1. Chapter 24 Edited Lecture
Speciation
Chapter 24 Edited Lecture

2. What do you need to know? Biological definition of species
Prezygotic and postzygotic barriers
Allopatric vs. sympatric speciation
Autopolypolid or allopolyploid chromosomal changes  sympatric speciation
Punctuated equilibrium and gradualism describe two different tempos of speciation

3. (a) Similarity between different species
Figure 24.2
(a) Similarity between different species
Speciation is how new species arise
Biological species concept is based on ability to reproduce viable offspring rather than physical simliarities
(b) Diversity within a species

4. Microevolution consists of changes in allele frequency in a population over time
Macroevolution refers to broad patterns of evolutionary change above the species level

5. Prezygotic barriers (a) (c) (e) (f) (g) (d) (b) Figure 24.3_b Habitat
Isolation
Temporal
Isolation
Behavioral
Isolation
Mechanical
Isolation
Gametic
Isolation
Individuals of
different
species
MATING
ATTEMPT
FERTILIZATION
(a)
(c)
(e)
(f)
(g)
(d)
(b)
Figure 24.3 Exploring: Reproductive Barriers
Prevent mating or hinder fertilization!!!

6. Postzygotic barriers Reduced Hybrid Viability Reduced Hybrid Fertility
Figure 24.3_c
Postzygotic barriers
Reduced Hybrid
Viability
Reduced Hybrid
Fertility
Hybrid
Breakdown
VIABLE,
FERTILE
OFFSPRING
FERTILIZATION
(h)
(i)
(l)
(j)
Figure 24.3 Exploring: Reproductive Barriers
Prevent fertilized egg from developing into a fertile adult
(k)

7. Limitation to Biological Species Concept
Grizzly bear (U. arctos)
Polar bear (U. maritimus)
Not applied to fossils OR asexual organism
Gene flow can occur between distinct species
Hybrid “grolar bear”

8. Allopatric vs. Sympatric Speciation
Allopatric speciation.
A population forms a
new species while
geographically isolated
from its parent population.
(b)
Sympatric speciation.
A subset of a population
forms a new species
without geographic
separation.

9. Allopatric Speciation
Figure 24.6
Allopatric Speciation
A. harrisii
A. leucurus
The definition of barrier depends on the ability of a population to disperse
For example, a canyon may create a barrier for small rodents, but not birds, coyotes, or pollen
Gene flow is interrupted by geologic events or processes

10. Sympatric Speciation
Formation of autopolyploid plants through non-disjunction in meiosis. (Plants do this a lot!!)
Oats, cotton, potatoes, wheat, tobaccos are polyploid
Habitat Differentiation (new ecological niche)

11. Sympatric Speciation Species A 2n = 6 Species B 2n = 4 Meiotic error;
Figure
Sympatric Speciation
Species A
2n = 6
Species B
2n = 4
Meiotic error;
chromosome number not
reduced from 2n to n
Normal
gamete
n = 3
Unreduced gamete
with 4 chromosomes
Hybrid with
7 chromosomes
Normal
gamete
n = 3
Unreduced gamete
with 7 chromosomes
New species:
viable fertile hybrid
(allopolyploid) 2n = 10

12. Hybrid Zones Possible outcomes: Isolated population Hybrid diverges
Figure
Hybrid Zones
Possible
outcomes:
Isolated
population
diverges
Hybrid
zone
Reinforcement OR
Fusion OR
Gene flow
Population
Hybrid
individual
Barrier to
gene flow
Stability

13. Tempo of Speciation