Chapter 16Chapter 16

The OriginThe Originof Speciesof Species

Chapter 16 2

Speciation ISpeciation I

RequirementsRequirements• Isolation of populationsIsolation of populations• Genetic divergenceGenetic divergence

Speciation has seldom been observed in natureSpeciation has seldom been observed in natureAllopatric speciationAllopatric speciationSympatric speciationSympatric speciation• Ecological isolationEcological isolation• Chromosomal aberrationsChromosomal aberrations

– AnimalsAnimals– PlantsPlants

Chapter 16 3

Speciation IISpeciation II

Types of speciationTypes of speciation

• Divergent speciationDivergent speciation

• Phyletic speciationPhyletic speciation

Models of speciationModels of speciation

• GradualismGradualism

• Punctuated equilibriumPunctuated equilibrium

Chapter 16 4

Single species(white mice);homogeneous habitat

Geographical barrier(impassable river);isolated populations

Genetic drift;genetic divergence;

tan vs white mice

Barrier removed(river dries up);

mix but don’t interbreed

Allopatric SpeciationAllopatric Speciation(a)

(b)

(c)

(d)

Chapter 16 5

Sympatric SpeciationSympatric SpeciationSingle species(white mice);homogeneous habitat

(a)

Climate change;two habitats;isolated because don’t mix

(b)

Environmental pressure to adapt;genetic divergence;

tan vs white mice

(c)

Sufficient divergence;

now different species

(d)

Chapter 16 6

Isolation MechanismsIsolation MechanismsPrematingPremating• Geographical isolation (too far away/barrier)Geographical isolation (too far away/barrier)• Ecological isolation (bird vs. fish)Ecological isolation (bird vs. fish)• Temporal isolation (different mating seasons)Temporal isolation (different mating seasons)• Behavioral isolation (courtship and rituals)Behavioral isolation (courtship and rituals)•Mechanical incompatibility (tab A can’t fit Mechanical incompatibility (tab A can’t fit

into slot B)into slot B)PostmatingPostmating• Gametic incompatibility (sperm can’t fertilize)Gametic incompatibility (sperm can’t fertilize)• Hybrid inviabilityHybrid inviability• Hybrid infertilityHybrid infertility

Chapter 16 7

Speciation by PolyploidySpeciation by Polyploidy

DiploidGamete

Meiosis

Meiosis

DiploidGametes

FertilizationViable Tetraploid

Zygote

ViableDiploid

Gametes

HaploidGamete

Viable TriploidZygote

Meiosis(fails)

Meiosis

Fertilization

Triploids can’t do meiosis;No viable gametes.

TetraploidPlant

TetraploidPlant

DiploidPlant

Chapter 16 8

InterpretingInterpretingan Evolutionary Treean Evolutionary Tree

Lines that don't reachthe top representextinct species.

Forks representspeciation events.

Each line represents a

species.

Lines that reach thetop represent existing

species.

Steeper slope represents slow

phenotypic change.

More horizontal slope represents rapid phenotypic

change.

Chapter 16Chapter 16

Systematics:Systematics:Seeking OrderSeeking Order

Amidst DiversityAmidst Diversity

Chapter 16 10

Taxonomic PrinciplesTaxonomic Principles

Taxonomic categories form an increasingly Taxonomic categories form an increasingly inclusive, nested hierarchyinclusive, nested hierarchy• ““DDid id KKing ing PPhillip hillip CCame ame OOverver FForor GGood ood SS___" ___"

to remember categoriesto remember categories• Domain, Kingdom, phylum (animals and Domain, Kingdom, phylum (animals and

protists) or division (plants, fungi, bacteria, protists) or division (plants, fungi, bacteria, and plant-like protists), class, order, family, and plant-like protists), class, order, family, genus, and speciesgenus, and species• Domain - most inclusiveDomain - most inclusive• Species - least inclusiveSpecies - least inclusive

Scientific name—Scientific name—GenusGenus and and speciesspecies

Chapter 16 11

Origins of TaxonomyOrigins of TaxonomyAristotle (384–322 B.C.)Aristotle (384–322 B.C.)• Simple classificationSimple classification• Based on:Based on:

