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SpeciationSpeciation

Mark MayoMark Mayo

Cypress CollegeCypress College

Last Update 11/7/13

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SpeciesSpecies

Species definedSpecies defined morphological species morphological species

– a kind of animal– a kind of animal older meaningolder meaning form only was used to group organisms in the pastform only was used to group organisms in the past

new biological definition from Mayr – groups of new biological definition from Mayr – groups of interbreeding natural populations that are interbreeding natural populations that are reproductively isolated reproductively isolated

Best definition: organisms that can mate and Best definition: organisms that can mate and produce fertile offspringproduce fertile offspring

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Reproductive Isolation Reproductive Isolation

Definition of reproductive isolationDefinition of reproductive isolation: : methods by which interspecific mating is methods by which interspecific mating is prevented prevented

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Reproductive IsolationReproductive Isolation

Pre-zygotic isolationPre-zygotic isolation – occur before – occur before fertilization; prevents waste of gametesfertilization; prevents waste of gametes temporal isolationtemporal isolation – reproduction occurs at – reproduction occurs at

different times different times (aka – seasonal isolation)(aka – seasonal isolation)

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Reproductive IsolationReproductive Isolation

Pre-zygotic isolationPre-zygotic isolation behavioral isolationbehavioral isolation

– courtship rituals differ– courtship rituals differfrom one species to from one species to anotheranother if you don’t sing correctly, if you don’t sing correctly,

have cool feathers or have cool feathers or dance like they like dance like they like – you are not mating!– you are not mating!

(aka - ethological isolation)(aka - ethological isolation)

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Reproductive IsolationReproductive Isolation

Pre-zygotic isolationPre-zygotic isolation mechanical isolationmechanical isolation – physically different – physically different

and pollination or copulation is not possibleand pollination or copulation is not possible

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Reproductive IsolationReproductive Isolation

Pre-zygotic isolationPre-zygotic isolation ecological isolationecological isolation – microenvironment – microenvironment

requirements differ so they cannot live near requirements differ so they cannot live near enough to interbreed enough to interbreed

(aka – habitat segregation) (aka – habitat segregation)

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Reproductive IsolationReproductive Isolation

Pre-zygotic isolationPre-zygotic isolation gametic mortalitygametic mortality – the – the

gametes cannot survive to gametes cannot survive to cause zygote formationcause zygote formation the gametes are not the gametes are not

attractive to one another, attractive to one another, they might be destroyed or they might be destroyed or die before fertilization die before fertilization

Sperm may not be able to Sperm may not be able to penetrate eggpenetrate egg

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Reproductive IsolationReproductive Isolation

Post-zygotic isolationPost-zygotic isolation after fertilization occurs there is a problem that after fertilization occurs there is a problem that

prevents successful production of offspringprevents successful production of offspring the zygote may not be accepted by the female’s the zygote may not be accepted by the female’s

body (assuming internal fertilization)body (assuming internal fertilization) there may be physical there may be physical

size differences (dinosaur size differences (dinosaur baby in modern day lizard)baby in modern day lizard)

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Types of Speciation Types of Speciation

SpeciationSpeciation is the formation of a new species is the formation of a new species from an existing speciesfrom an existing species

Darwin, and modern Darwinists, conceived of Darwin, and modern Darwinists, conceived of gradual change as taking millions and millions gradual change as taking millions and millions of years to bring about evolution of one species of years to bring about evolution of one species into another. into another.

Phyletic gradualism brings about a very slow, brings about a very slow, steady branching and slow divergence of two steady branching and slow divergence of two populations, as modification of one or both populations, as modification of one or both branches results in two new species. branches results in two new species.

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Types of SpeciationTypes of Speciation

Phyletic gradualismLots of time and small changes cause a new species to evolve!

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Types of SpeciationTypes of Speciation

A new model, proposed by Niles Eldridge A new model, proposed by Niles Eldridge and Stephen Jay Gould in 1972, and Stephen Jay Gould in 1972, envisions sudden sharp branches in the envisions sudden sharp branches in the evolutionary tree followed by long periods evolutionary tree followed by long periods of stasis and no change.of stasis and no change.

They termed this model They termed this model punctuated equilibrium.

