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Population and Chromosome Genetics - Leitch > Reading - The role of hybridization in plant speciation > Flashcards

Reading - The role of hybridization in plant speciation Flashcards

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1
Q

Hybrid speciation at:

A
  • polyploid level
  • homoploid level
  • autopolyploid level
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2
Q

Polyploidy

A

more than 2 sets of homologous chromsomes

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3
Q

Homoploid level

A

betewen 2 species of the same ploidy

(same number of homologous chromosomes)

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4
Q

Autopolyploidy

A

genome doubling within species

(or between populations of the same species)

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5
Q

Hybridization

A

crossing betwee:

  • species
  • genetically divergent populations
  • races wihtin a species
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6
Q

Speciation in plants and animals:

similarities

A
  • gene flow in plants is more than originally thought
  • species reproductively isolated
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7
Q

Speciation in plants and animals:

differences

A
  • the high frequency of hybridization and its role in speciation
    • significant proportion of speciation in plants via hybridization → phylogenetic net, not bifurcating tree
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8
Q

Allopolyploid speciation is more common than homoploid speciation

A
  • homoploids have reduced fitness in early generation hybrids
    • not in allopolyploids - though possibile sterility bottleneck
  • genome doubling in allopolyploids
    • no/less backcrossing with parents
    • not the case in homoploids

→ new species via allopolyploidy are more likely

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9
Q

Many/most angiosperms are of

A

ancient polyploid origin

hybridization and genome doubling → species diversity

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10
Q

Allopolyploidy is more common no, so extrapolate that

A

most ancient polyploid events were allopolyploid

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11
Q

Masterson

A
  • studied leaf guard cells in fossils/relatives
  • found 70% of angiosperms have experienced polyploidy
  • by complete sequencing of the nuclear genome
    • found ancient polyploidy in angiosperms and eukaryotes
  • by sequencing all plant genomes
    • fond ancestor of Arabidopsis = hexaploid, subsequent duplications of Brassicales to get to Arabidopsis
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12
Q

Lynch and Conery

A

used genomic datat to infer occurrences of ancient genome duplication

  • used expressed sequence tags
  • to see if polyploid event occurred and when
  • found ancient polyploidy in a number of crops with multiple genome duplicationsi n some
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13
Q

Amborella

A

sister to angiosperms

  • shows no evidence of ancient polyploidy
    • signature may just be erased
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14
Q

Recept (within 150 years) polyploids

A
  • S. anglica (grass)
  • T. mirus and T. miscellus (flowers)
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15
Q

S. anglica shows

A

few changes in the genome but changes in methylaiton and epigenetic programming

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16
Q

Recent allotetraploids

A
  • Senecio and Tragopogon
  • loss of homeologues and DNA sequences, change in DNA expression
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17
Q

Types of polyploids

A
  • autopolyploids - multiplication of 1 chromosome set
  • allopolyploids - from merger of structurally different chromosome sets
  • segmental allopolyploids (Stebbins) - polyploids that comprise slightly differentiated chromosome sets
18
Q

Allopolyploids form hybrids between

A

distantly related species

→ combine divergent genomes with chromosomal complements that can’t pair

19
Q

Autopolyploid formation

A
  • doubling within an individual or crossing bewtween different populations within a species
  • with production and merger of unreduced gametes from genetically and chromosomally similar individuals
  • genetically different ~= speciation
20
Q

Allpolyploids/allotetraploids - expect

A

additivity of parental genotypes

BUT - will sequester parental genetic variation into its component genomes

→ some genetic diversity will segregate, some won’t

genetic variation in homologous chromosomes will segregate

genetic variation in homeologous chromosomes won’t

21
Q

Parents fixed for alternative alleles at all loci

→

A

complete additivity of the parental genes, appear heterozygous at all homeologous loci

  • segregating allelic variation between homologues
  • nonsegregating fixed heterozygosity at all homeologous loci
22
Q

Nearly all polyploid species comprise populations of independent formation from genetically distinct progenitor populations

A
  • if each of several constituent populations of each allotetraploid species of multiple origins had both segregating variation and fixed heterozygosity, then each allotetraploid populaiton would have its own set of genotypes and all populations would be genetically distinct
  • novel genotype from crossing between genetically different individuals
23
Q

