Slide 1

Case Study: Clarkia Cody Williams 3.27.2007 Rachel Jabaily Clarkia tenella Slide 2 Slide 3 Outline The genus Clarkia Origin of gracilis Origin of rhomboidea A couple of general origins and implications of polyploids/aneuploids Slide 4 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 n=5-9 to allo- and autopolyploids of n=12, 14, 17, 18, and 26 Slide 5 Lewis & Lewis, 1955 Slide 6 The origin of Clarkia gracilis Dean Wm. Taylor Clarkia gracilis ssp. albicaulis Slide 7 Parental diploids C. graciliss 14 chromosomes suggests allotetraploid formation from two n=7 diploid parents Hkansson 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 Hkansson using cytological evidence Lewis & Lewis suggested that C.lassenensis was the second parent Slide 8 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 C. a. ssp. huntiana C. lassenensis C. arcuata Slide 9 Abdel-Hameed & Snow, 1971 Inferred relationships: In nature Inferred relationships: Greenhouse progeny Slide 10 Cytological observations Clarkia concinna Bart and Susan Eisenberg Slide 11 Lewis & Raven, 1958 Chain Pairs, Chains and Rings Bivalents Ring Snow & Imam, 1964 Slide 12 Translocations: Forming a chain Species A Species B Slide 13 Translocations: Forming a ring Species A Species B Slide 14 Cytological observations: Interspecific hybrids 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 Examined crosses between species: C.amoena and C.lassenensis with C.gracilis Slide 15 Cytological observations: Interspecific hybrids 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) Examined crosses between species: C.amoena and C.lassenensis with C.gracilis Slide 16 Cytological observations: Interspecific hybrids amoena X lassenensis Putative parents of Clarkia gracilis Both are n=7 diploids Strong isolationg mechanisms Examined crosses between species: C.amoena and C.lassenensis with C.gracilis Slide 17 Cytological observations: Synthetic alloploids Amphidiploids of F 1 hybrids formed by self-pollination as well as by crosses between F1s Selfings of F 1 plants 1000 selfings of F 1 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 Slide 18 Cytological observations: Synthetic alloploids Amphidiploids of F 1 hybrids formed by self-pollination as well as by crosses between F1s Crosses between F 1 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 M 1 was excellent Slide 19 Cytological observations: Diploid F 1 X C. gracilis Desired crosses between the synthetic and natural tetrapliods: but colchicine treatments of diploid F 1 s failed. So hybrids were obtained by crossing F 1 hybrids with the four gracilis subspecies Proved much more successful than crosses between F 1 hybrids Many bivalents Several (3c) Slide 20 Conclusions Little homology between C.amoena ssp. huntiana and C.lassenensis Supported by irregular meiotic behavior and difficulty in obtaining F 1 hybrids, sterility of F 1 s 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 Slide 21 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-- Slide 22 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 Slide 23 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 Slide 24 Clarkia gracilis ssp. albicaulis Clarkia amoena ssp. huntiana Br. Alfred Brousseau Saint Marys College Jo-Ann Ordano CAS George W. Hartwell Clarkia arcuata Clarkia lassenensis Steve Matson FlexicaulisFlexicaulis Slide 25 The origin of Clarkia rhomboidea Clarkia rhomboidea Steve Matson Slide 26 Lewis & Lewis, 1955 Slide 27 Clarkia rhomboidea Haploid chromosome number of n=12 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 (n=7) and C.virgata (n=5) Mosquin, 1963 Slide 28 Clarkia virgata Clarkia mildrediae Dean Wm. Taylor Slide 29 Clarkia mildrediae Michelle Cloud-Hughes Slide 30 Slide 31 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) Slide 32 Hybrids: the sequel C.mildrediae X C.virgata Produced sterile F 1 hybrids These hybrids were morphologically indistinguishable from C. rhomboidea Further supports origin of rhomboidea Extensive bivalent pairing as well as chain formation Slide 33 Hybrids:completing 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 Slide 34 Hybrids:completing the trilogy If the F 1 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 Slide 35 Hybrids:completing 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 Slide 36 Distribution of arrangements Open circles designate northern arrangement Open triangles designate northern arrangement The other four are variously marked Slide 37 Results of the hybridizations Slide 38 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 Slide 39 Summary of arrangements Maximum meiotic associations in F 1 hybrids between various populations of C. rhomboidea Mosquin, 1963 Slide 40 Clarkia franciscana California Native Plant Society Slide 41 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 F 1 hybrids Single origin of Clarkia rhomboidea Many chromosomal rearrangements-translocations and inversions Slide 42 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 Slide 43 Mosquin, 1963 Slide 44 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 Slide 45 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? Slide 46 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 Slide 47 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 Slide 48 Mosquin, 1963 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 Distribution change since Wisconsin glaciation Slide 49 General polyploidy and aneuploidy Clarkia cylindrica Christopher Christie Slide 50 Revised classification of Clarkia (Wagner, Hoch & Raven, 2005 ms.) Section/subsectionSpeciesn = Sect. Eucharidium C. breweri 7 C. concinna 7 Sect. ClarkiaC. 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 n=5,6,8,9 Multiple polyploid events lead to n=12,14,17,18,26 What are a few patterns that emerge? Slide 51 Distribution and habitat Considering specifically diploids Species with n=7 are more northern than, n=8 which are also more northern than n=9 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 Slide 52 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) Slide 53 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 Slide 54 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 Slide 55 Revised classification of Clarkia (Wagner, Hoch & Raven, 2005 ms.) Section/subsectionSpeciesn = Sect. Eucharidium C. breweri 7 C. concinna 7 Sect. ClarkiaC. 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 n=5,6,8,9 Multiple polyploid events lead to n=12,14,17,18,26 Slide 56 Clarkia purpurea Norman Jensen Charles Webber-CAS Clarkia williamsonii Slide 57 Images from: http://calphotos.berkeley.edu/ Thanks to KenThanks to Rachel Matt Below Clarkia williamsonii Slide 58 Fin