Helianthus anomalus presentation

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Ecological speciation of a hybrid sunflower,
Helianthus anomalus Yuval Sapir, Loren H.
Rieseberg Dept. of Biology, Indiana
University, Bloomington, IN 47405, USA
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Ecological speciation
Speciation facilitated by divergent selection
in contrasting environments
Pre-/post-zygotic isolating barriers - reduce
gene-flow. Niche shift promotes genomic
differentiation (selection). Selection against
unfit hybrid progeny (reinforcement).
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Role of hybridization in ecological speciation

• Hybridization
• Increases genetic variation and creates new
  combinations
• Complementary gene action
• Simultaneous change at multiple traits/genes

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Helianthus annuus
Helianthus petiolaris
Helianthus anomalus
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Distribution of hybrids parental spp in the US
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• Methods
• 96 individuals from each parental species (3
  populations each)
• 192 individuals from 4 populations of
  Helianthus anomalus
• DNA extraction
• Microsatellites markers from EST library
• Preliminary survey ? 49 loci amplified in all 3
  spp were chosen

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Indices for detecting selection footprint
Genetic variance -
Schlötterer C., 2002. Genetics 160753-763
Genetic diversity -
H gene diversity expected heterozigosity
Schlötterer C. Dieringer, D., 2005. in
Nurminsky D. (ed) Selective Sweep. Landes
Bioscience, Georgetown, TX, pp 55-64
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Footprint of selection
Reduction in genetic variance or genetic
diversity Selective sweeps hitch-hiking effect
non-significant effect (95 interval)
significant reduction (Plt0.05)
Example from Harr et al., 2002. PNAS
99(20)12949-12954
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Results
12 loci showed significant effect in both allele
variance and genetic diversity
lnRH lnRV
18 22 ano/ann
20 22 ano/pet
23 26 ano/PSP
PSP pooled data from Parental Species ano H.
anomalus ann H. annuus pet H. petiolaris
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lnRV and lnRH distributions lnRVdifference in
allele variance lnRHdifference in gene diversity
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lnRV and lnRH distributions lnRVdifference in
allele variance lnRHdifference in gene diversity
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Reduced gene diversity and shared alleles
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Gene function locus HT424 as an example lnRH
-2.47 4 alleles in H. anomalus 10 in
parents Proportion of shared alleles 0.85
Sequence AACTTATACAATGTAGAGATATGGTTGTTCCAAAGAAGAT
TCAACGTAGTAATCCTTATGAAGAGCGTGTTCCTGTCGGATTGGCTATTG
TTGCAGCAGTCATAGTTCGGTTACAGCTTGCAAATACTGCTGCTGGTGGA
ATTGAAACACATGTTGGTGGTTCTATGTTAGTTGATGTGGTTAACAGCTC
GTGGCTGCAAGTTATTCTAGCCGGTGTTACTTGGTATCTCATTGGTCTGG
CTGCGGTTGAGATTATAGCAGTCCTTCGAATAAAATCGAACGATATTGAA
GAATGAATAAAATAGTATATATATACAGGTATGTAGTATGTATAGGTTAA
GCTGTTATAGGAATCATATATTCATTATTATATACACTCTCGAAAGAAAG
CTCAGTCAAGCGTATGTTCATTACCCCAAAAAAAATCTTTAAAGTCGGAA
CACAAAAAATGTCGGGGGAAAAAAAA
Putative translation LIQCRDMVVPKKIQRSNPYEERVPVGLA
IVAAVIVRLQLANTAAGGIETHVGGSMLVDVVNSSWLQVILAGVTWYLIG
LAAVEIIAVLRIKSNDIEE

• Interact with heat-shock proteins
• Can function as chaperones on their own
• Role in targeting and folding of polypeptides
• Regulation of gravitropism

BLAST results DNAJ heat shock N-terminal
domain-containing protein Arabidopsis thaliana
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Summary and conclusion

• Twelve of 49 loci exhibited significant reduction
  in variation compared to both parental species.
• The proportion of shared alleles is correlated
  with reduced variation.
• Genes exhibit footprint of selection may
  contribute to drought tolerance, heat tolerance,
  or deepening the root.
• Selection on ecologically important genes allowed
  H. anomalus to colonize desert sand dunes.

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Future directions

• Finer-scale hitch-hiking mapping to determine
  size of genomic regions affected by selective
  sweep
• Sequence analyses to confirm history of selection
• Functional analyses (correlations with QTLs, gene
  expression studies, transformations)

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Thanks
University of Georgia Beau Brouillette Lisa
Donovan
Rieseberg lab, IU Amanda Posto Briana Gross
Nolan Kane Rebecca Randel Yoko Kakugawa Zhao Lai
University of Veterinary Medicine,
Vienna Christian Schlötterer Daniel Dieringer
upported by BARD-Vaadia post-doctoral fellowship
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Proportion of shared alleles with parental species
Kruskal-Wallis Test c2245.95 Plt0.001 Paired
tests - Wilcoxon Sign Ranked