Lecture 6: 11/14

How can reproductive isolation evolve in sympatry? -bc at one time it was ______ and moved back together and became sympatric. -rise in allele. How does this arise in the face of gene flow and recombination? -Cant happen at once, must be a gene association (_______ ________). -requires the evolution of __________mating. (mate with each other PrR & PrR / PbB & PbB) -like will mate with like

-allopatric -linkage disequilibrium -assorative

Example of Parapatric evolution of reproductive isolation: -populations have __________ and __________ divergence -even if close to another, selection drives them to speciate

-ecological, prezygotic

Reinforcement selection in Green tree frogs and barking tree frogs: -Green and barking frogs sometimes ______. When in contact, hybrids have _______ fitness. -Females from sympatric populations prefer ______ calls more than females from allopatric population. -sympatric: better recognized the same species. >familiar with calls from both species -allopatry: mate with _____ call.

-hybridize, lower -conspecific-call for same species -loudest

Evidence for allopatric speciation 1) Many species show __________ incipient reproductive isolation as populations become more __________ separated. -incipient: beging to happen, initial stage

-increased -geographically

Reinforcement selection in Drosophilia: -expect sister species living in sympatry should have _____ prezygotic barrier compared to sisters living in allopatry. - Assume, ______ distance should be related to time since divergence. Measure prezygotic isolation: 1- (freq. successful herterospecific matings/freq successful ________ mating)

-increased -genetic homospecific

Two cases of sympatric speciation: 2) Chilcild fish in a Nicaraguan Lake -________ shows that both fishes are genetically differentiated. the implies _____ isolation. -difference in _____ shape, pharyngeal ____, difference in ____.

-microsattelites, reproductive -body, jaw, diet

Allopatric speciation -geographic separation is a _____ for a divergence. -isolating mechanisms are a ____ of divergence.

-prerequisite - byproduct

Two cases of sympatric speciation: 2) Chilcild fish in a Nicaraguan Lake -The sister species must have sympatric distributions throughout speciation. -there must be genetic evidence for ________ isolation - Sister must be a _________ group. all descendants of a ______ common ancestor -Must inhabit an ecological settings in which allopatric speciation is unlikely.-NO _______

-reproductive -monophyletic, single -barrieer

Two cases of sympatric speciation: 1) poplyploid speciation -more that ______ homologous set of of chromosomes -cant ____ w/ diploid (1 set) -polyploid has _____ fitness. -immediate _______ isolaiton.

-two -mate -lower -reproductive

Evidence for allopatric speciation 3) Peripatric evolution in Hawaiian Drosophila 1. nearest relatives reside on different islands 2.Almost all species are ______ to a single island 3. Observers suggest that every colonization leads to either a) __________ of a colonist b) a ______ event 4. Relationship b/w phylogeny and island age is consistent with ______ model. endemic: condition found among particular area

1. relatives 2. endemic 3.extinction, speciation 4. peripatric

Allopatric Speciation >> classical view: Mountain range 1. speciation is ____ and ____ event. 2. 3 stage process a) genetic _______ b) __________ in traits c) __________ isolation.

1. slow and rare 2. isolation divergence reproductive

Mechanisms for evolution of isolating barriers in allopatry 1.Dobzhansky-Miller incompatibilities 2. Reproductive isolation may arise and a byproduct of _______ isolation.

2. ecological

Mechanisms for evolution of isolating barriers allopatry 1.Dobzhansky-Miller incompatibilities 2. Ecological isolation 3. Sexual selection may influence _______ via the evolution of mate recognition. -PROMISCUOUS (vs nonpromisuous ) mate w/ more different individuals. -leads to more intense ______ selection bc more options. -drives speciation bc more evolution for male _______ along species.

3. speciation -sexual -recognition

Mechanisms for evolution of isolating barriers allopatry 1.Dobzhansky-Miller incompatibilities 2. Ecological isolation 3. Sexual selection 4. Reinforcement selection: adaptation to prevent the production of _______ hybrids. -Closely related species evolve some postzygotic isolation, ______ pressures then arise to favor the evolution of ________ isolating barriers..

4. unfit -selection -prezygotic

>Isolation increases with ______ divergence. >Prezygotic isolation evolves ___ than post zygotic. -why? bc _____ selection occurs

> genetic > faster -natural

Genetic mechanism for hybrid inviability and hybrid sterility: ______-________ incompatibilities

Dobzhansky-Muller

Sympatric speciation: -Coexistance requires that populations develop sufficient ______ divergence to coexist after ______ divergence.

