Ecological speciation of a hybrid sunflower, Helianthus

anomalus

Yuval Sapir, Loren H. Rieseberg

Dept. of Biology, Indiana University,Bloomington, IN 47405, USA

Pre-/post-zygotic isolating barriers - reduce gene-flow.

Niche shift promotes genomic differentiation (selection).

Selection against unfit hybrid progeny (reinforcement).

Ecological speciation

= Speciation facilitated by divergent

selection in contrasting environments

Hybridization:

•Increases genetic variation and creates new combinations

•Complementary gene action

•Simultaneous change at multiple traits/genes

Role of hybridization in ecological speciation

If hybrid colonize different ecological habitat

Habitat-specific ecological selection promote hybrid speciation

Helianthus annuus Helianthus petiolaris

Helianthus anomalus

Distribution of hybrids & parental spp in the US

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

Indices for detecting selection footprint

)2(

)1(lnln

popVAR

popVARRV

1)2(1

1

1)1(1

1

lnln 2

2

popH

popHRH

Schlötterer C., 2002. Genetics 160:753-763

Schlötterer C. & Dieringer, D., 2005. in: Nurminsky D. (ed) Selective Sweep. Landes Bioscience, Georgetown, TX, pp 55-64

Genetic diversity -

Genetic variance -

H =gene diversity = expected heterozigosity

Reduction in genetic variance or genetic diversity

Selective sweeps = hitch-hiking effect

Footprint of selection

Example from: Harr et al., 2002. PNAS 99(20):12949-12954

non-significant effect(95% interval)

significant reduction(P<0.05)

Locus lnRV ano/ann lnRV ano/pet lnRH ano/ann lnRH ano/pet lnRV ano/PSP lnRH ano/PSP