Polyploid evolution

A
  • genomes merge → genomic shock
  • newly formed polyploid genomes undergo movement of transposable elements and rapid changes in the genome size and structure, epigenetic control
  • polyploid → restructuring of transcriptome, metabolome, proteome
24
Q

Brassica

A
  • structural changes in first few generations
25
Q

Tragopogon

A
  • major structural changes (including translocations) in natural populations not more than 30-40 generations
26
Q

Polyploidy → changes in:

A
  • gene silencing
  • DNA methylation
  • tissue-specific expression

= role in modifying patterns of gene expression

→ source of genetic novelty to play a role in evolutionary success

  • individuals with modified phenotype, ecological preferences
    • to exploit new niches and outcompete competitors
27
Q

Are rates of diversification higher in diploids or polyploids?

Soltis

A
  • compared species richness in clades that are ancient polyploids with sister clades that aren’t

→ polyploidy = major force behind diversification of angiosperms

→ genome doubling may have led to a dramatic increase in species richness ins esveral angiosperm lineages

28
Q

Conditions that favor polyploidization v hybridization

A
  • closely related diploids are less likely to form a polyploid than are more divergent diploid species
    • more distantly related diploids make polyploids
  • successful allopolyploids could be derived more easiliy than homoploids from distantly related parents
    • distant homoploids are more successful allopolyploids than close (Digby)
  • parents of allopolyploids typically twice as divergent as parents of homoploid hybrid species (Chapman)

homoploids - parents of low divergence

allopolyploids - parents of high divergence

29
Q

Muntzing

A
  • chromosomal races within species are distinct evolutionary lineages
  • 58 chromsome races
  • autopolyploid morphologically distinct from diploid parent, chromosomal races reproductively isolated
30
Q

Allopolyploids are more common than

A

autopolyploids

  • autopolyploids difficult to detect)
31
Q

Methods of polyploidization

A
  • fusion of unreduced gametes more likely than somatic doubling
  • unclear how frequent a 1-step (fusion of unreduced gametes) is vs. 2-step via triploid bridges
    • 1 haploid gamete + 1 unreduced gamete
    • then fusion of triploid gamete with reduced gamete → tetraploid
  • recurrent formation from genetically distinct diploid parental populations introduces genetic variation into a polyploid species
32
Q

Werth and Windham

A
  • if alternative homologs were silenced across an allopolyploid genome in different polyploid individuals (reciprocal silencing)

→ reproductive isolation and incipient speciation

33
Q

Polyploid populations of independent origin

(formation from genetically divergent parents)

A

may have distinct and cytogenetic signatures

  • changes in chromosomes might be responsible for reproductive isolation between allopolyploid populations

(Ownbrey and McCollum)

34
Q

Ownbrey and McCollum

A
  • crossed reciprocally formed populations of T. miscellus
  • reproductive barriers between populations (chromosomal changes)

→ if different population s have different chromosomal attributes there may be reduced fertility between, or reproductive isolation

35
Q

Preservation of duplicated gene copies

A

nonrandom

  • some functional categories preferentially retained, reduplicated

see Gaeta

36
Q

Gaeta

A
  • using identically produced synthetic lines of B. napus, showed repeatability of the evolutionary process
  • changes in expression, homeologue loss, structural changes occurred across 50 separate polyploid lines
  • → functional categories preferentially retained, reduplicated (preservation of duplicated gene copies)
37
Q

Tragopogon populations of independent origin

A

show evidence of repeated gene loss

  • preservation of duplicated gene copies
  • some functional categories preferentially retained, reduplicated
38
Q

Even if a hybrid survives and reproduces

A

subsequent generations may be increasing less fit

= hybrid breakdown

  • may not have a sustainable niche, forced into parental where less fitlow frequency of mate → excluded from population with parents
  • repeat exclusion → maintain integrity of parental species, long-term barrier to interspecific mating
39
Q

Introduced species

A
  • other pollinators visit close relatives → hybridize
    • Tragopogon in N. america plus pollinators that don’t discriminate
  • change in phenology → overlap flowering times → hybridization
  • climate change → change in distibution and phenology
40
Q
A

Population and Chromosome Genetics - Leitch (6 decks)

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