Post on 27-Dec-2015
11
SpeciationSpeciation
Mark MayoMark Mayo
Cypress CollegeCypress College
Last Update 11/7/13
22
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
33
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
44
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)
55
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)
66
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
77
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)
88
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
99
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)
1010
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.
1111
Types of SpeciationTypes of Speciation
Phyletic gradualismLots of time and small changes cause a new species to evolve!
1212
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.
1313
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
1414
Types of SpeciationTypes of Speciation
1515
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.
1616
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
1717
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
1818
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
1919
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
2020
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
2121
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
2222
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)
2323
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
2424
Special Patterns of SpeciationSpecial Patterns of Speciation
Adaptive radiation of Darwin’s FinchesAdaptive radiation of Darwin’s Finches
2525
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