1. Chapter 14
The Origin of Species

2. Mosquito Mystery Speciation is the emergence of new species
How do we know that a distinctly new species has evolved?
In London, two populations of mosquitoes exist with very little overlap in their respective habitats
Evidence indicates that the two species did not diverge from one species

3. In the United States the two species appeared to hybridize into one species, which transmits West Nile virus
How could the mosquitoes behave like two species on one continent and one species on another?

4. 14.1 The origin of species is the source of biological diversity
Microevolution, gradual adaptation of a species to its environment, does not produce new species
Speciation, the origin of new species, is at the focal point of evolution
Macroevolution, dramatic biological changes that begin with the origin of new species, has led to Earth's great biodiversity

6. CONCEPTS OF SPECIES 14.2 What is a species?
Taxonomy is the branch of biology concerned with naming and classifying the diverse forms of life
The binomial system was introduced by Linnaeus in the 18th century
Similarities between some species and variation within a species can make defining species difficult

9. The biological species concept
Defines a species as a population or group of populations whose members can interbreed and produce fertile offspring
Reproductive isolation of different species prevents gene flow
Cannot be used as the sole criterion for species assignment

10. The morphological species concept
Classifies organisms based on observable phenotypic traits
The ecological species concept
Defines a species by its ecological role
The phylogenetic species concept
Defines a species as a set of organisms with a unique genetic history

11. 14.3 Reproductive barriers keep species separate
Reproductive barriers serve to isolate a species' gene pool and prevent interbreeding
Prezygotic barriers prevent mating or fertilization between species
Temporal isolation: Species breed at different times
Behavioral isolation: There is little or no sexual attraction between species due to specific behaviors

14. Mechanical isolation: Female and male sex organs or gametes are not compatible
Gametic isolation: After copulation, gametes do not unite to form a zygote

16. Postzygotic barriers operate after hybrid zygotes are formed
Hybrid inviability: Hybrids do not survive
Hybrid sterility: Hybrid offspring between two species are sterile and therefore cannot mate
Hybrid breakdown: Hybrids that mate with each other or either parent species produce feeble or sterile offspring

17. Video: Albatross Courtship Ritual
Video: Blue-footed Boobies Courtship Ritual
Video: Giraffe Courtship Ritual

18. MECHANISMS OF SPECIATION
14.4 Geographic isolation can lead to speciation
In allopatric speciation, a population is geographically divided
Barriers include geologic processes such as emergence of a mountain or subsidence of a lake
Changes in allele frequencies are unaffected by gene flow from other populations
New species often evolve, but only after reproductive barriers develop

19. LE 14-4
A. harrisi
A. leucurus
Video: Grand Canyon

20. 14.5 Reproductive barriers may evolve as populations diverge
Diane Dodd tested the hypothesis that reproductive barriers can evolve as a by-product of the adaptive divergence of populations in different environments
Fruit flies bred for several generations on a certain food tended to choose mates that were raised on the same food
Reproductive isolation was well under way after several generations of evolutionary divergence

21. Initial sample of fruit flies Starch medium Maltose medium Results of
LE 14-5a
Initial sample
of fruit flies
Starch medium
Maltose medium
Results of
mating experiments
Female
Female
Same
population
Different
populations
Starch
Maltose
Starch
Same 22 9 18 15
Male
Male 8 20
Different 12 15
Maltose
Mating frequencies
in experimental group
Mating frequencies
in control group

22. Video: Galápagos Marine Iguana
Geographic isolation in Death Valley led to allopatric speciation of pupfish
By genetic drift or natural selection, the isolated populations evolved into separate species
Video: Galápagos Marine Iguana

23. LE 14-5b
A pupfish

24. 14.6 New species can also arise within the same geographic area as the parent species
In sympatric speciation, new species may arise without geographic isolation
Not widespread among animals but important in plant evolution
Many plant species have evolved by polyploidy, multiplication of the chromosome number due to errors in cell division
First discovered by Hugo de Vries
Most polyploid plants arise from the hybridization of two parent species

25. 2n = 6 Diploid 4n = 12 Tetraploid Unreduced diploid gametes
LE 14-6a
Parent species
Zygote
Offspring
may be
viable and
self-fertile
Meiotic
error
Self-
fertilization
2n = 6
Diploid
4n = 12
Tetraploid
Unreduced
diploid gametes

26. LE 14-6b
O. lamarckiana
O. gigas

27. 14.7 Polyploid plants clothe and feed us
CONNECTION
14.7 Polyploid plants clothe and feed us
20—25% of all plant species are polyploids
Most result from hybridization between two species
Many of our food and fiber plants are polyploids
Bread wheat, Triticum aestivum, is a polyploid with 42 chromosomes that evolved over 8,000 years ago
Today, plant geneticists create new polyploids in the laboratory