Ecological genetic

Postzygotic Barriers: a) __________: (hybrid fitness depends on context) 1. ______ inviabiility- hybrids do not have ecological niche in which they are competitively equal to parent species. 2. ______ sterility (hybrids are _____ successful than parent species in obtaining mates)

Extrinsic 1. Ecological 2. Behavioral, less

Model of speciation Allopatry- population rages do ______ overlap during speciation.

NOT

Allopatric Speciation: (____ model ) 1)Population occurs throughout an area . 2) area divided by ______ barrier to gene flow. 3) intrinsic barriers to gene flow evolve (D-M ____________) 4) if populations hybridize, there is at least ______ isolation.

Vicariance 2) physical 3) incompatibilities 4) partial

Model of speciation Parapatry- population ranges are _______ during speciation.

adjacent

How do species arise? (under the BSC): Models of speciation 1) _________ model 2) ________model 3) ________model

allopatric, parpatric, sympatric

Mechanisms for evolution of isolating barriers in allopatry 1. Dobzhansky-Miller incompatibilities may arise through _____.

drift

Example of Parapatric evolution of reproductive isolation: Sweet vernal grass-plants on mine are tolerant of heavy metals . Cline- gradual change in allele _______ . steep & gradual. -difference between timing flowering from mine and off mine: -on mine: emerges earlier, _____ fitness of self fertilization. -off mine: later emerge.

frequencies -higher

In allopatry, reproductive isolation can arise bc of the absence of ____ flow between populations, thus allows _______.

gene, divergence

Evidence for allopatric speciation 2) Speciation can be related to the ______ history of barriers. - Two different clades diverged bc climate changes caused barriers.

geological

Dobzhansky-Muller incompatibilities: aabb>> AAbb & aaBB if AAbb & aaBB try to mate, A and B are ______. aa and bb are compatible bc share common trait.

incompatible

Sympatric speciation- evolution of reproductive isolation among member and _______ population.

interbreeding

Allopatric > non-overlapping ranges>_____ gene flow> reproductive isolation. Can populations evolve reproductive isolation in the face of gene flow? -Yes, in allopatry but don't know the historical aspect

low

Postxygotic barriers: a) Extrinsic B) Intrinsic: (hybrid fitness is ____ bc of problems that are relatively ______ of environmental context)

low independent

Dobzhansky-Muller incompatibilities: aabb>> AAbb & aaBB -substitution must occur at ___ than 2 loci. -derived alleles cause ____. -incompatibilities are _____- although Bis incompatible with A, b cannot be incompatible with a.

more incompatibilities asymmetric

Model of speciation Sympatry- population ranges _____ during speciation.

overlap

Allopatric Speciation: (____ model )-dispersal and ______ in text. 1) Population occur throughout an area. 2) A population arises through _____ effect on the ____ of the existing range. 3) ____barriers to gene flow evolve; these may be D-M effectors of "____ (leaping or passing from one thing or state to another.) effects" involving genome rearrangement due to small population size. 4) in the future, populations hybridize there is partial isolation.

peripatric, colonization 2) founder, perimeter 3) intrinsic, transilient

Hybrid inviability: is a______-zygotic barrier, which reduces a hybrid's capacity to _______ into a healthy, fit adult.

post mature

Allopatric Speciation >> Modern view -speciation can sometimes be very ______, occurring over very ____ generations.

rapid few

Postzygotic Barriers: Hybrid zygotes are formed but have _______ fitness.

reduced

Postzygotic barriers: a) Extrinsic B) Intrinsic: 1. hybrid inviability: ( developmental problems cause by _______ survival) 2.Hybrid sterility (usually due to reduce ability to _______ viable gametes; also "behavioral sterility", neurological incapacity to perform normal courtship)

reduced produce

Evidence for allopatric speciation 3) In many cases, ______ species replace each other geographically (Genus Rana ranges do not overlap or overlap only slightly)

related

Parapatric speciation- evolution of _______ isolation between 2 populations that ______ genes, but not freely. -theoretically possible, difficult to prove in nature.

reproductive, exchange

Isolating barriers for _________.

speciation

Reinforcement selection in Drosophilia: Prezygotic isolation also measured using two types of crosses between_____. -from each cross, female and male were determined sterile or ____. -Counted the # each type that were sterile/inviable and dived by 4. 0= ______ ______ 0.5= 50% sterile 1.0= _______

species -inviable: not capable of working successfully not sterile sterile

Horse 65 chromosomes mates with donkey 62 chromosomes and progeny become _________

sterile

Prezygotic isolation evolves faster in ______ than allopatry. -more divergence.

sympatry