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?

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

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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)

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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

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Hippidion and other genera