28. AA BB AB AA BB DD ABD  AA BB DD Wild Triticum (14 chromo- somes)
Triticum monococcum
(14 chromosomes) AB
AA BB DD
ABD
Sterile hybrid
Meiotic error and
self-fertilization
T. turgidum
Emmer wheat
(28 chromosomes) 
T. tauschii
(wild)
(21 chromosomes)
T. aestivum
Bread wheat
(42 chromosomes)
AA BB DD

29. 14.8 Adaptive radiation may occur in new or newly vacated habitats
Adaptive radiation: the evolution of many new species from a common ancestor in a diverse environment
Occurs when mass extinctions or colonization provide organisms with new environments

30. Video: Galapágos Islands Overview
Island chains with physically diverse habitats are often sites of explosive adaptive radiation
14 species of Galápagos finches differ in feeding habits and beak type
Evidence indicates that all 14 species evolved from a single small population of ancestors that colonized one island
Video: Galapágos Islands Overview

31. LE 14-8a Cactus-seed-eater (cactus finch) Tool-using insect-eater
(woodpecker finch)
Seed-eater
(medium ground finch)

32. LE 14-8b A B B B B C C C C D C D D

33. 14.9 Peter and Rosemary Grant study the evolution of Darwin's finches
TALKING ABOUT SCIENCE
14.9 Peter and Rosemary Grant study the evolution of Darwin's finches
Peter and Rosemary Grant have documented natural selection acting on populations of Galápagos finches
Finch beaks adapted to different food sources through natural selection, as Darwin hypothesized
Occasional hybridization of finch species may have been important in their adaptive radiation

35. 14.10 The tempo of speciation can appear steady or jumpy
Gradualism model: New species evolve by the gradual accumulation of changes brought about by natural selection
Darwin's original model
Not well supported by the fossil record, because most new species seem to appear suddenly in rock strata without intermediary transitional forms

36. Punctuated equilibrium model: periods of rapid evolutionary change and speciation interrupted by long periods of little or no detectable change
Fossil record shows species changing most as they arise from an ancestral species and then relatively little for the rest of their existence
Most evolutionary biologists now see both models as having merit
Current research is focused on the tempo of evolution

37. LE 14-10a
Time

38. LE 14-10b
Time

39. MACROEVOLUTION 14.11 Evolutionary novelties may arise in several ways
Darwin's theory of gradual change can account for the evolution of intricate structures
Complex structures may evolve in stages from simpler versions having the same basic function
Example: Eyes of molluscs
Existing structures may be gradually adapted to new functions
Exaptation: a feature that evolved in one context and was later adapted for another function

40. Transparent protective Animation: Macroevolution
LE 14-11
Light-sensitive
cells
Light-sensitive
cells
Transparent protective
tissue (cornea)
Fluid-filled cavity
Cornea
Lens
Eye cup
Layer of
light-sensitive
cells (retina)
Nerve
fibers
Nerve
fibers
Retina
Optic
nerve
Optic
nerve
Optic
nerve
Patch of light-
sensitive cells
Eye cup
Simple pinhole
camera-type eye
Eye with
primitive lens
Complex
camera-type eye
Limpet
Abalone
Nautilus
Marine snail
Squid
Animation: Macroevolution

41. 14.12 Genes that control development are important in evolution
"Evo-devo" combines evolutionary and developmental biology
Studies how slight genetic changes can be magnified into significant phenotypic changes
Many striking evolutionary transformations are the result of a change in the rate or timing of developmental changes
Paedamorphosis: retention in adult of features that were juvenile in its ancestors

42. Animation: Allometric Growth
LE 14-12b
Chimpanzee fetus
Chimpanzee adult
Human fetus
Human adult
Animation: Allometric Growth

43. Important in human evolution
Large skull and long childhood provide humans with more space for brain and more opportunity to learn from adults
Juvenile physical traits may make adults more caring and protective
Example: "evolution" of Mickey Mouse

44. 14.13 Evolutionary trends do not mean that evolution is goal directed
Evolutionary trends reflect the unequal speciation or unequal survival of species on a branching evolutionary tree
Example: lineages of horses that died out
Evolutionary trends do not imply an intrinsic drive toward a goal
If environmental conditions change, an apparent trend may cease or reverse

45. Hippidion and other genera
LE 14-13
RECENT
Equus
Hippidion and other genera
PLEISTOCENE
Nannippus
Pliohippus
Hipparion
Neohipparion
PLIOCENE
Sinohippus
Megahippus
Callippus
Archaeohippus
Merychippus
MIOCENE
Anchitherium
Hypohippus
Parahippus
Miohippus
OLIGOCENE
Mesohippus
Paleotherium
Epihippus
Propalaeotherium
Pachynolophus
Orohippus
EOCENE
Grazers
Hyracotherium
Browsers