Chapter 14 The Origin of Species. Mosquito Mystery Speciation is the emergence of new species How do we know that a distinctly new species has evolved?
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Chapter 14Chapter 14
The Origin of Species
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
– 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?
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
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
• 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
• 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
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
• Mechanical isolation: Female and male sex organs or gametes are not compatible
• Gametic isolation: After copulation, gametes do not unite to form a zygote
– 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
Video: Albatross Courtship RitualVideo: Albatross Courtship Ritual
Video: Blue-footed Boobies Courtship RitualVideo: Blue-footed Boobies Courtship Ritual
Video: Giraffe Courtship RitualVideo: Giraffe Courtship Ritual
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
LE 14-4
A. harrisi A. leucurus
Video: Grand CanyonVideo: Grand Canyon
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
LE 14-5a
Starch medium
Initial sampleof fruit flies
Results ofmating experiments
Female
Starch Maltose
922
8 20
18 15
12 15
FemaleSame
populationDifferent
populations
Mal
e
Mal
e
Mal
tose
Dif
f er e
nt
Sam
e
Sta
rch
Mating frequenciesin control group
Mating frequenciesin experimental group
Maltose medium
• 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 IguanaVideo: Galápagos Marine Iguana
LE 14-5b
A pupfish
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
LE 14-6a
Parent species
Meioticerror
Self-fertilization
2n = 6Diploid
4n = 12Tetraploid
Unreduceddiploid gametes
Zygote
Offspringmay beviable andself-fertile
LE 14-6b
O. lamarckiana
O. gigas
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
AA BB WildTriticum(14 chromo-somes)
Triticum monococcum(14 chromosomes)
AB
AA BB DD
ABD
Sterile hybrid(14 chromosomes)
Meiotic error andself-fertilization
T. turgidumEmmer wheat(28 chromosomes)
T. tauschii(wild)(14 chromosomes)
Sterile hybrid(21 chromosomes)
Meiotic error andself-fertilization
T. aestivumBread wheat(42 chromosomes)
AA BB DD
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
• 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 OverviewVideo: Galapágos Islands Overview
LE 14-8a
Cactus-seed-eater(cactus finch)
Seed-eater(medium ground finch)
Tool-using insect-eater(woodpecker finch)
LE 14-8b
A B
B
B
C C
C
B
C C
D
D
D
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
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
• 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
LE 14-10a
Time
LE 14-10b
Time
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
LE 14-11
Light-sensitivecells
Nervefibers
Light-sensitivecells
Eye cup
Nervefibers
Fluid-filled cavity
Eye cup
Opticnerve
Simple pinholecamera-type eye
Layer oflight-sensitivecells (retina)
Opticnerve
Transparent protectivetissue (cornea)
Lens
Cornea
Retina
Opticnerve
Eye withprimitive lens
Complexcamera-type eye
Nautilus Marine snail Squid
Patch of light-sensitive cells
AbaloneLimpet
Animation: MacroevolutionAnimation: Macroevolution
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
LE 14-12b
Chimpanzee fetus Chimpanzee adult
Human fetus Human adult
Animation: Allometric GrowthAnimation: Allometric Growth
• 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
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
LE 14-13
Hyracotherium
Pachynolophus Orohippus
Propalaeotherium
Paleotherium
Mesohippus
Miohippus
Parahippus
Epihippus
GrazersBrowsers
Merychippus
Callippus
Hypohippus
Archaeohippus
Megahippus
Anchitherium
Sinohippus
Equus
Hipparion Neohipparion
Nannippus
Pliohippus
RE
CE
NT
PL
EIS
TO
CE
NE
PL
IOC
EN
EM
IOC
EN
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LIG
OC
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OC
EN
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Hippidion and other genera
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