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Ecological speciation of a hybrid sunflower, Helianthus anomalus Yuval Sapir, Loren H. Rieseberg Dept. of Biology, Indi

Ecological speciation of a hybrid sunflower, Helianthus anomalus Yuval Sapir, Loren H. Rieseberg Dept. of Biology, Indiana University, Bloomington, IN 47405, USA. Ecological speciation. = Speciation facilitated by divergent selection in contrasting environments.

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Ecological speciation of a hybrid sunflower, Helianthus anomalus Yuval Sapir, Loren H. Rieseberg Dept. of Biology, Indi

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  1. Ecological speciation of a hybrid sunflower, Helianthus anomalus Yuval Sapir, Loren H. Rieseberg Dept. of Biology, Indiana University, Bloomington, IN 47405, USA

  2. 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).

  3. If hybrid colonize different ecological habitat Habitat-specific ecological selection promote hybrid speciation Role of hybridization in ecological speciation • Hybridization: • Increases genetic variation and creates new combinations • Complementary gene action • Simultaneous change at multiple traits/genes

  4. Helianthus annuus Helianthus petiolaris Helianthus anomalus

  5. Distribution of hybrids & parental spp in the US

  6. 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

  7. Indices for detecting selection footprint Genetic variance - Schlötterer C., 2002. Genetics 160:753-763 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

  8. Footprint of selection Reduction in genetic variance or genetic diversity Selective sweeps = hitch-hiking effect non-significant effect (95% interval) significant reduction (P<0.05) Example from: Harr et al., 2002. PNAS 99(20):12949-12954

  9. Results 12 loci showed significant effect in both allele variance and genetic diversity PSP = pooled data from Parental Species; ano = H. anomalus ; ann = H. annuus ; pet = H. petiolaris

  10. lnRV and lnRH distributions lnRV=difference in allele variance; lnRH=difference in gene diversity

  11. lnRV and lnRH distributions lnRV=difference in allele variance; lnRH=difference in gene diversity

  12. Reduced gene diversity and shared alleles

  13. 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: AACTTATACAATGTAGAGATATGGTTGTTCCAAAGAAGATTCAACGTAGTAATCCTTATGAAGAGCGTGTTCCTGTCGGATTGGCTATTGTTGCAGCAGTCATAGTTCGGTTACAGCTTGCAAATACTGCTGCTGGTGGAATTGAAACACATGTTGGTGGTTCTATGTTAGTTGATGTGGTTAACAGCTCGTGGCTGCAAGTTATTCTAGCCGGTGTTACTTGGTATCTCATTGGTCTGGCTGCGGTTGAGATTATAGCAGTCCTTCGAATAAAATCGAACGATATTGAAGAATGAATAAAATAGTATATATATACAGGTATGTAGTATGTATAGGTTAAGCTGTTATAGGAATCATATATTCATTATTATATACACTCTCGAAAGAAAGCTCAGTCAAGCGTATGTTCATTACCCCAAAAAAAATCTTTAAAGTCGGAACACAAAAAATGTCGGGGGAAAAAAAA Putative translation: LIQCRDMVVPKKIQRSNPYEERVPVGLAIVAAVIVRLQLANTAAGGIETHVGGSMLVDVVNSSWLQVILAGVTWYLIGLAAVEIIAVLRIKSNDIEE* • 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]

  14. 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.

  15. 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)

  16. Thanks Rieseberg lab, IU Amanda Posto Briana Gross Nolan Kane Rebecca Randel Yoko Kakugawa Zhao Lai University of Georgia Beau Brouillette Lisa Donovan University of Veterinary Medicine, Vienna Christian Schlötterer Daniel Dieringer $upported by: BARD-Vaadia post-doctoral fellowship

  17. Proportion of shared alleles with parental species Kruskal-Wallis Test: c22=45.95; P<0.001; Paired tests - Wilcoxon Sign Ranked

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