Case Study: Clarkia

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Case Study Clarkia
Clarkia tenella
Cody Williams 3.27.2007
Rachel Jabaily
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Outline

• The genus Clarkia
• Origin of gracilis
• Origin of rhomboidea
• A couple of general origins and implications of
  polyploids/aneuploids

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Clarkia (Onagraceae)

• Genus of 42 species of annual flowering plants
• Endemic to temperate Western North america
  (except one species, Clarkia tenella, which
  occurs in South America)
• Studied extensively- gene duplications,
  speciation, pollination biology, floral
  development...
• Wide range of chromosome numbers. From diploids
  of n5-9 to allo- and autopolyploids of n12, 14,
  17, 18, and 26

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Lewis Lewis, 1955
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The origin of Clarkia gracilis
Clarkia gracilis ssp. albicaulis
Dean Wm. Taylor
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Parental diploids

• C. graciliss 14 chromosomes suggests
  allotetraploid formation from two n7 diploid
  parents
• Håkansson suggested that one parent was likely
  C.amoena
• Hiorth suggested (based on morphological data)
  that the other parent was C.arcuata
• This was later ruled out by Håkansson using
  cytological evidence
• Lewis Lewis suggested that C.lassenensis was
  the second parent

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Distribution Clarkia Gracilis

• Clarkia gracilis is divided into 4 subspecies
• Sympatric distributions and hybridization
  common-though not universal
• Geographical relationship to putative parents-C.
  amoena ssp. Huntiana and C.lassenensis
• C.lassenensis and C.amoena ssp. huntiana

Abdel-Hameed Snow, 1971
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Abdel-Hameed Snow, 1971
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Cytological observations
Clarkia concinna

Bart and Susan Eisenberg
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Pairs, Chains and Rings
Ring
Chain
Bivalents
Lewis Raven, 1958
Snow Imam, 1964
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Translocations Forming a chain
Species A
Species B
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Translocations Forming a ring
Species A
Species B
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Cytological observationsInterspecific hybrids

• Examined crosses between species C.amoena and
  C.lassenensis with C.gracilis

• amoena X gracilis
• highly successful
• 7 amoena chromosomes paired very regularly with
  one set of 7 chrmomosomes in gracilis
• Other set of 7 chromosomes in gracilis left as
  univalents or occasionally pairing
  non-homologously

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Cytological observationsInterspecific hybrids

• Examined crosses between species C.amoena and
  C.lassenensis with C.gracilis

• lassenensis X gracilis
• Difficult to obtain and relatively unsuccessful
• Best association was a chain of 5 chromosomes
  (also found a 3 chromosome chain)
• Largest number of bivalents found was 5
• Others merely formed 21 univalents
• Formation of 3c and 5c suggests some relatedness
  of some chromosomes of the genomes, but less than
  would be expected for homologous genomes (also
  suggests at least 2 translocations)

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Cytological observationsInterspecific hybrids

• Examined crosses between species C.amoena and
  C.lassenensis with C.gracilis

• amoena X lassenensis
• Putative parents of Clarkia gracilis
• Both are n7 diploids
• Strong isolationg mechanisms

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Cytological observationsSynthetic alloploids

• Amphidiploids of F1 hybrids formed by
  self-pollination as well as by crosses between
  F1s
• Selfings of F1 plants
• 1000 selfings of F1 hybrids
• produced only one (!) capsule with three normal
  seeds (only two germinated and only one grew to
  maturity)
• The mature plant was shown to posses 27
  chromosomes (fertilization between 13 and 14
  chromosome gametes)
• 70 pollen viability and high seed set

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Cytological observationsSynthetic alloploids

• Amphidiploids of F1 hybrids formed by
  self-pollination as well as by crosses between
  F1s
• Crosses between F1 plants
• several hundred crosses
• produced only one seed which set and grew to
  maturity
• The mature plant possessed 28 chromosomes and was
  found to have been produced by fertilization
  between two unreduced gametes
• Meiotic pairing at M1 was excellent

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Cytological observationsDiploid F1 X C. gracilis