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Types of SpeciationTypes of Speciation

Both phyletic gradualism and punctuated Both phyletic gradualism and punctuated equilibrium are in effect on earthequilibrium are in effect on earth

punctuated punctuated equilibriumequilibrium

phyletic phyletic gradualismgradualism

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Types of SpeciationTypes of Speciation

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Types of SpeciationTypes of Speciation

allopatric speciation allopatric speciation ** – geographic – geographic isolation caused by physical barriers – isolation caused by physical barriers – lakes, mountain ranges, river, oceans, lakes, mountain ranges, river, oceans, freeways etc.freeways etc.

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Types of SpeciationTypes of Speciation

Parapatric speciation Parapatric speciation ** – no barrier – no barrier exists, but buffer zone of hybrids exists exists, but buffer zone of hybrids exists between two speciesbetween two species there is still contact along a common borderthere is still contact along a common border there are hybrid organisms in the buffer zone between the there are hybrid organisms in the buffer zone between the

speciesspecies

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Types of SpeciationTypes of Speciation

sympatric speciation sympatric speciation ** – both species – both species reside within the same geographic regionreside within the same geographic region may be a result of factors like feeding may be a result of factors like feeding

preference or other differencespreference or other differences

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Types of SpeciationTypes of Speciation

polyploidypolyploidy – multiples of the – multiples of the chromosome number result in chromosome number result in new plant speciesnew plant species almost always happens exclusively almost always happens exclusively

in plantsin plants over 50% or all plants are polyploidover 50% or all plants are polyploid gametes are usually haploid (2N/2 gametes are usually haploid (2N/2

= N) N+N = 2N zygote= N) N+N = 2N zygote usually lethal in humans (even one usually lethal in humans (even one

extra chromosome is serious extra chromosome is serious hazard)hazard)

Passion flower: a tetraploid

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Special Patterns of SpeciationSpecial Patterns of Speciation

CladogenesisCladogenesis – – branching pattern branching pattern where speciation where speciation occurs. occurs.

the branching of the the branching of the phylogenetic tree is phylogenetic tree is due to speciationdue to speciation

S = cladogenesisE = extinction

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Special Patterns of SpeciationSpecial Patterns of Speciation

Cladogenesis vs. Cladogenesis vs. anagenesisanagenesis anagenesisanagenesis –– non-branching non-branching

pattern where the same pattern where the same species has changes in allele species has changes in allele frequencies. Directional frequencies. Directional change within a single lineagechange within a single lineage

cladogenesiscladogenesis – a branching – a branching diagram depicting speciationdiagram depicting speciation

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Special Patterns of SpeciationSpecial Patterns of Speciation

Evolutionary trees Evolutionary trees trunk = original species, each trunk = original species, each

branch is a new species off of branch is a new species off of the original speciesthe original species

gradualgradual – slightly divergent at – slightly divergent at first and then over time it first and then over time it becomes more pronouncedbecomes more pronounced

punctuatedpunctuated – distinct – distinct changes with pronounced changes with pronounced differences immediatelydifferences immediately

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Special Patterns of SpeciationSpecial Patterns of Speciation

Adaptive radiation Adaptive radiation ** – burst of species – burst of species from a single lineage (genetic from a single lineage (genetic divergence) divergence)

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Special Patterns of SpeciationSpecial Patterns of Speciation

all mammals all mammals are related to are related to a primitive a primitive precursor and precursor and present-day present-day mammals are mammals are the ultimate the ultimate result of result of adaptive adaptive radiation radiation

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Special Patterns of SpeciationSpecial Patterns of Speciation

Adaptive radiation of Darwin’s FinchesAdaptive radiation of Darwin’s Finches

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Special Patterns of SpeciationSpecial Patterns of Speciation each member of the lineage may radiate to each member of the lineage may radiate to

unfilled zones and this is governed by three main unfilled zones and this is governed by three main forces:forces: physical accessphysical access – must be able to reach the new – must be able to reach the new

environment to allow speciation to occurenvironment to allow speciation to occur evolutionary accessevolutionary access – must evolve a new body part of – must evolve a new body part of

adaptation to allow the lineage to flourish in the new adaptation to allow the lineage to flourish in the new environment environment (land to water or water to land)(land to water or water to land) toes to wingstoes to wings legs to flipperslegs to flippers air hole (blow hole) on dorsal surface vs. anteriorair hole (blow hole) on dorsal surface vs. anterior

ecological accessecological access – enter an unoccupied zone or – enter an unoccupied zone or displace another population displace another population