric speciation –
- when a geographic barrier isolates a population blocks gene flow
- ex. mountain range emerging, new river dividing a field, island
- Adaptive radiation
- evolution of many diversely adapted species from a
common ancestor
- Seen on islands
- Sympatric speciation
- intrinsic factors such as chromosomal changes (plants) or
non-random mating alter gene flow
- Autopolyploidy
- An individual has more than 2 chromosome sets derived from
a single species from an error in meiosis
- Allopolyploidy
- 2 different species produce the polyploid hybrid
Figure 24.9 One mechanism for allopolyploid speciation in plants
Unreduced gamete
with 4 chromosomes
Hybrid with
7 chromosomes
Species A
2n = 4
Unreduced gamete
with 7 chromosomes
Viable fertile hybrid
(allopolyploid)
Meiotic error;
chromosome
number not
reduced from
2n to n
2n = 10
Normal gamete
n=3
Species B
2n = 6
Normal gamete
n=3
Sympatric speciation: non-random mating
EXPERIMENT
Researchers from the University of Leiden placed males and females of Pundamilia pundamilia and
P. nyererei together in two aquarium tanks, one with natural light and one with a monochromatic orange
lamp. Under normal light, the two species are noticeably different in coloration; under monochromatic orange
light, the two species appear identical in color. The researchers then observed the mating choices of the fish
in each tank.
Monochromatic
orange light
Normal light
P. pundamilia
P. nyererei
RESULTS
Under normal light, females of each species mated only with males of their own species. But
under orange light, females of each species mated indiscriminately with males of both species.
The resulting hybrids were viable and fertile.
CONCLUSION
The researchers concluded that mate choice by females based on coloration is the main
reproductive barrier that normally keeps the gene pools of these two species separate. Since
the species can still interbreed when this prezygotic behavioral barrier is breached in the
laboratory, the genetic divergence between the species is likely to be small. This suggests
that speciation in nature has occurred relatively recently.
Figure 24.10
Chapter 24: The Origin of Species
1.
2.
3.
4.
What is a species?
What kinds of barriers keep different species isolated so they cannot mate?
How are new species created?
What is the difference between gradualism & punctuated equlibrium?
Figure 24.13 Two models for the tempo of speciation
Time
(a) Gradualism model. Species
descended from a common
ancestor gradually diverge
more and more in their
morphology as they acquire
unique adaptations.
(b) Punctuated equilibrium
model. A new species
changes most as it buds
from a parent species and
then changes little for the
rest of its existence.
Pigmented cells
(photoreceptors)
Pigmented
cells
Epithelium
Nerve fibers
Nerve fibers
(a) Patch of pigmented cells.
The limpet Patella has a simple
patch of photoreceptors.
Fluid-filled cavity
Epithelium
Optic
nerve
(c)
Cornea
Cellular
fluid
(lens)
Pigmented
layer (retina)
Pinhole camera-type eye.
The Nautilus eye functions
like a pinhole camera
(an early type of camera
lacking a lens).
Lens
Optic nerve
Figure 24.14 A–E
(b) Eyecup. The slit shell
mollusc Pleurotomaria
has an eyecup.
Optic nerve
(d)
Cornea
Eye with primitive lens. The
marine snail Murex has
a primitive lens consisting of a mass of
crystal-like cells. The cornea is a
transparent region of epithelium
(outer skin) that protects the eye
and helps focus light.
Retina
(e) Complex camera-type eye. The squid Loligo has a complex
eye whose features (cornea, lens, and retina), though similar to
those of vertebrate eyes, evolved independently.
Chapter 24: The Origin of Species
5. What other mechanisms can influence evolution/speciation?
DEVELOPMENTAL FACTORS…
A) Differences in allometric growth (proportional growth of body structures)
(b) Comparison of chimpanzee and human skull
Chimpanzee fetus
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.
Figure 24.15 B
Human fetus
Chimpanzee adult
Human adult
(a) Ground-dwelling salamander. A longer time
peroid for foot growth results in longer digits and
less webbing.
(b)
Tree-dwelling salamander. Foot growth ends
sooner. This evolutionary timing change accounts
for the shorter digits and more extensive webbing,
which help the salamander climb vertically on tree
branches.
Figure 24.16 A, B
Chapter 24: The Origin of Species
5. What other mechanisms can influence evolution/speciation?
DEVELOPMENTAL FACTORS…
A) Differences in allometric growth (proportional growth of body structures)
B) The expression of homeotic genes (which determine the “body plan”
of an organism) may change through mutation.
Chicken leg bud
Zebrafish fin bud
Figure 24.18
Region of
Hox gene
expression