1. The Origin of Species
Chapter 24

2. Speciation The origin of new species, or speciation
Is at the focal point of evolutionary theory, because the appearance of new species is the source of biological diversity
Evolutionary theory
Must explain how new species originate in addition to how populations evolve
Macroevolution
Refers to evolutionary change above the species level – brought about by microevolution (change in allele frequencies in a population over time)

3. Speciation
Speciation is the boundary between microevolution and macroevolution.
Speciation is the origin of new species.
This is the key process because any genus, family, or higher taxon originates with a new species that is novel enough to be the inaugural member of the higher taxon.

4. What is a Species?
Species is a Latin word meaning “kind” or “appearance.”
Traditionally, morphological differences have been used to distinguish species.
Today, differences in both body function, biochemistry, behavior, and genetic makeup are also used to differentiate species.

5. Biological Species Concept
Defines a species as a population or group of populations whose members have the potential to interbreed with one another in nature to produce viable, fertile offspring, but who cannot produce viable, fertile offspring with members of other species.

6. Other Definitions of Species
The morphological species concept characterizes a species in terms of its body shape, size, and other structural features
The paleontological species concept focuses on morphologically discrete species known only from the fossil record
The ecological species concept views a species in terms of its ecological niche
The phylogenetic species concept defines a species as a set of organisms with a unique genetic history

7. Similarity Between Different Species Figure 24.2a
Eastern Meadowlock and Western Meadowlock – songs are distinct, and a behavioral difference helps prevent interbreeding between the two species.

8. Reproductive Isolation
The key to speciation is reproductive isolation:
Reproductive isolation is the existence of biological factors that impede members of two species from producing viable, fertile hybrids
Is a combination of various reproductive barriers

9. Barriers to Speciation
Prezygotic:
Prevent mating or successful fertilization.
Postzygotic:
Prevent the hybrid zygote from developing into viable, fertile adult.

10. Prezygotic Barriers Habitat isolation Temporal isolation
Living in different habitats – not encountering each other
Temporal isolation
Breeding at different times
Behavioral isolation
Different behaviors to attract a mate
Mechanical isolation
Two species may attempt to made but physically cannot
Gametic isolation
Gametes from two different species will not fuse to become a zygote

11. Postzygotic Barriers
Reduced Hybrid Viability: genetic incompatibility between the two species may abort the development of the hybrid at some embryonic stage or produce frail offspring.
Reduced Hybrid Fertility: even if the hybrid offspring are vigorous, they may be infertile and cannot backbreed to either parent.
Reduced Hybrid Breakdown: in some cases, first generation hybrids are viable and fertile, but, when they mate with either parent or with each other, the next generation is feeble or sterile.

13. Limitations to Biological Species Concept
Infertility concept does NOT apply to:
Asexually reproducing organisms
Extinct species

14. Modes of Speciation
Speciation can take place with or without geographic isolation:
Ways in which speciation CAN OCCUR:
Allopatric Speciation
Sympatric Speciation

15. Two Modes of Speciation Figure 24. 6 http://bcs. whfreeman
A population forms a new species while geographically isolated from its parent population
A small population becomes a new species without geographic separation from its parent population 15

16. Allopatric Speciation
Gene flow is interrupted or reduced when a population is divided into two or more geographically isolated subpopulations
New species forms while geographically isolated from an ancestor.
Modern examples – adaptive radiation on island chains.

17. Allopatric Speciation of Squirrels in the Grand Canyon Figure 24.7
Once geographic separation has occurred one or both populations may undergo evolutionary change during the period of separation

18. Adaptive Radiation
The evolution of many diversely adapted species from a common ancestor upon introduction to various new environmental opportunities and challenges is called adaptive radiation.
Adaptive radiation typically occurs when a few organisms make their way to new, often distant areas or when environmental changes cause numerous extinctions, opening up ecological niches for the survivors.
Fossil evidence indicates that mammals underwent a dramatic adaptive radiation after the mass extinctions of dinosaurs 65 mya. 18