279 0.370063306 -0.582473871 0.616871722 -0.665118053 -0.33558 -0.19432

283 -3.959820226 -4.342449119 -4.624676908 -3.384418966 -4.17432 -4.28447

285 -0.201700483 -0.460701278 -0.091107944 -0.496282049 -0.39421 -0.59403

289 -1.082327545 -0.901026376 -2.392140467 -1.874146478 -0.99647 -2.4265

313 -0.353491339 -0.668690377 -0.972340453 0.7922876 -0.54449 -0.52819

317 -2.211069594 -2.213149476 -2.25805302 -1.799079708 -2.23718 -2.28374

321 0.515002212 -0.750125252 0.531176522 -0.613313962 -0.35225 -0.257

323 -0.177087018 -1.402019453 -0.09917793 -2.04257327 -0.96884 -1.07669

324 -1.291081689 -1.169741318 0.347214221 1.100793562 -1.23441 0.69088

356 -3.090069816 -1.568625393 -0.403263699 -0.26715323 -2.60808 -0.35278

382 -1.645997933 -2.138230301 -2.485190161 -2.715321614 -2.22197 -3.21965

424 -5.841082394 -5.752628469 -2.316011577 -2.533400084 -5.79674 -2.47042

426 0.904128942 -0.149556001 -0.012490882 -3.561364411 -0.00308 -2.17582

429 -1.34775602 -1.832156726 -0.34592679 -0.578370591 -1.67122 -1.30204

439 -2.727556354 -1.004600964 -2.025595886 -0.483410193 -2.43943 -2.01536

440 -2.231910445 -1.733416744 -2.377568129 -1.082526042 -2.04003 -2.43532

441 -3.265653326 -1.101263355 -0.78466602 -0.430370161 -2.77961 -0.73815

446 -4.885154939 -3.293560928 -3.331557892 -1.181931246 -4.50563 -2.58138

451 -0.526901367 0.102891354 -2.537209852 -3.050925384 -0.28008 -2.8457

459 -2.445276465 0.399010384 -1.660772719 -2.119456688 -1.8683 -2.22423

466 -2.798428392 -1.332973231 -1.574383794 -1.253664018 -2.58618 -2.26334

520 0.0122101 -0.188976128 -0.464936489 -0.034136815 -1.04396 -1.40242

536 -1.261861746 -2.066244116 0.264362191 -1.999019143 -1.83283 -1.33293

538 1.798784834 2.398645674 1.162760445 0.24347485 1.80622 -0.26914

540 -0.199616395 0.827318193 -0.369147716 -0.379104687 0.14808 -0.49121

541 -2.682534099 -3.098202516 -3.027836248 -4.274103908 -3.14006 -4.0106

595 0.471601821 0.688469857 -0.013263357 -1.595789278 0.51352 -1.96624

612 -0.276136693 -0.738612043 -0.795295327 -1.657499122 -0.87573 -1.82525

615 0.521900569 -0.177102153 -0.084882787 -0.328026906 0.08111 -0.51209

621 -0.864374377 -1.374634628 -0.075610784 -0.509381005 -1.17825 -0.52207

668 -0.780715628 -0.614952751 -2.997374904 -3.079441486 -0.85056 -3.44805

677 -1.238041458 -2.516353793 -0.736806034 -1.425133687 -2.06577 -1.11932

692 -1.911487283 -2.447325171 0.507665556 -0.618505211 -2.40762 -0.7656

701 -1.774588809 -2.347849394 -3.494156724 -2.209051038 -2.11067 -3.57664

715 -7.573484869 -8.495438799 -8.964794845 -9.52644981 -8.10658 -9.5255

716 -3.413981133 -4.219405945 0.013514175 -2.148381915 -3.90258 -0.8879

732 -3.215636315 -3.136654452 -0.94256986 -2.155353082 -3.18543 -1.86963

739 -2.584307071 -3.971471926 -1.53976839 -2.409974258 -3.44103 -1.9973

765 -3.233822114 -4.160246433 -2.845909362 -3.91960935 -3.74782 -3.54954

772 -2.721618745 -3.083268656 -0.951886552 -0.836050438 -2.88519 -0.97619

813 -4.27710209 -4.380146113 -1.560635087 -2.885146452 -4.31745 -2.13002

815 -1.692166716 -3.025941688 -1.302680114 -1.867084736 -2.46333 -1.67498

834 -3.129918282 -3.570995678 -2.080027201 -2.374887972 -3.33086 -2.24646

848 -0.515982271 -1.095057596 -1.230462474 -1.209710918 -0.80583 -1.35894

854 -1.087410062 -1.642350663 -5.896708133 -5.846963648 -1.35952 -6.24423

953 -5.105017897 -5.42942434 -7.086745021 -6.520438521 -5.24619 -7.04584

985 -2.970893202 -2.552517359 -0.878278244 0.625854692 -2.81222 -0.37285989 -1.833147039 -1.466087702 -1.218420058 0.544332327 -1.69181 -0.60376998 -6.05431568 -5.728273309 -2.656400129 -0.281287565 -5.96192 -1.92316

lnRVlnRHano/ann2218ano/pet2220ano/PSP2623

PSP = pooled data from Parental Species; ano = H. anomalus ; ann = H. annuus ; pet = H. petiolaris

12 loci showed significant effect in both allele variance and genetic diversity

Results

lnRV and lnRH distributionslnRV=difference in allele variance; lnRH=difference in gene diversity

lnRV and lnRH distributionslnRV=difference in allele variance; lnRH=difference in gene diversity

r=0.561-10

-8

-6

-4

-2

0

2

-10 -8 -6 -4 -2 0 2

lnRV

lnR

H

Reduced gene diversity and shared alleles

a

jaia ffps ,, ,min

-10

-8

-6

-4

-2

0

2

0 0.2 0.4 0.6 0.8 1

Proportion of shared alleles

lnR

H

Gene function – locus HT424 as an example

lnRH = -2.47; 4 alleles in H. anomalus; 10 in parentsProportion of shared alleles: 0.85

Sequence:AACTTATACAATGTAGAGATATGGTTGTTCCAAAGAAGATTCAACGTAGTAATCCTTATGAAGAGCGTGTTCCTGTCGGATTGGCTATTGTTGCAGCAGTCATAGTTCGGTTACAGCTTGCAAATACTGCTGCTGGTGGAATTGAAACACATGTTGGTGGTTCTATGTTAGTTGATGTGGTTAACAGCTCGTGGCTGCAAGTTATTCTAGCCGGTGTTACTTGGTATCTCATTGGTCTGGCTGCGGTTGAGATTATAGCAGTCCTTCGAATAAAATCGAACGATATTGAAGAATGAATAAAATAGTATATATATACAGGTATGTAGTATGTATAGGTTAAGCTGTTATAGGAATCATATATTCATTATTATATACACTCTCGAAAGAAAGCTCAGTCAAGCGTATGTTCATTACCCCAAAAAAAATCTTTAAAGTCGGAACACAAAAAATGTCGGGGGAAAAAAAA

Putative translation:LIQCRDMVVPKKIQRSNPYEERVPVGLAIVAAVIVRLQLANTAAGGIETHVGGSMLVDVVNSSWLQVILAGVTWYLIGLAAVEIIAVLRIKSNDIEE*

BLAST results:DNAJ heat shock N-terminal domain-containing protein [Arabidopsis thaliana]

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

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.

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)

University of GeorgiaBeau BrouilletteLisa Donovan

ThanksRieseberg lab, IUAmanda PostoBriana Gross Nolan KaneRebecca RandelYoko KakugawaZhao Lai

$upported by:

BARD-Vaadia post-doctoral fellowship

University of Veterinary Medicine, ViennaChristian SchlöttererDaniel Dieringer

a a

b

0

0.1

0.2

0.3

0.4

0.5

0.6

Hano-Hann Hano-Hpet Hann-Hpet

Pro

porti

on o

f sha

red

alle

les

Kruskal-Wallis Test: 22=45.95; P<0.001; Paired tests - Wilcoxon Sign Ranked

a

jaia ffps ,, ,min

Proportion of shared alleles with parental species