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

EO

LIG

OC

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Hippidion and other genera

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