1. Evolutionary Patterns, Rates and Trends
Chapter 20 / 22

2. Natural Selection
Results in adaptations of a population to the biotic and abiotic environment
Evolution by Natural Selection requires:
Variation
Inheritance
Differential adaptiveness
Differential reproduction

3. Speciation Speciation
process by which one species splits into two or more
explains the features shared between organisms due to inheritance from their recent common ancestor
forms a conceptual bridge between microevolution and macroevolution
Microevolution
consists of changes in allele frequency in a population over time
Macroevolution
refers to broad patterns of evolutionary change above the species level 3

4. Speciation & Natural Selection
Natural selection can lead to speciation
New biological species evolve
Changes in a gene pool allele and genotypic frequencies
Speciation can also occur as a result of other micro-evolutionary processes
Genetic drift
Founder effect
Bottleneck effect
Mutation

5. Biological Species Concept
a group of populations whose members have the potential to
interbreed in nature and produce viable, fertile offspring
they do not breed successfully with other populations
Gene flow between populations holds the populations together genetically 5

6. Reproductive Isolation
Existence of biological barriers that impede two species from producing viable, fertile offspring
Arises as a by-product of genetic change
Speciation is the attainment of reproductive isolation
Cornerstone of the biological species concept
Can be classified by whether barriers act before or after fertilization

7. Pre-Zygotic Isolating Mechanisms
Prezygotic barriers block fertilization from occurring by
Habitat Isolation
Two species encounter each other rarely, or not at all, because they occupy different habitats
Temporal Isolation
reproduce at different times of the year
Mechanical Isolation
animal genitalia or plant floral structures are incompatible

8. Pre-Zygotic Isolating Mechanisms
Behavioral Isolation
courtship behaviors
Gamete Isolation
sperm of 1 species may not be able to survive in the reproductive tract of another species
Polyploidy
occurs in plants
can’t reproduce with plants that have polyploidy

9. Reproductive Isolation
Albatross courtship

10. Post Zygotic Isolating Mechanisms
Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult by
Reduced hybrid viability / zygote mortality
Genes of the different parent species may interact and impair the hybrid’s development or survival
Reduced hybrid fertility
Even if hybrids are vigorous, they may be sterile
Hybrid breakdown
Some first-generation hybrids are fertile
when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile

11. Mechanisms of Speciation
Speciation can occur in three ways:
Allopatric speciation (other country)
gene flow is interrupted when a population is divided into geographically isolated subpopulations
the definition of a geographic barrier depends on the ability of a population to disperse
a canyon may create a barrier for small rodents, but not birds, coyotes, or pollen 11

12. Allopatric Speciation
Separate populations may evolve independently through mutation, natural selection, and genetic drift
Reproductive isolation may arise as a result of genetic divergence
For example, mosquitofish in the Bahamas comprise several isolated populations in different ponds 12

13. body shape that enables rapid bursts of speed Under low predation:
Figure 22.6 Reproductive isolation as a by-product of selection
Under high predation:
body shape that enables
rapid bursts of speed
Under low predation:
body shape that favors
long, steady swimming 13

14. Allopatric speciation on an archipelago
Models of Speciation
Allopatric speciation on an archipelago

15. Sympatric Speciation Sympatric Speciation (same country)
speciation takes place in populations that live in the same geographic area
occurs when gene flow is reduced between groups that remain in contact through factors including
Habitat differentiation
Sexual selection
Polyploidy

16. Allopatric speciation: forms a new species while
Figure 22.5 Two main modes of speciation
Allopatric speciation: forms
a new species while
geographically isolated.
(a)
(b)
Sympatric speciation: a subset
forms a new species without
geographic separation. 16

17. Polyploidy Polyploidy
presence of extra sets of chromosomes due to accidents during cell division
much more common in plants than in animals
Autopolyploid
an individual with more than two chromosome sets, derived from one species
the offspring of matings between autopolyploids and diploids have reduced fertility 17

18. Polyploidy Allopolyploid
a species with multiple sets of chromosomes derived from different species
Allopolyploids cannot interbreed with either parent species 18

19. Parapatric Speciation: Hybrid zones
region in which members of different species mate and produce hybrids
Hybrids are the result of mating between species with incomplete reproductive barriers
Hybrids often have reduced fitness compared with parent species 19

20. B. variegata-specific allele Distance from hybrid zone center (km)
Figure 22.11
Fire-bellied
toad range
Fire-bellied toad, Bombina
bombina
Hybrid zone
Yellow-bellied
toad range
0.99
Hybrid
zone
0.9
Figure A narrow hybrid zone for Bombina toads in Europe
B. variegata-specific allele
Frequency of
0.5
Yellow-bellied
toad range
Fire-bellied
toad range
Yellow-bellied toad, Bombina
variegata
0.1
0.01 40 30 20 10 10 20
Distance from hybrid zone center (km) 20

21. Parapatric Speciation
BULLOCK’S ORIOLE
BALTIMORE ORIOLE
HYBRID ZONE

22. Hybrid Zones over Time
When closely related species meet in a hybrid zone, there are three possible outcomes:
Reinforcement
occurs when hybrids are less fit than the parent species
natural selection strengthens (reinforces) reproductive barriers, and, over time, the rate of hybridization decreases
where reinforcement occurs, reproductive barriers should be stronger for sympatric than for allopatric species 22

