Charles DarwinCharles Darwin

• Wrote in 1859Wrote in 1859: “On the Origin of “On the Origin of Species by Means of Natural Selection”Species by Means of Natural Selection”

Two main points:Two main points:1.1. Species were not created in their Species were not created in their present form, but evolved from present form, but evolved from ancestral species. (Descent With ancestral species. (Descent With Modification) Modification) 2.2. Proposed a mechanism for Proposed a mechanism for evolution:evolution: NATURAL SELECTIONNATURAL SELECTION

SpeciationSpeciation

• The evolutionevolution of new species.

What are the two driving forcesWhat are the two driving forcesbehind speciation?behind speciation?

SpeciesSpecies

• A group of populationspopulations whose individualsindividuals have the potential to interbreedinterbreed and produce fertilefertile offspring in a natural environment. (Ernst Mayr)

Liger

Result of male lion and female tiger mating in captivity. Offspring are infertile.

TigonTigonResult of male tiger and female lion mating incaptivity. Offspring are infertile.

Separated both geographically and ecologically.

The biological species concept is based on interfertility rather than physical similarity

Ethnic Groups

Speciation in African Cichlids

Macroevolution vs. Microevolution?Macroevolution vs. Microevolution?

MacroevolutionMacroevolutionis above the is above the species level. species level.

MicroevolutionMicroevolution is at the species levelis at the species level..

Speciation can take place withSpeciation can take place withor without geographic barriers.or without geographic barriers.

Geographic IsolationGeographic Isolation

• Induced when the ancestralancestral population becomes separatedseparated by a geographical barrier.geographical barrier.

• Example:Example:

Grand Canyon ground squirrels

Geographic Isolation

KaibabSquirrel (left)

AbertSquirrel (right)

Reproductive Isolating Mechanisms

Geographic Isolation

Has speciation occurred during geographic isolation?

Allopatric Speciation

Reproductive BarriersReproductive Barriers

• Any mechanismmechanism that impedesimpedes two species from producing fertile and/or hybrid offspringfertile and/or hybrid offspring.

Figure 24.3 Courtship ritual as a behavioral barrier between species Blue-Footed Boobies in theBlue-Footed Boobies in theGalapagos IslandsGalapagos Islands

Behavioral Isolation (Courtship Rituals)Behavioral Isolation (Courtship Rituals)

Reproductive Isolating Mechanisms

Sciurus niger, the fox squirrel breeds in May and June

Sciurus carolinensis, the gray squirrel, breeds in July and August

Temporal Isolation (a specific type of

reproductive isolation)

Bishop’s Pine releases Bishop’s Pine releases pollen in summerpollen in summer

Monterey Pine releasesMonterey Pine releases pollen in early spring pollen in early spring

• Behavioral Isolation

Ornate butterflyfish

Bluestripe butterflyfish

Reproductive Isolating MechanismReproductive Isolating Mechanism

Mechanical Isolation

Ensatina eschscholtzii, a ring species, here in the Golden State, an example of reduced hybrid viability and adaptive radiation

Ecological Isolation

White-throated SparrowWhite-throated Sparrowfeeds in dense thicketsfeeds in dense thickets White-crowned SparrowWhite-crowned Sparrow

inhabits fields and meadowsinhabits fields and meadows

A Model for Adaptive Radiation on Island Chains

HawaiianHawaiianSilverswordSilversword

EvolvedEvolved5 million 5 million years ago;years ago;28 endemic28 endemicspeciesspecies

Adaptive RadiationAdaptive Radiation

• Emergence of numerous speciesEmergence of numerous species from a common ancestorcommon ancestor introduced to new and diverse environments.

• Occurs as a result of Divergent Evolution

• Examples:Examples:

Darwin’s Finches, African Cichlid FishDarwin’s Finches, African Cichlid Fish

Different geographic regions, different mammalian “brands” – Eutherian vs. Marsupials

ConvergentConvergentEvolutionEvolution

Gradualism Punctuated Equilibrium

Interpretations of SpeciationInterpretations of Speciation• Two theoriesTwo theories::

1.1. Gradualist ModelGradualist Model::Slow changes in species

overtime.

2.2. Punctuated EquilibriumPunctuated Equilibrium::Evolution occurs in spurts of

relatively rapid change. (Eldredge and Gould)

Macroevolutionary changes canMacroevolutionary changes canaccumulate through manyaccumulate through manyspeciation events. speciation events.

“Evo-Devo” biologists compare developmental processes of different multicellular organisms

Development is intimately connectedto evolution because all changes in form come about through changes in development.

Homeotic Genes – any of the master regulatory genes that control overall body plan of animals and plants by controlling the developmental fate of groups of cells

The products of one class of homeotic genes called Hox genes provide positional information in an animal embryo.

Hox mutations and the origin of vertebrates

Homologous genes that affect pattern formation in a fruit fly and a mouse

“The amazing diversity of organismshas been produced by a modest number of genes” (Sean Carroll – author of Endless Forms Most Beautiful)

The biggest difference betweenThe biggest difference betweenamphibian eggs and reptilian eggsamphibian eggs and reptilian eggswas the development of the. . .was the development of the. . .

The five groups of vertebrates are:The five groups of vertebrates are:

Reptiles can reproduce in three Reptiles can reproduce in three ways. These are: ways. These are:

Name two characteristics Name two characteristics common to almost all members common to almost all members of the following classes of of the following classes of animals:animals:• amphibiansamphibians• reptilesreptiles• mammalsmammals

A phylogenetic tree can be used to A phylogenetic tree can be used to show . . ..show . . ..

All mammals are classified into All mammals are classified into these three groups:these three groups:

Which two characteristics do all Which two characteristics do all chordates have?chordates have?

Speciation that occurs in Speciation that occurs in which members are separatedwhich members are separatedfrom each other is from each other is called ____________ speciationcalled ____________ speciation..

Speciation that occurs in Speciation that occurs in which members have no barrierswhich members have no barriersbetween them is called between them is called ______________ speciation______________ speciation. .

1)1)Other than the example given Other than the example given in the powerpoint presentation, givein the powerpoint presentation, givean example of convergent evolutionan example of convergent evolutionamong species.among species.

2) What are the two theories regard-2) What are the two theories regard-ing the pace of evolution?ing the pace of evolution?

Peter and Rosemary Grant arePeter and Rosemary Grant arefamous for …famous for …

If two or more species repro-If two or more species repro-duce at different times this isduce at different times this iscalled ____________ isolation.called ____________ isolation.