• Desired crosses between the synthetic and natural
  tetrapliods but colchicine treatments of diploid
  F1s failed. So hybrids were obtained by crossing
  F1 hybrids with the four gracilis subspecies
• Proved much more successful than crosses between
  F1 hybrids
• Many bivalents
• Several (3c)

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Conclusions

• Little homology between C.amoena ssp. huntiana
  and C.lassenensis
• Supported by irregular meiotic behavior and
  difficulty in obtaining F1 hybrids, sterility of
  F1s
• Poor pairing observed between C.lassenensis and
  C.gracilis suggest significant differences
  between the two
• Pairing that occured differed from standard
  C.lassenensis by at least two translocations

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Conclusions

• C.gracilis combines one subgenome of C.amoena
  ssp. huntiana and another from a diploid Clarkia
  in the section Flexicaulis
• What species is the donor of the second
  subgenome?

--Two hypotheses--
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C.lassenensis IS the donor

• Would suggest that the lassenensis genome has
  undergone significant rearrangement
• Pre-gracilis- C.lassenensis is cytologically very
  uniform in natural populations
• Post-gracilis- inter/intragenome changes
• Consistently found 7 bivalents with C.amoena X
  C.gracilis crosses
• Would have seen multiple associations
• Could argue that sympatric associations between
  C.amoena/C.gracilis resulted in a closer
  structural arrangement

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An extinct member of Flexicaulis

• Supported by several observations
• low homology between Clarkia gracilis and the
  extant species of Flexicaulis
• Morphological similarity of Clarkia gracilis to
  Clarkia arcuata (especially Clarkia gracilis ssp.
  albicaulis)
• Geographical location of Clarkia gracilis and
  members of Flexicaulis
• Ecological preference for serpentine soils which
  is a characteristic edaphic feature of Clarkia
  arcuata

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Clarkia gracilis ssp. albicaulis
Jo-Ann Ordano CAS
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The origin of Clarkia rhomboidea
Clarkia rhomboidea
Steve Matson
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Lewis Lewis, 1955
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Clarkia rhomboidea

• Haploid chromosome number of n12
• Wide distribution (as well as several disjunct
  populations)
• Wide range of habitats
• Wide range of flower pollination
• Lewis lewis 1955 proposed that parents were
  C.mildrediae (n7) and C.virgata (n5)

Mosquin, 1963
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Clarkia virgata
Clarkia mildrediae
Dean Wm. Taylor
Dean Wm. Taylor
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Clarkia mildrediae
Michelle Cloud-Hughes
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Hybrids

• C.mildrediae X C.rhomboidea
• 25- 7(pr) 5(un)
• other 75- chains of 3, 4 and 5 chromosomes
• C.virgata X C.rhomboidea
• Regular 5(pr) 7(un)

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Hybrids the sequel

• C.mildrediae X C.virgata
• Produced sterile F1 hybrids
• These hybrids were morphologically
  indistinguishable from C. rhomboidea
• Further supports origin of rhomboidea
• Extensive bivalent pairing as well as chain
  formation

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Hybridscompleting the trilogy

• Hybrids of 26 total populations of C.rhomboidea
• Used a strain from Shaver Lake, CA as standard
• This strain was crossed with 18 other populations
• 9 others were crossed with the Winnemucca, NV
  population
• Each population was also crossed with 5 others
  randomly

Chris Wagner
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Hybridscompleting the trilogy

• If the F1 formed 12 bivalents, the two
  populations were considered identical
• If the hybrids formed bridges with accompanying
  fragments the parental colonies were considered
  to possess inversions
• Six major types of chromosomal arrangements were
  found

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Hybridscompleting the trilogy

• Two main and most widespread arrangements
• Northern- Basically San Francisco north
• Southern- Replaces northern arrangement in
  Yosemite and continues south
• The other four are more local
• Winnemucca- In Winnemucca, Nevada
• Figueroa- Mtn. slope in S. central CA coast
• Kyburz and Dog Creek- N. CA but surrounded by
  populations with the northern arrangement

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Distribution of arrangements
Open circles designate northern arrangement
Open triangles designate northern arrangement
The other four are variously marked
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Results of the hybridizations
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Summary of arrangements