– Structural complexityStructural complexity– BehaviorBehavior– Degree of development at birthDegree of development at birth

Carolus Linnaeus (1707–1778)Carolus Linnaeus (1707–1778)• Based on resemblance to other life formsBased on resemblance to other life forms• Established binomial nomenclatureEstablished binomial nomenclature

Charles Darwin (1809–1882)Charles Darwin (1809–1882)• Categories reflect evolutionary relationshipCategories reflect evolutionary relationship

Chapter 16 12

The Changing Classification SystemThe Changing Classification SystemPrior to 1970—two-kingdom systemPrior to 1970—two-kingdom system• Plants and animalsPlants and animals

1969—Roger Whittaker—five-kingdom 1969—Roger Whittaker—five-kingdom systemsystem•Monera, Protista, Fungi, Plantae, AnimaliaMonera, Protista, Fungi, Plantae, Animalia

1990—Carl Woese—three-domain system1990—Carl Woese—three-domain system• Bacteria, Archaea, EukaryaBacteria, Archaea, Eukarya

Discovered that kingdom Monera included Discovered that kingdom Monera included two very distinct groups (Bacteria and two very distinct groups (Bacteria and Archaea) based on nucleotide sequences of Archaea) based on nucleotide sequences of ribosomal RNAribosomal RNA

Chapter 16 13

Problems concerning Problems concerning classification of speciesclassification of species

The The biological species conceptbiological species concept defines species defines species as “groups of interbreeding natural as “groups of interbreeding natural populations, which are reproductively isolated populations, which are reproductively isolated from other such groups”from other such groups”• Cannot be applied to asexually reproducing Cannot be applied to asexually reproducing

organismsorganismsThe The phylogenetic species conceptphylogenetic species concept defines a defines a

species as “the smallest diagnosable group species as “the smallest diagnosable group that contains all the descendants of a single that contains all the descendants of a single common ancestor”common ancestor”• Can be applied to sexually and asexually Can be applied to sexually and asexually

reproducing organismsreproducing organisms• May eventually replace the biological species May eventually replace the biological species

conceptconcept

Chapter 16 14

BiodiversityBiodiversity

How many species exist?How many species exist?

• 1.5 million species categorized1.5 million species categorized

• Up to 30 million species may existUp to 30 million species may exist

7000 to 10,000 new species described/y7000 to 10,000 new species described/y

Many classified species are becoming Many classified species are becoming extinct as their habitats are destroyedextinct as their habitats are destroyed

Chapter 16 15

Microscopic StructuresMicroscopic StructuresHelp to Classify OrganismsHelp to Classify Organisms

(a) (b) (c)

Bristles on aBristles on amarine wormmarine worm

““Teeth” on aTeeth” on asnail’s radulasnail’s radula

Shape andShape andsurface featuressurface featureson a pollen grainon a pollen grain

Chapter 16 16

Similarity of Human andSimilarity of Human andChimp ChromosomesChimp Chromosomes

H = HumanH = HumanC = ChimpC = Chimp

Chapter 16 17

Modern Criteria for ClassificationModern Criteria for Classification

Anatomy - homologous structuresAnatomy - homologous structures

Developmental stages - embryologyDevelopmental stages - embryology

Biochemical similarities - use of genetic Biochemical similarities - use of genetic informationinformation

Chapter 16 18

The Tree of LifeThe Tree of Life

Chapter 16 19

Representative ProkaryotesRepresentative ProkaryotesVibrio choleraeVibrio cholerae of the domain Bacteria of the domain Bacteria

Methanococcus jannaschi Methanococcus jannaschi of the domain Archaeaof the domain Archaea

Chapter 16 20

The Concept of MonophylyThe Concept of Monophyly

MonophyleticMonophyletic NOTNOTMonophyleticMonophyletic

(a)(a) (b)(b)

(c)(c)

Reptiles not MonophyleticReptiles not Monophyletic

Chapter 16 21

Relatedness by DNA SequencesRelatedness by DNA Sequences

Chapter 16 22

The Origin of The Origin of HIV VirusHIV Virus

Chapter 16Chapter 16

The EndThe End