23. Fusion
when parent species fuses into a single species may occur if hybrids are as fit as parents, allowing substantial gene flow between species
Figure Fusion: the breakdown of reproductive barriers 23

24. hybrids continue to be produced over time
Stability
hybrids continue to be produced over time 24

25. Gene flow Population Barrier to gene flow
Figure Formation of a hybrid zone and possible outcomes for hybrids over time (step 1)
Population
Barrier to
gene flow 25

26. Isolated population diverges. Gene flow Population Barrier to
Figure Formation of a hybrid zone and possible outcomes for hybrids over time (step 2)
Population
Barrier to
gene flow 26

27. Isolated population diverges. Hybrid zone Gene flow Population
Figure Formation of a hybrid zone and possible outcomes for hybrids over time (step 3)
Population
Barrier to
gene flow
Hybrid
individual 27

28. Isolated population diverges. Possible outcomes: Hybrid zone
Reinforcement
Fusion
Gene flow
Figure Formation of a hybrid zone and possible outcomes for hybrids over time (step 4)
Population
Barrier to
gene flow
Hybrid
individual
Stability 28

29. Evolutionary tree diagram
Evolutionary Trees
Evolutionary tree diagram

31. Gradual Model
Speciation model in which species emerge through many small morphological changes that accumulate over a long time period

32. Punctuated Model
Speciation model in which most changes in morphology are compressed into brief period near onset of divergence

33. Phylogeny
The scientific study of evolutionary relationships among related species
Practical applications
allows predictions about the needs or weaknesses of one species on the basis of its known relationship to another
the discipline of systematics classifies organisms and determines their evolutionary relationships

34. TAXONOMY
Early taxonomists classified all species as either plants or animals
Later, five kingdoms were recognized:
Monera (prokaryotes)
Protista
Fungi
Plantae
Animalia 34

35. TAXONOMY More recently, the three-domain system has been adopted
Archaea
Eubacteria
single celled
prokaryotes
Eukarya
dominated by multicellular organisms
consists of Fungi, Plants and Animals
The three-domain system is supported by data from many sequenced genomes

36. Euglenozoans Forams Diatoms Ciliates Domain Eukarya Red algae
Green algae
Land plants
Amoebas
Fungi
Animals
Nanoarchaeotes
Archaea
Domain
Methanogens
COMMON
ANCESTOR
OF ALL LIFE
Thermophiles
Figure The three domains of life
Proteobacteria
(Mitochondria)*
Chlamydias
Spirochetes
Domain Bacteria
Gram-positive
bacteria
Cyanobacteria
(Chloroplasts)* 36

37. Binomial System Devised by Carl von Linneas
Each species has a two-part Latin name
First part is generic
Second part is specific name 37

38. Higher Taxa
Kingdom
Phylum
Class
Order
Family
Genus
Species 38

39. Figure 20.3 Linnaean classification39

40. Cladistics Cladistics classifies organisms by common descent
(a) Monophyletic group
(clade)
(b) Paraphyletic group
(c) Polyphyletic group A A A 1 1 B
Group I B B
Group III C C C D D D E E
Group II E 2 2 F F F G G G
Cladistics classifies organisms by common descent
A clade is a group of species that includes an ancestral species and all its descendants 40

41. A valid clade is monophyletic, signifying that
it consists of the ancestor species and all its descendants A 1 B
Group I C D
Figure 20.10a Monophyletic, paraphyletic, and polyphyletic groups (part 1: monophyletic) E F G 41

42. A paraphyletic grouping consists of an ancestral species
and some, but not all, of the descendants A B C D
Figure 20.10b Monophyletic, paraphyletic, and polyphyletic groups (part 2: paraphyletic) E
Group II 2 F G 42

43. A polyphyletic grouping consists of various taxa with
different ancestors A 1 B
Group III C D
Figure 20.10c Monophyletic, paraphyletic, and polyphyletic groups (part 3: polyphyletic) E 2 F G 43

44. Shared Ancestral and Shared Derived Characters
In comparison with its ancestor, an organism has both shared and different characteristics
shared ancestral character
a character that originated in an ancestor of the taxon
shared derived character
an evolutionary novelty unique to a particular clade 44

45. Phylogenetic Trees with Proportional Branch Lengths
In some trees, the length of a branch can reflect the number of genetic changes that have taken place in a particular DNA sequence in that lineage
Drosophila
Lancelet
Zebrafish
Frog
Chicken
Human
Mouse 45

46. In other trees, branch length can represent chronological time, and branching points can be determined from the fossil record
Drosophila
Lancelet
Zebrafish
Frog
Figure Branch lengths can indicate time
Chicken
Human
Mouse
PALEOZOIC
MESOZOIC
CENOZOIC
251
65.5 Present
542
Millions of years ago 46

47. Patterns of Change in a Lineage
Cladogenesis
Branching pattern
Lineage splits, isolated populations diverge
Anagenesis
No branching
Changes occur within single lineage
Gene flow throughout process