• Arbitrarily designate Northern as standard
• Southern varies by 2 translocations in 3 pairs of
  chromosomes
• Winnemucca differs by 1 translocation involving 2
  pairs of chromosomes (one of which is the same as
  in southern)
• Kyburz differs from southern by 1 translocation
  (which is different than that found in
  Winnemucca)
• There are multiple arrangements possible for
  Figueroa and Dog Creek

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Summary of arrangements
Maximum meiotic associations in F1 hybrids
between various populations of C. rhomboidea
Mosquin, 1963
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Clarkia franciscana
California Native Plant Society
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Conclusions

• Clarkia rhomboidea is a segmental allotetraploid
  from a hybridization between C.virgata and
  C.mildrediae followed by a doubling of
  chromosomes
• Supported by morphology and diploid F1 hybrids
• Single origin of Clarkia rhomboidea
• Many chromosomal rearrangements-translocations
  and inversions

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Effects of rearrangements Pollen fertility

• General decrease in fertile pollen as the
  chromosomes are more rearranged
• Garden grown plants from wild seed typically have
  95 good pollen
• Hybrids between populations showed a decrease in
  pollen yield likely due to aberrant meiosis
• Hybrids with 6 or 8 chromosome chains seemed
  especially effected

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Mosquin, 1963
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Effects of polyploidy on C.rhomboidea

• Much greater distribution (and greater tolerance)
  than either of the diploid parents
• Suggests a better adaptive system
• Likely from close homology of the subgenomes
  which would allow for intergenomic changes to
  occur and increase variation
• This pattern is also seen in many other examples
  in Clarkia

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Effects of polyploidy on C.rhomboidea

• Reciprocal translocations
• Many rearrangements of genetic material
• Usually involve a large portion of the chromosome
  arm
• Mostly form chains (few rings)
• translocations in C.rhomboidea involve only six
  of the twelve chromosomes- Why?

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Origin of Clarkia rhomboidea

• The original chromosomal arrangement was likely
  the Northern form
• The distribution of the northern form overlaps
  both of the parents
• In the genus as a whole, occupation of drier
  sites is often accompanied by a change in
  karyotype

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Origin of Clarkia rhomboidea

• C.rhomboidea likely arose during the late
  Pleistocene
• Not unlikely considering rapid differentiation in
  the genus as a whole
• In the genus as a whole, occupation of drier
  sites is often accompanied by a change in
  karyotype
• Climate in the Wisconsin glaciation favored a
  more widespread distribution
• Vicariance explains the isolated populations
  found in Arizona and Utah

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Distribution change since Wisconsin glaciation
Wide vertical lines Suggested previous range of
Northern form
Wide horizontal lines Suggested previous range
of Southern form
Narrow vertical lines Current range of Northern
form
Narrow horizontal lines Current range of
Southern form
Mosquin, 1963
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General polyploidy and aneuploidy
Clarkia cylindrica
Christopher Christie
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Revised classification of Clarkia (Wagner, Hoch
Raven, 2005 ms.) Section/subsection Species n
Sect. Eucharidium C. breweri 7 C.
concinna 7 Sect. Clarkia C. pulchella
12 Sect. Rhodanthos Subsect. Primigenia C.
amoena 7 C. franciscana 7 C.
rubicunda 7 Subsect. Flexicaules C.
arcuata 7 C. lassenensis 7 Subsect.
Jugales C. gracilis 14 Sect. Myxocarpa C.
australis 5 C. borealis 7 C.
mildrediae 7 C. mosquinii 6 C.
rhomboidea 12 C. stellata 7 C.
virgata 5 Sect. Godetia C. davyi
17 C. imbricata 8 C. prostrata
26 C. purpurea 26 C. speciosa
9 C. tenella 17 C. williamsonii
9 Sect. Biortis C. affinis 26 Sect.
Phaeostoma Subsect. Xantianae C. xantiana
9 Subsect. Fibula C. bottae 9 C.
joloensis 9 Subsect. Lautiflorae C.
biloba 8 C. lingulata 9 C.
modesta 8 Subsect. Prognatae C. similis
17 Subsect. Micranthae C. epilobioides 9
Subsect. Connubium C. delicata 18 Subsect.
Sympherica C. cylindrica 9 C. lewisii
9 C. rostrata 9 Subsect. Phaeostoma C.
exilis 9 C. springvillensis 9 C.
tembloriensis 9 C. unguiculata
9 Subsectional/Sectional placement
uncertain C. heterandra 9 Sect.
Heterogaura? C. dudleyana 9 Sect.
Phaeostoma subsect. Lautiflorae?

