1. Chapter 24: The Origin of Species

2. Macroevolution: the origin of new taxonomic groups
Speciation: the origin of new species
Anagenesis (phyletic evolution): accumulation of heritable changes
Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity)
Animation: Macroevolution

3. What is a species? Biological species concept (Mayr)
a population or group of populations whose members have the potential to interbreed and produce viable, fertile offspring (genetic exchange is possible and that is genetically isolated from other populations)

4. Reproductive Isolation (isolation of gene pools), I
Prezygotic barriers: impede mating between species or hinder the fertilization of the ova
Habitat
(snakes; water/terrestrial)
Behavioral
(fireflies; mate signaling)
Temporal
(salmon; seasonal mating)
Mechanical
(flowers; pollination anatomy)
Gametic
(frogs; egg coat receptors)
Video: Albatross Courtship Ritual
Video: Giraffe Courtship Ritual
Video: Blue-footed Boobies Courtship Ritual

5. Fig. 24-4a
Prezygotic barriers
Habitat Isolation
Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Individuals of
different
species
Mating
attempt
(a)
(c)
(e)
(f)
(d)
Figure 24.4 Reproductive barriers
(b)

6. Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown
Fig. 24-4i
Prezygotic barriers
Postzygotic barriers
Gametic Isolation
Reduced Hybrid Viability
Reduced Hybrid Fertility
Hybrid Breakdown
Viable,
fertile
offspring
Fertilization
(g)
(h)
(i)
(l)
(j)
Figure 24.4 Reproductive barriers
(k)

7. Reproductive Isolation, II
Postzygotic barriers: fertilization occurs, but the hybrid zygote does not develop into a viable, fertile adult
Reduced hybrid viability (frogs; zygotes fail to develop or reach sexual maturity)
Reduced hybrid fertility (mule; horse x donkey; cannot backbreed)
Hybrid breakdown (cotton; 2nd generation hybrids are sterile)

8. Limitations of the Biological Species Concept
The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes)
Other species concepts emphasize the unity within a species rather than the separateness of different species
The morphological species concept defines a species by structural features
It applies to sexual and asexual species but relies on subjective criteria

9. The ecological species concept views a species in terms of its ecological niche
It applies to sexual and asexual species and emphasizes the role of disruptive selection
The phylogenetic species concept: defines a species as the smallest group of individuals on a phylogenetic tree
It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species

10. Modes of speciation (based on how gene flow is interrupted)
Allopatric: populations segregated by a geographical barrier; can result in adaptive radiation (island species)
Sympatric: reproductively isolated subpopulation in the midst of its parent population (change in genome); polyploidy in plants; cichlid fishes

11. (a) Allopatric speciation (b) Sympatric speciation
Fig. 24-5
Fig 24.5 Two main modes of speciation
(a) Allopatric speciation
(b) Sympatric speciation

12. Isolated population diverges
Fig
Isolated population
diverges
Possible
outcomes:
Hybrid
zone
Reinforcement OR
Fusion
Gene flow
Hybrid OR
Figure Formation of a hybrid zone and possible outcomes for hybrids over time
Barrier to
gene flow
Population
(five individuals
are shown)
Stability

13. Punctuated equilibria
Tempo of speciation: gradual vs. divergence in rapid bursts; Niles Eldredge and Stephen Jay Gould (1972); helped explain the non-gradual appearance of species in the fossil record

14. You should now be able to:
Define and discuss the limitations of the four species concepts
Describe and provide examples of prezygotic and postzygotic reproductive barriers
Distinguish between and provide examples of allopatric and sympatric speciation
Explain how polyploidy can cause reproductive isolation
Define the term hybrid zone and describe three outcomes for hybrid zones over time