19. Argyroxiphium sandwicense
Islands can be living laboratories for the study of species – and adaptive radiation.
See figure 24.11
The Hawaiian archipelago is one of the world’s great showcases of adaptive radiation
Figure 24.12
Dubautia laxa
Dubautia waialealae
KAUA'I
5.1
million
years
O'AHU
3.7
LANAI
MOLOKA'I
1.3 million years
MAUI
HAWAI'I
0.4
Argyroxiphium sandwicense
Dubautia scabra
Dubautia linearis N

20. Adaptive Radiation in Darwin’s Finches
These finches, better known as 'Darwin's Finches' illustrated adaptive radiation. This is where species all deriving from a common ancestor have over time successfully adapted to their environment via natural selection.
Previously, the finches occupied the South American mainland, but somehow managed to occupy the Galapagos islands, over 600 miles away. They occupied an ecological niche with little competition.
As the population began to flourish in these advantageous conditions, intraspecific competition became a factor, and resources on the islands were squeezed and could not sustain the population of the finches for long.

21. Sympatric Speciation
Speciation occurs when biological barriers prevent gene flow in overlapping populations as seen in
autopolyploidy
allopolyploidy
mate preference
Etc
Speciation takes place in geographically overlapping populations

22. Polyploidy Polyploidy
Is the presence of extra sets of chromosomes in cells due to accidents during cell division
Has caused the evolution of some plant species

23. Autopolploidy
An autopolyploid is an individual that has more than two chromosome sets, all derived from a single species
Figure 24.8
2n = 6
4n = 12 2n 4n
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.

24. Allopolyploidy
An allopolyploid is a species with multiple sets of chromosomes derived from different species
Figure 24.9
Meiotic error;
chromosome
number not
reduced from
2n to n
Unreduced gamete
with 4 chromosomes
Hybrid with
7 chromosomes
with 7 chromosomes
Viable fertile hybrid
(allopolyploid)
Normal gamete
n = 3
Species A
2n = 4
Species B
2n = 6
2n = 10

25. Habitat Differentiation and Sexual Selection
Sympatric speciation
Can also result from the appearance of new ecological niches
In cichlid fish
Sympatric speciation has resulted from nonrandom mating due to sexual selection

26. Allopatric and Sympatric Speciation: A Summary
In allopatric speciation
A new species forms while geographically isolated from its parent population
In sympatric speciation
The emergence of a reproductive barrier isolates a subset of a population without geographic separation from the parent species

27. Hybrid Zones
Where divergent allopatric populations come back and interbreed.
Biologist look for patterns to study reproductive isolation.
When closely related species meet in a hybrid zone, there are 3 possible outcomes:
strengthening of reproductive barriers
weakening of reproductive barriers
continued formation of hybrid individuals 27

28. 28

29. Timing of Evolution Gradualism (Lyell, Darwin)
Slow, steady change over time.
Punctuated Equilibrium (Gould)
Evolution occurs in spurts and is interspersed with long periods of stasis.

30. Punctuated Equilibrium
Punctuated equilibrium is a pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change
Typically occurs when new niches become available following a mass extinction 30

31. Gradualism v/s Punctuated Equilibrium
Species descended from a common ancestor gradually diverge more and more in morphology as they acquire unique adaptations.
A new species changes most as it buds from a parent species, and then changes little for the rest of its existence.

32. Convergent Evolution
Convergent evolution describes 2 unrelated species that share similar traits.
These similarities are not due to common ancestry, but rather a result of similar environmental factors. 32

33. Coevolution
Coevolution describes the evolution of one species in response to new adaptations that appear in another species of which the first shares close interaction 33

34. Speciation Flow Chart Section 17-4 Species Go to Section: that are
Unrelated
Related
form in
under
under in in
Inter-relationshiops
Similar environments
Intense environmental pressure
Small populations
Different environments
can undergo
can undergo
can undergo
can undergo
can undergo
Coevolution
Convergent evolution
Extinction
Punctuated equilibrium
Adaptive radiation
Go to Section: 34

35. ON YOUR OWN Read text pages 476 – 481.
Be sure you can discuss all terminology, understand all graphics, etc.