• Basic chromosome number is 7
• Multiple aneuploid events lead to n5,6,8,9
• Multiple polyploid events lead to
  n12,14,17,18,26
• What are a few patterns that emerge?

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Distribution and habitat

• Considering specifically diploids
• Species with n7 are more northern than, n8
  which are also more northern than n9
• In general there is a moisture gradient where
  northern sites are more mesic habitats with
  longer growing seasons than those further south
• Small, 1972 attributed this adaptation to
  morphological and physiological changes not
  necessarily associated with speciation, but when
  speciation does occur it involves populations
  adapting to the xeric margins of the parental
  species

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Speciation

• Often involves
• Extended period of draught reducing a population
  to few individuals
• inbreeding of these few individuals
• structural rearrangement of chromosomes
• Chance formation of a homozygous combination of a
  rearrangement
• Increase in the frequency of this rearrangement
• Establishment of species (even when in contact
  with parental species)

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Polyploidy

• Multiple possible combinations of diploid
  chromosome numbers
• Species hybrids can form and can successfully
  grow to maturity (though often sterile)
• Duplication of chromosomes
• Gives rise to a fertile hybrid polyploid plant
• Seen throughout the genus

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Polyploids and range

• Often the case that a polyploid species will have
  a very wide distribution
• All of the diploid taxa in Clarkia are largely
  restricted to California
• The polyploids derived from these diploids
  however have much wider ranges of distribution
• More likely to get beneficial (and successful)
  rearrangements increases variation and therefore
  adaptability to new habitats

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Revised classification of Clarkia (Wagner, Hoch
Raven, 2005 ms.) Section/subsection Species n
Sect. Eucharidium C. breweri 7 C.
concinna 7 Sect. Clarkia C. pulchella
12 Sect. Rhodanthos Subsect. Primigenia C.
amoena 7 C. franciscana 7 C.
rubicunda 7 Subsect. Flexicaules C.
arcuata 7 C. lassenensis 7 Subsect.
Jugales C. gracilis 14 Sect. Myxocarpa C.
australis 5 C. borealis 7 C.
mildrediae 7 C. mosquinii 6 C.
rhomboidea 12 C. stellata 7 C.
virgata 5 Sect. Godetia C. davyi
17 C. imbricata 8 C. prostrata
26 C. purpurea 26 C. speciosa
9 C. tenella 17 C. williamsonii
9 Sect. Biortis C. affinis 26 Sect.
Phaeostoma Subsect. Xantianae C. xantiana
9 Subsect. Fibula C. bottae 9 C.
joloensis 9 Subsect. Lautiflorae C.
biloba 8 C. lingulata 9 C.
modesta 8 Subsect. Prognatae C. similis
17 Subsect. Micranthae C. epilobioides 9
Subsect. Connubium C. delicata 18 Subsect.
Sympherica C. cylindrica 9 C. lewisii
9 C. rostrata 9 Subsect. Phaeostoma C.
exilis 9 C. springvillensis 9 C.
tembloriensis 9 C. unguiculata
9 Subsectional/Sectional placement
uncertain C. heterandra 9 Sect.
Heterogaura? C. dudleyana 9 Sect.
Phaeostoma subsect. Lautiflorae?

• Basic chromosome number is 7
• Multiple aneuploid events lead to n5,6,8,9
• Multiple polyploid events lead to n12,14,17,18,26

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Clarkia purpurea
Norman Jensen
Clarkia williamsonii
Charles Webber-CAS
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• Thanks to Ken

• Thanks to Rachel

Clarkia williamsonii

• Images from
• http//calphotos.berkeley.edu/

Matt Below
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Fin